research papers
ISSN 2053-2296
Synthesis, crystal structure and spectroscopic properties of trans-dibromidobis(2,2-dimethylpropane-1,3-diamine-j2N,N0 )chromium(III) perchlorate Dohyun Moona and Jong-Ha Choib*
Received 13 February 2015 Accepted 24 March 2015
a
Pohang Accelerator Laboratory, POSTECH, Pohang 790-784, Republic of Korea, and bDepartment of Chemistry, Andong National University, Andong 760-749, Republic of Korea. *Correspondence e-mail: [email protected]
Edited by U. Englert, RWTH Aachen, Germany Keywords: chromium(III) complex; spectroscopic properties; crystal structure; synchrotron radiation; bromide ligand; anti conformer. CCDC reference: 1055916 Supporting information: this article has supporting information at journals.iucr.org/c
The title complex salt, trans-anti-[CrBr2(Me2tn)2]ClO4 (where Me2tn = 2,2dimethylpropane-1,3-diamine, C5H14N2), was prepared and its structure determined by single-crystal X-ray diffraction at 100 K. The asymmetric unit contains three conformationally similar complex cations and three perchlorate anions. In each complex cation, the CrIII centre is coordinated by four N atoms of two chelating Me2tn ligands in the equatorial plane and by two Br atoms in a transaxial arrangement, to give a distorted octahedral geometry. Interionic contacts are dominated by extensive hydrogen bonding, involving the NH groups of the Me2tn ligand as donors and the anion O atoms or coordinated Br atoms as acceptors, resulting in two-dimensional layers in the bc plane. Ligand field analysis based on the angular overlap model, and IR and electronic spectroscopic properties, are also discussed.
1. Introduction The geometry and conformation of the chelating ligands in metal complexes are highly relevant for medical applications and likely to be major factors in determining antiviral activity and its side effects (Ronconi & Sadler, 2007; Ross et al., 2012). 2,2-Dimethylpropane-1,3-diamine (Me2tn) can form a stable six-membered chelate ring in combination with many transition metals, and chair, boat or twist conformations are possible. The [CrL2(Me2tn)2]+ cation (where L is a monodentate ligand) can adopt either the trans or the cis geometric isomer. In addition, two different kinds of conformation with respect to the chelate rings of Me2tn occur in the trans isomer (see Scheme 1).
# 2015 International Union of Crystallography
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The C atoms of the two chelate rings of the two conformers may be on the same side (syn conformer) or on opposite sides (anti conformer) of the coordination plane. In the case of trans-anti/syn-[CrBr2(Me2tn)2]Br (Moon, Lee & Choi, 2014), http://dx.doi.org/10.1107/S2053229615006026
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research papers trans-anti/syn-[CrBr2(Me2tn)2]2Br2HClO4 (Choi et al., 2002) and trans-anti/syn-[CrCl2(Me2tn)]Cl (Choi et al., 2007), independent syn and anti conformational isomers were found within the same crystal. However, the structural analyses of trans-anti-[Cr(NCS)2(Me2tn)2]NCS0.5H2O (Choi & Lee, 2009), trans-anti-[CrCl2(Me2tn)2]ClO4 (Choi, Lee & Lee, 2008), transanti-[Cr(N3)2(Me2tn)2]ClO42H2O (Moon & Choi, 2015), transanti-[Cr(OH)(Me2tn)2(H2O)](ClO4)2 (Moon, Lee et al., 2014) and trans-anti-[CrCl2(Me2tn)2]2ZnCl4 (Choi, Joshi & Spiccia, 2011) indicate that the two chelate rings of the Me2tn ligand adopt only the anti chair–chair conformation. The arrangement of the two six-membered chelate rings of the Me2tn ligand may depend on their contribution to hydrogen bonding with the monodentate ligands, solvent water molecules or counter-anions in the crystal structure. The preference for the syn or anti conformation of two six-membered rings in a transisomer is subtle and worthy of further study. X-ray crystallography is used to establish the presence of either conformation, as these conformers cannot be distinguished using methods such as IR and UV–Vis spectroscopy. The anionic species also play very important roles in chemistry, pharmacy, molecular assembly, biology and environmental processes, yet their binding characteristics have not received much recognition (Martı´nez-Ma´n˜ez & Sanceno´n, 2003; Fabbrizzi & Poggi, 2013). The study of anion effects and isomerism in octahedral metal complexes can result in a variety of new structures and properties of chemical and biological relevance. The elucidation of the factors that stabilize either the syn or the anti conformation in these complex cations continues to be of interest. As part of our current research on the conformation referring to the position of the C atoms of the Me2tn chelate rings with respect to the equatorial coordination plane, we describe here the preparation, conformational structure and spectroscopic analysis of trans-[CrBr2(Me2tn)2]ClO4, (I).
2,2-Dimethyl-1,3-propanediamine was obtained from Aldrich Chemical Co. and was used as supplied. All chemicals were of reagent grade and were used without further purification. The starting material, trans-anti-[Cr(OH)(Me2tn)2(H2O)](ClO4)2, was prepared according our earlier work (Moon, Lee et al., 2014). Pink crystals (0.031 g) of trans-anti[Cr(OH)(Me2tn)2(H2O)](ClO4)2 were dissolved in HBr (48%, 0.8 ml) and HClO4 (60%, 0.4 ml). The mixture was refluxed at 373 K for 10 min and then cooled to room temperature. Bright-green crystals of (I) suitable for X-ray analysis were deposited overnight. These were collected by filtration, washed with propan-2-ol and air dried (yield 35%). 2.2. Elemental analysis and spectroscopic data
Elemental analysis calculated for C10H28Br2ClCrN4O4: C 23.29, H 5.47, N 10.87%; found: C 22.92, H 5.31, N 10.90%. UV–Vis data for an aqueous solution, max in nm (" in M1 cm1): 390 (34.5), 467 (sh, 25.0), 622 (28.9). IR spectrum (KBr, cm1): 3436 (br, OH), 3270 (vs), 3228 (vs) and 3143 (s) ( NH), 2964 (vs), 2924 (s) and 2876 (s) ( CH), 2106 (s), 1586 (s) and 1576 (vs) ( NH2), 1476 (vs) and 1467 (s) ( CH2), 1443 (w), 1385 (s) ( CN), 1341 (w), 1321 (m), 1298 (w), 1275 (s), 1230 (m), 1217 (s), 1156 (vs), 1137 (vs), 1119 (s) ( CN), 1108 (s), 1090 (vs) (as Cl—O), 1063 (vs), 1037 (vs), 984 (vs), 893 (s) ( CH2), 816 (vw) and 773 (s) ( NH2), 656 (m), 636 (m), 622 (vs) ( OClO), 563 (s), 550 (s), 443 (m) and 418 (m) ( Cr—N). Table 1 Experimental details. Crystal data Chemical formula Mr Crystal system, space group Temperature (K) ˚) a, b, c (A ˚ 3) V (A Z Radiation type (mm1) Crystal size (mm) Data collection Diffractometer Absorption correction
2. Experimental The room-temperature visible absorption spectrum was recorded on an HP 8453 diode array spectrophotometer. The mid-IR spectrum was obtained using a JASCO 460 Plus series FT–IR spectrometer in a KBr pellet. Analyses for C, H and N were performed on a Carlo Erba 1108 Elemental Vario EL analyser. 2.1. Synthesis and crystallization
Caution! Although we experienced no difficulty with the perchlorate salt described in this study, the compound is potentially explosive and should be handled with very great care.
