Synthesis and spectral characterization of alkaline earth metal complexes: Crystal structure of a Ca(II) hippuric acid complex

Polyhedron 29 (2010) 3164–3169

Contents lists available at ScienceDirect

Polyhedron journal homepage: www.elsevier.com/locate/poly

Synthesis and spectral characterization of alkaline earth metal complexes: Crystal structure of a Ca(II) hippuric acid complex K.R. Jisha a, S. Suma a,⇑, M.R. Sudarsanakumar b a b

Department of Chemistry, S.N. College Kollam, Kerala 691001, India Department of Chemistry, M.G. College, Thiruvananthapuram 695004, Kerala, India

a r t i c l e

i n f o

Article history: Received 25 January 2010 Accepted 12 August 2010 Available online 31 August 2010 Keywords: Hippuric acid X-ray diffraction studies Polymeric structure Thermal analysis Non-linear optical activity

a b s t r a c t Alkaline earth metal (Mg, Ca, Sr and Ba) complexes of hippuric acid (hipH) have been synthesized and characterized by elemental analyses and IR spectroscopy. One of the complexes, [Ca(hip)2(H2O)2]H2O, was characterized by single crystal X-ray diffraction studies. The polymeric structure is based on a dimeric unit and each calcium is coordinated to four hippurate anions and two coordinated water molecules. The hippurate anion functions as a bidentate ligand through the oxygen atoms of the carboxylate groups, one of which is bridging, forming a two dimensional coordination polymer. The water coordination is further confirmed by thermal analysis. The non-linear optical activity of the complexes was also measured. Ó 2010 Elsevier Ltd. All rights reserved.

1. Introduction As compared to the reports of d block transition metal polymers, alkaline earth polymeric complexes are less common. There have been a few studies in recent years on the coordination chemistry of these metals in both aqueous media and non-aqueous media [1–5]. Magnesium and calcium are essential elements and it has been suggested that these elements were in fact involved with some of the earliest forms of life because of their important role in DNA and protein synthesis [6]. Barium and strontium metals have been known as antagonists for potassium and calcium, respectively [7]. Carboxylate containing ligands have attracted attention because of the diversity of the binding modes of the carboxylate group. Hippuric acid (hipH), N-benzoylglycine, (Fig. 1) is one of the important amino acids because it is synthesized in the liver as a metabolite of benzoic acid urinary excretion [8,9]. Moster et al. reported that the excretion of between 0.7 and 1.0 g of hippuric acid was suggestive of impaired liver function [10]. Hippuric acid was also identified as a constituent of the non-protein nitrogen fraction of milk [11]. Many natural amino acids, including benzoylglycine, individually exhibit non-linear optical properties because they have a donor NH2 and acceptor COOH, and intermolecular charge transfer is also possible [12]. Hippuric acid is a monocarboxylic acid with three types of donor sites, the nitrogen and oxygen atoms of the amide group and ⇑ Corresponding author. Tel.: +91 471 2592617. E-mail address: [email protected] (S. Suma). 0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2010.08.026

the oxygen atoms of the carboxylic acid group. The literature reveals that hippuric acid is potentially capable of forming coordinate bonds with many metal ions through the carboxylic oxygen as a monodentate or a bidentate ligand [13–18]. The NH of the ligand coordinates to the central metal in some complexes [19,20]. The X-ray crystal structure of a Ba(II) complex of hippuric acid, [Ba2(C9H8NO3)4(H2O)3], indicated that the hippurate anion is coordinated to Ba(II) as a bidentate ligand via the two oxygen atoms of the carboxylic acid group after being deprotonated [21]. In this paper we report the synthesis and spectral studies of Mg, Ca, Sr and Ba complexes of hippuric acid, along with the crystal structure of the compound [Ca(hip)2(H2O)2]H2O. 2. Experimental 2.1. Materials Hippuric acid (CDH), magnesium chloride, calcium chloride, strontium chloride and barium chloride (CDH) were of AR grade and were used without further purification. The solvents used were methanol, ammonium hydroxide and water. 2.2. Synthesis of the complexes The complexes 1–4 have been synthesized starting from the respective metal chloride essentially by following a similar synthetic procedure. MCl2 (5 mmol) and hippuric acid (10 mmol, 0.3 g) were dissolved in a water (15 ml) and methanol (30 ml) mixture, and the resulting solution was warmed to 50 °C for one hour.

