Succinato-bridged copper(II) supramolecular 3D framework: Synthesis, crystal structure and magnetic property

Inorganica Chimica Acta 360 (2007) 1771–1775 www.elsevier.com/locate/ica

Succinato-bridged copper(II) supramolecular 3D framework: Synthesis, crystal structure and magnetic property Debajyoti Ghoshal a, Ananta Kumar Ghosh b, Golam Mostafa c, Joan Ribas d,*, Nirmalendu Ray Chaudhuri b,* b

a Department of Chemistry, Jadavpur University, Jadavpur, Kolkata 700 032, India Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032, India c Department of Physics, Jadavpur University, Jadavpur, Kolkata 700 032, India d Departament de Quı´mica Inorga`nica, Universitat de Barcelona, Diagonal, 647, 08028 Barcelona, Spain

Received 11 May 2006; received in revised form 25 August 2006; accepted 30 August 2006 Available online 27 September 2006

Abstract A new succinato-bridged copper(II) complex, [{Cu(L)(H2O)2}(H2O)2]n (1) (L, succinate dianion) has been synthesized and characterized by single crystal X-ray diffraction analysis and low temperature magnetic study. The structure determination reveals that the complex 1 is a one-dimensional coordination chain of copper(II), bridged through the succinate dianion approximately along the crystallographic ac diagonal and extended to supramolecular 3D net work by H-bonding. The low temperature magnetic study reveals significant antiferromagnetic interactions between the copper centers corroborating the existence of H-bonding in 1.  2006 Elsevier B.V. All rights reserved. Keywords: Copper(II); Succinate dianion; Crystal structure; Magnetic property; H-bonding

1. Introduction The manipulation of covalent and non-covalent interactions in order to tune the properties of the bulk material is one of the key objectives of the advanced crystal engineering [1]. However, it is an assigned fact that [2] crystal packing governs specific classes of functional materials like catalyst [3], molecular magnetic material [4,5], thermal sensor, non-linear optical material [6], material having selective guest exchange property [7] and solvated host structures recognizing biological systems [8]. Due to the extensive implicational possibilities the crystal engineering of metal organic coordination network has been extensively studied for last a few years [1–8]. Recently, there has been considerable interest in coordination chemistry *

Corresponding authors. Fax: +91 33 2473 2805 (N. Ray Chaudhuri). E-mail addresses: [email protected] (J. Ribas), [email protected] (N. Ray Chaudhuri). 0020-1693/$ - see front matter  2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2006.08.054

of carboxylate as their polymeric metal complexes are unique for structural networks, exchange coupling interactions between adjacent metal ions leading to magnetic material and channel networks by hydrogen bonding [5]. Moreover, dicarboxylate ligands could yield a variety of crystal structures of coordination complex, even in similar ratio of metal ion and carboxylate anion, depending on various conformation and different bridging mode of the carboxylate [5,9]. But the controlling factors behind the formation of different topologies are not yet explored properly. Recently, many groups including us reported the synthesis and magnetic property of various metal dicarboxylate complexes [5]. But the reports related to succinate ligand are scanty [9,10] due to the low solubility of the metal succinate complexes in common organic solvents. Among the dicarboxylates, succinate dianion is useful to create structural diversity not only for its various binding modes but also for several conformational modes originating from its flexibility [9].

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Herein, we report synthesis, crystal structure, magnetic property and thermal behavior of Cu-succinate complex, [{Cu(L)(H2O)2}(H2O)2]n (L, succinate dianion). The structural analysis reveals that 1D coordination chain, –Cu(II)– L–Cu(II)– which is extended to supramolecular 3D network through H-bonding, having small channels filled with water molecules. The low temperature magnetic study indicates significant antiferromagnetic coupling between the copper centers corroborating the extensive H-bonding network. 2. Experimental 2.1. Materials