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[CrBr2(C5H14N2)2]ClO4 515.63 Orthorhombic, Pbca 100 20.656 (4), 17.666 (4), 31.305 (6) 11423 (4) 24 ˚ Synchrotron, = 0.62998 A 3.60 0.12 0.10 0.05
ADSC Q210 CCD area-detector diffractometer Empirical (using intensity measurements) (HKL3000sm SCALEPACK; Otwinowski & Minor, 1997) 0.670, 0.841 115348, 15666, 13691
Tmin, Tmax No. of measured, independent and observed [I> 2(I)] reflections Rint ˚ 1) (sin /)max (A
0.036 0.696
Refinement R[F2> 2(F2)], wR(F2), S No. of reflections No. of parameters No. of restraints H-atom treatment ˚ 3) max, min (e A
0.031, 0.086, 1.04 15666 636 6 H-atom parameters constrained 1.25, 1.42
Computer programs: PAL ADSC Quantum-210 ADX (Arvai & Nielsen, 1983), HKL3000sm SCALEPACK (Otwinowski & Minor, 1997), SHELXT (Sheldrick, 2015a), SHELXL (Sheldrick, 2015b), DIAMOND (Putz & Brandenburg, 2014), publCIF (Westrip, 2010) and PLATON (Spek, 2009).
Acta Cryst. (2015). C71, 351–356
research papers 2.3. Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. All H atoms were placed in geometrically idealized positions and constrained to ride on ˚ and Uiso(H) = their parent atoms, with C—H = 0.98 A ˚ and Uiso(H) = 1.5Ueq(C) for methyl groups, C—H = 0.99 A ˚ and 1.2Ueq(C) for methylene groups, and N—H = 0.91 A Uiso(H) = 1.2Ueq(N) for amine groups. One perchlorate anion is disordered about a noncrystallographic local threefold axis; distance restraints were used to ensure chemically reasonable geometry.
Table 2 ˚ ). Selected bond lengths (A Cr1A—N3A Cr1A—N4A Cr1A—N2A Cr1A—N1A Cr1A—Br1A Cr1A—Br2A Cr2B—N2B Cr2B—N1B Cr2B—N3B Cr2B—N4B Cr2B—Br1B Cr2B—Br2B Cr3C—N4C Cr3C—N3C Cr3C—N2C
2.0819 (17) 2.0881 (17) 2.0990 (19) 2.1044 (18) 2.4714 (6) 2.4867 (6) 2.0815 (17) 2.0918 (18) 2.0940 (17) 2.0959 (17) 2.4653 (6) 2.4778 (6) 2.0761 (19) 2.0795 (18) 2.0958 (19)
Cr3C—N1C Cr3C—Br1C Cr3C—Br2C Cl1P—O2P Cl1P—O3P Cl1P—O4P Cl1P—O1P Cl2Q—O2Q Cl2Q—O4Q Cl2Q—O3Q Cl2Q—O1Q Cl3R—O1R Cl3R—O2R Cl3R—O4R Cl3R—O3R
2.0982 (18) 2.4732 (6) 2.4735 (6) 1.429 (2) 1.4311 (19) 1.4358 (19) 1.4469 (17) 1.4245 (19) 1.430 (2) 1.4383 (16) 1.442 (2) 1.432 (2) 1.4357 (10) 1.4415 (10) 1.4422 (10)
3. Results and discussion The single-crystal X-ray structure determination was carried out from synchrotron data at 100 K. Selected bond lengths and angles are listed in Table 2. The structure analysis of (I) shows it to crystallize in the orthorhombic space group Pbca with Z = 24. The compound consists of an isolated [CrBr2(Me2tn)2]+ complex cation and a perchlorate counter-ion. There are three crystallographically independent complex ions and anions in the asymmetric unit; an ellipsoid plot of these, together with the atomic labelling scheme, is depicted in Fig. 1. H atoms in the amino groups are shown as spheres of arbitrary radii. Atoms associated with the minority orientation of the disordered perchlorate anion have been omitted for clarity. The CrIII cation is in a distorted octahedral coordination, with four N atoms of two chelating Me2tn ligands in the equatorial plane and two Br atoms in the trans-axial positions. The six-membered chelate rings are in stable chair conformations, with N—Cr—N angles in the range 87.93 (7)– 90.03 (7) . The two chelate rings in each Cr complex cation adopt the same anti chair–chair conformation with respect to each other. The conformational arrangement differs from the unique syn conformer observed in trans-anti/syn-[CrCl2(Me2tn)2]Cl (Choi et al., 2007), trans-anti/syn-[CrBr2(Me2tn)2]Br
(Moon, Lee & Choi, 2014) and trans-anti/syn-[CrBr2(Me2tn)2]2Br2HClO4H2O (Choi et al., 2002) containing the two types of conformer. However, the anti conformer of (I) is consistent with the conformation found in trans-anti[Cr(NCS)2(Me2tn)2]NCS0.5H2O (Choi & Lee, 2009), transanti-[CrCl2(Me2tn)2]ClO4 (Choi, Lee & Lee, 2008), trans-anti[Cr(OH)(Me2tn)2(H2O)](ClO4)2 (Moon, Lee et al., 2014), trans-anti-[Cr(N3)2(Me2tn)2]ClO42H2O (Moon & Choi, 2015) and trans-anti-[CrCl2(Me2tn)2]2ZnCl4 (Choi, Joshi & Spiccia, 2011). The difference in the conformations of the two chelate rings appears to be responsible for the differences in packing forces and hydrogen-bonding networks among the auxiliary ligand, solvent molecule, complex cation and anion in these chromium(III) complexes. The Cr—N bond distances for the N atoms of the Me2tn ligand vary from ˚ (Table 2) and are comparable 2.0761 (19) to 2.1044 (18) A with those observed in trans-anti-[CrCl2(Me2tn)2]ClO4 ˚ ; Choi, Lee & Lee, 2008], trans-anti/syn[2.090 (3)–2.100 (3) A ˚ ; Choi [CrCl2(Me2tn)2]Cl [range = 2.0861 (18)–2.1076 (18) A et al., 2007] and trans-anti-[Cr(N3)2(Me2tn)2]ClO42H2O ˚ ; Moon & Choi, 2015]. The [range = 2.066 (13)–2.0824 (10) A
Figure 1 A perspective view of the three independent complex cations and three perchlorate anions in (I). Only the amine H atoms are shown for clarity. Acta Cryst. (2015). C71, 351–356
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Figure 2 The molecular packing in (I), viewed along the b axis. Dashed lines represent N—H O (purple) and N—H Br (cyan) hydrogen-bonding interactions. H atoms bonded to C atoms have been omitted.
˚ , range 2.4653 (6)– Cr—Br distances [average 2.4747 (6) A ˚ 2.4867 (6) A] are in good agreement with the values of ˚ found in trans-anti/syn2.476 (1), 2.4796 (9) and 2.4743 (12) A [CrBr2(Me2tn)2]Br (Moon, Lee & Choi, 2014), trans-anti/syn[CrBr2(Me2tn)2]2Br2HClO4 (Choi et al., 2002) and trans[CrBr2(en)2]ClO4 (Choi et al., 2010), respectively. The mean Br1—Cr—Br2 angle is 178.732 (15) . The other N—C and C—C bond distances and Cr—N—C, N—C—C and C—C—C angles of (I) are typical for Me2tn ligands in a chair conformation (Choi, Lee & Lee, 2008; Moon & Choi, 2015). The presence of two substituted methyl groups on the C atom of the Me2tn molecule does not disturb the essential features of the tn chelate ring. The perchlorate counter-anions remain
Table 3 ˚ , ). Hydrogen-bond geometry (A D—H A
D—H
H A
D A
D—H A
N2A—H2A2 O4P N3A—H3A2 O3Q N4A—H4A2 O4P N2B—H2B1 O1P N3B—H3B1 O2Q N3B—H3B2 O1R N1C—H1C1 O5R N4C—H4C1 O3R N4C—H4C1 O5R N1A—H1A1 O1Pi N3A—H3A1 O1Pi N3A—H3A1 O3Pi N2C—H2C2 O2Ri N2C—H2C2 O7Ri N3C—H3C2 O2Ri N2B—H2B2 O1Qii N4B—H4B2 O1Qii N4A—H4A1 Br1B N1B—H1B2 Br2A N4B—H4B1 Br1Cii N1C—H1C2 Br1Aiii N3C—H3C1 Br2Bi N4A—H4A2 Br2Civ
0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91
2.04 2.22 2.36 2.50 2.07 2.41 2.34 2.01 2.34 2.55 2.19 2.52 2.11 2.03 2.05 2.03 2.48 2.67 2.77 2.85 2.67 2.68 2.93
2.940 (3) 3.075 (2) 3.110 (3) 3.376 (3) 2.965 (3) 3.275 (3) 3.097 (3) 2.867 (5) 3.180 (5) 3.393 (3) 3.004 (2) 3.354 (3) 2.889 (4) 2.841 (4) 2.878 (4) 2.925 (3) 3.054 (3) 3.4808 (17) 3.6017 (18) 3.6715 (17) 3.5081 (18) 3.4568 (18) 3.6665 (17)
172 157 139 161 166 159 140 155 153 155 149 153 143 147 151 169 121 148 152 150 153 145 139
Symmetry codes: (i) x þ 32 ; y þ 12 ; z; (ii) x þ 32 ; y 12 ; z; (iii) x þ 32 ; y þ 1; z 12; (iv) x þ 32 ; y þ 1; z þ 12.
