Synthesis, characterization and X-ray structural studies of four copper (II) complexes containing dinuclear paddle wheel structures

Four compounds, each containing dinuclear Copper (II) units (with the most robust, frequently occurring paddle wheel structures) were synthesized and characterised by single crystal X-ray diffraction and by IR spectroscopy. The compounds 1 & 2 have the general formula Cu2(RCOO) 4(L)2 [(for (1) RCOO= 4-Chloro Benzoate , L= Isopropanol ; for 2 RCOO= Benzoate , L= 2-Amino-4,6-dimethyl pyrimidine )] while 3 & 4 have the general formula, Cu2(RCOO) 4(S)2 Cu2(RCOO) 4(L)2 [RCOO=5-Chloro-thiophene-2-carboxylate L= 2-Amino-4,6-dimethyl pyrimidine, for 3 S= ethanol ; for 4 S= methanol ]. A wide range of hydrogen bonds (of the O-H...O, N-H...O and N-H...N type) and pi-pi stacking interactions are present in the crystal structures.All compounds contain the dinuclear units, in which two Cu(II) ions are bridged by four syn,syn-eta1:eta1:mu carboxylates, showing a paddle-wheel cage type with a distorted octahedral geometry. The compounds 1 & 2 contain a single dimeric unit while 3 & 4 contain two dimeric units. The structures 3 and 4 are very interesting co-crystals of two paddle wheel molecules. Also it is interesting to note that the compounds 3 & 4 are isostructural with similar cell parameters. Both the compounds 3 & 4 differ in the solvent molecule coordinated to copper in one of the dimeric units. In all the four compounds, each of the copper dimers has an inversion centre. Every copper has a distorted octahedral centre, formed by four oxygen atoms (from different carboxylate) in the equatorial sites. The two axial positions are occupied by copper and the corresponding ligand.