3165

K.R. Jisha et al. / Polyhedron 29 (2010) 3164–3169

O N H

O

Table 1 Color, elemental analyses and stoichiometries of the hippuric acid complexes. Compound

Color

C

N

H

[Mg(hip)2(H2O)2] (H2O)2 (1) [Ca(hip)2(H2O)2] H2O (2) [Sr(hip)2(H2O)2] H2O (3) [Ba(hip)2(H2O)2] (4)

colorless

48.19 (47.73)

6.58 (6.19)

5.19 (5.30)

colorless

47.47 (47.96)

6.18 (6.2)

5.51 (4.88)

colorless

43.19 (43.38)

5.50 (5.56)

4.6 (4.42)

colorless

41.23 (40.78)

4.63 (3.77)

5.72 (5.28)

OH

Fig. 1. Hippuric acid.

Aqueous NH3 (25%) was added dropwise to this solution to obtain a pH of 9–10, and the resulting mixture was heated to 80 °C. The resulting turbid reaction mixture was filtered and allowed to stand at room temperature. After five or six days, the crystals obtained were separated and washed with methanol. 2.3. Physical measurements Elemental analysis of the complexes was carried out on a Vario EL III CHNS analyzer; the IR spectra were recorded on a Thermo Nicolet Avtar 310 DTGS spectrometer (4000–400 cm1) in KBr pellets. The SHG efficiency of hippuric acid and the complexes was measured with respect to KDP by the powder technique developed by Kurtz and Perry [22] using a Quanta Ray Spectra Physics Model: Prolab 170 Nd: YAG 10 ns laser with a first harmonic output of 1064 nm at a pulse repetition rate of 10 Hz. The homogenous powder was tightly packed in a microcapillary tube and mounted in the path of the laser beam of pulse energy 6.85 mJ, obtained by the split beam technique. The thermogravimetric analysis (TG/DTG) was carried out in air with a heating rate of 10 °C/min, using a Perkin Elmer Diamond TG/DTA analyzer. 2.4. X-ray crystallography Single crystals of the compound [Ca(hip)2(H2O)2]H2O suitable for X-ray diffraction studies were grown from a solution of hippuric acid and calcium chloride in 25% ammonia solution by slow evaporation in air. A single crystal of dimensions 0.30  0.20  0.20 mm was selected and mounted on a Bruker axs Kappa apex 2 CCD diffractometer, equipped with a graphite crystal incident beam monochromator and a fine focus sealed tube Mo Ka (k = 0.71073) X-ray source. The SMART [23] program was used for collecting frames of data, indexing the reflections and determination of lattice parameters, the SADABS [24] program was used for absorption correction and the SHELXL [25] program for space group. The structure was solved by the direct method and refined by the full-matrix least-squares method on F2, with all non-hydrogen atoms refined with anisotropic thermal parameters. All hydrogen atoms attached to carbon and nitrogen atoms were geometrically fixed at calculated positions and refined using the riding model, and the coordinated water hydrogen atoms were refined from Fourier maps. The lattice water O9 is disordered over two sites, with relative occupancies of 0.53 and 0.47 for the A and B components, respectively. Lattice water hydrogens could not be located in the difference Fourier map, probably due to the large thermal motion of the water molecule. The molecular graphics tools used were PLATON [26] and DIAMOND Version 3.1f [27]. 3. Results and discussion The complexes [Mg(hip)2(H2O)2](H2O)2, [Ca(hip)2(H2O)2]H2O, [Sr(hip)2(H2O)2]H2O and [Ba(hip)2(H2O)2], 1–4, respectively, are formed by the reaction of hippuric acid with MgCl2, CaCl2, SrCl2 and BaCl2 by slow evaporation in air. The colors, elemental analyses and stoichiometries of the hippuric acid complexes are presented in Table 1. The complexes are readily soluble in water. All the complexes are found to be non-electrolytes. In all the com-

