Spectral studies and crystal structures of molybdenum(VI) complexes containing pyridine or picoline as auxiliary ligands: interaction energy calculations and free radical scavenging studies

Three cis-MoO complexes [MoO(CAB)(py)] (1), [MoO(CAB)(3-pic)] (2) and [MoO(CAB)(4-pic)] (3) which vary in the nature of the heterocyclic bases in the auxiliary coordination site derived from an ONO donor aroylhydrazone (HCAB) have been synthesized and characterized by various physicochemical methods. The single-crystal X-ray diffraction studies reveal that the complexes adopt a distorted octahedral NO coordination sphere around the Mo(VI) center in which the ONO donor atoms of hydrazone moiety and one oxido oxygen constitute the NO basal plane and the axial position by the other oxido oxygen and nitrogen atom of coordinated pyridine molecule in [MoO(CAB)(py)] (1) or picoline molecule in [MoO(CAB)(3-pic)] (2) and [MoO(CAB)(4-pic)] (3). The hydrogen bonding interaction generates a two-dimensional supramolecular sheet-like architecture in [MoO(CAB)(py)] (1) and [MoO(CAB)(3-pic)] (2), whereas a three-dimensional network was observed in [MoO(CAB)(4-pic)] (3). The interaction energy calculations reveal that the dispersion energy component dominates over other components and [MoO(CAB)(3-pic)] (2) is found to be energetically more stable. Furthermore, the aroylhydrazone shows free radical scavenging activity, whereas the complexes are inactive.