A new heterometallic heptanuclear oxalato-bridged [K₄^ICr₃^III] complex with pyridinium type counter cations: synthesis, crystal structure, thermal behavior, magnetism and antibacterial activities

Abstract

A new heterometallic heptanuclear oxalato-bridged [K₄^ICr₃^III] hybrid salt, (C₆H₉N₂)₃[K₄Cr₃(C₂O₄)₈(H₂O)_2.5] (1) (C₆H₉N₂⁺= 2-amino-3-methylpyridinium cation) has been synthesized through an ion-exchange reaction strategy by combining in aqueous solution two salts, (C₆H₉N₂)₂C₂O₄ and K₃[Cr(C₂O₄)₃]·3H₂O in a 1:2 M ratio. It has been characterized by elemental and TGA/DSC analyses, IR and UV–Vis spectroscopies, powder and single-crystal X-ray diffraction, and variable temperature magnetic susceptibility measurements. Salt 1 is composed of a bimetallic heptanuclear [K₄Cr₃(C₂O₄)₈(H₂O)_2.5]^3- anionic complex and three 2-amino-3-methylpyridinium C₆H₉N₂⁺ cations ensuring the charge balance. Each Cr³⁺ center exhibits distorted octahedral coordination. K1 and K2 centers are 9- and 7-coordinate, respectively. The crystal structure of 1 is characterized by an extended anionic network delineating voids accommodating disordered organic cations. The O–H∙∙∙O and N–H∙∙∙O hydrogen bonds linking polymeric oxalato-bridged anionic assemblies and organic cations contribute to the stabilization of the three-dimensional network. Salt 1 is thermally stable up to 145 °C. Temperature-dependence susceptibility measurements investigated in the temperature range 2–300 K revealed weak antiferromagnetic coupling at low temperatures in salt 1. The antimicrobial effects of the oxalate ligand, the precursor salt K₃[Cr(C₂O₄)₃]·3H₂O, the pyridine derivative and the target salt 1 have been evaluated in vitro against five bacteria species. Salt 1 has an activity higher than that of the reference antibacterial drug (ciprofloxacin) against the Salmonella enteritidis strain.

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