Dalton Transactions View Article Online
Published on 15 August 2014. Downloaded by Stockholms Universitet on 27/10/2014 14:34:06.
PAPER
Cite this: Dalton Trans., 2014, 43, 15526
View Journal | View Issue
Structural complexity in the rare earth metallocene hydride complexes, [(C5Me5)2LnH]2† Shan-Shan Liu,a,b Song Gao,b Joseph W. Zillera and William J. Evans*a X-ray crystallographic data obtained on the metallocene hydrides, [(C5Me5)2LnH]2 (Ln = Gd, Tb, and Dy), of interest for their magnetic properties, have revealed unexpected structural variability in a closely related series of rare earth complexes that can complicate magnetic analysis. Crystals of the two larger metals, Gd and Tb, were structurally straightforward and isomorphous with crystals of [(C5Me5)2SmH]2. However, only for Tb were the locations of the hydride ligands in this structural type identified for the first time and found to be consistent with a (C5Me5)2Ln(μ-H)2Ln(C5Me5)2 structure. In contrast, for Ln = Dy, the [(C5Me5)2H]3− ligand set does not appear to have one optimum crystal structure. Two different types of crystals and one other solid form of [(C5Me5)2DyH]2 were repeatedly isolated upon crystallization and demonstrated that the structure of any particular crystalline sample selected for magnetic analysis could
Received 21st July 2014, Accepted 14th August 2014
be variable. Asymmetric structures with a single hydride bridge, (C5Me5)2Dy(μ-H)DyH(C5Me5)2, were identifiable for the two crystalline forms. This demonstrated uncertainty in structure and highlights the
DOI: 10.1039/c4dt02194k
importance of having a coordination environment with one preferred form for magnetically interesting
www.rsc.org/dalton
complexes.
Introduction Recent studies of the magnetochemistry of rare earth complexes have revealed that many types of complexes exhibit single-molecule magnet behavior.1–5 Polymetallic and monometallic complexes have received the most attention, but recently bimetallic complexes have also been found to exhibit magnetically interesting properties. The (N2)3− radical-bridged complexes, {[(R2N)2(THF)Ln]2(μ-η2:η2-N2)}1− (Ln = Dy,2,4 Tb3,4 R = SiMe3) and the bridging hydride complexes, [Ln(Me5trenCH2)(μ-H)3Ln(Me6tren)]2+ (Ln = Gd, Dy, tren = tris(2aminoethyl)amine),5 are two examples. The [(C5Me5)2LnH]2 complexes6–10 constitute a variant of the latter hydride-bridged species that would allow a comparison of magnetism versus structure and ancillary ligand. Accordingly, examples of [(C5Me5)2LnH]2 that are the magnetically interesting, i.e., Ln = Gd, Tb, and Dy, were synthesized for study. Before magnetic measurements were taken, structural
a Department of Chemistry, University of California, Irvine, California 92697-2025, USA. E-mail: [email protected] b Beijing National Laboratory of Molecular Science, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, P. R. China † Electronic supplementary information (ESI) available: X-ray data collection, structure solution and refinement for 1, 2, 3B, and 3C. CCDC 1008453 (1), 1008454 (2), 1008455 (3B) and 1008456 (3C). For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4dt02194k
15526 | Dalton Trans., 2014, 43, 15526–15531
evidence on these complexes was sought so that the magnetic data could be correlated with structure. Previous structural studies of [(C5Me5)2LnH]2 complexes were limited to Ln = Sm6 and Y.7 In the samarium case, a symmetrical structure was found in terms of the arrangement of the [(C5Me5)2Ln]1+ metallocene units, but no hydride ligands were observable from the crystallographic data. The presumption from the symmetrical nature of the metallocene components is that both hydride ligands were bridging and the complex had a (C5Me5)2Sm(μ-H)2Sm(C5Me5)2 structure. NMR evidence on the hydride ligands was not available due to the paramagnetism of Sm3+. On the other hand, 1H NMR evidence on the yttrium analog initially suggested an asymmetric (C5Me5)2Y(μ-H)YH(C5Me5)2 bimetallic structure,8 but subsequent studies showed it to be a symmetric doubly-bridged species at low temperature in solution, i.e. (C5Me5)2Y(μ-H)2Y(C5Me5)2.9 Recently, the asymmetric (C5Me5)2Y(μ-H)YH(C5Me5)2·toluene structure was found in the solid state by X-ray diffraction.7 Since the ionic radii of eight coordinate Gd3+, 1.053 Å, Tb3+, 1.040 Å, and Dy3+, 1.027 Å, are intermediate in size compared to Sm3+, 1.079 Å, and Y3+, 1.019 Å, it was unclear which structural type the new complexes would adopt. To resolve this question, structural data on the Gd, Tb, and Dy complexes were collected and are reported here. The results demonstrate an example in which structural variability in an analogous series of rare earth complexes can preclude the appropriate correlation of magnetic properties with structure based on a single crystal structure.
This journal is © The Royal Society of Chemistry 2014
View Article Online
Dalton Transactions
Published on 15 August 2014. Downloaded by Stockholms Universitet on 27/10/2014 14:34:06.
Experimental details All manipulations and syntheses described below were conducted with the rigorous exclusion of air and water using standard Schlenk line, high vacuum line, and glovebox techniques under an argon or dinitrogen atmosphere. Solvents were sparged with UHP argon and dried by passage through columns containing Q-5 and molecular sieves prior to use. Benzene-d6 was dried over NaK alloy, degassed by three freeze– pump–thaw cycles, and vacuum transferred before use. 1H NMR spectra were recorded on a Bruker GN500 MHz spectrometer at 298 K. IR samples were prepared as KBr pellets and the spectra were obtained on a Varian 1000 FT-IR spectrometer. Elemental analyses were conducted on a Perkin-Elmer 2400 Series II CHNS elemental analyzer. The (C5Me5)2Ln(C3H5) complexes (Ln = Gd, Tb, and Dy) were synthesized following the literature preparation of Ln = Gd11 and X-ray crystallographic data were obtained for Ln = Tb and Dy.12 KN(SiMe3)2 (Sigma, 95%) was dissolved in toluene, centrifuged, filtered, and dried under vacuum before use as a white powder. C5Me5H was dried over 3 Å molecular sieves and degassed by three freeze–pump–thaw cycles before use. KC5Me5 was synthesized by treatment of C5Me5H with 1.05 equiv. of KN(SiMe3)2 in toluene, followed by filtration of the resulting white solid and washing with toluene and hexane. Anhydrous LnCl3 (Ln = Gd, Tb, Dy) was dried according to the literature.13 H2 was purchased from Praxair and used as received. Allylmagnesium chloride (2.0 M solution in tetrahydrofuran) was purchased from Aldrich and used as received. Anhydrous 1,4dioxane was purchased from Sigma-Aldrich and used without further purification. [(C5Me5)2GdH]2, 1 This procedure follows the literature synthesis of [(C5Me5)2NdH]2.10 (C5Me5)2Gd(C3H5), 1a (0.405 g, 0.86 mmol) was dissolved in 10 mL of pentane and transferred to a sealable Schlenk flask with a Teflon stopcock. The apparatus was attached to a high vacuum line. After three freeze–pump–thaw cycles, H2 (1 atm) was added and the reaction was stirred for 20 min in an ice bath. A yellow precipitate formed. The unreacted H2 and byproduct C3H6 were removed under vacuum and an atmosphere of H2 was reestablished. This process was repeated 3 times and the reaction mixture was stirred at 0 °C for 20 min each time. After stirring under the third addition of H2, the flask was taken into a glovebox free of coordinating solvents. The reaction product was filtered and washed with cold pentane to provide [(C5Me5)2GdH]2, 1,
Paper
(0.230 g, 62%) as a bright yellow powder. Complex 1 is temperature sensitive and should be kept at −30 °C. IR: 2971s, 2905s, 2858s, 2725w, 1492w, 1438s, 1379m, 1250m br, 1170w, 1061w, 1020m, 994w, 907m, 802m br, 646m cm−1. Anal. Calcd for C40H62Gd2: C, 56.03; H, 7.29. Found: C, 56.13; H, 7.50. Single crystals suitable for X-ray diffraction were grown from cold hexane solution at −30 °C over several days. [(C5Me5)2TbH]2, 2 Complex 2 was isolated as a yellow powder in 78% yield following the procedure for 1. IR: 2973s, 2904s, 2857s, 2725w, 1490w, 1438s, 1380s, 1278s br, 1167w, 1062w, 1020m, 954w, 916w, 803w, 648s cm−1. Anal. Calcd for C40H62Tb2: C, 55.81; H, 7.26. Found: C, 55.93; H, 7.40. Single crystals were grown in cold hexane at −30 °C over several days. [(C5Me5)2DyH]2, 3 Complex 3 was isolated as a yellow powder in 64% yield following the procedure for 1. IR: 2973s, 2903s, 2857s, 2725w, 1491m, 1438s, 1381s, 1292s br, 1167w, 1061w, 1022m, 923w, 802w, 654s cm−1. Anal. Calcd for C40H62Dy2: C, 55.35; H, 7.20. Found: C, 55.33; H, 7.28. Many samples of crystalline 3 were examined on the X-ray diffractometer. One solid form and two different types of crystals of 3 were repeatedly found and are designated 3A and 3B, 3C, respectively. Crystals of 3A were grown by the same method described for 1 and 2, i.e. crystallization from cold hexane, but a suitable model for the crystallographic data was never found possibly due to twinning, disorder, or some other problem. Data on single crystals grown from 2 : 1 hexane–toluene, labelled 3B, could be modelled and revealed the formula, (C5Me5)2Dy(µ-H)DyH(C5Me5)2·toluene. When less toluene was used in the recrystallization, yet another form, 3C, could also be analysed by X-ray diffraction and had the formula, (C5Me5)2Dy(µ-H)DyH(C5Me5)2. X-ray crystallographic data Crystallographic information for complexes 1, 2, 3B, and 3C is summarized in Table 1 and in the ESI.†
Results Synthesis The hydrides, [(C5Me5)2LnH]2 (Ln = Gd, Tb, Dy) were prepared by hydrogenolysis of the allyl complexes, (C5Me5)2Ln(C3H5), as originally demonstrated for Ln = Nd,10 eqn (1).
