Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 211–215

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Molecular spectrum of lanthanide complexes with 2,3-dichlorobenzoic acid and 2,2-bipyridine Shu-Mei He a,⇑, Shu-Jing Sun b, Jun-Ru Zheng a, Jian-Jun Zhang a a b

Testing and Analysis Center, Hebei Normal University, Shijiazhuang 050024, PR China No.1 High School of Dezhou, Dezhou 253000, PR China

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

 The molecular vibration spectral

bands of lanthanide ternary complexes were analyzed.  Wave-number of characteristic bands increases with increasing atomic number of Ln3+.  The vibration frequencies of C=O bonds were studied by the second derivative spectrum.

a r t i c l e

i n f o

Article history: Received 2 May 2013 Received in revised form 29 November 2013 Accepted 3 December 2013 Available online 18 December 2013 Keywords: Lanthanide complexes FT-IR FT-Raman Vibrational assignment Second derivative

a b s t r a c t With 2,3-dichlorobenzoic acid as the first ligands and 2,20 -bipyridine as the second ligands, the lanthanide complexes [Ln(2,3-DClBA)3bipy]2 [Ln = Nd(a), Sm(b), Eu(c), Tb(d), Dy(e), Ho(f)] have been synthesized. By using Infrared (IR) and Raman (R) spectra, the characteristics of the groups can be identified. The bands of lanthanide complexes have been analyzed and attributed, and clearly demonstrated with the use of the complementarity of IR and R. The experiment reveals that the bands of complexes are affected by lanthanide elements (Ln). The frequency of stretching vibration and breathing vibration of ring, together with the stretching vibration of the carbonyl group (mC@O), tends to be rising as the atomic number of lanthanide increasing. Meanwhile, crystallography data demonstrate that the six carbonyl groups have different bond length and bond angle, which can lead to different vibration frequency. The second derivatives of IR show that there are multiple vibration frequencies existing in the symmetrical stretching vibration of the carbonyl group (msC@O). Therefore the second derivative of IR spectrum is a characteristic band of different coordination modes of carbonyl group. Ó 2013 Elsevier B.V. All rights reserved.

Introduction Lanthanide elements are used to form binary and ternary complexes with a variety of ligands, due to their special nature such as the specific structure of f-electronic shells, large atomic magnetic moment and strong spin orbit coupling. Lanthanide complexes, which bear particularly optoelectronic, magnetic and electrical ⇑ Corresponding author. Tel.: +86 31180786458; fax: +86 31180786312. E-mail address: [email protected] (S.-M. He). 1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2013.12.023

properties, can be found in an array of applications in many fields. As a result, lanthanides complexes have been intensively studied [1–8]. While the crystal structures and the thermodynamic properties of the title complexes have been published [9], the study of molecular vibration spectra was seldom reported. Due to the fact that Infrared and Raman spectra are complementary to each other, combining them can do more precise observation and study [10,11]. At present, the Infrared spectroscopy has been widely used in the study of the structure of the material [12,13]. The Raman spectroscopy, although started much later, appeared constantly

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in the study of the structure in recent years [14,15]. In the study of complexes by Raman spectra, He et al. [16] and Ma et al. [17] found that the coordination mode of carboxyl associated with difference of wave number (Dm(mas  ms)), which are consistent with the results from infrared spectra. In this study of the title complexes, the coordination mode of carbonyl is much more complicated. The seven-coordinate of six carbonyls not only demonstrated two bidentate chelating and two bidentate bridging, but also showed two tridentate chelating–bridging. The study is the first one that use the second derivative IR spectrum of symmetrical stretching vibration of the carbonyl group and shows multiple different vibration frequencies of carbonyl, which has guiding significance to the research for the structure of carbonylic complexes. Experimental Preparation of complexes a–f The synthesis method is according to the literature [9].

peaks of the asymmetric stretching vibration (mas(COO–))and the stretching vibration (ms(COO–))are observed at 1573 cm1 and 1387 cm1, respectively, and the m(CAC) bridging bond of the second ligand (2,20 -bipyridine) is observed at 1316 cm1. The bands at 354 cm1 and 205 cm1 in the complexes are assigned to m(LnAO) and m(LnAN). Meanwhile in the IR spectrum of the complexes, the mC@O (ACOOH) of the first ligand at 1693 cm1 disappears, whereas the msC@O (COO–) of carboxylate presents a strong broadband at 1407 cm1. Therefore, the characteristic peaks of the complexes can be observed in the IR-R spectra. IR-R spectra analysis of the title complexes The title complexes IR and R spectra are given in Fig. 2 and Fig. 3. The IR and R spectra for all complexes are similar, indicating that they may be isostructural. The attributes of the bands are listed in Table 1. The vibration frequencies in R spectrum are consistent with those in the IR spectrum. However, they have great differences in vibration intensities, which reflect the complementarity between IR and R spectra.

