Copper(II) complex as a precursor for formation of cyano-bridged pentanuclear FeIII-CuII bimetallic assembly: Synthesis, characterization, crystal structure and antibacterial activity

[CuL(ClO4)2] (1) (L = 3,10-diisobutyl-1,3,5,8,10,12-hexaazacyclotetradecane) was synthesized by condensation reaction of ethylenediamine, formaldehyde and iso-butylamine in absolute ethanol. Characterization of 1 utilized various spectroscopic techniques, viz. elemental analysis, electrospray ionization-mass spectrometry (ESI-MS), Fourier-transform infrared spectroscopy (FT-IR), ultraviolet-visible spectroscopy (UV-Vis), diffuse reflectance spectroscopy (DRS) and thermogravimetric analysis (TGA). Based on these techniques, the structure of 1 was proposed as Cu(II) ion occupying octahedral geometry with four secondary amine nitrogens of the hexaazamacrocyclic ligand and two perchlorato anions. 1 was used as a precursor in the preparation of cyano-bridged bimetallic compound, [CuL]3[Fe(CN)6]2⋅5H2O (2), by reaction with K3[Fe(CN)6] in aqueous solution. Single-crystal X-ray analysis indicated that 2 crystallized in the monoclinic system with space group P21/n. The structure of 2 consisted of cyano-bridged FeIII-Cu II pentanuclear molecules having two [Fe(CN)6] 3− anions connected to three cis-[CuL] 2+ cations via two cis-cyanide ligands from each ferrate unit. In each of pentanuclear unit, the central [CuL] 2+ cation exhibited a distorted octahedral geometry while the other two units exhibited a distorted square pyramidal geometry. The room temperature magnetic moments of both complexes were measured to be 1.92 B.M. for 1 and 5.61 B.M. for 2. The in vitro antibacterial activity of 1 against Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, and Pseudomonas aeruginosa ATCC 27853 strains were studied and compared with standard drugs, which showed moderate antibacterial activity compared with Penicillin and Gentamicin.