ð1Þ
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 15526–15531 | 15527
View Article Online
Paper
Dalton Transactions
Published on 15 August 2014. Downloaded by Stockholms Universitet on 27/10/2014 14:34:06.
Table 1 X-ray data collection parameters for (C5Me5)2Gd(μ-H)2Gd(C5Me5)2, 1, (C5Me5)2Tb(μ-H)2Tb(C5Me5)2, 2, (C5Me5)2Dy(μ-H)DyH(C5Me5)2· toluene, 3B, (C5Me5)2Dy(μ-H)DyH(C5Me5)2, 3C
Formula
C40H62Gd2 (1)
C40H62Tb2 (2)
C40H62Dy2·C7H8 (3B)
C40H62Dy2 (3C)
Formula weight Crystal system Space group a/Å b/Å c/Å α β γ V/Å3 Z T/K F(000) λ/Å Dcalcd (Mg m−3) μ (mm−1) R1 a [I ≥ 2σ(I)] wR2 a(all data) Sa
857.4 Monoclinic C2/c 16.2167(13) 14.1780(11) 16.7183(13) 90° 104.3396(8)° 90° 3724.1(5) 4 143(2) 1720 0.71073 1.529 3.555 0.0269 0.0677 1.106
860.7 Monoclinic C2/c 16.1651(13) 14.1669(11) 16.6568(13) 90° 104.1168(9)° 90° 3699.4(5) 4 143(2) 1728 0.71073 1.545 3.817 0.0209 0.0550 1.043
960.0 Monoclinic P21/n 10.9652(7) 31.175(2) 12.5094(8) 90° 99.6529(7)° 90° 4215.7(5) 4 83(2) 1936 0.71073 1.513 3.547 0.0216 0.0440 1.202
867.9 Triclinic ˉ P1 10.6726(6) 10.7773(6) 17.0691(9) 100.7439(5)° 103.4896(5)° 97.8657(6)° 1841.97(18) 2 143(2) 868 0.71073 1.565 4.050 0.0200 0.0484 1.017
a
Definitions: R1 = ∑kFo| − |Fck/∑|Fo|, wR2 = [∑[w(Fo2 − Fc2)2]/∑[w(Fo2)2]]1/2, S = [∑[w(Fo2 − Fc2)2]/(n–p)]1/2.
The complexes are highly reactive: in solution, the Ln–H linkage can effect C–H bond activation of the methyl groups of the (C5Me5)1− ligands to form the tuck-over complexes of formula (C5Me5)2Ln[μ-η1:η5-C5Me4(CH2)](μ-H)Ln(C5Me5).9,14 Accordingly, these compounds are best stored at low temperature in an inert atmosphere glovebox containing no coordinating solvents. Structure [(C5Me5)2GdH]2, 1, and [(C5Me5)2TbH]2, 2. The crystal structures of the gadolinium and terbium complexes, 1 and 2, are shown in Fig. 1. These complexes crystallize in the C2/c space group found for [(C5Me5)2SmH]2 6 and are isomorphous with the samarium complex. Table 2 shows a comparison of the relevant bond distances and angles. In each of these complexes, the [(C5Me5)2Ln]1+ moieties are oriented so that one metallocene unit is almost perpendicular to the other. The angle between the plane defined by Ln1 and its two ring centroids and the plane defined by Ln2 and its two
ring centroids is 94.5° for 1, 94.8° for 2, and 93.3° for [(C5Me5)2SmH]2.6 Although the hydride ligands could not be located in the Sm6 and Gd cases, the crystallographic data for Ln = Tb allowed the hydride positions to be located and refined. The data indicate that they are both bridging, i.e., these isomorphous complexes have a (C5Me5)2Ln(μ-H)2Ln(C5Me5)2 structure. Since the error limits on the Tb–H distances are large, it is not appropriate to talk about these lengths. The Tb2H2 plane is located in between the metallocene planes defined for each metallocene unit by the metal and its two ring centroids. The Tb2H2 plane makes a 44.1° angle with one of these metallocene planes and a 50.7° angle with the other. This structural situation is similar to that found in (C5Me5)2Sm(μ-N2)Sm(C5Me5)2 15 which crystallizes in the same space group as 1, 2, and [(C5Me5)2SmH]2 and has similar cell constants to those of [(C5Me5)2SmH]2.6 In the dinitrogen complex, the Sm2N2 plane makes a 62.9° angle with one of the metallocene planes and a 29.3° angle with the other metallocene plane.
Fig. 1 Thermal ellipsoid diagrams of [(C5Me5)2GdH]2, 1 (left), and [(C5Me5)2TbH]2, 2 (right) drawn at the 50% probability level. Hydrogen atoms, except the bridging hydrides in 2, are omitted for clarity.
15528 | Dalton Trans., 2014, 43, 15526–15531
This journal is © The Royal Society of Chemistry 2014
View Article Online
Dalton Transactions
Paper
Published on 15 August 2014. Downloaded by Stockholms Universitet on 27/10/2014 14:34:06.