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Figure 3 The FT–IR spectrum of (I).
outside the coordination sphere. They show a distorted tetrahedral arrangement of the O atoms around the central Cl atom. The packing in the structure involves intermolecular hydrogen bonds, not only of the N—H O type between the amine group of the Me2tn ligand and an O atom of the perchlorate anion, but also of the N—H Br type between the amine group of the Me2tn ligand and the Br ligand of an adjacent molecule (Table 3), forming a rigid supramolecular sheet structure parallel to the bc plane (Fig. 2). IR spectroscopy is useful for assigning the configuration of cis- and trans-isomers of diacidobis(diamine)chromium(III) complexes. The IR absorption spectrum of the trans-isomer reveals a simpler pattern than that of the cis-isomer. This pattern may be rationalized on the basis of the higher symmetry of the trans-isomer. Fig. 3 shows the FT–IR spectrum of (I). The strong absorption band at 1583 cm1 and the two bands at 1476 and 1467 cm1 can be assigned to NH2 and CH2 bending modes. The splitting of the absorption bands at 1586 and 1576 cm1 of the asymmetric NH2 deformation may be due to the site effect. The region from 800 to 900 cm1 is one of the best for distinguishing the trans- and cis-isomers of octahedral chromium(III) complexes. The medium peaks at 893, 816 and 773 cm1 are assigned to the CH2 and NH2 rocking vibrational frequencies. Complex (I), with a trans configuration, shows two bands near 890 cm1 and one near 810 cm1, while those with a cis configuration have several bands spread fairly evenly between 900 and 800 cm1. The absorption positions of the bending (), wagging (!), twisting ( ) and rocking () bands of NH2 and CH2 deformations are not significantly affected by differing counter-anions. The very strong split absorptions at 1090 and 622 cm1 are assigned to (ClO4) and as(Cl—O) of ionic perchlorate (Moon & Choi, 2015). The metal–ligand stretching and ringdeformation bands occur in the far-IR range. There are consistent differences between the IR spectra of the cis- and trans-isomers of diacidobis(diamine)chromium(III) complexes in the region 550–400 cm1. All the cis complexes show Acta Cryst. (2015). C71, 351–356
research papers Table 4 Observed band positions and calculated transition energies (cm1) in the electronic spectrum of the trans-[CrBr2(Me2tn)2]+ cation of (I). Assignment
Observed†
Calculated‡
4
16100 21460 24095 26385
16103 21459 24096 26385 38859 40425
B1g B1g 4 B1g 4 B1g 4 B1g 4 B1g 4
! 4 Eag ! 4 B2g ! 4 Aa2g ! 4 Ebg ! 4 Ab2g ! 4 Ecg
† Obtained from the Gaussian component deconvolution. ‡ Calculated using the following parameters (all in cm1): e (N) = 7153, e (Br) = 4837, e (Br) = 752 and B = 723.
Figure 4 The visible absorption spectrum and resolved overlapping peaks of (I) in aqueous solution.
four bands in this region, whereas all the trans complexes show three strong bands. Complex (I) shows a pattern of three bands: one strong band at 550 cm1, and two other bands at 443 and 418 cm1, which can be assigned to the Cr—N stretching modes. The IR spectroscopic properties are in agreement with the structural analysis, which shows that the geometry adopts a trans configuration. The assignment of the geometric configuration is also suggested by inspection of the d–d absorption spectra. The positions of the spin-allowed transitions in the electronic spectra, the number of bands and their coefficients are usually reliable indicators for distinguishing cis and trans geometric isomers. The more symmetrical trans chromium(III) complexes, with two bromides and two Me2tn ligands, have three symmetric bands in the visible region, and these bands are located at higher wavelengths and have lower extinction coefficients than those of less symmetrical cis-isomers. The visible absorption spectrum (solid purple line) of (I) in aqueous solution is shown in Fig. 4. It exhibits two main bands, one at 16080 cm1 (1) and the other at 25640 cm1 (2), corresponding to the 4A2g!4T2g and 4A2g!4T1g (Oh) transitions, respectively. The quartet band shows an asymmetric profile and has a shoulder at 21415 cm1, indicative of a trans configuration. In order to have some point of reference for the splitting of the bands, we have fitted the band profiles using four Gaussian curves, as shown in Fig. 4. A deconvolution procedure on the experimental band pattern yielded maxima at 16100, 21460, 24095 and 26385 cm1 for the noncubic (D4h) split levels (4Eag + 4B2g and 4A2g + 4Ebg ) of 4T2g and 4T1g (Oh), respectively. These band positions were used as the observed spin-allowed transition energies in the ligand field calculation. The ligand field potential matrix was generated for trans[CrBr2(Me2tn)2]+ from four coordinated N atoms and two Br atoms. In the framework of the angular overlap model, metal– ligand interactions are described in terms of localized bonding parameters of - and -types. Throughout the ligand field optimization, we assumed D4h tetragonal symmetry for (I). The parameters varied during the optimization were the Acta Cryst. (2015). C71, 351–356
Racah interelectronic repulsion parameter B (Ballhausen, 1980) plus the AOM (angular overlap model) parameters e(Br) and e (Br) for the Cr—Br interaction, and e(N) for the Cr—N interaction of Me2tn. The -interaction of the bromide with the metal ion was considered to be isotropic. The
-interaction of amine N atoms with sp3 hybridization in the Me2tn ligand was assumed to be negligible. However, it is noteworthy that the peptide N atom with sp2 hybridization has weak -donor character (Choi, Hong & Park, 2002). The AOMX program (Adamsky, 1996) was used to find the global minimum. The results of the optimization and details of the parameter set used to generate the best-fit energies (cm1) are listed in Table 4. The following values were finally obtained for the ligand field parameters: e (N) = 7153, e (Br) = 4837, e (Br) = 752 and B = 723 cm1. The AOM parameters are plausible and reproduce the spectrum pretty well. A ligand field analysis of the aqueous solution spectrum indicates that the bromide is a weak - and -donor. The value of 7153 cm1 for e(N) is comparable with values for the other amines (Choi & Lee, 2009; Moon & Choi, 2015). The e(N), e(Br) and e (Br) values are located in the normal ranges but are smaller than those extracted from the single-crystal data or from diffuse reflectance spectra at low temperature. However, no great difference is observed between the AOM parameter in aqueous solution and that from single-crystal data, suggesting that the coordination geometry in the solid state is preserved in solution. Table 5 contains a comparison of the AOM parameters for trans-[CrL2(Me2tn)2]+ with other anionic ligands. The parameter values reported here appear to be significant, as deduced on the basis of the electronic transitions which were obtained from the absorption spectrum in aqueous solution at room temperature, because a solution environment is more similar to naturally occurring systems. The parameter B is about 79% of the value for a free chromium(III) cation in Table 5 AOM parameters (cm1) for trans-[CrL2(Me2tn)2]+ complexes. L
e (N)
e (L)
F Cl Br NCS N3
7175 7360 7153 7130 6195
7510 5265 4837 6160 5290
e (L) 1710 860 752 30 515
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Reference Choi, Ryoo & Lee (2011) Choi et al. (2007) This work Choi & Lee (2009) Moon & Choi (2015)
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research papers the gas phase. AOM parameters can also be used in determining the photolabilized ligand of the photoreaction in chromium(III) complexes and in predicting the relative efficiency of the 3d–4f energy transfer in heterometal dinuclear complexes (Vanquickenborne & Ceulemans, 1983; Subhan et al., 2003). The IR and electronic spectroscopic properties of (I) are in good agreement with the results from X-ray crystallography, showing that the CrIII cation is in an octahedral environment, coordinated by two bidentate Me2tn ligands in the equatorial plane and by two Br atoms in the trans-axial positions. However, the IR and UV–Vis spectroscopic data do not give any evidence as to whether (I) has a syn or an anti conformation of the two six-membered chelate rings. Ligand field analysis shows that the N atoms of the Me2tn ligand have a strong -donor character, but the bromide has weak - and
-donor properties toward the chromium(III) cation in aqueous solution.