was solved by direct method and followed by successive Fourier and difference Fourier syntheses. Full matrix least squares refinements on F2 were carried out using SHELXL-97 [12] with anisotropic displacement parameters for all nonhydrogen atoms for the complex. All calculations were carried out using SHELXL 97 [12], SHELXS 97 [12], PLATON [13], ORTEP-32 [14] and the WinGX system, Ver 1.64 [15]. Crystallographic data: empirical formula, C4H12CuO8; formula weight (g mol1), 251.69; crystal system, monoclinic; space ˚ ), 8.3053(14); b (A ˚ ), 7.2256(13); c group, C2/m (no. 12); a (A ˚ ˚ 3), (A), 8.4336(15); a (), 90; b (), 112.205(3); c (), 90; V (A 3 468.57(14); Z, 2; T (K), 294; Dcalc (g cm ), 1.784; l (mm1), 2.345; F(0 0 0), 258; k (Mo Ka), 0.71073; h range (), 2.6–28.1; total data, 1450; unique data, 577; data [I > 2r(I)], 563; Ra, 0.0355; Rbw , 0.0932; S, 1.06; Rint, 0.035.

All reagents used were of analytical grade and they were used as received.

4. Results and discussion

2.2. Physical measurements

4.1. IR spectroscopy

Elemental analyses (carbon and hydrogen) were performed using a Perkin–Elmer 240C elemental analyzer. Infrared spectra (4000–400 cm1) were taken using a Nicolet Magna-IR 750 spectrometer, series-II, where KBr was used as the dispersal medium. Thermal analysis (TGA– DTA) was carried out on a Shimadzu DT-30 thermal analyzer under dinitrogen (flow rate: 30 cm3 min1). The XRD of powder sample was done by Seifert 3000P diffractometer. Magnetic measurements of polycrystalline samples (20 mg) were carried out in the ‘‘Servei de Magnetoquı´mica (Universitat de Barcelona)’’ with a Quantum Design SQUID MPMS-XL susceptometer working in the 2– 300 K range. The magnetic field was 0.1 T. The diamagnetic corrections were evaluated from Pascal’s constants [11].

The IR spectra of complex 1 show broad band in the region 3300–3500 cm1, which can be assigned to the stretching vibrations, m(O–H), of the hydroxyl group in the water molecules [16]. The next group of bands appears at around 2900–3100 cm1 and corresponds to the stretching vibration, m(C–H), of the succinate ligands [16]. The uncoordinated carboxylate ligand shows strong [mas(OCO)] band at 1700 cm1 and [ms(OCO)] band at 1450 cm1. It also shows two medium intensity bands at 800 and 750 cm1 assigned to the OCO bending frequencies [16]. These frequencies are significantly shifted to lower frequencies on coordination. In complex 1, [mas(OCO)] and [ms(OCO)] bands appear at 1623 and 1436 cm1 respectively, which are significantly lower and indicative of the coordination of the carboxylate group to copper(II) centers [16,17]. Finally the bending vibrations corresponding to the d(C@O) group are observed in the 1180–1300 cm1 range [16].

2.3. Synthesis of [{Cu(L)(H2O)2}(H2O)2]n (1) An aqueous solution (5 ml) of disodium succinate (0.162 g, 1 mmol) was added dropwise to a methanolic solution (15 ml) of copper(II) chloride dihydrate (0.170 g, 1 mmol) with constant stirring for 20 m. The resulting reaction mixture was refluxed for 2 h and then it was cooled and filtered. The blue filtrate was kept in an open atmosphere. After a few weeks shiny blue diamond shaped single crystals suitable for X-ray analysis were obtained. Yield 85%. Anal. Calc. for C4H12CuO8: C, 19.07; H, 4.77. Found: C, 19.02; H, 4.74%. The purity of the powder sample taken for analysis was supported by the XRPD analysis (Fig. S1). 3. Crystallographic data collection and refinement Suitable single crystal of complex 1 was mounted on a Bruker SMART CCD diffractometer equipped with a ˚) graphite monochromator using Mo Ka (k = 0.71073 A radiation. The intensity data were corrected for Lorentz and polarization effects for the complex. The structure