Table 2 Bond lengths [Å] and angles [°] for (C5Me5)2Gd(μ-H)2Gd(C5Me5)2, 1, (C5Me5)2Tb(μ-H)2Tb(C5Me5)2, 2, (C5Me5)2Dy(μ-H)DyH(C5Me5)2·toluene, 3B, (C5Me5)2Dy(μ-H)DyH(C5Me5)2, 3C, and (C5Me5)2Y(μ-H)YH(C5Me5)2·toluene7 (Y)
Parameter
1
2
3B
3C
Y
Ln(1)–Cnt1 Ln(1)–Cnt2 Ln(2)–Cnt3 Ln(2)–Cnt4 Ln(1)⋯Ln(2) Cnt–Ln(1)–Cnt Cnt–Ln(2)–Cnt
2.427 2.431
2.413 2.415
3.8336(4) 132.9 131.3
3.7770(4) 131.8 131.0
2.396 2.387 2.337 2.354 4.3340(2) 139.0 135.1
2.394 2.369 2.356 2.348 4.3212(2) 138.8 135.2
2.392 2.382 2.329 2.349 4.3303(4) 138.6 135.1
This tilt of the Tb2H2 plane with respect to the metallocene wedge is unusual compared to transition metal metallocenes, which have their ligands in a plane that bisects the plane formed by the metal and its two ring centroids.16,17 As discussed for [(C5Me5)2SmH]2 6,17 and [(C5Me5)2Sm]2(μ-N2)15 and found for 1 and 2, the two metallocene units in all of these bimetallic compounds are oriented such that the four ring centroids approximate a tetrahedron, not a square plane. If the bridging hydrides or (N2)2− ligand are in either of the planes that bisect the plane formed by the metal and its two ring centroids, as is common for the transition metals, this would have unfavourable steric interactions with the C5Me5 rings of the other metallocene. Accordingly, the bridging ligands are in between the two perpendicular metallocene planes. [(C5Me5)2DyH]2, 3. Crystallographic analysis of the dysprosium complex 3 proved to be more difficult. Many crystalline samples were analysed on the diffractometer and these multiple data collections revealed two different types of crystals and one other solid form. Crystallization of 3 from cold hexane initially gave crystals designated 3A. The apparent space group was C2/c with unit cell parameters of a = 64.4910 Å; b = 14.1364 Å; c = 40.3429 Å; β = 114.979°. However, nothing could be concluded from these data; a model for the data was not obtainable. Crystallization of 3 from 2 : 1 hexane–toluene gave a set of crystals that could be fully analyzed crystallographically and the structure proved to be the asymmetrical dimer, (C5Me5)2Dy(μ-H)DyH(C5Me5)2·toluene, 3B, Fig. 2, with toluene in the lattice. This complex is isomorphous with the recently reported yttrium complex, (C5Me5)2Y(μ-H)YH(C5Me5)2·
toluene.7 Crystallization of 3 with smaller amounts of toluene in hexane (hexane–toluene = 2.5 : 1–2.8 : 1) gave mixtures of crystals that included the asymmetrical dimer (C5Me5)2Dy(μ-H)DyH(C5Me5)2, 3C, which is like 3B without toluene present, as well as crystals of 3A identified by unit cell determination. Subsequent crystallizations of 3 using 1 : 1, 2 : 1, and 3 : 1 hexane– toluene with the same sample of 3 each gave crystals that matched the unit cell of 3A. Given the variability in the composition of the mixtures of crystals obtained from closely related crystallization procedures, it seemed impossible to predict which form(s) of 3 would be present in a given sample (e.g. one selected for magnetic studies). Crystallographic data on 3B and 3C are shown in Fig. 2 and metrical parameters are compared in Table 2. There is disorder in one of the four (C5Me5)1− rings in the crystal of 3C. Hence, the crystals that formed with toluene in the lattice provided the best structural data of all three of the crystalline variations of complex 3. As shown in Table 2, the (C5Me5)2Dy(μ-H)DyH(C5Me5)2 components of 3B and 3C are quite similar. This includes the Dy-(C5Me5 ring centroid) distances, the (C5Me5 ring centroid)–Dy–(C5Me5 ring centroid) angles and the 4.334 and 4.321 Å Dy⋯Dy distances. Hence, the presence of toluene in the lattice does not affect the molecular structure of the bimetallic hydride unit, except to give a more ordered structure to 3B.
Discussion The structural studies on [(C5Me5)2GdH]2, 1, [(C5Me5)2Tb(μ-H)]2, 2, and [(C5Me5)2DyH]2, 3, serve as a reminder of the
Fig. 2 Thermal ellipsoid diagrams of two crystalline variations of [(C5Me5)2DyH]2, 3: (C5Me5)2Dy(μ-H)DyH(C5Me5)2·toluene, 3B (left), and (C5Me5)2Dy(μ-H)DyH(C5Me5)2, 3C (right) drawn at the 50% probability level. Hydrogen atoms except for the hydride ligands are omitted for clarity.
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 15526–15531 | 15529
View Article Online
Published on 15 August 2014. Downloaded by Stockholms Universitet on 27/10/2014 14:34:06.
Paper
importance to structure and crystallinity of small changes in the size of the rare earth metal in a homologous series. [(C5Me5)2LnH]2 complexes of the larger lanthanides, Sm, Gd and Tb, crystallize in a single structural type with relatively symmetric metallocene locations such that the four rings approximate a tetrahedron. However, only in the Tb structure were the data of high enough quality to reveal the hydride ligands. Hence, reducing the size of the metal by 0.039 Å did not change the structural type, but led to crystals of high quality for hydride location. However, reducing the size of the metal by another 0.013 Å to Dy, led to a situation in which this combination of ligands and metals did not crystallize to a single preferred structure. Three crystalline solids, 3A, 3B, and 3C, were isolated from this system and for 3B and 3C, the asymmetric (C5Me5)2Dy(μ-H)DyH(C5Me5)2 structure was observed. Further variability was found between 3B and 3C in that the disorder found in one (C5Me5)1− ring in 3C was absent in 3B which had toluene solvent present. Reducing the size of the metal by another 0.008 Å to Y eliminated the structural variability found for the three forms of Dy while maintaining the (C5Me5)2Ln(μ-H)LnH(C5Me5)2 structure. Evidently, the combination of the [(C5Me5)2H]3− ligand set with a metal the size of Dy is not a good match to give one preferred crystalline arrangement. This is unfortunate since [(C5Me5)2DyH]2 is of interest as a single molecule magnet and it would be optimum to correlate magnetic data with a single structure. Efforts were tried to separate pure 3B or 3C from 3A by microscopy, but these failed due to the temperature sensitivity of the complexes and high degree of co-crystallization. This complex is not suitable for magnetic analysis, since multiple structural types exist with Dy and it is not clear which one would be present in a selected sample. Although complexes 3B and 3C are similar in the (C5Me5)2Dy(μ-H)DyH(C5Me5)2 part of the structure, they differ in molecular weight and the crystals cannot be differentiated from 3A which has an unknown structure. This emphasizes the importance of choosing the ligands for potential single molecule magnets such that structural ambiguity does not occur. At present, this can only be determined by collecting the structural data, but hopefully future developments in theory will make such information predictable. In many applications employing rare earth metals, selecting a slightly different metal size will be acceptable. However, for magnetic studies, the specific rare earth metal is very important and optimization of structural type by size variation cannot be done. In this case, a different ligand system must be chosen to avoid structural ambiguity.
Conclusion Structural analysis of [(C5Me5)2LnH]2 complexes of Ln = Sm, Gd, Tb, Dy, and Y shows the importance of matching the size of the metal with the size of the ligand set. The Sm, Gd, and Tb complexes have a symmetrical arrangement of the metallocene units consistent with [(C5Me5)2Ln(μ-H)]2 structures, but
15530 | Dalton Trans., 2014, 43, 15526–15531
Dalton Transactions
only with Tb could the hydride ligands be located crystallographically. In contrast, the smaller metals Dy and Y have (C5Me5)2Ln(μ-H)LnH(C5Me5)2 structures containing one formally seven coordinate rare earth metal and one eight coordinate site. Although the Y complex provided good crystallographic data on a single structural type, the Dy system does not have a single optimum crystal structure. Instead, with this metal ligand combination, two different types of crystals and one other solid form can be obtained depending on crystallization conditions. Since these co-crystallize and can only be differentiated by X-ray diffraction, this complicates magnetic analysis on bulk samples. Magnetic data on [(C5Me5)2Dy(μ-H)]2 cannot be reliably correlated with structure. Hence, examination of single molecule magnet behavior for a Dy2H2 unit should be pursued with ancillary ligands other than (C5Me5)1−. These studies emphasize the fact that a single crystal structure may not represent the full structural situation in a given complex. If magnetic data do not match that predicted based on a single crystal structure, it might be prudent to examine more samples to see if there is structural variability as demonstrated here.