Acknowledgements The X-ray crystallography experiment on the PLS-II BL2DSMC beamline was supported in part by MSIP and POSTECH.
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supporting information Acta Cryst. (2015). C71, 351-356
[doi:10.1107/S2053229615006026]
Synthesis, crystal structure and spectroscopic properties of transdibromidobis(2,2-dimethylpropane-1,3-diamine-κ2N,N′)chromium(III) perchlorate Dohyun Moon and Jong-Ha Choi Computing details Data collection: PAL ADSC Quantum-210 ADX (Arvai & Nielsen, 1983); cell refinement: HKL3000sm (Otwinowski & Minor, 1997); data reduction: HKL3000sm (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXS2013 (Sheldrick, 2015); program(s) used to refine structure: SHELXL2014/7 (Sheldrick, 2015); molecular graphics: DIAMOND (Brandenburg, 2014); software used to prepare material for publication: publCIF (Westrip, 2010) and PLATON (Spek, 2009). trans-dibromidobis(2,2-dimethylpropane-1,3-diamine-κ22N,N′)chromium(III) perchlorate Crystal data [CrBr2(C5H14N2)2]ClO4 Mr = 515.63 Orthorhombic, Pbca a = 20.656 (4) Å b = 17.666 (4) Å c = 31.305 (6) Å V = 11423 (4) Å3 Z = 24 F(000) = 6216
Dx = 1.799 Mg m−3 Synchrotron radiation, λ = 0.62998 Å Cell parameters from 352345 reflections θ = 0.4–33.6° µ = 3.60 mm−1 T = 100 K Plate, green 0.12 × 0.10 × 0.05 mm
Data collection ADSC Q210 CCD area-detector diffractometer Radiation source: PLSII 2D bending magnet ω scans Absorption correction: empirical (using intensity measurements) (HKL3000sm SCALEPACK; Otwinowski & Minor, 1997) Tmin = 0.670, Tmax = 0.841
115348 measured reflections 15666 independent reflections 13691 reflections with I > 2σ(I) Rint = 0.036 θmax = 26.0°, θmin = 1.8° h = −28→28 k = −23→23 l = −43→43
Refinement Refinement on F2 Least-squares matrix: full R[F2 > 2σ(F2)] = 0.031 wR(F2) = 0.086 S = 1.04 15666 reflections
Acta Cryst. (2015). C71, 351-356
636 parameters 6 restraints Hydrogen site location: inferred from neighbouring sites H-atom parameters constrained
sup-1
supporting information w = 1/[σ2(Fo2) + (0.0577P)2 + 5.702P] where P = (Fo2 + 2Fc2)/3 (Δ/σ)max = 0.003 Δρmax = 1.25 e Å−3 Δρmin = −1.42 e Å−3
Extinction correction: SHELXL2014/7 (Sheldrick, 2015), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 Extinction coefficient: 0.00083 (5)
Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2)
Cr1A Br1A Br2A N1A H1A1 H1A2 N2A H2A1 H2A2 N3A H3A1 H3A2 N4A H4A1 H4A2 C1A H1A3 H1A4 C2A C3A H3A3 H3A4 C4A H4A3 H4A4 H4A5 C5A H5A1 H5A2 H5A3 C6A H6A1 H6A2 C7A
x
y
z
Uiso*/Ueq
0.73021 (2) 0.69990 (2) 0.76227 (2) 0.76335 (9) 0.7377 0.7561 0.82196 (9) 0.8222 0.8257 0.63830 (8) 0.6349 0.6365 0.69737 (8) 0.7004 0.7257 0.83200 (11) 0.8391 0.8382 0.88357 (11) 0.88151 (11) 0.8851 0.9195 0.88047 (14) 0.8383 0.8863 0.9148 0.94937 (13) 0.9527 0.9526 0.9846 0.57964 (10) 0.5407 0.5789 0.57586 (10)
0.60628 (2) 0.61566 (2) 0.60157 (2) 0.71878 (10) 0.7468 0.7354 0.56954 (11) 0.5710 0.5200 0.64035 (9) 0.6907 0.6351 0.49462 (9) 0.4795 0.4658 0.73755 (13) 0.7920 0.7296 0.69270 (13) 0.60849 (14) 0.6025 0.5835 0.70619 (16) 0.6898 0.7602 0.6773 0.72192 (17) 0.7765 0.7121 0.6957 0.60288 (11) 0.6274 0.6112 0.51758 (11)
0.61679 (2) 0.69298 (2) 0.54027 (2) 0.61996 (5) 0.6024 0.6470 0.63681 (6) 0.6659 0.6292 0.59742 (5) 0.6031 0.5685 0.61381 (5) 0.5861 0.6290 0.60917 (7) 0.6150 0.5781 0.63286 (7) 0.62206 (8) 0.5907 0.6352 0.68088 (8) 0.6917 0.6868 0.6950 0.61612 (9) 0.6214 0.5854 0.6310 0.61545 (7) 0.6033 0.6467 0.60673 (6)
0.01368 (7) 0.02048 (5) 0.02102 (5) 0.0179 (3) 0.022* 0.022* 0.0235 (4) 0.028* 0.028* 0.0171 (3) 0.021* 0.021* 0.0164 (3) 0.020* 0.020* 0.0242 (4) 0.029* 0.029* 0.0226 (4) 0.0259 (5) 0.031* 0.031* 0.0351 (6) 0.053* 0.053* 0.053* 0.0384 (6) 0.058* 0.058* 0.058* 0.0184 (4) 0.022* 0.022* 0.0163 (3)
Acta Cryst. (2015). C71, 351-356
Occ. (
ISSN 2053-2296
Synthesis, crystal structure and spectroscopic properties of trans-dibromidobis(2,2-dimethylpropane-1,3-diamine-j2N,N0 )chromium(III) perchlorate Dohyun Moona and Jong-Ha Choib*
Received 13 February 2015 Accepted 24 March 2015
a
Pohang Accelerator Laboratory, POSTECH, Pohang 790-784, Republic of Korea, and bDepartment of Chemistry, Andong National University, Andong 760-749, Republic of Korea. *Correspondence e-mail: [email protected]
Edited by U. Englert, RWTH Aachen, Germany Keywords: chromium(III) complex; spectroscopic properties; crystal structure; synchrotron radiation; bromide ligand; anti conformer. CCDC reference: 1055916 Supporting information: this article has supporting information at journals.iucr.org/c
The title complex salt, trans-anti-[CrBr2(Me2tn)2]ClO4 (where Me2tn = 2,2dimethylpropane-1,3-diamine, C5H14N2), was prepared and its structure determined by single-crystal X-ray diffraction at 100 K. The asymmetric unit contains three conformationally similar complex cations and three perchlorate anions. In each complex cation, the CrIII centre is coordinated by four N atoms of two chelating Me2tn ligands in the equatorial plane and by two Br atoms in a transaxial arrangement, to give a distorted octahedral geometry. Interionic contacts are dominated by extensive hydrogen bonding, involving the NH groups of the Me2tn ligand as donors and the anion O atoms or coordinated Br atoms as acceptors, resulting in two-dimensional layers in the bc plane. Ligand field analysis based on the angular overlap model, and IR and electronic spectroscopic properties, are also discussed.