Found (calculated) (%)

plexes, hippuric acid deprotonates and coordinates to the metal ion as a bidentate ligand, as proven by the IR spectral data. 3.1. Infrared spectral studies The tentative assignment for selected vibrational bands of the free ligand and their complexes, which are useful for determining the mode of coordination of the ligand, are given in Table 2. A sharp band at 1744 cm1 in hippuric acid can be attributed to the characteristic >C@O of the carboxylic acid group. Several bands in the region 2750–2478 cm1 are characteristic peaks of OH of the COOH group [15]. These bands disappear in the complexes, indicating the coordination of the carboxylate group to the metal ion, by the deprotonation of carboxylic acid group. It is further supported by the appearance of two new bands at 1524 and 1429 cm1 in complex 1, assignable to mas and ms of COO. These bands are observed at 1533 and 1408 cm1 in complex 2, 1532 and 1404 cm1 in complex 3 and 1524 and 1430 cm1 in complex 4 [28]. The band at 3342 cm1 due to mNH of hippuric acid appears at 3367, 3373, 3379 and 3399 cm1 in complexes 1–4, respectively. The shift in frequency is attributed to the weaker hydrogen bonding interactions in the complexes than in the ligand. The m(M–O) band is observed at 557, 589, 590 and 586 cm1 in the complexes 1–4, respectively. 3.2. Crystal structure of the compound [Ca(hip)2(H2O)2]H2O (2) The molecular structure of the compound 2, along with atom numbering scheme, is given in Fig. 2. The crystal data and structure refinement parameters are given in Table 3 and the selected bond lengths and bond angles of the molecule are summarized in Table 4. Compound 2 crystallizes in the monoclinic space group P21/c. The unit cell contains four molecules. The hippurate ion acts as a bidentate ligand. The molecular structure of [Ca(hip)2(H2O)2]H2O, obtained from the single crystal X-ray diffraction studies, showed that the Ca(II) centre is octacoordinated with a distorted dodecahedral geometry. The bond parameter value shows that the geometry around Ca(II) is distorted significantly from a perfect dodecahedron [29]. Here two hippuric acid molecules deprotonate and coordinate to the Ca(II) centre as bidentate carboxylate groups. The fifth and sixth coordination positions are occupied by bridging oxygen atoms of hippurate ligands and the other coordination positions are satisfied by water molecules. The Ca(II) centre is coordinated to eight oxygen atoms O8b and O5a from two different hippurate ligands of adjacent complex units, O5, O8, O2 and O4 from two hippurate ligands and O6 and O7 from coordinated water molecules (Fig. 3). It results in the formation of an eight membered ring between adjacent calcium atoms. The Ca1 and Ca2 polyhedra are edge shared through O5 and O8b on one side and O5a, O8 on the other side, which creates two dimensional infinite polymeric chains, as schematized in Fig. 4. The Ca1–Ca2 non-bonding distance of 3.977 Å is close to those reported for binuclear complexes with a

3166

K.R. Jisha et al. / Polyhedron 29 (2010) 3164–3169

Table 2 Infrared spectroscopic assignments (cm1) for hippuric acid and its complexes. Compound

mNH

mOH

mOH (COOH)

mC@O (COOH)

mC@O (amide)

mas COO

ms COO

mMO

hipH [Mg(hip)2(H2O)2](H2O)2 [Ca(hip)2(H2O)2]H2O [Sr(hip)2(H2O)2]H2O [Ba(hip)2(H2O)2]

3342(b) 3367(b) 3373(b) 3379(b) 3367(b)

3399(b) 3293(b) 3302(b) 3399(b)

2750–2478(w) – – – –

1744(s) – – – –

1600(s) 1600(s) 1600(s) 1600(s) 1600(s)

1524(s) 1533(s) 1532(s) 1524(s)

1429(m) 1408(m) 1404(m) 1430(m)

557(w) 589(w) 590(w) 586(w)

s = strong, b = broad, m = medium, w = weak.