Acknowledgements We thank the U. S. National Science Foundation under CHE-1265396 for support of this research, Jordan F. Corbey for help with the crystallography, and Megan E. Fieser for helpful discussion. We thank the China Scholarship Council 201206010106 for support of Shan-Shan Liu.
References 1 (a) N. Ishikawa, M. Sugita, T. Ishikawa, S.-Y. Koshihara and Y. Kaizu, J. Am. Chem. Soc., 2003, 125, 8694–8695; (b) M. A. AlDamen, J. M. Clemente-Juan, E. Coronado, C. Martí-Gastaldo and A. Gaita-Ariño, J. Am. Chem. Soc., 2008, 130, 8874–8875; (c) E. Coronado, C. Giménez-Saiz, A. Recuenco, A. Tarazón, F. M. Romero, A. n. Camón and F. Luis, Inorg. Chem., 2011, 50, 7370–7372; (d) S.-D. Jiang, B.-W. Wang, G. Su, Z.-M. Wang and S. Gao, Angew. Chem., Int. Ed., 2010, 49, 7448–7451; (e) S.-D. Jiang, B.-W. Wang, H.-L. Sun, Z.-M. Wang and S. Gao, J. Am. Chem. Soc., 2011, 133, 4730–4733; (f) M. Jeletic, P.-H. Lin, J. J. Le Roy, I. Korobkov, S. I. Gorelsky and M. Murugesu, J. Am. Chem. Soc., 2011, 133, 19286–19289; (g) G. Cucinotta, M. Perfetti, J. Luzon, M. Etienne, P.-E. Car, A. Caneschi, G. Calvez, K. Bernot and R. Sessoli, Angew. Chem., Int. Ed., 2012, 51, 1606–1610; (h) J.-L. Liu, Y.-C. Chen, Y.-Z. Zheng, W.-Q. Lin, L. Ungur, W. Wernsdorfer, L. F. Chibotaru and M.-L. Tong, Chem. Sci., 2013, 4, 3310–3316; (i) F. Tuna, C. A. Smith, M. Bodensteiner, L. Ungur, L. F. Chibotaru, E. J. L. McInnes, R. E. P. Winpenny, D. Collison and R. A. Layfield, Angew. Chem., Int. Ed., 2012, 51, 6976–6980; ( j) S. A. Sulway, R. A. Layfield, F. Tuna, W. Wernsdorfer and
This journal is © The Royal Society of Chemistry 2014
View Article Online
Published on 15 August 2014. Downloaded by Stockholms Universitet on 27/10/2014 14:34:06.
Dalton Transactions
2 3 4 5
6 7
R. E. P. Winpenny, Chem. Commun., 2012, 48, 1508–1510; (k) K. R. Meihaus and J. R. Long, J. Am. Chem. Soc., 2013, 135, 17952–17957; (l) L. Ungur, J. J. Le Roy, I. Korobkov, M. Murugesu and L. F. Chibotaru, Angew. Chem., Int. Ed., 2014, 53, 4413–4417; (m) F. Habib, J. Long, P.-H. Lin, I. Korobkov, L. Ungur, W. Wernsdorfer, L. F. Chibotaru and M. Murugesu, Chem. Sci., 2012, 3, 2158–2164; (n) R. J. Blagg, L. Ungur, F. Tuna, J. Speak, P. Comar, D. Collison, W. Wernsdorfer, E. J. L. McInnes, L. F. Chibotaru and R. E. P. Winpenny, Nat. Chem., 2013, 5, 673–678; (o) J. Tang, I. Hewitt, N. T. Madhu, G. Chastanet, W. Wernsdorfer, C. E. Anson, C. Benelli, R. Sessoli and A. K. Powell, Angew. Chem., Int. Ed., 2006, 45, 1729–1733; ( p) P. Zhang, L. Zhang, C. Wang, S. Xue, S.-Y. Lin and J. Tang, J. Am. Chem. Soc., 2014, 136, 4484– 4487; (q) E. M. Fatila, M. Rouzières, M. C. Jennings, A. J. Lough, R. Clérac and K. E. Preuss, J. Am. Chem. Soc., 2013, 135, 9596–9599; (r) D. N. Woodruff, R. E. P. Winpenny and R. A. Layfield, Chem. Rev., 2013, 113, 5110–5148; (s) R. A. Layfield, Organometallics, 2014, 33, 1084–1099. J. D. Rinehart, M. Fang, W. J. Evans and J. R. Long, J. Am. Chem. Soc., 2011, 133, 14236–14239. J. D. Rinehart, M. Fang, W. J. Evans and J. R. Long, Nat. Chem., 2011, 3, 538–542. K. R. Meihaus, J. F. Corbey, M. Fang, J. W. Ziller, J. R. Long and W. J. Evans, Inorg. Chem., 2014, 53, 3099–3107. A. Venugopal, F. Tuna, T. P. Spaniol, L. Ungur, L. F. Chibotaru, J. Okuda and R. A. Layfield, Chem. Commun., 2013, 49, 901–903. W. J. Evans, I. Bloom, W. E. Hunter and J. L. Atwood, J. Am. Chem. Soc., 1983, 105, 1401–1403. C. L. Webster, J. W. Ziller and W. J. Evans, Organometallics, 2014, 33, 433–436.
This journal is © The Royal Society of Chemistry 2014
Paper
8 (a) K. H. den Haan and J. H. Teuben, J. Chem. Soc., Chem. Commun., 1986, 682–683; (b) K. H. Den Haan, Y. Wielstra and J. H. Teuben, Organometallics, 1987, 6, 2053–2060. 9 M. Booij, B. J. Deelman, R. Duchateau, D. S. Postma, A. Meetsma and J. H. Teuben, Organometallics, 1993, 12, 3531–3540. 10 W. J. Evans, C. A. Seibel and J. W. Ziller, J. Am. Chem. Soc., 1998, 120, 6745–6752. 11 W. J. Evans, B. L. Davis, T. M. Champagne and J. W. Ziller, Proc. Natl. Acad. Sci. U. S. A., 2006, 103, 12678–12683. 12 (a) T. J. Mueller, M. E. Fieser, J. W. Ziller and W. J. Evans, unpublished results, Sept 2010; (b) S. Demir, J. M. Zadrozny, M. Nippe and J. R. Long, J. Am. Chem. Soc., 2012, 134, 18546–18549. 13 M. D. Taylor and C. P. Carter, J. Inorg. Nucl. Chem., 1962, 24, 387–391. 14 (a) W. J. Evans, T. A. Ulibarri and J. W. Ziller, Organometallics, 1991, 10, 134–142; (b) W. J. Evans, J. M. Perotti and J. W. Ziller, Inorg. Chem., 2005, 44, 5820–5825; (c) W. J. Evans, T. M. Champagne and J. W. Ziller, J. Am. Chem. Soc., 2006, 128, 14270–14271; (d) W. J. Evans, K. A. Miller, A. G. DiPasquale, A. L. Rheingold, T. J. Stewart and R. Bau, Angew. Chem., Int. Ed., 2008, 47, 5075–5078; (e) E. Montalvo, K. A. Miller, J. W. Ziller and W. J. Evans, Organometallics, 2010, 29, 4159–4170; (f ) K. R. D. Johnson and P. G. Hayes, Chem. Soc. Rev., 2013, 42, 1947–1960; (g) B. M. Schmiege, M. E. Fieser, J. W. Ziller and W. J. Evans, Organometallics, 2012, 31, 5591–5598. 15 W. J. Evans, T. A. Ulibarri and J. W. Ziller, J. Am. Chem. Soc., 1988, 110, 6877–6879. 16 J. W. Lauher and R. Hoffmann, J. Am. Chem. Soc., 1976, 98, 1729–1742. 17 J. V. Ortiz and R. Hoffmann, Inorg. Chem., 1985, 24, 2095– 2104.