Experimental equipment and conditions FT-IR spectra were recorded by a Bruker VERTEX-70 FTIRRAMANII equipped with a DTGS detector at a resolution of 4 cm1 via KBr disk over the range of 400–4000 cm1, and scanned 32 times. The second derivative IR spectra were obtained on 5 smoothing points. FT-Raman spectra were recorded by the same instrument with a liquid nitrogen cooling-InGaAs with Nd:YAG laser(k = 1.064 lm) with 300 mW power operating at a resolution of 4 cm1 over the range of 50–4000 cm1, and scanned 64 times. The single crystal X-ray diffraction data were obtained by an AFC10/Saturn724 + diffractometer with graphite monochromated Mo Ka radiation (k = 0.71073 Å) at 93 K. The structure was solved by direct methods using SHELXS-97 program and refined by Fullmatrix least squares on F2 using SHELXL-97 program.

CAH stretching vibration In the complexes, the unsaturated carbon hydrogen groups (@CAH) exist in both benzene ring and the pyridine ring, the stretching vibrations (mCAH) appear at 3086 cm1, which is affected by the hygroscopic water. But the band is very weak and illegible in IR spectrum. In R spectrum, the main peak at 3068 cm1 is moderately strong with two shoulder peaks on each side. All of these phenomena are characteristics for the stretching vibration of unsaturated CAH bond. The vibration of the benzene ring and pyridine ring The stretching vibrations of benzene and bipyridyl rings show strong bands in both IR and R spectra. In Fig. 2, the first peak located at 1620 cm1 is very strong in IR spectrum, and the wave

Results and discussion Structural validation The title complexes are isostructural for sharing the same coordination modes of the ligands and coordination number. As an example, the IR-R spectra of complex (b) are shown in Fig. 1. In the Raman spectrum, the mC@O (ACOOH) of the first ligand (2,3dichlorobenzoic acid), which was at 1650 cm1, completely disappears in the R spectrum of the complexes. While the characteristic

Fig. 1. The IR-R spectra of complex (b). IR-b: IR spectrum of complex (b) (T%); R-b: R spectrum of complex (b), R-II: R spectrum of 2,2-Bipyridyl, R-I: R spectrum of 2,3DClBA.

Fig. 2. The IR spectra of the title complexes.

213

205 354

205 354

747

768 C62H34Cl12 Dy 2N4O12

1154 1390 1631 1598 1439 3068 3086 3071 C62H34Cl12 Ho 2N4O12

1629 1597 1439

1627 1598 1439

3092 3073 3086 C62H34Cl12 Tb 2N4O12

3090 3068 3068

1625 1598 1438 3087 C62H34Cl12 Eu 2N4O12

3068

1623 1602 1438 C62H34Cl12 Sm2N4O12

3068 3072

C62H34Cl12 Nd 2N4O12

m: stretching vibration, ms: symmetrical stretching vibration, mas: antisymmetric stretching, d: bending vibration, vs: very strong, s: strong, m: moderately strong, w: weak, vw: very weak.

1015 1015 1048, 1049

1014 1015 1048 1049

1316 1164 1316 1164 1154 1390

1014 1014 1048 1049 1154 1388

1154 1387

1155 1387

747

205 354 768 747

205 352 768 747

762 715 762 715 762 715 763 715 1014 1014 1078

1012 1013 1048 1048

1048

205 354 767

205 351 767

762 747 714 761, 747 1012 1048 1048

3084 3043 3086

3082 3062 3076 3063 3069 3094

2,3-Dichlorobenzoic acid 2,2-Bipyridyl

R

1316 1163 1316 1163 1316 1164 1316 1155 1386

1407 1397 1408 1397 1408 1397 1412 1397 1412 1397 1412 1397 1579 1555 1579 1557 1580 1555 1580 1557 1580 1556 1582 1550 1579 1557 1453 1415 1619 1602, 1437

1581 1564 1590 1573 1597 1496 1595 1459 1598 1497 1599 1496 1598 1497 1599 1497

1693

1650

1575 1549 1573 1549 1575 1549 1575 1549 1575 1550 1575 1550

vs

IR R

s s

IR R

m vw

vw

IR R IR

vs

msC@O masC@O mAC@C mAC@N mC@H Complexes

Table 1 The IR and R bands assignment of the title complexes cm1.