Table 4 Selected bond lengths (Å) and angles (°) of compound 2.

Fig. 2. The molecular structure of [Ca(hip)2(H2O)2]H2O along with atom numbering scheme. Lattice water molecules are omitted for clarity.

Table 3 Crystal data and structure refinement parameters for [Ca(hip)2(H2O)2]H2O. Empirical formula Formula weight Color T (K) k (Å) Crystal system Space group V (Å3) Z q (Mg m3) Absorption coefficient (mm1) F(0 0 0) Crystal size (mm3) Color, nature h Range for data collection (°) Limiting indices Reflections collected Unique reflections (Rint) Completeness to h Absorption correction Maximum and minimum transmission Refinement method Data/restraints/parameters Goodness-of-fit (GOF) on F2 Final R indices [I > 2r(I)] R indices (all data) Largest difference peak and hole (e Å3)

C18H16N2O6Ca3H2O 450.46 Colorless 293(2) 0.71073 Monoclinic P21/c 2129.3(9) 4 1.405 0.346 944 0.30  0.20  0.20 Colorless, plate 1.27–29.30 12 6 h 6 12, 43 6 k 6 44, 10 6 l 6 10 5803 4344 25.00 (99.6%) Multi scan 0.852 and 0.910

Bond lengths (Å) Ca1–O2 2.519(2) Ca1–O4 2.4353(19) Ca1–O5 2.719(2) Ca1–O6 2.385(2) Ca1–O7 2.394(2) Ca1–O8 2.6038(19) Ca1–O5a 2.3321(17) Ca1–O8b 2.3256(17) O1–C7 1.245(3) O3–C16 1.229(3) O2–C9 1.245(3) O8–C9 1.246(3) O5–C18 1.240(3) O4–C18 1.253(3) O6–H6A 0.844(10) O7–H7A 0.845(10) Bond angles (°) O2–Ca1–O4 89.50(8) O2–Ca1–O5 70.58(7) O2–Ca1–O8 50.33(5) O2–Ca1–O8b 78.59(6) O4–Ca1–O5 82.14(7) O4–Ca1–O6 86.89(9) O4–Ca1–O8 76.44(7) O4–Ca1–O5a 49.87(5) O6–Ca1–O7 110.45(9) O6–Ca1–O5a 84.90(7) O8–Ca1–O5a 75.44(6) O5–Ca1–O8b 73.29(6) O6–Ca1–O8b 77.15(7) O7–Ca1–O5a 78.37(8) Torsion angles (°) C18–O5–Ca1–O4 8.47(14) C9–O2–Ca1–O8 4.56(14)

Full-matrix least-squares on F2 5803/6/296 1.115 R1 = 0.0608, wR2 = 0.1587 R1 = 0.0841, wR2 = 0.1756 0.833 and 0.660

P P wR2 ¼ ½ wðF 2o  F 2c Þ2 = wðF 2o Þ2 1=2 . P P R1 ¼ kF o j  jF c k= jF o j.

Fig. 3. Illustration of hippuric acid bridging with the atom numbering around Ca(II) centre.

Ca–Ca distance of 3.9033(14) Å. The distance between the Ca1 and the Ca2 atoms indicates the existence of Ca  Ca interaction in this complex [30]. Thus each hippurate ligand coordinates to two calcium atom with the carboxylate group adopting a bridging l2g2g1 (one oxygen atom connects two metal ions, the other con-

nects one metal atom) coordination mode as shown in Scheme 1. The Ca1 and Ca2 atoms are bridged by two carboxylate groups in a syn–syn mode (Fig. 4). The two independent carboxylate bridges each in Ca unit exhibit a little distortion from an ideal syn-syn mode with one metal ion deviating little from the O–C–O plane,

K.R. Jisha et al. / Polyhedron 29 (2010) 3164–3169

3167

Fig. 4. Illustration of the polymeric chains formed by [Ca(hip)2(H2O)2]H2O in the solid state.