Dalton Trans., 2014, 43, 15526–15531 | 15531
Published on 15 August 2014. Downloaded by Stockholms Universitet on 27/10/2014 14:34:06.
PAPER
Cite this: Dalton Trans., 2014, 43, 15526
View Journal | View Issue
Structural complexity in the rare earth metallocene hydride complexes, [(C5Me5)2LnH]2† Shan-Shan Liu,a,b Song Gao,b Joseph W. Zillera and William J. Evans*a X-ray crystallographic data obtained on the metallocene hydrides, [(C5Me5)2LnH]2 (Ln = Gd, Tb, and Dy), of interest for their magnetic properties, have revealed unexpected structural variability in a closely related series of rare earth complexes that can complicate magnetic analysis. Crystals of the two larger metals, Gd and Tb, were structurally straightforward and isomorphous with crystals of [(C5Me5)2SmH]2. However, only for Tb were the locations of the hydride ligands in this structural type identified for the first time and found to be consistent with a (C5Me5)2Ln(μ-H)2Ln(C5Me5)2 structure. In contrast, for Ln = Dy, the [(C5Me5)2H]3− ligand set does not appear to have one optimum crystal structure. Two different types of crystals and one other solid form of [(C5Me5)2DyH]2 were repeatedly isolated upon crystallization and demonstrated that the structure of any particular crystalline sample selected for magnetic analysis could
Received 21st July 2014, Accepted 14th August 2014
be variable. Asymmetric structures with a single hydride bridge, (C5Me5)2Dy(μ-H)DyH(C5Me5)2, were identifiable for the two crystalline forms. This demonstrated uncertainty in structure and highlights the
DOI: 10.1039/c4dt02194k
importance of having a coordination environment with one preferred form for magnetically interesting
www.rsc.org/dalton
complexes.
Introduction Recent studies of the magnetochemistry of rare earth complexes have revealed that many types of complexes exhibit single-molecule magnet behavior.1–5 Polymetallic and monometallic complexes have received the most attention, but recently bimetallic complexes have also been found to exhibit magnetically interesting properties. The (N2)3− radical-bridged complexes, {[(R2N)2(THF)Ln]2(μ-η2:η2-N2)}1− (Ln = Dy,2,4 Tb3,4 R = SiMe3) and the bridging hydride complexes, [Ln(Me5trenCH2)(μ-H)3Ln(Me6tren)]2+ (Ln = Gd, Dy, tren = tris(2aminoethyl)amine),5 are two examples. The [(C5Me5)2LnH]2 complexes6–10 constitute a variant of the latter hydride-bridged species that would allow a comparison of magnetism versus structure and ancillary ligand. Accordingly, examples of [(C5Me5)2LnH]2 that are the magnetically interesting, i.e., Ln = Gd, Tb, and Dy, were synthesized for study. Before magnetic measurements were taken, structural
a Department of Chemistry, University of California, Irvine, California 92697-2025, USA. E-mail: [email protected] b Beijing National Laboratory of Molecular Science, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, P. R. China † Electronic supplementary information (ESI) available: X-ray data collection, structure solution and refinement for 1, 2, 3B, and 3C. CCDC 1008453 (1), 1008454 (2), 1008455 (3B) and 1008456 (3C). For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4dt02194k
15526 | Dalton Trans., 2014, 43, 15526–15531
evidence on these complexes was sought so that the magnetic data could be correlated with structure. Previous structural studies of [(C5Me5)2LnH]2 complexes were limited to Ln = Sm6 and Y.7 In the samarium case, a symmetrical structure was found in terms of the arrangement of the [(C5Me5)2Ln]1+ metallocene units, but no hydride ligands were observable from the crystallographic data. The presumption from the symmetrical nature of the metallocene components is that both hydride ligands were bridging and the complex had a (C5Me5)2Sm(μ-H)2Sm(C5Me5)2 structure. NMR evidence on the hydride ligands was not available due to the paramagnetism of Sm3+. On the other hand, 1H NMR evidence on the yttrium analog initially suggested an asymmetric (C5Me5)2Y(μ-H)YH(C5Me5)2 bimetallic structure,8 but subsequent studies showed it to be a symmetric doubly-bridged species at low temperature in solution, i.e. (C5Me5)2Y(μ-H)2Y(C5Me5)2.9 Recently, the asymmetric (C5Me5)2Y(μ-H)YH(C5Me5)2·toluene structure was found in the solid state by X-ray diffraction.7 Since the ionic radii of eight coordinate Gd3+, 1.053 Å, Tb3+, 1.040 Å, and Dy3+, 1.027 Å, are intermediate in size compared to Sm3+, 1.079 Å, and Y3+, 1.019 Å, it was unclear which structural type the new complexes would adopt. To resolve this question, structural data on the Gd, Tb, and Dy complexes were collected and are reported here. The results demonstrate an example in which structural variability in an analogous series of rare earth complexes can preclude the appropriate correlation of magnetic properties with structure based on a single crystal structure.
This journal is © The Royal Society of Chemistry 2014
View Article Online
Dalton Transactions
Published on 15 August 2014. Downloaded by Stockholms Universitet on 27/10/2014 14:34:06.
Experimental details All manipulations and syntheses described below were conducted with the rigorous exclusion of air and water using standard Schlenk line, high vacuum line, and glovebox techniques under an argon or dinitrogen atmosphere. Solvents were sparged with UHP argon and dried by passage through columns containing Q-5 and molecular sieves prior to use. Benzene-d6 was dried over NaK alloy, degassed by three freeze– pump–thaw cycles, and vacuum transferred before use. 1H NMR spectra were recorded on a Bruker GN500 MHz spectrometer at 298 K. IR samples were prepared as KBr pellets and the spectra were obtained on a Varian 1000 FT-IR spectrometer. Elemental analyses were conducted on a Perkin-Elmer 2400 Series II CHNS elemental analyzer. The (C5Me5)2Ln(C3H5) complexes (Ln = Gd, Tb, and Dy) were synthesized following the literature preparation of Ln = Gd11 and X-ray crystallographic data were obtained for Ln = Tb and Dy.12 KN(SiMe3)2 (Sigma, 95%) was dissolved in toluene, centrifuged, filtered, and dried under vacuum before use as a white powder. C5Me5H was dried over 3 Å molecular sieves and degassed by three freeze–pump–thaw cycles before use. KC5Me5 was synthesized by treatment of C5Me5H with 1.05 equiv. of KN(SiMe3)2 in toluene, followed by filtration of the resulting white solid and washing with toluene and hexane. Anhydrous LnCl3 (Ln = Gd, Tb, Dy) was dried according to the literature.13 H2 was purchased from Praxair and used as received. Allylmagnesium chloride (2.0 M solution in tetrahydrofuran) was purchased from Aldrich and used as received. Anhydrous 1,4dioxane was purchased from Sigma-Aldrich and used without further purification. [(C5Me5)2GdH]2, 1 This procedure follows the literature synthesis of [(C5Me5)2NdH]2.10 (C5Me5)2Gd(C3H5), 1a (0.405 g, 0.86 mmol) was dissolved in 10 mL of pentane and transferred to a sealable Schlenk flask with a Teflon stopcock. The apparatus was attached to a high vacuum line. After three freeze–pump–thaw cycles, H2 (1 atm) was added and the reaction was stirred for 20 min in an ice bath. A yellow precipitate formed. The unreacted H2 and byproduct C3H6 were removed under vacuum and an atmosphere of H2 was reestablished. This process was repeated 3 times and the reaction mixture was stirred at 0 °C for 20 min each time. After stirring under the third addition of H2, the flask was taken into a glovebox free of coordinating solvents. The reaction product was filtered and washed with cold pentane to provide [(C5Me5)2GdH]2, 1,
Paper
(0.230 g, 62%) as a bright yellow powder. Complex 1 is temperature sensitive and should be kept at −30 °C. IR: 2971s, 2905s, 2858s, 2725w, 1492w, 1438s, 1379m, 1250m br, 1170w, 1061w, 1020m, 994w, 907m, 802m br, 646m cm−1. Anal. Calcd for C40H62Gd2: C, 56.03; H, 7.29. Found: C, 56.13; H, 7.50. Single crystals suitable for X-ray diffraction were grown from cold hexane solution at −30 °C over several days. [(C5Me5)2TbH]2, 2 Complex 2 was isolated as a yellow powder in 78% yield following the procedure for 1. IR: 2973s, 2904s, 2857s, 2725w, 1490w, 1438s, 1380s, 1278s br, 1167w, 1062w, 1020m, 954w, 916w, 803w, 648s cm−1. Anal. Calcd for C40H62Tb2: C, 55.81; H, 7.26. Found: C, 55.93; H, 7.40. Single crystals were grown in cold hexane at −30 °C over several days. [(C5Me5)2DyH]2, 3 Complex 3 was isolated as a yellow powder in 64% yield following the procedure for 1. IR: 2973s, 2903s, 2857s, 2725w, 1491m, 1438s, 1381s, 1292s br, 1167w, 1061w, 1022m, 923w, 802w, 654s cm−1. Anal. Calcd for C40H62Dy2: C, 55.35; H, 7.20. Found: C, 55.33; H, 7.28. Many samples of crystalline 3 were examined on the X-ray diffractometer. One solid form and two different types of crystals of 3 were repeatedly found and are designated 3A and 3B, 3C, respectively. Crystals of 3A were grown by the same method described for 1 and 2, i.e. crystallization from cold hexane, but a suitable model for the crystallographic data was never found possibly due to twinning, disorder, or some other problem. Data on single crystals grown from 2 : 1 hexane–toluene, labelled 3B, could be modelled and revealed the formula, (C5Me5)2Dy(µ-H)DyH(C5Me5)2·toluene. When less toluene was used in the recrystallization, yet another form, 3C, could also be analysed by X-ray diffraction and had the formula, (C5Me5)2Dy(µ-H)DyH(C5Me5)2. X-ray crystallographic data Crystallographic information for complexes 1, 2, 3B, and 3C is summarized in Table 1 and in the ESI.†
Results Synthesis The hydrides, [(C5Me5)2LnH]2 (Ln = Gd, Tb, Dy) were prepared by hydrogenolysis of the allyl complexes, (C5Me5)2Ln(C3H5), as originally demonstrated for Ln = Nd,10 eqn (1).