1. Introduction The geometry and conformation of the chelating ligands in metal complexes are highly relevant for medical applications and likely to be major factors in determining antiviral activity and its side effects (Ronconi & Sadler, 2007; Ross et al., 2012). 2,2-Dimethylpropane-1,3-diamine (Me2tn) can form a stable six-membered chelate ring in combination with many transition metals, and chair, boat or twist conformations are possible. The [CrL2(Me2tn)2]+ cation (where L is a monodentate ligand) can adopt either the trans or the cis geometric isomer. In addition, two different kinds of conformation with respect to the chelate rings of Me2tn occur in the trans isomer (see Scheme 1).
# 2015 International Union of Crystallography
Acta Cryst. (2015). C71, 351–356
The C atoms of the two chelate rings of the two conformers may be on the same side (syn conformer) or on opposite sides (anti conformer) of the coordination plane. In the case of trans-anti/syn-[CrBr2(Me2tn)2]Br (Moon, Lee & Choi, 2014), http://dx.doi.org/10.1107/S2053229615006026
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research papers trans-anti/syn-[CrBr2(Me2tn)2]2Br2HClO4 (Choi et al., 2002) and trans-anti/syn-[CrCl2(Me2tn)]Cl (Choi et al., 2007), independent syn and anti conformational isomers were found within the same crystal. However, the structural analyses of trans-anti-[Cr(NCS)2(Me2tn)2]NCS0.5H2O (Choi & Lee, 2009), trans-anti-[CrCl2(Me2tn)2]ClO4 (Choi, Lee & Lee, 2008), transanti-[Cr(N3)2(Me2tn)2]ClO42H2O (Moon & Choi, 2015), transanti-[Cr(OH)(Me2tn)2(H2O)](ClO4)2 (Moon, Lee et al., 2014) and trans-anti-[CrCl2(Me2tn)2]2ZnCl4 (Choi, Joshi & Spiccia, 2011) indicate that the two chelate rings of the Me2tn ligand adopt only the anti chair–chair conformation. The arrangement of the two six-membered chelate rings of the Me2tn ligand may depend on their contribution to hydrogen bonding with the monodentate ligands, solvent water molecules or counter-anions in the crystal structure. The preference for the syn or anti conformation of two six-membered rings in a transisomer is subtle and worthy of further study. X-ray crystallography is used to establish the presence of either conformation, as these conformers cannot be distinguished using methods such as IR and UV–Vis spectroscopy. The anionic species also play very important roles in chemistry, pharmacy, molecular assembly, biology and environmental processes, yet their binding characteristics have not received much recognition (Martı´nez-Ma´n˜ez & Sanceno´n, 2003; Fabbrizzi & Poggi, 2013). The study of anion effects and isomerism in octahedral metal complexes can result in a variety of new structures and properties of chemical and biological relevance. The elucidation of the factors that stabilize either the syn or the anti conformation in these complex cations continues to be of interest. As part of our current research on the conformation referring to the position of the C atoms of the Me2tn chelate rings with respect to the equatorial coordination plane, we describe here the preparation, conformational structure and spectroscopic analysis of trans-[CrBr2(Me2tn)2]ClO4, (I).
2,2-Dimethyl-1,3-propanediamine was obtained from Aldrich Chemical Co. and was used as supplied. All chemicals were of reagent grade and were used without further purification. The starting material, trans-anti-[Cr(OH)(Me2tn)2(H2O)](ClO4)2, was prepared according our earlier work (Moon, Lee et al., 2014). Pink crystals (0.031 g) of trans-anti[Cr(OH)(Me2tn)2(H2O)](ClO4)2 were dissolved in HBr (48%, 0.8 ml) and HClO4 (60%, 0.4 ml). The mixture was refluxed at 373 K for 10 min and then cooled to room temperature. Bright-green crystals of (I) suitable for X-ray analysis were deposited overnight. These were collected by filtration, washed with propan-2-ol and air dried (yield 35%). 2.2. Elemental analysis and spectroscopic data
Elemental analysis calculated for C10H28Br2ClCrN4O4: C 23.29, H 5.47, N 10.87%; found: C 22.92, H 5.31, N 10.90%. UV–Vis data for an aqueous solution, max in nm (" in M1 cm1): 390 (34.5), 467 (sh, 25.0), 622 (28.9). IR spectrum (KBr, cm1): 3436 (br, OH), 3270 (vs), 3228 (vs) and 3143 (s) ( NH), 2964 (vs), 2924 (s) and 2876 (s) ( CH), 2106 (s), 1586 (s) and 1576 (vs) ( NH2), 1476 (vs) and 1467 (s) ( CH2), 1443 (w), 1385 (s) ( CN), 1341 (w), 1321 (m), 1298 (w), 1275 (s), 1230 (m), 1217 (s), 1156 (vs), 1137 (vs), 1119 (s) ( CN), 1108 (s), 1090 (vs) (as Cl—O), 1063 (vs), 1037 (vs), 984 (vs), 893 (s) ( CH2), 816 (vw) and 773 (s) ( NH2), 656 (m), 636 (m), 622 (vs) ( OClO), 563 (s), 550 (s), 443 (m) and 418 (m) ( Cr—N). Table 1 Experimental details. Crystal data Chemical formula Mr Crystal system, space group Temperature (K) ˚) a, b, c (A ˚ 3) V (A Z Radiation type (mm1) Crystal size (mm) Data collection Diffractometer Absorption correction
2. Experimental The room-temperature visible absorption spectrum was recorded on an HP 8453 diode array spectrophotometer. The mid-IR spectrum was obtained using a JASCO 460 Plus series FT–IR spectrometer in a KBr pellet. Analyses for C, H and N were performed on a Carlo Erba 1108 Elemental Vario EL analyser. 2.1. Synthesis and crystallization
Caution! Although we experienced no difficulty with the perchlorate salt described in this study, the compound is potentially explosive and should be handled with very great care.
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[CrBr2(C5H14N2)2]ClO4 515.63 Orthorhombic, Pbca 100 20.656 (4), 17.666 (4), 31.305 (6) 11423 (4) 24 ˚ Synchrotron, = 0.62998 A 3.60 0.12 0.10 0.05
ADSC Q210 CCD area-detector diffractometer Empirical (using intensity measurements) (HKL3000sm SCALEPACK; Otwinowski & Minor, 1997) 0.670, 0.841 115348, 15666, 13691
Tmin, Tmax No. of measured, independent and observed [I> 2(I)] reflections Rint ˚ 1) (sin /)max (A
0.036 0.696
Refinement R[F2> 2(F2)], wR(F2), S No. of reflections No. of parameters No. of restraints H-atom treatment ˚ 3) max, min (e A
0.031, 0.086, 1.04 15666 636 6 H-atom parameters constrained 1.25, 1.42
Computer programs: PAL ADSC Quantum-210 ADX (Arvai & Nielsen, 1983), HKL3000sm SCALEPACK (Otwinowski & Minor, 1997), SHELXT (Sheldrick, 2015a), SHELXL (Sheldrick, 2015b), DIAMOND (Putz & Brandenburg, 2014), publCIF (Westrip, 2010) and PLATON (Spek, 2009).
Acta Cryst. (2015). C71, 351–356
research papers 2.3. Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. All H atoms were placed in geometrically idealized positions and constrained to ride on ˚ and Uiso(H) = their parent atoms, with C—H = 0.98 A ˚ and Uiso(H) = 1.5Ueq(C) for methyl groups, C—H = 0.99 A ˚ and 1.2Ueq(C) for methylene groups, and N—H = 0.91 A Uiso(H) = 1.2Ueq(N) for amine groups. One perchlorate anion is disordered about a noncrystallographic local threefold axis; distance restraints were used to ensure chemically reasonable geometry.