Ca

O N H

O O

Ca

μ2η2η1 Scheme 1. Coordination mode of the carboxylate group.

as indicated by the torsion angles of C18–O5–Ca1–O4, 8.47(14)° and C9–O2–Ca1–O8, 4.56(14)° [31]. Thus each hippurate ligand, apart from acting as a chelating ligand through its carboxylate group, also bridges the neighboring Ca2+, forming infinite zigzag chains (Fig. 5). The variation in Ca–O bond distances, Ca1–O2 (2.519 Å), Ca1– O4 (2.4353 Å), Ca1–O5 (2.719 Å), Ca1–O8 (2.6038 Å), Ca1–O5a (2.3321 Å) and Ca1–O8b (2.3256 Å), indicates the difference in strength of the bonds formed by each of the coordinating O atoms.

The difference in the bond length can be attributed to the difference in back bonding between the amide and phenyl ring. Lattice water molecules occupied the voids of the 2D network and serve as receptors or donors of O–H  O hydrogen bonds. The hydrogen bonding interaction in 2 becomes more complex due to the presence of lattice water molecules, in addition to the two coordinated water molecules. There are eight different O–H  O, N–H  O and C–H  O hydrogen bonds which are responsible for the supramolecular assembly, as depicted in Fig. 6 (Table 5). All the phenyl rings are arranged at a dihedral angle of 45° to each other within the unit cell. The phenyl rings Cg (I) and Cg (2) are involved in p  p interactions, with a distance of 4.618(3) Å in [Ca(hip)2(H2O)2]H2O. In addition to the p  p stacking, C–H  p interactions of the methylene hydrogen with the phenyl hydrogen contributes to the stability of the unit cell packing. 3.3. Thermal analysis Thermal analysis of the calcium hippurate complex has been carried out to establish the presence of coordinated and

Fig. 5. Polyhedral environments for Ca in the 2D network.

3168

K.R. Jisha et al. / Polyhedron 29 (2010) 3164–3169

Table 5 H-bonding, p–p and C–H  p interaction parameters of [Ca(hip)2(H2O)2]H2O. D–H (Å)

H  A (Å)

D  A (Å)

Hydrogen bonding N1–H1A  O3 0.89(3) 2.01(4) N2–HA  O1a 0.90(4) 2.11(4) O6–H6A  O4b 0.842(17) 1.897(18) O6–H6B  O1c 0.84(2) 2.00(3) O7–H7A  O9 0.85(3) 1.97(3) O7–H7B  O2d 0.85(3) 1.91(3) C8–H8B  O1 0.97 2.39 e C13–H13  O3 0.93 2.58 Equivalent position codes: a = 1 + x, y, 1 + z; b = x, 1/2 + z; d = x, 1/2  y, 1/2 + z; e = x, y, 1 + z Cg(I) Cg(J)

Cg–Cg (Å)

a (°)

D–H  A (°)

2.01(4) 162(3) 2.915(3) 149(3) 2.735(3) 174(3) 2.830(4) 167(3) 2.810(7) 171(3) 2.748(3) 169(4) 2.789(4) 104 3.502(5) 169 1/2y, 1/2 + z; c = 1 + x, 1/2y, b (°)

c (°)

[p  p interactions] Cg(1)  Cg(2)a 4.618(3) 5.10(19) 9.23 16.33 Cg(1)  Cg(2)b 4.891(3) 5.10(19) 2.19 67.02 a Cg(2)  Cg(1) 4.618(3) 5.10(19) 6.33 59.23 Cg(2)  Cg(1)c 5.440(3) 5.10(19) 2.55 86.36 Equivalent position codes: a = x, y, z; b = 1  x, 1  y, 1  z; c = 1 + x, y, 1 + z Cg(I) = C(1),C(2),C(3),C(4),C(5),C(6) Cg(2) = C(10),C(11),C(12),C(13),C(14),C(15) X–H(I)  Cg(J)