ð1Þ
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 15526–15531 | 15527
View Article Online
Paper
Dalton Transactions
Published on 15 August 2014. Downloaded by Stockholms Universitet on 27/10/2014 14:34:06.
Table 1 X-ray data collection parameters for (C5Me5)2Gd(μ-H)2Gd(C5Me5)2, 1, (C5Me5)2Tb(μ-H)2Tb(C5Me5)2, 2, (C5Me5)2Dy(μ-H)DyH(C5Me5)2· toluene, 3B, (C5Me5)2Dy(μ-H)DyH(C5Me5)2, 3C
Formula
C40H62Gd2 (1)
C40H62Tb2 (2)
C40H62Dy2·C7H8 (3B)
C40H62Dy2 (3C)
Formula weight Crystal system Space group a/Å b/Å c/Å α β γ V/Å3 Z T/K F(000) λ/Å Dcalcd (Mg m−3) μ (mm−1) R1 a [I ≥ 2σ(I)] wR2 a(all data) Sa
857.4 Monoclinic C2/c 16.2167(13) 14.1780(11) 16.7183(13) 90° 104.3396(8)° 90° 3724.1(5) 4 143(2) 1720 0.71073 1.529 3.555 0.0269 0.0677 1.106
860.7 Monoclinic C2/c 16.1651(13) 14.1669(11) 16.6568(13) 90° 104.1168(9)° 90° 3699.4(5) 4 143(2) 1728 0.71073 1.545 3.817 0.0209 0.0550 1.043
960.0 Monoclinic P21/n 10.9652(7) 31.175(2) 12.5094(8) 90° 99.6529(7)° 90° 4215.7(5) 4 83(2) 1936 0.71073 1.513 3.547 0.0216 0.0440 1.202
867.9 Triclinic ˉ P1 10.6726(6) 10.7773(6) 17.0691(9) 100.7439(5)° 103.4896(5)° 97.8657(6)° 1841.97(18) 2 143(2) 868 0.71073 1.565 4.050 0.0200 0.0484 1.017
a
Definitions: R1 = ∑kFo| − |Fck/∑|Fo|, wR2 = [∑[w(Fo2 − Fc2)2]/∑[w(Fo2)2]]1/2, S = [∑[w(Fo2 − Fc2)2]/(n–p)]1/2.
The complexes are highly reactive: in solution, the Ln–H linkage can effect C–H bond activation of the methyl groups of the (C5Me5)1− ligands to form the tuck-over complexes of formula (C5Me5)2Ln[μ-η1:η5-C5Me4(CH2)](μ-H)Ln(C5Me5).9,14 Accordingly, these compounds are best stored at low temperature in an inert atmosphere glovebox containing no coordinating solvents. Structure [(C5Me5)2GdH]2, 1, and [(C5Me5)2TbH]2, 2. The crystal structures of the gadolinium and terbium complexes, 1 and 2, are shown in Fig. 1. These complexes crystallize in the C2/c space group found for [(C5Me5)2SmH]2 6 and are isomorphous with the samarium complex. Table 2 shows a comparison of the relevant bond distances and angles. In each of these complexes, the [(C5Me5)2Ln]1+ moieties are oriented so that one metallocene unit is almost perpendicular to the other. The angle between the plane defined by Ln1 and its two ring centroids and the plane defined by Ln2 and its two
ring centroids is 94.5° for 1, 94.8° for 2, and 93.3° for [(C5Me5)2SmH]2.6 Although the hydride ligands could not be located in the Sm6 and Gd cases, the crystallographic data for Ln = Tb allowed the hydride positions to be located and refined. The data indicate that they are both bridging, i.e., these isomorphous complexes have a (C5Me5)2Ln(μ-H)2Ln(C5Me5)2 structure. Since the error limits on the Tb–H distances are large, it is not appropriate to talk about these lengths. The Tb2H2 plane is located in between the metallocene planes defined for each metallocene unit by the metal and its two ring centroids. The Tb2H2 plane makes a 44.1° angle with one of these metallocene planes and a 50.7° angle with the other. This structural situation is similar to that found in (C5Me5)2Sm(μ-N2)Sm(C5Me5)2 15 which crystallizes in the same space group as 1, 2, and [(C5Me5)2SmH]2 and has similar cell constants to those of [(C5Me5)2SmH]2.6 In the dinitrogen complex, the Sm2N2 plane makes a 62.9° angle with one of the metallocene planes and a 29.3° angle with the other metallocene plane.
Fig. 1 Thermal ellipsoid diagrams of [(C5Me5)2GdH]2, 1 (left), and [(C5Me5)2TbH]2, 2 (right) drawn at the 50% probability level. Hydrogen atoms, except the bridging hydrides in 2, are omitted for clarity.
15528 | Dalton Trans., 2014, 43, 15526–15531
This journal is © The Royal Society of Chemistry 2014
View Article Online
Dalton Transactions
Paper
Published on 15 August 2014. Downloaded by Stockholms Universitet on 27/10/2014 14:34:06.