The stretching vibration of carbonyl There is no free carbonyl (C@O) in the complex after carboxyl coordinates with lanthanide cation (Ln3+), due to electron cloud homogenization, the two carbon oxygen bonds (COO) become equivalent. The two bands appear both symmetric and asymmetric stretching vibration. Besides, the vibrational frequencies also increase (IR:1407–1412 cm1, R:1386–1390 cm1) with the increasing atomic number of lanthanide elements. In Raman spectrum, the symmetric and asymmetric stretching vibrations bands locate at 1580 cm1 and 1410 cm1, respectively. In IR spectrum, the asymmetric stretching vibration (mas(COO–),1580 cm1) locates at the benzene ring vibration area (1600–1450 cm1), which is indistinguishable. The locations of symmetric stretching vibrations (ms(COO–)) range from 1410 to 1380 cm1, and the main peak with a right-side strong shoulder peak is at 1410 cm1, as is seen in Fig. 4. The crystallographic data

w

Fig. 3. The Raman spectra of the title complexes.

number is increased by 20 cm1 compared to those with m(C@C) and m(C@N) in the free ligands. The reason is that the electron in oxygen (nitrogen) atom migrates to the empty orbital of metal elements. The inductive effect leads to the decrease of the electron cloud density, together with increase in C@C (C@N) bonds constant and frequency. The crystallographic data also show that[9] the average bond lengths of the LnAN are 2.6255 Å, 2.607 Å, 2.584 Å, 2.552 Å, 2.511 Å respectively, indicating a decreasing of bond lengths while increasing of bond energy. Therefore, the wave numbers of benzene and bipyridyl rings increase (1619–1631 cm1) as that the atomic number of metal elements increases. The secondary peak at 1598 cm1 shows a very strong band in R spectrum. The third peak (1497 cm1) is moderately strong in R spectrum, whereas the peak interferes with carbonyl band in IR spectrum. The fourth peak being observed at 1438 cm1 is weak both in IR and R spectra. The breathing vibration band of ring (1013 cm1) is very strong in R spectrum, and its frequency also tends to increase (from 1012 to 1015 cm1) with the increasing atomic number for lanthanide elements.

1012

765 758 1040

995

690 753 704 1053 1053

1156 1107 1302 1170

R

w w

R R

w m

IR R

m w

IR R

s m

IR R IR

vs m

dCAH Ring breathing

mCACl mCAC

w

mNA mOALn

Ln

S.-M. He et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 211–215

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S.-M. He et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 211–215 Table 2 Relevanted bond lengths and bond angles of bipyridyl carboxyl for the complex (b). Coordination mode

Lengths (Å)

Angles (°)

Bidentate chelating Tridentate chelating– bridging Bidentate bridging

C21AO5 1.246 C14AO3 1.238

O6AC21 1.277 O4AC14 1.278

O5AC21AO6 123.1 O3AC14AO4 121.9

C7AO1 1.263

C7AO2 1.264

O1AC7AO2 125.3

Fig. 4. IR Spectra of carboxyl symmetric stretching vibration for the title complexes.

also shows that the six carboxylic groups of the complex (b) demonstrate have three kinds of coordination modes: OAC21AO bidentate chelating, OAC14AO tridentate chelating–bridging, and OAC7AO bidentate bridging (Fig. 5). The bond lengths and angles of the three modes are all different. For example, as Table 2 shows, the bond length of carbon oxygen has relatively large difference in chelating mode, while in the chelating–bridging mode, the two bonds lengths of the CAO are close to each other. Among all of the three modes, the bond angle from the tridentate chelating– bridging mode is the minimum, and for its two bonds of carbon oxygen, one is the longest and the other is the shortest. Because the bonds demonstrate different lengths and angles, their energies are different, thus the frequencies of vibration are different. It leads to the fact that the ms(COO–) appears a composite vibration band with multiple shoulder peaks in IR spectra, as Fig. 4 shows, the bands shape are not completely the same in the title complexes, but the multiple convex peaks wave-number of the second derivative spectrum are the same (see Fig. 6), and conform to the different vibration frequencies from carboxyl groups. Therefore, the IR second derivative spectra can be used as the characteristic bands for the different coordination modes of carbonyl.

Fig. 6. The second derivative IR spectra of carboxyl symmetric stretching vibration for the title complexes.

The vibration of CAC bonds There are two kinds of CAC bonds in the complex. They are the bridged bond connecting the two pyridine rings, and the bond connecting the carboxyl carbon with the benzene ring, respectively. The bridged bond is very weak in IR spectrum, but it is a strong characteristic band located at 1316 cm1 of R spectrum. The other

Fig. 5. Molecular structure of complex (b).

