Discrete versus polymeric structures of coordination compounds of copper (II) with (pyridin-2-yl)methylenenicotinohydrazide and a library of dicarboxylic acids

A series of copper(II) discrete and polymeric coordination compounds, namely [{CuL(H2O)}(2)(fum)] (1), [{CuL(H2O)}(2)(mes)] (2), [Cu2L2(glu)](n)2n(H2O) (32n(H2O)) and [Cu3L2(adi)(2)](n) (4) were fabricated from (pyridin-2-yl)methylenenicotinohydrazide (HL) and a library of dicarboxylic acids, namely fumaric acid (H(2)fum), mesaconic acid (H(2)mes), glutaric acid (H(2)glu) and adipic acid (H(2)adi), using evaporative crystallization, grinding and slurry synthesis methods. The obtained coordination compounds have been fully characterized by single crystal X-ray diffraction revealing different types of complexes depending on the linker length, viz. from dinuclear complexes for the shorter linkers (fumaric and mesaconic acids) to 1D and 2D coordination polymers for longer glutaric and adipic acids. Thermal stability and spectroscopic features (FTIR and diffuse reflectance) of complexes were also studied. For the nonpolymeric compounds 1 and 2, the supramolecular assemblies driven by a combination of antiparallel pi-stacking and hydrogen bonding interactions have been studied and compared using DFT calculations, MEP surface analysis and a combination of QTAIM and NCIplot computational tools.