Table 2 ˚ ). Selected bond lengths (A Cr1A—N3A Cr1A—N4A Cr1A—N2A Cr1A—N1A Cr1A—Br1A Cr1A—Br2A Cr2B—N2B Cr2B—N1B Cr2B—N3B Cr2B—N4B Cr2B—Br1B Cr2B—Br2B Cr3C—N4C Cr3C—N3C Cr3C—N2C
2.0819 (17) 2.0881 (17) 2.0990 (19) 2.1044 (18) 2.4714 (6) 2.4867 (6) 2.0815 (17) 2.0918 (18) 2.0940 (17) 2.0959 (17) 2.4653 (6) 2.4778 (6) 2.0761 (19) 2.0795 (18) 2.0958 (19)
Cr3C—N1C Cr3C—Br1C Cr3C—Br2C Cl1P—O2P Cl1P—O3P Cl1P—O4P Cl1P—O1P Cl2Q—O2Q Cl2Q—O4Q Cl2Q—O3Q Cl2Q—O1Q Cl3R—O1R Cl3R—O2R Cl3R—O4R Cl3R—O3R
2.0982 (18) 2.4732 (6) 2.4735 (6) 1.429 (2) 1.4311 (19) 1.4358 (19) 1.4469 (17) 1.4245 (19) 1.430 (2) 1.4383 (16) 1.442 (2) 1.432 (2) 1.4357 (10) 1.4415 (10) 1.4422 (10)
3. Results and discussion The single-crystal X-ray structure determination was carried out from synchrotron data at 100 K. Selected bond lengths and angles are listed in Table 2. The structure analysis of (I) shows it to crystallize in the orthorhombic space group Pbca with Z = 24. The compound consists of an isolated [CrBr2(Me2tn)2]+ complex cation and a perchlorate counter-ion. There are three crystallographically independent complex ions and anions in the asymmetric unit; an ellipsoid plot of these, together with the atomic labelling scheme, is depicted in Fig. 1. H atoms in the amino groups are shown as spheres of arbitrary radii. Atoms associated with the minority orientation of the disordered perchlorate anion have been omitted for clarity. The CrIII cation is in a distorted octahedral coordination, with four N atoms of two chelating Me2tn ligands in the equatorial plane and two Br atoms in the trans-axial positions. The six-membered chelate rings are in stable chair conformations, with N—Cr—N angles in the range 87.93 (7)– 90.03 (7) . The two chelate rings in each Cr complex cation adopt the same anti chair–chair conformation with respect to each other. The conformational arrangement differs from the unique syn conformer observed in trans-anti/syn-[CrCl2(Me2tn)2]Cl (Choi et al., 2007), trans-anti/syn-[CrBr2(Me2tn)2]Br
(Moon, Lee & Choi, 2014) and trans-anti/syn-[CrBr2(Me2tn)2]2Br2HClO4H2O (Choi et al., 2002) containing the two types of conformer. However, the anti conformer of (I) is consistent with the conformation found in trans-anti[Cr(NCS)2(Me2tn)2]NCS0.5H2O (Choi & Lee, 2009), transanti-[CrCl2(Me2tn)2]ClO4 (Choi, Lee & Lee, 2008), trans-anti[Cr(OH)(Me2tn)2(H2O)](ClO4)2 (Moon, Lee et al., 2014), trans-anti-[Cr(N3)2(Me2tn)2]ClO42H2O (Moon & Choi, 2015) and trans-anti-[CrCl2(Me2tn)2]2ZnCl4 (Choi, Joshi & Spiccia, 2011). The difference in the conformations of the two chelate rings appears to be responsible for the differences in packing forces and hydrogen-bonding networks among the auxiliary ligand, solvent molecule, complex cation and anion in these chromium(III) complexes. The Cr—N bond distances for the N atoms of the Me2tn ligand vary from ˚ (Table 2) and are comparable 2.0761 (19) to 2.1044 (18) A with those observed in trans-anti-[CrCl2(Me2tn)2]ClO4 ˚ ; Choi, Lee & Lee, 2008], trans-anti/syn[2.090 (3)–2.100 (3) A ˚ ; Choi [CrCl2(Me2tn)2]Cl [range = 2.0861 (18)–2.1076 (18) A et al., 2007] and trans-anti-[Cr(N3)2(Me2tn)2]ClO42H2O ˚ ; Moon & Choi, 2015]. The [range = 2.066 (13)–2.0824 (10) A
Figure 1 A perspective view of the three independent complex cations and three perchlorate anions in (I). Only the amine H atoms are shown for clarity. Acta Cryst. (2015). C71, 351–356
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Figure 2 The molecular packing in (I), viewed along the b axis. Dashed lines represent N—H O (purple) and N—H Br (cyan) hydrogen-bonding interactions. H atoms bonded to C atoms have been omitted.
˚ , range 2.4653 (6)– Cr—Br distances [average 2.4747 (6) A ˚ 2.4867 (6) A] are in good agreement with the values of ˚ found in trans-anti/syn2.476 (1), 2.4796 (9) and 2.4743 (12) A [CrBr2(Me2tn)2]Br (Moon, Lee & Choi, 2014), trans-anti/syn[CrBr2(Me2tn)2]2Br2HClO4 (Choi et al., 2002) and trans[CrBr2(en)2]ClO4 (Choi et al., 2010), respectively. The mean Br1—Cr—Br2 angle is 178.732 (15) . The other N—C and C—C bond distances and Cr—N—C, N—C—C and C—C—C angles of (I) are typical for Me2tn ligands in a chair conformation (Choi, Lee & Lee, 2008; Moon & Choi, 2015). The presence of two substituted methyl groups on the C atom of the Me2tn molecule does not disturb the essential features of the tn chelate ring. The perchlorate counter-anions remain
Table 3 ˚ , ). Hydrogen-bond geometry (A D—H A
D—H
H A
D A
D—H A
N2A—H2A2 O4P N3A—H3A2 O3Q N4A—H4A2 O4P N2B—H2B1 O1P N3B—H3B1 O2Q N3B—H3B2 O1R N1C—H1C1 O5R N4C—H4C1 O3R N4C—H4C1 O5R N1A—H1A1 O1Pi N3A—H3A1 O1Pi N3A—H3A1 O3Pi N2C—H2C2 O2Ri N2C—H2C2 O7Ri N3C—H3C2 O2Ri N2B—H2B2 O1Qii N4B—H4B2 O1Qii N4A—H4A1 Br1B N1B—H1B2 Br2A N4B—H4B1 Br1Cii N1C—H1C2 Br1Aiii N3C—H3C1 Br2Bi N4A—H4A2 Br2Civ
0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91
2.04 2.22 2.36 2.50 2.07 2.41 2.34 2.01 2.34 2.55 2.19 2.52 2.11 2.03 2.05 2.03 2.48 2.67 2.77 2.85 2.67 2.68 2.93
2.940 (3) 3.075 (2) 3.110 (3) 3.376 (3) 2.965 (3) 3.275 (3) 3.097 (3) 2.867 (5) 3.180 (5) 3.393 (3) 3.004 (2) 3.354 (3) 2.889 (4) 2.841 (4) 2.878 (4) 2.925 (3) 3.054 (3) 3.4808 (17) 3.6017 (18) 3.6715 (17) 3.5081 (18) 3.4568 (18) 3.6665 (17)
172 157 139 161 166 159 140 155 153 155 149 153 143 147 151 169 121 148 152 150 153 145 139
Symmetry codes: (i) x þ 32 ; y þ 12 ; z; (ii) x þ 32 ; y 12 ; z; (iii) x þ 32 ; y þ 1; z 12; (iv) x þ 32 ; y þ 1; z þ 12.
