Modeling the coordination mode of hydroxamate inhibitors in urease: preparation, X-ray crystal structure and spectroscopic characterization of the dinuclear complex [Ni2(O2CMe)(LH)2(tmen)2](O2CMe).0.9H2O.0.6EtOH (LH2 = benzohydroxamic acid; tmen = N, N, N', N'-tetramethylethylenediamine)

Abstract

Reaction of [Ni2(H2O)(O2CMe)4(tmen)2], (tmen = N, N, N′, N′-tetramethylethylenediamine) with two equivalents of benzohydroxamic acid (LH2) in H2O/EtOH gives the complex [Ni2(O2CMe)(LH)2(tmen)2](O2CMe) · 0.9H2O · 0.6EtOH (1) yield: ca. 65%. Complex (1) can also be prepared by the direct reaction of Ni(O2CMe)2 · 4H2O, tmen with LH2 in H2O/EtOH, but in lower yields (ca. 25%). The structure of the complex has been determined by single-crystal X-ray crystallography. The dinuclear cation consists of a triply bridged pair of six-coordinate NiII atoms. The Ni·Ni distance is 3.001(2) A. Two of the bridging ligands are the LH− ions, the third being the η 1 : η 1 : μ 2 acetate group; the deprotonated hydroxamate hydroxyl oxygen of each LH− bridges the two NiII centres, while the carbonyl oxygen coordinates only one metal ion. A chelating tmen molecule completes octahedral coordination at each NiII atom. The complex was characterized by its room-temperature effective magnetic moment and by spectroscopic (i.r., ligand field) techniques; the data are discussed in terms of the nature of bonding and known structure. The crystallographically established coordination modes of the hydroxamate group are also reviewed. The coordination mode of the hydroxamate(−1) group of LH− in (1) is the same as that observed in the structures of the acetohydroxamate-inhibited C319A mutant of Klebsiella aerogenes urease and the acetohydroxamate-inhibited Bacillus pasteurii urease. The biological implication of our results is discussed.