4.2. Structure description The structure determination reveals that the complex 1 is a one-dimensional coordination chain of copper(II) bridged through the succinate ligand aligned approximately along the crystallographic ac diagonal. The ORTEP drawing of the chain with atom numbering scheme is shown in Fig. 1. In the chain, each Cu(II) is ligated with two bridging succinate ligands and two water molecules in square planar environment with CuO4 chromophore. The Cu–O bond lengths are in the region 1.959(3)– ˚ . The each copper atom perfectly sits on the 1.971(4) A square plane and there is no distortion from the ideal square planar geometry that is reflected from the cisoid and transoid angles. It is worth mentioning that here the succinate ligand is strictly planar. Hydrogen bonding between coordinated water, O1w and succinate oxygen, O1 of adjacent chains connect copper atoms resulting a

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˚ ) and angles () Cu–O1, 1.959(3); Cu–O1w, Fig. 1. ORTEP diagram of the 1D coordination chain of 1 with atom labeling scheme. Selected bond lengths (A 1.971(4); Cu–O1*, 1.959(3); Cu–O1w**, 1.971(4); O1–C1, 1.270(5); O2–C1, 1.231(6); O1–Cu–O1w, 90.00(1); O1–Cu–O1*, 180.00; O1–Cu–O1w**, 90.00(1); O1*–Cu–O1w, 90.00(1); O1w–Cu–O1w**, 180.00; O1*–Cu–O1w**, 90.00(1); Cu–O1–C1, 113.3(3) [symmetry code: * = x, y, z; ** = x, y, z].

layer in ab plane (Fig. 2). Thereby O–H  O bonds generate two primary cyclic motifs, R24 (8) and R22 (8) along with one secondary cyclic motif, R44 (16) in Etter’s graph notation [18] (Fig. 2). The distance between two adjacent layers ˚ . The layers are held together through bridging is 8.366 A succinate ligands leading to an overall 3D solid state struc˚ · 3.19 A ˚ and ture with small channels of 3.19 A ˚ · 3.5 A ˚ (atom to atom) in the [1 0 1] and ½ 6.4 A 1 1 0 directions, respectively (Figs. 3 and 4). The O2w atoms from the lattice water fill the spaces of the channels. Surprisingly, the free succinate oxygens are not involved in hydrogen bond˚ . Within ing. The intra-chain Cu  Cu separation is 9.336 A a given layer, the shortest distance between the metal cen˚ . The overall average ters of the adjacent chains is 5.504 A O  O separation between hydrogen-bonded groups is ˚ , indicative of weak hydrogen bonding found to be 3.192 A in the structure.

Fig. 3. Molecular packing diagram of complex 1 showing water filled channel along [1 0 1] direction.

Fig. 4. Molecular packing diagram of complex 1 showing water filled channels formed by joining H-bonded sheets through succinate ligands along ½1 1 0 direction.

4.3. Magnetic properties

Fig. 2. Infinite 2D H-bonded sheet of complex 1 lying on the ab-plane ˚ /) D–H  A, D–H, H  A, D  A, D–H  A; O1w– [hydrogen bonding (A H11w  O1i, 0.8525, 2.3558, 3.192(3), 167.05; O1w–H11w  O1ii, 0.8525, 2.3558, 3.192(3), 167.05; symmetry code: (i) = 1/2  x, 1/2 + y, z; (ii) = 1/2  x, 1/2  y, z].

The magnetic properties of the complex 1 in the form of vMT versus T plot (vM is the molar magnetic susceptibility for one CuII ion) are shown in Fig. 5. The value of vMT at 300 K is 0.33 cm3 mol1 K (close to the expected value for one isolated copper(II) ion, 0.4 cm3 mol1 K) and decreases while lowering the temperature to 0 cm3 mol1 K at 2 K. This feature is characteristic of a medium antiferromagnetic coupling between CuII ions. It is to note that the magnetic data of its dehydrated analogue are almost similar to that of hydrated 1.

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erature related to hydrogen bonds, such as J =  90 cm1 ˚ [23]. for a Cu dimer with O–H  O distance of 2.32 A Even for other metals, like chromium(III), considerable J values are also reported [24]. Not only antiferromagnetic coupled systems with appreciable J values are to date reported but also the number of ferromagnetically coupled hydrogen bond systems is growing exponentially, either some supramolecular copper structures [25], or even some organic radicals [26]. The most striking feature is that the hydrogen bond can create, thus, not only ferromagnetic coupling, but also can be responsible for the long-range ordering in some recently described moleculebased magnets [27].