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Figure 3 The FT–IR spectrum of (I).
outside the coordination sphere. They show a distorted tetrahedral arrangement of the O atoms around the central Cl atom. The packing in the structure involves intermolecular hydrogen bonds, not only of the N—H O type between the amine group of the Me2tn ligand and an O atom of the perchlorate anion, but also of the N—H Br type between the amine group of the Me2tn ligand and the Br ligand of an adjacent molecule (Table 3), forming a rigid supramolecular sheet structure parallel to the bc plane (Fig. 2). IR spectroscopy is useful for assigning the configuration of cis- and trans-isomers of diacidobis(diamine)chromium(III) complexes. The IR absorption spectrum of the trans-isomer reveals a simpler pattern than that of the cis-isomer. This pattern may be rationalized on the basis of the higher symmetry of the trans-isomer. Fig. 3 shows the FT–IR spectrum of (I). The strong absorption band at 1583 cm1 and the two bands at 1476 and 1467 cm1 can be assigned to NH2 and CH2 bending modes. The splitting of the absorption bands at 1586 and 1576 cm1 of the asymmetric NH2 deformation may be due to the site effect. The region from 800 to 900 cm1 is one of the best for distinguishing the trans- and cis-isomers of octahedral chromium(III) complexes. The medium peaks at 893, 816 and 773 cm1 are assigned to the CH2 and NH2 rocking vibrational frequencies. Complex (I), with a trans configuration, shows two bands near 890 cm1 and one near 810 cm1, while those with a cis configuration have several bands spread fairly evenly between 900 and 800 cm1. The absorption positions of the bending (), wagging (!), twisting ( ) and rocking () bands of NH2 and CH2 deformations are not significantly affected by differing counter-anions. The very strong split absorptions at 1090 and 622 cm1 are assigned to (ClO4) and as(Cl—O) of ionic perchlorate (Moon & Choi, 2015). The metal–ligand stretching and ringdeformation bands occur in the far-IR range. There are consistent differences between the IR spectra of the cis- and trans-isomers of diacidobis(diamine)chromium(III) complexes in the region 550–400 cm1. All the cis complexes show Acta Cryst. (2015). C71, 351–356
research papers Table 4 Observed band positions and calculated transition energies (cm1) in the electronic spectrum of the trans-[CrBr2(Me2tn)2]+ cation of (I). Assignment
Observed†
Calculated‡
4
16100 21460 24095 26385
16103 21459 24096 26385 38859 40425
B1g B1g 4 B1g 4 B1g 4 B1g 4 B1g 4
! 4 Eag ! 4 B2g ! 4 Aa2g ! 4 Ebg ! 4 Ab2g ! 4 Ecg
† Obtained from the Gaussian component deconvolution. ‡ Calculated using the following parameters (all in cm1): e (N) = 7153, e (Br) = 4837, e (Br) = 752 and B = 723.
Figure 4 The visible absorption spectrum and resolved overlapping peaks of (I) in aqueous solution.
four bands in this region, whereas all the trans complexes show three strong bands. Complex (I) shows a pattern of three bands: one strong band at 550 cm1, and two other bands at 443 and 418 cm1, which can be assigned to the Cr—N stretching modes. The IR spectroscopic properties are in agreement with the structural analysis, which shows that the geometry adopts a trans configuration. The assignment of the geometric configuration is also suggested by inspection of the d–d absorption spectra. The positions of the spin-allowed transitions in the electronic spectra, the number of bands and their coefficients are usually reliable indicators for distinguishing cis and trans geometric isomers. The more symmetrical trans chromium(III) complexes, with two bromides and two Me2tn ligands, have three symmetric bands in the visible region, and these bands are located at higher wavelengths and have lower extinction coefficients than those of less symmetrical cis-isomers. The visible absorption spectrum (solid purple line) of (I) in aqueous solution is shown in Fig. 4. It exhibits two main bands, one at 16080 cm1 (1) and the other at 25640 cm1 (2), corresponding to the 4A2g!4T2g and 4A2g!4T1g (Oh) transitions, respectively. The quartet band shows an asymmetric profile and has a shoulder at 21415 cm1, indicative of a trans configuration. In order to have some point of reference for the splitting of the bands, we have fitted the band profiles using four Gaussian curves, as shown in Fig. 4. A deconvolution procedure on the experimental band pattern yielded maxima at 16100, 21460, 24095 and 26385 cm1 for the noncubic (D4h) split levels (4Eag + 4B2g and 4A2g + 4Ebg ) of 4T2g and 4T1g (Oh), respectively. These band positions were used as the observed spin-allowed transition energies in the ligand field calculation. The ligand field potential matrix was generated for trans[CrBr2(Me2tn)2]+ from four coordinated N atoms and two Br atoms. In the framework of the angular overlap model, metal– ligand interactions are described in terms of localized bonding parameters of - and -types. Throughout the ligand field optimization, we assumed D4h tetragonal symmetry for (I). The parameters varied during the optimization were the Acta Cryst. (2015). C71, 351–356
Racah interelectronic repulsion parameter B (Ballhausen, 1980) plus the AOM (angular overlap model) parameters e(Br) and e (Br) for the Cr—Br interaction, and e(N) for the Cr—N interaction of Me2tn. The -interaction of the bromide with the metal ion was considered to be isotropic. The
-interaction of amine N atoms with sp3 hybridization in the Me2tn ligand was assumed to be negligible. However, it is noteworthy that the peptide N atom with sp2 hybridization has weak -donor character (Choi, Hong & Park, 2002). The AOMX program (Adamsky, 1996) was used to find the global minimum. The results of the optimization and details of the parameter set used to generate the best-fit energies (cm1) are listed in Table 4. The following values were finally obtained for the ligand field parameters: e (N) = 7153, e (Br) = 4837, e (Br) = 752 and B = 723 cm1. The AOM parameters are plausible and reproduce the spectrum pretty well. A ligand field analysis of the aqueous solution spectrum indicates that the bromide is a weak - and -donor. The value of 7153 cm1 for e(N) is comparable with values for the other amines (Choi & Lee, 2009; Moon & Choi, 2015). The e(N), e(Br) and e (Br) values are located in the normal ranges but are smaller than those extracted from the single-crystal data or from diffuse reflectance spectra at low temperature. However, no great difference is observed between the AOM parameter in aqueous solution and that from single-crystal data, suggesting that the coordination geometry in the solid state is preserved in solution. Table 5 contains a comparison of the AOM parameters for trans-[CrL2(Me2tn)2]+ with other anionic ligands. The parameter values reported here appear to be significant, as deduced on the basis of the electronic transitions which were obtained from the absorption spectrum in aqueous solution at room temperature, because a solution environment is more similar to naturally occurring systems. The parameter B is about 79% of the value for a free chromium(III) cation in Table 5 AOM parameters (cm1) for trans-[CrL2(Me2tn)2]+ complexes. L
e (N)
e (L)
F Cl Br NCS N3
7175 7360 7153 7130 6195
7510 5265 4837 6160 5290
e (L) 1710 860 752 30 515
Moon and Choi
Reference Choi, Ryoo & Lee (2011) Choi et al. (2007) This work Choi & Lee (2009) Moon & Choi (2015)
[CrBr2(C5H14N2)2]ClO4
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research papers the gas phase. AOM parameters can also be used in determining the photolabilized ligand of the photoreaction in chromium(III) complexes and in predicting the relative efficiency of the 3d–4f energy transfer in heterometal dinuclear complexes (Vanquickenborne & Ceulemans, 1983; Subhan et al., 2003). The IR and electronic spectroscopic properties of (I) are in good agreement with the results from X-ray crystallography, showing that the CrIII cation is in an octahedral environment, coordinated by two bidentate Me2tn ligands in the equatorial plane and by two Br atoms in the trans-axial positions. However, the IR and UV–Vis spectroscopic data do not give any evidence as to whether (I) has a syn or an anti conformation of the two six-membered chelate rings. Ligand field analysis shows that the N atoms of the Me2tn ligand have a strong -donor character, but the bromide has weak - and
-donor properties toward the chromium(III) cation in aqueous solution.
Acknowledgements The X-ray crystallography experiment on the PLS-II BL2DSMC beamline was supported in part by MSIP and POSTECH.
References Adamsky, H. (1996). AOMX. University of Du¨sseldorf, Germany. Arvai, A. J. & Nielsen, C. (1983). ADSC Quantum-210 ADX. AreaDetector System Corporation, Poway, California, USA. Ballhausen, C. J. (1980). In Molecular Electronic Structure of Transition Metal Complexes. New York: McGraw–Hill. Choi, J.-H., Clegg, W., Harrington, R. W. & Lee, S. H. (2010). J. Chem. Crystallogr. 40, 567–571.