S.-M. He et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 211–215

CAC bond is a moderately strong band at 1155 cm1 in IR spectrum, whereas it is relatively weak in R spectrum (1163 cm1). The vibration of CACl bonds When the halogen is connected to the aromatic ring, the stretching vibration of CAX bond (1175–1000 cm1) is slightly larger than that of aliphatic series. In the complex (b), the band of CACl bond, which locates at 1048 cm1, is moderately strong. The vibration of LnAO and LnAN bonds In the Raman spectrum, the weak but clear band at 355 cm1 in the complexes can be assigned to m(LnAO), and the band at 205 cm1 can be assigned to m(LnAN). The bending vibration of CAH on rings In the IR spectrum, the bands of benzene ring are located at 715 cm1and 762 cm1, which corresponds to the aromatic skeleton vibration and out-plane flexural vibration of the three adjacent hydrogen on the benzene ring, respectively. The band of out-plane flexural vibration of pyridine ring is almost at the same place in both R and IR spectrum. But the peak at 747 cm1 of R spectrum is weaker. Conclusions Using the methodology of complementary of IR and Raman, bands of characteristic groups have been analyzed one by one. The characteristic bands of carbonyl (carboxylate), bridged CAC bond in dipyridyl, together with LnAO and LnAN bonds have been determined by IR-R spectra. The vibration frequencies for breathing and stretching vibration of rings increase with the increment of atomic number of lanthanide elements. The crystallographic data show that the bond energy is different from six carboxyl groups of the complex (b), thus the frequency of vibration is different. The second derivative IR spectrum of the

215

ms(COO ) can be better reflected the different vibration frequency –

from carboxyl groups. Therefore it is a characteristic band of different coordination modes. Acknowledgment This project was supported by the National Natural Science Foundation of China (Nos. 21073053 and 20773034). References [1] C.C. Bryan, C. Radu, O.R. Joanne, A.B. Lynn, Inog. Chim. Acta 384 (2012) 23–28. [2] X.Q. Song, Y. Yu, W.S. Liu, W. Dou, J.R. Zheng, J.N. Yao, Solid State Chem. 180 (2007) 2616–2624. [3] J.K. Tang, Q.L. Wang, S.F. Si, D.Z. Liao, Z.H. Jiang, S.P. Yan, P. Cheng, Inog. Chim. Acta, 358 (2005) 325–330. [4] J.F. Wang, H. Li, J.J. Zhang, N. Ren, K.Z. Wu, Sci China Chem. 55 (2012) 2161– 2175. [5] K. Tang, J.J. Zhang, N. Ren, J.R. Zheng, J.Y. Liu, K.Z. Wu, Sci China Chem. 55 (2012) 1283–1293. [6] H.M. Ye, N. Ren, J.J. Zhang, S.J. Sun, J.F. Wang, New J. Chem. 34 (2010) 533–540. [7] L. Tian, N. Ren, J.J. Zhang, H.M. Liu, J.H. Bai, H.M. Ye, S.J. Sun, Inorg. Chim. Acta 362 (2009) 3388–3394. [8] K. Tang, H.M. Liu, N. Ren, J.J. Zhang, K.Z. Wu, J. Chem. Thermodynamics 47 (2012) 428–436. [9] S.J. Sun, J.F. Wang, N. Ren, J.J. Zhang, H.M. Ye, S.P. Wang, Struct. Chem. 23 (2012) 79–89. [10] J.G. Wu, Fourier transform infrared spectroscopy, Appl Sci Technol, Press, 1994. ISBN7-5023-2214-0. [11] K. Nakamoto, Infrared and Raman spectra of inorganic and coordination compounds, John Wiley & Sons, Press, 1997. ISBN0471163929, 9780471163923. [12] W.L. Xie, Spectrosc Spect. Anal. 19 (6) (1999) 827–830. [13] M.Z. Ali, S. Ali, S. Shahzadi, Russ. J. Inorg. Chem. 56 (11) (2011) 1752–1756. [14] V.S. Naumov, Russ. J. Inorg. Chem. 55 (8) (2010) 1202–1208. [15] V.V. Bruevich, T.Sh. Makhmutov, S.G. Elizarov, E.M. Nechvolodova, D.Yu. Paraschuk, J Exp. Theor. Phys. 105 (3) (2007) 469–478. [16] S.M. He, S.J. Sun, J.F. Wang, Y. Lang, J. Chinese Soc. Rare Earths 29 (4) (2011) 402–406 (in Chinese). [17] S.Z. Ma, Q.Z. He, Z.F. Yang, D.F. Xu, D.Z. Sun, J. Chem. Res. Appl. 20 (9) (2008) 1138–1142 (in Chinese).