Synthesis, X-Ray characterization and molecular structure of a novel supramolecular compound of antimony(III); Theoretical investigation on molecular and electronic properties based on the ab initio HF and various DFT methods

A new compound of Sb(III), formulated as (pipzH2)[Sb2(pydc)4].2H2O (1), was synthesized and characterized by IR, 1H and 13C NMR spectroscopy, elemental analysis and single crystal X-ray diffractometry. The compound (1) is a member of a great family of supramolecular metallic compounds recently derived from a proton transfer ion pair i.e. (pipzH2)(pydc), where pipz is piperazine and pydcH2 is pyridine-2,6-dicarboxylic acid. In the title compound with a binuclear structure, Sb(III) atoms are pentacoordinated and the coordination polyhedra show distortion from a regular trigonal bipyramid due to stereochemically active lone pair on metallic centers. The four (pydc)2− ligands of the formula unit behave differently against metallic centers, i.e. two act as tridentate, and the other two as bidentate ligands. A variety of intermolecular O-H…O, N-H…O and C-H⋯O hydrogen bonds involving water molecules, cationic and anionic fragments are responsible for the extension of the supramolecular network of the compound. Optimized geometries were calculated for the title compound with the HF, B3LYP, B3PW91, B3P86 and B1LYP methods of theory by using the combination of LanL2DZ basis set with standard basis set 6-31G (d,p). The agreement between the optimized and experimental geometries was in the decreasing order: B3P86, B3PW91, B1LYP, B3LYP and HF. Electronic properties of the title compound were also investigated based on the natural bond orbital (NBO) analysis.