0.2

3

-1

χ MT / cm mol K

0.3

0.1

0.0 0

50

100

150

200

250

300

T/K Fig. 5. Plot of vMT vs. T for complex 1 (vM is the molar magnetic susceptibility for one CuII ion, solid line represents the best fit results).

As shown in the crystallographic part, complex 1 is made up of one-dimensional Cu-succinate systems, linked among them in a pseudo two-dimensional net through hydrogen bonds. Taking into account that the very scarce data about magnetic properties on Cu-succinate complexes indicate as predicted for the four carbon skeleton very small or negligible coupling [10] and the medium antiferromagnetic coupling must be due to the hydrogen bonds formed through the water molecules of copper(II) ions (see structural part). It is difficult (almost impossible) to fit the data in such a structure. There are two special formulae reported by Lines [19] and Rushbrooke–Wood [20], valid for copper(II) quadratic two-dimensional systems with only one J value, assuming no interactions between the layers. This formula is valid mainly in the high temperature region. Considering the crystal structure, the low temperature zone should not be good for the fit. Thus, we have cut the experimental points from 300 to 50 K and fitted according to the Rushbrooke formula [20]. P This formula, based on the spin Hamiltonian H =  2J ijSiSj is as follows: vM T = Ng2b2/4k * [1  2/x + 2/x2  1.333/x3 + 0.25/x4 + 0.4833/x5 + 0.003797/x6]1 (where x = kT/J, N is Avogadro’s number, b = Bohr magneton and k = Boltzmann constant. The best-fit parameters are: 2J =  21 ± 1 cm1, g = 2.08 ± 0.02 and R =P 1.1 · 105 (R is the agree2 ment factor defined as i[(vMT)obs  (vMT)calc] / P 2 i[(vMT)obs] (Fig. 5). This J value indicates that the coupling between the CuII centers is noticeable antiferromagnetic. The role that hydrogen bonds play in the transmission of magnetic interactions is still not completely understood. For many years, hydrogen bonds have been reported to propagate essentially antiferromagnetic interactions between metal centers in variety of transition metal complexes [21]. Recent theoretical studies have been able to rationalize the antiferromagnetic coupling between CuII complexes mediated by hydrogen bonds [22]. In certain complexes the high J values have been reported in lit-

4.4. Thermogravimetric analysis The blue [{Cu(L)(H2O)2}(H2O)2]n (1) loses two crystalline water molecules on keeping it in a CaCl2 desiccator and the residual two coordinated water molecules lose upon heating at 110 C. The dehydrated sky blue complex does not decompose up to 270 C and it does not revert on keeping it in humid atmosphere (RH  60%). The loss of crystalline water molecules taking place in desiccator indicates that these molecules are not closely bound in the lattice. The single crystal structure also corroborates that the crystalline water molecules are not involving in Hbonding (Fig. 4), which makes them more labile. 5. Conclusions Through the use of the succinate ligand we have successfully synthesized [{Cu(L)(H2O)2}(H2O)2]n (1) which is a 1D coordination chain bridged through the succinate ligand and extended to supramolecular 3D net work through O– H  O bonds. The O–H  O bonds generate two cyclic motifs R24 (8) and R44 (16). The eight-membered ring formed by water molecule and the carboxylate group is a unique structural motif in supramolecular chemistry. This novel feature provides supramolecular channels where the crystalline guest waters are located. The magnetic studies are performed in 2–300 K and magneto-structural correlation corroborates the extensive H-bonding in the 3D supramolecular network. Acknowledgements The authors acknowledge the Seed Support under the Potential for Excellence Scheme of Jadavpur University (DG & GM), Grant BQU2003–00539 of the Spanish Government (JR) and Council of Scientific and Industrial Research, New Delhi (NRC). Appendix A. Supplementary material CCDC 191752 contains the supplementary crystallographic data for the structure reported in this paper. These data can be obtained free of charge via http://www.ccdc.

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