Synthesis, spectral (UV–Vis, IR, ESI-MS), magnetic and structural characterizations, and the antimicrobial effect of potassium isothiocyanato-(N-salicylidene-amino-acidato)cuprates

A series of potassium isothiocyanato-(N-salicylidene-amino acidato)cuprates with the general formulas of K2[Cu2(sal-aa)2(μ-NCS)2]·nH2O, where n = 0 or 4 and (sal-aa) stands for the dianion of N-salicylideneamino acid derived from glycine (I), dl-α-alanine (II), dl-valine (III), dl-phenylalanine (IV), and {K[Cu(sal-β-ala)(μ-NCS)]}n for β-alanine (V), respectively, was synthesized and fully characterized by elemental analysis, UV–Vis and IR spectroscopy, ESI-MS spectrometry, magnetic measurements, and X-ray structural analysis (II and IV). It has been found that the copper(II) atom adopts a distorted square-pyramidal surrounding in the dimeric complexes I–IV, while the geometry in the polymeric complex V can be described as distorted square-bipyramidal. The analysis of magnetic properties revealed weak antiferromagnetic exchanges in the dinuclear species I–IV and an alternating ferro/antiferromagnetic exchange in the case of 1D-polymeric compound V. Moreover, the complexes were tested for their antibacterial activity against the G+ bacteria Staphylococcus aureus, G− bacteria Escherichia coli, filamentous fungi Microsporum gypseum, and yeast Candida albicans. The best results were achieved with G+ bacteria S. aureus with MIC values in the range of 0.22–0.57 mmol L−1. It may be concluded that both the antimicrobial and antifungal activity decreased within the tested group of cuprates derived from α-amino acids with the increasing lipophility of the complexes, i.e. I → IV.