Synthesis, crystal structure, spectroscopic, magnetic, theoretical, and microbiological studies of a nickel(II) complex of L-tyrosine and imidazole, [Ni(Im)2(L-tyr)2]·4H2O.

The [Ni(Im)(2)(L-tyr)(2)]·4H(2)O (1) complex was obtained in crystalline form as a product of interaction of L-tyrosine sodium salt, imidazole, and NiSO(4). The X-ray structure was determined, and the spectral (IR, FIR, NIR-vis-UV, HF EPR) and magnetic properties were studied. The Ni(2+) ion is hexacoordinated by the N and O atoms from two L-tyrosine molecules and by two N atoms of imidazole, resulting in a slightly distorted octahedral [NiN(2)N(2)'O(2)] geometry with a tetragonality parameter T = 0.995. The bands observed in the electronic spectra were ascribed to the six spin-allowed electronic transitions (3)B(1g) → (3)E(g) and (3)B(2g), (3)B(1g) → (3)A(2g) and (3)E(g), and (3)B(1g) → (3)A(2g) and (3)E(g). The spin Hamiltonian parameters g, D, and E, which were determined from high-field HF EPR spectra, excellently reproduced the magnetic properties of the complex. Calculation of the zero-field splitting in the S = 1 state of nickel(II) using DFT and UHF was attempted. The biological activity of the complexes has been tested for antifungal and antibacterial effects against Aspergillus flavus, Fusarium solani, Penicillium verrucosu, Bacillus subtilis, Serratia marcescens, Pseudomonas fluorescens, and Escherichia coli.