H  Cg (Å)

C–H  p interactions C(17)–H(17B)   Cg(1)a 2.96 Equivalent position codes: a = 1 + x, y, z

X  Cg (Å)

X–H–Cg (°)

3.518(3)

18

D, donor; A, acceptor; Cg, centroid; a, dihedral angle between planes I and J; b, angle between Cg(I)  Cg(J) and Cg(I) perp.; c, angle between Cg  Cg and Cg(J) perp.

uncoordinated water molecules in the complex. The TG curve (Fig. 7) starts with a small weight loss and this may be due to the presence of uncoordinated water molecules. The first weight loss occurs in the range 50–110 °C and corresponds to the elimination of coordinated water molecules along with the lattice water molecules. The mass loss percentage of the elimination of water (11.92%) is in good agreement with the calculated value (11.72%) for three water molecules. There are four clear stages in the thermogram. The first stage corresponds to a DTG peak at 110 °C. The second DTG peak at 341 °C occurs along with a shoulder at 292 °C. The third and fourth stages correspond to the DTG peaks at 432 and 654 °C respectively. The final mass (11.02%) agrees with the conversion of the complex into CaO (12.45% observed).

0.05

3.5

0.00

3.0

-0.05

tg curve

-0.10

2.5

mass/mg

D–H  A

4.0

-0.15

2.0

DTG curve

1.5

-0.20 -0.25

1.0

-0.30

0.5

Derivative mass/mg min–1

Fig. 6. Packing diagram showing hydrogen bonding interactions between polymeric chains in [Ca(hip)2(H2O)2]H2O, viewed along the c axis.

-0.35 0.0 200

400

600

800

1000

Temperature/°C Fig. 7. TG and DTG curves of [Ca(hip)2(H2O)2]H2O in air.

Table 6 Measured SHG values of the metal complexes of hippuric acid. Compound

SHG signal (mV)

Efficiency with respect to KDP

[Mg(hip)2(H2O)2](H2O)2 [Ca(hip)2(H2O)2]H2O [Sr(hip)2(H2O)2]H2O [Ba(hip)2(H2O)2] hipH KDP

4 7 3 3 61 25

0.16 0.28 0.12 0.12 2.44 1

3.4. Second harmonic generation efficiency The SHG measurement was carried out for hippuric acid and its complexes. Throughout the experiment the laser power was kept constant. The SHG outputs are given in Table 6. The data show that the Ca(II) complex has two times more efficiency than the other complexes.

K.R. Jisha et al. / Polyhedron 29 (2010) 3164–3169

4. Supplementary data CCDC 750936 contains the supplementary crystallographic data for [Ca(hip)2(H2O)2]H2O. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected]. Acknowledgements The authors are grateful to the authorities of SAIF, Cochin University of Science and Technology, Kochi, India for IR spectra, CHN and thermal analysis. We are grateful to Dr. Babu Varghese, SAIF, IIT Chennai, India for single crystal studies. We are also grateful to Dr. M.R.P. Kurup, Department of Applied Chemistry, Cochin University of Science and Technology for the use of software DIAMOND version 3.1f. One of the authors, SS, is grateful to UGC for financial assistance and JKR is thankful to the University of Kerala for the award of a Fellowship. References [1] M. Morshedi, M. Amirnasr, A.M.Z. Slawin, J.D. Woollins, A.D. Khalaji, Polyhedron 28 (2009) 167. [2] S.K. Hiltunen, M. Matilainen, J.J. Vepsäläinen, M. Ahlgrén, Polyhedron 28 (2009) 200. [3] R. Murugavel, N. Gogoi, Bull. Mater. Sci. 32 (2009) 321. [4] B.R. Srinivasan, S. Shetgaonkar, P. Raghavaiah, J. Chem. Sci. 120 (2008) 249. [5] A.I. Smolentsev, A.I. Gubanov, A.M. Danilenko, Acta Crystallogr., Sect., C 63 (2007) i99. [6] M. Abdulla, A. Behbehani, H. Bashti, Magnesium in Health and Disease, John Libby and Co., Ltd., London, 1989. pp. 111–117. [7] H. Schmidbaur, P. Mikulik, G. Müller, Chem. Ber. 123 (1990) 1599.