Table 2 Bond lengths [Å] and angles [°] for (C5Me5)2Gd(μ-H)2Gd(C5Me5)2, 1, (C5Me5)2Tb(μ-H)2Tb(C5Me5)2, 2, (C5Me5)2Dy(μ-H)DyH(C5Me5)2·toluene, 3B, (C5Me5)2Dy(μ-H)DyH(C5Me5)2, 3C, and (C5Me5)2Y(μ-H)YH(C5Me5)2·toluene7 (Y)
Parameter
1
2
3B
3C
Y
Ln(1)–Cnt1 Ln(1)–Cnt2 Ln(2)–Cnt3 Ln(2)–Cnt4 Ln(1)⋯Ln(2) Cnt–Ln(1)–Cnt Cnt–Ln(2)–Cnt
2.427 2.431
2.413 2.415
3.8336(4) 132.9 131.3
3.7770(4) 131.8 131.0
2.396 2.387 2.337 2.354 4.3340(2) 139.0 135.1
2.394 2.369 2.356 2.348 4.3212(2) 138.8 135.2
2.392 2.382 2.329 2.349 4.3303(4) 138.6 135.1
This tilt of the Tb2H2 plane with respect to the metallocene wedge is unusual compared to transition metal metallocenes, which have their ligands in a plane that bisects the plane formed by the metal and its two ring centroids.16,17 As discussed for [(C5Me5)2SmH]2 6,17 and [(C5Me5)2Sm]2(μ-N2)15 and found for 1 and 2, the two metallocene units in all of these bimetallic compounds are oriented such that the four ring centroids approximate a tetrahedron, not a square plane. If the bridging hydrides or (N2)2− ligand are in either of the planes that bisect the plane formed by the metal and its two ring centroids, as is common for the transition metals, this would have unfavourable steric interactions with the C5Me5 rings of the other metallocene. Accordingly, the bridging ligands are in between the two perpendicular metallocene planes. [(C5Me5)2DyH]2, 3. Crystallographic analysis of the dysprosium complex 3 proved to be more difficult. Many crystalline samples were analysed on the diffractometer and these multiple data collections revealed two different types of crystals and one other solid form. Crystallization of 3 from cold hexane initially gave crystals designated 3A. The apparent space group was C2/c with unit cell parameters of a = 64.4910 Å; b = 14.1364 Å; c = 40.3429 Å; β = 114.979°. However, nothing could be concluded from these data; a model for the data was not obtainable. Crystallization of 3 from 2 : 1 hexane–toluene gave a set of crystals that could be fully analyzed crystallographically and the structure proved to be the asymmetrical dimer, (C5Me5)2Dy(μ-H)DyH(C5Me5)2·toluene, 3B, Fig. 2, with toluene in the lattice. This complex is isomorphous with the recently reported yttrium complex, (C5Me5)2Y(μ-H)YH(C5Me5)2·
toluene.7 Crystallization of 3 with smaller amounts of toluene in hexane (hexane–toluene = 2.5 : 1–2.8 : 1) gave mixtures of crystals that included the asymmetrical dimer (C5Me5)2Dy(μ-H)DyH(C5Me5)2, 3C, which is like 3B without toluene present, as well as crystals of 3A identified by unit cell determination. Subsequent crystallizations of 3 using 1 : 1, 2 : 1, and 3 : 1 hexane– toluene with the same sample of 3 each gave crystals that matched the unit cell of 3A. Given the variability in the composition of the mixtures of crystals obtained from closely related crystallization procedures, it seemed impossible to predict which form(s) of 3 would be present in a given sample (e.g. one selected for magnetic studies). Crystallographic data on 3B and 3C are shown in Fig. 2 and metrical parameters are compared in Table 2. There is disorder in one of the four (C5Me5)1− rings in the crystal of 3C. Hence, the crystals that formed with toluene in the lattice provided the best structural data of all three of the crystalline variations of complex 3. As shown in Table 2, the (C5Me5)2Dy(μ-H)DyH(C5Me5)2 components of 3B and 3C are quite similar. This includes the Dy-(C5Me5 ring centroid) distances, the (C5Me5 ring centroid)–Dy–(C5Me5 ring centroid) angles and the 4.334 and 4.321 Å Dy⋯Dy distances. Hence, the presence of toluene in the lattice does not affect the molecular structure of the bimetallic hydride unit, except to give a more ordered structure to 3B.
Discussion The structural studies on [(C5Me5)2GdH]2, 1, [(C5Me5)2Tb(μ-H)]2, 2, and [(C5Me5)2DyH]2, 3, serve as a reminder of the
Fig. 2 Thermal ellipsoid diagrams of two crystalline variations of [(C5Me5)2DyH]2, 3: (C5Me5)2Dy(μ-H)DyH(C5Me5)2·toluene, 3B (left), and (C5Me5)2Dy(μ-H)DyH(C5Me5)2, 3C (right) drawn at the 50% probability level. Hydrogen atoms except for the hydride ligands are omitted for clarity.
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 15526–15531 | 15529
View Article Online
Published on 15 August 2014. Downloaded by Stockholms Universitet on 27/10/2014 14:34:06.
Paper
importance to structure and crystallinity of small changes in the size of the rare earth metal in a homologous series. [(C5Me5)2LnH]2 complexes of the larger lanthanides, Sm, Gd and Tb, crystallize in a single structural type with relatively symmetric metallocene locations such that the four rings approximate a tetrahedron. However, only in the Tb structure were the data of high enough quality to reveal the hydride ligands. Hence, reducing the size of the metal by 0.039 Å did not change the structural type, but led to crystals of high quality for hydride location. However, reducing the size of the metal by another 0.013 Å to Dy, led to a situation in which this combination of ligands and metals did not crystallize to a single preferred structure. Three crystalline solids, 3A, 3B, and 3C, were isolated from this system and for 3B and 3C, the asymmetric (C5Me5)2Dy(μ-H)DyH(C5Me5)2 structure was observed. Further variability was found between 3B and 3C in that the disorder found in one (C5Me5)1− ring in 3C was absent in 3B which had toluene solvent present. Reducing the size of the metal by another 0.008 Å to Y eliminated the structural variability found for the three forms of Dy while maintaining the (C5Me5)2Ln(μ-H)LnH(C5Me5)2 structure. Evidently, the combination of the [(C5Me5)2H]3− ligand set with a metal the size of Dy is not a good match to give one preferred crystalline arrangement. This is unfortunate since [(C5Me5)2DyH]2 is of interest as a single molecule magnet and it would be optimum to correlate magnetic data with a single structure. Efforts were tried to separate pure 3B or 3C from 3A by microscopy, but these failed due to the temperature sensitivity of the complexes and high degree of co-crystallization. This complex is not suitable for magnetic analysis, since multiple structural types exist with Dy and it is not clear which one would be present in a selected sample. Although complexes 3B and 3C are similar in the (C5Me5)2Dy(μ-H)DyH(C5Me5)2 part of the structure, they differ in molecular weight and the crystals cannot be differentiated from 3A which has an unknown structure. This emphasizes the importance of choosing the ligands for potential single molecule magnets such that structural ambiguity does not occur. At present, this can only be determined by collecting the structural data, but hopefully future developments in theory will make such information predictable. In many applications employing rare earth metals, selecting a slightly different metal size will be acceptable. However, for magnetic studies, the specific rare earth metal is very important and optimization of structural type by size variation cannot be done. In this case, a different ligand system must be chosen to avoid structural ambiguity.
Conclusion Structural analysis of [(C5Me5)2LnH]2 complexes of Ln = Sm, Gd, Tb, Dy, and Y shows the importance of matching the size of the metal with the size of the ligand set. The Sm, Gd, and Tb complexes have a symmetrical arrangement of the metallocene units consistent with [(C5Me5)2Ln(μ-H)]2 structures, but
15530 | Dalton Trans., 2014, 43, 15526–15531
Dalton Transactions
only with Tb could the hydride ligands be located crystallographically. In contrast, the smaller metals Dy and Y have (C5Me5)2Ln(μ-H)LnH(C5Me5)2 structures containing one formally seven coordinate rare earth metal and one eight coordinate site. Although the Y complex provided good crystallographic data on a single structural type, the Dy system does not have a single optimum crystal structure. Instead, with this metal ligand combination, two different types of crystals and one other solid form can be obtained depending on crystallization conditions. Since these co-crystallize and can only be differentiated by X-ray diffraction, this complicates magnetic analysis on bulk samples. Magnetic data on [(C5Me5)2Dy(μ-H)]2 cannot be reliably correlated with structure. Hence, examination of single molecule magnet behavior for a Dy2H2 unit should be pursued with ancillary ligands other than (C5Me5)1−. These studies emphasize the fact that a single crystal structure may not represent the full structural situation in a given complex. If magnetic data do not match that predicted based on a single crystal structure, it might be prudent to examine more samples to see if there is structural variability as demonstrated here.
