Synthesis, characterization, and antimicrobial properties of two new Bis(oxalato)metalate(III) hybrid salts with 2,2’-bipyridinium cation

Abstract

Two new isostructural hybrid salts, 2,2′-bipyridinium (2,2′-bipyridine-к2N1, N2)bis[oxalato(2-)-к2O1,O2]metalate(III)] hydrate (MIII = CrIII and CoIII), (C10H9N2)[Cr(C2O4)2(C10H8N2)]·H2O (1) and (C10H9N2)[Co(C2O4)2(C10H8N2)]·H2O (2), (C10H8N2 or bipy = 2,2′-bipyridine and (C10H9N2)+ or bipyH+ = 2,2′-bipyridinium) were prepared in H2O/EtOH (2:1) solution by slow evaporation at room temperature. They were characterized by FTIR and UV–Vis spectroscopies, elemental, thermal, single-crystal X-ray diffraction, and Hirshfeld surface analyses. Both compounds crystallize in the monoclinic P21/c space group and are made up of 2,2′- bipyridinium cations, water molecules, and the mononuclear anionic tectons: 2,2′-bipyridinebis(oxalato)chromate(III) for 1 or 2,2′-bipyridinebis(oxalato)cobaltate(III) for 2. The CrIII and CoIII environments in 1 and 2 are distorted octahedral geometries with two bidentate oxalate groups and one bidentate bipy ligand. The MIII ̶ O and MIII ̶ N bond distances vary in the ranges 1.942(1) - 1.967(1) Å and 2.055(2) - 2.066(1) Å respectively. The cohesion of both structures is reinforced by intermolecular N H···O, O H···O and C(π) H···O hydrogen bond interactions which connect the ionic entities and the water molecules into 3-D supramolecular frameworks. All the oxygen atoms are involved in the hydrogen bonding system. The H···O/O···H, H···H, H···C/ C···H, C···C and O···C/C···O contacts contribute with 38.6, 31.1, 14.4, 7.1 and 4.2 % respectively to the Hirshfield surface (HS) of 1 and close values are found for 2. Thermal studies reveal that 1 and 2 are thermally stable up to 130 °C and 110 °C, respectively. The ligands, metal salt, and complexes were evaluated for their antimicrobial activities in vitro against seven pathogens (four bacteria and three fungi species). The complexes have an activity higher than those of the metal salts and the oxalate ligand but lower than those of the 2,2′-bipyridine ligand. The cobalt (III) complex 2 shows a higher activity compared to the chromium(III) complex 1. These results illustrate the fact that an appropriate combination of ligands and metal ions can lead to complex salts with enhanced biological activities.