3169

[8] N. Sewald, H.D. Jakube, Peptides: Chemistry and Biology, Wiley VCH Verlag GmbH & Co. KGaA, Weinheim, 2002. [9] M. Currie, A.L. MacDonald, J. Chem. Soc., Perkin 1 11 (1974) 784. [10] R.H. Moser, B.D. Rosenak, R.J. Hasterlik, Am. J. Dig. Dis 9 (1942) 183. [11] S. Patton, J. Dairy Sci. 36 (1953) 943. [12] R.R. Babu, N. Vijayan, R. Gopalakrishnan, P. Ramaswamy, Cryst. Res. Technol. 41 (2006) 405. [13] M.S. Refat, S.A. EI-Korashy, A.S. Ahmed, Spectrochim. Acta, Part A 70 (2008) 840. [14] S.A. Sadeek, M.S. Refat, S.M. Teleb, S.M. EI-Megharbel, J. Mol. Struct. 737 (2005) 139. [15] M.S. Refat, S.M. Teleb, S.A. Sadeek, H.M. Khater, S.M. EI-Megharbel, J. Korean Chem. Soc. 49 (2005) 261. [16] W. Brzyska, M. Hakim, J. Therm. Anal. 34 (1988) 47. [17] E.D. Vieira, G. Facchin, M.H. Torre, A.J. Costa-Filho, J. Braz. Chem. Soc. 19 (2008) 1614. [18] D. Dobrzyn´ska, T. Lis, J. Woz´niak, J. Jezierska, M. Duczmal, A. Wojciechowska, R. Wysokin´ski, Polyhedron 28 (2009) 3150. [19] G. Marcotrigiano, G.C. Pellacani, Z. Anorg. Allg. Chem. 415 (1975) 268. [20] J.R. Allan, J. Dalrymple, J. Thermochim. Acta 185 (1991) 83. [21] S. Natarajan, S.A.M.B. Dhas, J. Suresh, R.V. Krishnakumar, Acta Crystallogr., Sect., E 63 (2007) m1408. [22] S.K. Kurtz, T.T. Perry, J. Appl. Phys. 39 (1968) 3798. [23] SMART Software Reference Manuals, version 5.0, Bruker AXSInc, Madison, WI, 1998. [24] G.M. Sheldrick, SADABS, Program for Area Detector Adsorption Correction, Institute for Inorganic Chemistry, University of Göttingen, Germany, 1996. [25] G.M. Sheldrick, SHELXL-97, Program for Refinement of Crystal Structures, University of Göttingen, Germany, 1997. [26] A.L. Spek, PLATON, a Multipurpose Crystallographic Tool, Utrecht University, Utrecht, The Netherlands, 1999. [27] K. Brandenburg, DIAMOND Version 3.1f, Crystal Impact GbR, Bonn, Germany, 2008. [28] K.R. Jisha, S. Suma, M.R. Sudarsanakumar, J. Therm. Anal. Calorim. 99 (2010) 509. [29] Z.M. Wang, W.T. Yu, D.R. Yuan, X.Q. Wang, G. Xue, X.Z. Shi, D. Xu, M.K. Lu, Z. Kristallogr, NCS 218 (2003) 389. [30] H.F. Zhu, Z.H. Zhang, W.Y. Sun, T.A. Okamura, N. Ueyama, Cryst. Growth Des. 5 (2005) 177. [31] C.Y. Tian, W.W. Sun, Q.X. Jia, H. Tian, E.Q. Gao, J. Chem. Soc., Dalton Trans. (2009) 6109, doi:10.1039/b900110g.