Acknowledgements We thank the U. S. National Science Foundation under CHE-1265396 for support of this research, Jordan F. Corbey for help with the crystallography, and Megan E. Fieser for helpful discussion. We thank the China Scholarship Council 201206010106 for support of Shan-Shan Liu.
References 1 (a) N. Ishikawa, M. Sugita, T. Ishikawa, S.-Y. Koshihara and Y. Kaizu, J. Am. Chem. Soc., 2003, 125, 8694–8695; (b) M. A. AlDamen, J. M. Clemente-Juan, E. Coronado, C. Martí-Gastaldo and A. Gaita-Ariño, J. Am. Chem. Soc., 2008, 130, 8874–8875; (c) E. Coronado, C. Giménez-Saiz, A. Recuenco, A. Tarazón, F. M. Romero, A. n. Camón and F. Luis, Inorg. Chem., 2011, 50, 7370–7372; (d) S.-D. Jiang, B.-W. Wang, G. Su, Z.-M. Wang and S. Gao, Angew. Chem., Int. Ed., 2010, 49, 7448–7451; (e) S.-D. Jiang, B.-W. Wang, H.-L. Sun, Z.-M. Wang and S. Gao, J. Am. Chem. Soc., 2011, 133, 4730–4733; (f) M. Jeletic, P.-H. Lin, J. J. Le Roy, I. Korobkov, S. I. Gorelsky and M. Murugesu, J. Am. Chem. Soc., 2011, 133, 19286–19289; (g) G. Cucinotta, M. Perfetti, J. Luzon, M. Etienne, P.-E. Car, A. Caneschi, G. Calvez, K. Bernot and R. Sessoli, Angew. Chem., Int. Ed., 2012, 51, 1606–1610; (h) J.-L. Liu, Y.-C. Chen, Y.-Z. Zheng, W.-Q. Lin, L. Ungur, W. Wernsdorfer, L. F. Chibotaru and M.-L. Tong, Chem. Sci., 2013, 4, 3310–3316; (i) F. Tuna, C. A. Smith, M. Bodensteiner, L. Ungur, L. F. Chibotaru, E. J. L. McInnes, R. E. P. Winpenny, D. Collison and R. A. Layfield, Angew. Chem., Int. Ed., 2012, 51, 6976–6980; ( j) S. A. Sulway, R. A. Layfield, F. Tuna, W. Wernsdorfer and
This journal is © The Royal Society of Chemistry 2014
View Article Online
Published on 15 August 2014. Downloaded by Stockholms Universitet on 27/10/2014 14:34:06.
Dalton Transactions
2 3 4 5
6 7
R. E. P. Winpenny, Chem. Commun., 2012, 48, 1508–1510; (k) K. R. Meihaus and J. R. Long, J. Am. Chem. Soc., 2013, 135, 17952–17957; (l) L. Ungur, J. J. Le Roy, I. Korobkov, M. Murugesu and L. F. Chibotaru, Angew. Chem., Int. Ed., 2014, 53, 4413–4417; (m) F. Habib, J. Long, P.-H. Lin, I. Korobkov, L. Ungur, W. Wernsdorfer, L. F. Chibotaru and M. Murugesu, Chem. Sci., 2012, 3, 2158–2164; (n) R. J. Blagg, L. Ungur, F. Tuna, J. Speak, P. Comar, D. Collison, W. Wernsdorfer, E. J. L. McInnes, L. F. Chibotaru and R. E. P. Winpenny, Nat. Chem., 2013, 5, 673–678; (o) J. Tang, I. Hewitt, N. T. Madhu, G. Chastanet, W. Wernsdorfer, C. E. Anson, C. Benelli, R. Sessoli and A. K. Powell, Angew. Chem., Int. Ed., 2006, 45, 1729–1733; ( p) P. Zhang, L. Zhang, C. Wang, S. Xue, S.-Y. Lin and J. Tang, J. Am. Chem. Soc., 2014, 136, 4484– 4487; (q) E. M. Fatila, M. Rouzières, M. C. Jennings, A. J. Lough, R. Clérac and K. E. Preuss, J. Am. Chem. Soc., 2013, 135, 9596–9599; (r) D. N. Woodruff, R. E. P. Winpenny and R. A. Layfield, Chem. Rev., 2013, 113, 5110–5148; (s) R. A. Layfield, Organometallics, 2014, 33, 1084–1099. J. D. Rinehart, M. Fang, W. J. Evans and J. R. Long, J. Am. Chem. Soc., 2011, 133, 14236–14239. J. D. Rinehart, M. Fang, W. J. Evans and J. R. Long, Nat. Chem., 2011, 3, 538–542. K. R. Meihaus, J. F. Corbey, M. Fang, J. W. Ziller, J. R. Long and W. J. Evans, Inorg. Chem., 2014, 53, 3099–3107. A. Venugopal, F. Tuna, T. P. Spaniol, L. Ungur, L. F. Chibotaru, J. Okuda and R. A. Layfield, Chem. Commun., 2013, 49, 901–903. W. J. Evans, I. Bloom, W. E. Hunter and J. L. Atwood, J. Am. Chem. Soc., 1983, 105, 1401–1403. C. L. Webster, J. W. Ziller and W. J. Evans, Organometallics, 2014, 33, 433–436.
This journal is © The Royal Society of Chemistry 2014
Paper
8 (a) K. H. den Haan and J. H. Teuben, J. Chem. Soc., Chem. Commun., 1986, 682–683; (b) K. H. Den Haan, Y. Wielstra and J. H. Teuben, Organometallics, 1987, 6, 2053–2060. 9 M. Booij, B. J. Deelman, R. Duchateau, D. S. Postma, A. Meetsma and J. H. Teuben, Organometallics, 1993, 12, 3531–3540. 10 W. J. Evans, C. A. Seibel and J. W. Ziller, J. Am. Chem. Soc., 1998, 120, 6745–6752. 11 W. J. Evans, B. L. Davis, T. M. Champagne and J. W. Ziller, Proc. Natl. Acad. Sci. U. S. A., 2006, 103, 12678–12683. 12 (a) T. J. Mueller, M. E. Fieser, J. W. Ziller and W. J. Evans, unpublished results, Sept 2010; (b) S. Demir, J. M. Zadrozny, M. Nippe and J. R. Long, J. Am. Chem. Soc., 2012, 134, 18546–18549. 13 M. D. Taylor and C. P. Carter, J. Inorg. Nucl. Chem., 1962, 24, 387–391. 14 (a) W. J. Evans, T. A. Ulibarri and J. W. Ziller, Organometallics, 1991, 10, 134–142; (b) W. J. Evans, J. M. Perotti and J. W. Ziller, Inorg. Chem., 2005, 44, 5820–5825; (c) W. J. Evans, T. M. Champagne and J. W. Ziller, J. Am. Chem. Soc., 2006, 128, 14270–14271; (d) W. J. Evans, K. A. Miller, A. G. DiPasquale, A. L. Rheingold, T. J. Stewart and R. Bau, Angew. Chem., Int. Ed., 2008, 47, 5075–5078; (e) E. Montalvo, K. A. Miller, J. W. Ziller and W. J. Evans, Organometallics, 2010, 29, 4159–4170; (f ) K. R. D. Johnson and P. G. Hayes, Chem. Soc. Rev., 2013, 42, 1947–1960; (g) B. M. Schmiege, M. E. Fieser, J. W. Ziller and W. J. Evans, Organometallics, 2012, 31, 5591–5598. 15 W. J. Evans, T. A. Ulibarri and J. W. Ziller, J. Am. Chem. Soc., 1988, 110, 6877–6879. 16 J. W. Lauher and R. Hoffmann, J. Am. Chem. Soc., 1976, 98, 1729–1742. 17 J. V. Ortiz and R. Hoffmann, Inorg. Chem., 1985, 24, 2095– 2104.
Dalton Trans., 2014, 43, 15526–15531 | 15531