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Choi, J.-H., Clegg, W., Nichol, G. S., Lee, S. H., Park, Y. C. & Habibi, M. H. (2007). Spectrochim. Acta Part A, 68, 796–801. Choi, J.-H., Hong, Y. P. & Park, Y. C. (2002). Spectrochim. Acta Part A, 56, 1653–1660. Choi, J.-H., Joshi, T. & Spiccia, L. (2011). Z. Anorg. Allg. Chem. 637, 1194–1198. Choi, J.-H. & Lee, S. H. (2009). J. Mol. Struct. 932, 84–89. Choi, J.-H., Lee, S. H. & Lee, U. (2008). Acta Cryst. E64, m1429. Choi, J.-H., Ryoo, K. S. & Lee, S. H. (2011). Bull. Korean Chem. Soc. 32, 296–298. Choi, J.-H., Suzuki, T. & Kaizaki, S. (2002). Acta Cryst. C58, m539– m541. Fabbrizzi, L. & Poggi, A. (2013). Chem. Soc. Rev. 42, 1681–1699. Martı´nez-Ma´n˜ez, R. & Sanceno´n, F. (2003). Chem. Rev. 103, 4419– 4476. Moon, D. & Choi, J.-H. (2015). Spectrochim. Acta Part A, 138, 774– 779. Moon, D., Lee, C.-S. & Choi, J.-H. (2014). J. Chem. Crystallogr. 44, 306–311. Moon, D., Lee, C.-S., Ryoo, K. S. & Choi, J.-H. (2014). Bull. Korean Chem. Soc. 35, 3099–3102. Otwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M. Sweet, pp. 307–326. New York: Academic Press. Putz, H. & Brandenburg, K. (2014). DIAMOND. Crystal Impact GbR, Bonn, Germany. Ronconi, L. & Sadler, P. J. (2007). Coord. Chem. Rev. 251, 1633– 1648. Ross, A., Choi, J.-H., Hunter, T. M., Pannecouque, C., Moggach, S. A., Parsons, S., De Clercq, E. & Sadler, P. J. (2012). Dalton Trans. 41, 6408–6418. Sheldrick, G. M. (2015a). Acta Cryst. A71, 3–8. Sheldrick, G. M. (2015b). Acta Cryst. C71, 3–8. Spek, A. L. (2009). Acta Cryst. D65, 148–155. Subhan, Md. A., Nakata, H., Suzuki, T., Choi, J.-H. & Kaizaki, S. (2003). J. Lumin. 101, 307–315. Vanquickenborne, L. G. & Ceulemans, A. (1983). Coord. Chem. Rev. 48, 157–202. Westrip, S. P. (2010). J. Appl. Cryst. 43, 920–925.
Acta Cryst. (2015). C71, 351–356
supporting information
supporting information Acta Cryst. (2015). C71, 351-356
[doi:10.1107/S2053229615006026]
Synthesis, crystal structure and spectroscopic properties of transdibromidobis(2,2-dimethylpropane-1,3-diamine-κ2N,N′)chromium(III) perchlorate Dohyun Moon and Jong-Ha Choi Computing details Data collection: PAL ADSC Quantum-210 ADX (Arvai & Nielsen, 1983); cell refinement: HKL3000sm (Otwinowski & Minor, 1997); data reduction: HKL3000sm (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXS2013 (Sheldrick, 2015); program(s) used to refine structure: SHELXL2014/7 (Sheldrick, 2015); molecular graphics: DIAMOND (Brandenburg, 2014); software used to prepare material for publication: publCIF (Westrip, 2010) and PLATON (Spek, 2009). trans-dibromidobis(2,2-dimethylpropane-1,3-diamine-κ22N,N′)chromium(III) perchlorate Crystal data [CrBr2(C5H14N2)2]ClO4 Mr = 515.63 Orthorhombic, Pbca a = 20.656 (4) Å b = 17.666 (4) Å c = 31.305 (6) Å V = 11423 (4) Å3 Z = 24 F(000) = 6216
Dx = 1.799 Mg m−3 Synchrotron radiation, λ = 0.62998 Å Cell parameters from 352345 reflections θ = 0.4–33.6° µ = 3.60 mm−1 T = 100 K Plate, green 0.12 × 0.10 × 0.05 mm
Data collection ADSC Q210 CCD area-detector diffractometer Radiation source: PLSII 2D bending magnet ω scans Absorption correction: empirical (using intensity measurements) (HKL3000sm SCALEPACK; Otwinowski & Minor, 1997) Tmin = 0.670, Tmax = 0.841
115348 measured reflections 15666 independent reflections 13691 reflections with I > 2σ(I) Rint = 0.036 θmax = 26.0°, θmin = 1.8° h = −28→28 k = −23→23 l = −43→43
Refinement Refinement on F2 Least-squares matrix: full R[F2 > 2σ(F2)] = 0.031 wR(F2) = 0.086 S = 1.04 15666 reflections
Acta Cryst. (2015). C71, 351-356
636 parameters 6 restraints Hydrogen site location: inferred from neighbouring sites H-atom parameters constrained
sup-1
supporting information w = 1/[σ2(Fo2) + (0.0577P)2 + 5.702P] where P = (Fo2 + 2Fc2)/3 (Δ/σ)max = 0.003 Δρmax = 1.25 e Å−3 Δρmin = −1.42 e Å−3
Extinction correction: SHELXL2014/7 (Sheldrick, 2015), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 Extinction coefficient: 0.00083 (5)
Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2)
Cr1A Br1A Br2A N1A H1A1 H1A2 N2A H2A1 H2A2 N3A H3A1 H3A2 N4A H4A1 H4A2 C1A H1A3 H1A4 C2A C3A H3A3 H3A4 C4A H4A3 H4A4 H4A5 C5A H5A1 H5A2 H5A3 C6A H6A1 H6A2 C7A
x
y
z
Uiso*/Ueq
0.73021 (2) 0.69990 (2) 0.76227 (2) 0.76335 (9) 0.7377 0.7561 0.82196 (9) 0.8222 0.8257 0.63830 (8) 0.6349 0.6365 0.69737 (8) 0.7004 0.7257 0.83200 (11) 0.8391 0.8382 0.88357 (11) 0.88151 (11) 0.8851 0.9195 0.88047 (14) 0.8383 0.8863 0.9148 0.94937 (13) 0.9527 0.9526 0.9846 0.57964 (10) 0.5407 0.5789 0.57586 (10)
0.60628 (2) 0.61566 (2) 0.60157 (2) 0.71878 (10) 0.7468 0.7354 0.56954 (11) 0.5710 0.5200 0.64035 (9) 0.6907 0.6351 0.49462 (9) 0.4795 0.4658 0.73755 (13) 0.7920 0.7296 0.69270 (13) 0.60849 (14) 0.6025 0.5835 0.70619 (16) 0.6898 0.7602 0.6773 0.72192 (17) 0.7765 0.7121 0.6957 0.60288 (11) 0.6274 0.6112 0.51758 (11)
0.61679 (2) 0.69298 (2) 0.54027 (2) 0.61996 (5) 0.6024 0.6470 0.63681 (6) 0.6659 0.6292 0.59742 (5) 0.6031 0.5685 0.61381 (5) 0.5861 0.6290 0.60917 (7) 0.6150 0.5781 0.63286 (7) 0.62206 (8) 0.5907 0.6352 0.68088 (8) 0.6917 0.6868 0.6950 0.61612 (9) 0.6214 0.5854 0.6310 0.61545 (7) 0.6033 0.6467 0.60673 (6)
0.01368 (7) 0.02048 (5) 0.02102 (5) 0.0179 (3) 0.022* 0.022* 0.0235 (4) 0.028* 0.028* 0.0171 (3) 0.021* 0.021* 0.0164 (3) 0.020* 0.020* 0.0242 (4) 0.029* 0.029* 0.0226 (4) 0.0259 (5) 0.031* 0.031* 0.0351 (6) 0.053* 0.053* 0.053* 0.0384 (6) 0.058* 0.058* 0.058* 0.0184 (4) 0.022* 0.022* 0.0163 (3)
Acta Cryst. (2015). C71, 351-356
Occ. (
