NEW SOLVATOMORPH OF TETRAKIS ( μ 2-ACETATO-O , O ' )-BIS ( ISONICOTINAMIDE-N )-DI-COPPER ( II ) : SYNTHESIS , IR , TGA AND X-RAY STUDY

Abstract. Dinuclear tetracarboxylato-bridged copper(II) complex, [Cu2(OAc)4(ina)2]·2dmso (1), where OAc = CH3COO , ina=isonicotinamide and dmso=dimethylsulfoxide, has been prepared and crystal structure has been determined by single X-ray diffraction. The compound consists of dinuclear units, in which two Cu(II) ions are bridged by four syn,syn-η:η:μ-acetato bridges, showing a paddle-wheel cage-type with a square-pyramidal geometry. In the crystal structure, intermolecular N-H···O hydrogen bonds link the molecules into a 1D linear chain.


Introduction
The design and preparation of metal-organic frameworks have attracted intense interest in the fi eld of supramolecular chemistry and crystal engineering owing to their potential applications as well as their structural variations that are currently of interest in the fi eld of materials [1][2][3][4][5][6][7].A successful strategy in building such networks is to employ appropriate bridging ligands that can bind metal ions in different modes and provide a possible way to achieve diverse dimensionalities.Copper(II) metal-organic frameworks are of considerable interest because of their structural and photoluminescent biological function, catalytic and magnetic properties [8][9][10][11].Isonicotinamide and its related compounds are reported to represent a group of small molecules as a drug candidate to prevent and/or reverse diabetes by protecting β-cells from damage and death [12].

Materials and methods
All reagents and solvents were obtained from commercial sources and were used without further purifi cation.Elemental analysis was performed on an Elementar Analysen systeme GmbH Vario El III elemental analyzer.The IR spectra were obtained in vaseline oil on a FT IR Spectrum-100 Perkin Elmer spectrometer in the range of 400 -4000 cm -1 .The thermogravimetric analysis (TGA) was carried out with a Derivatograph Q-1500 thermal analyzer in an air fl ow at a heating rate of 10 °C/min in the temperature range of 25 -1000 °C.

X-ray structure determination
Diffraction measurement for 1 was carried out at room temperature on a Xcalibur "Oxford Diffraction" diffractometer equipped with CCD area detector and a graphite monochromator utilizing MoKa radiation.Final unit cell dimensions were obtained and refi ned on an entire data set.All calculations to solve the structure and to refi ne the proposed model were carried out with the programs SHELXS97 and SHELXL97 [31].The structure was solved by direct methods and refi ned by full-matrix least-squares methods on F 2 by using the SHELXL97 program package.All nonhydrogen atoms were refi ned anisotropically.Hydrogen atoms attached to carbon atoms were placed in geometrically idealized positions and refi ned by using a riding model.The X-ray data and the details of the refi nement for 1 are summarized in Table 1.Selected geometric parameters for 1 are given in Tables 2 and 3.The fi gures were produced using the Mercury program [32].CCDC-1408326 contains the supplementary crystallographic data for this paper.These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_ request/cif.

Crystal structure analysis
The interaction in the system Cu(OAc) 2 -isonicotinamide (ina) -pyridine-2,5-dicarboxylic acid (2,5-pdc) resulted in the acid-free dinuclear compound of the composition [Cu 2 (OAc) 4 (ina) 2 ]•2dmso (1).Complex 1 represents chromophore being intensively green colored.Upon exposure to air, the adduct is stable in solid state and is soluble in water and common organic solvents such as methanol and N,N-dimethylformamide.

Table 4
Structural data for some relevant paddle-wheel copper(II) complexes.

Infrared spectroscopy study
The IR spectrum confi rms the presence of the organic ligands used in the synthesis (through the typical vibrations of pyridine rings, amide, and carboxylic groups) [40].The spectrum exhibits very strong and broad bands due to stretching vibrations of coordinated carboxylate groups at 1408 cm -1 ν s (COO) and 1614 cm -1 ν as (COO) of acetate anions.The absorption bands at 3300, 3163 and 1619 cm -1 can be attributed to ν(NH) and δ(NH 2 ), respectively and the oscillations at 1557 and 1025 cm -1 show the presence of aromatic rings.The vibrations at 2953, 2924 and 2854 cm -1 are attributed to ν(CH), at 1347 cm -1 to δ(CH) and the vibrations at 1678 and 1230 cm -1 correspond to ν(-C=O) and ν(-C-N), respectively.The presence of dimethylsulfoxide in the complex is documented by the oscillations at 2794 cm -1 ν as (CH 3 ), 2921 cm -1 ν s (CH 3 ), 1069 and 1050 cm -1 ν(-S=O), 722 cm -1 ν(-C-S-C-) and 682 cm -1 ν(-C-S-).

Thermogravimetric analysis
The decomposition of 1 was investigated by combined TG-DTA.It was found that 1 has three separate weight loss steps (Figure 2).The fi rst weight loss step is observed in the range of 165-188 °C corresponding to the loss of the two solvated dmso molecules (found, 20.9%; calcd., 20.5 %).In the range of 195-239 o C takes place the second weight loss that can be attributed to two ina molecules (found, 31.5%;calcd., 31.7%).Both processes are endothermic.Beginning with 340 o C, a strong exothermic process was observed, with maximum at 430 o C, caused by oxidative degradation of the remaining compound.The fi nal residue corresponds to CuO with no changes to 1000 o C.

Conclusions
A new dinuclear tetracarboxylato-bridged copper(II) solvatomorph [Cu 2 (OAc) 4 (ina) 2 ]•2dmso (1) (OAc - =CH 3 COO -, ina=isonicotinamide and dmso=dimethylsulfoxide) was prepared and studied by IR spectroscopy, TGA analysis and single crystal X-ray method.Four carboxylate ligands bridge two copper ions in a syn, syn-η 1 :η 1 :μ mode showing a paddle-wheel unit.Isonicotinamide ligands coordinate to copper(II) in a monodentate form through the nitrogen atom of pyridine.The Cu(II) cation is pentacoordinated in a NO 4 -environment in the shape of distorted square-pyramid.The amide moiety of isonicotinamide ligands forms N-H•••O hydrogen bonds resulting in infi nite linear chains.

Figure 1 .
Figure 1.View of the: dinuclear Cu(II) molecule (a); infi nite chain of dinuclear Cu(II)-complexes held together by self-complementary amide•••amide hydrogen-bond interactions (b) and crystal packing in 1 with dmso molecules shown in the space-fi lling mode, C-bound H-atoms are omitted for clarity (c).