[Ni₂(ppepO)(C₆H₅COO)₂(CH₃COOH)]ClO₄·C₄H₁₀O:  Synthesis and Characterization of an Asymmetric Dinuclear Nickel(II) Complex Showing Unusual Coordination Behavior with Relevance to the Active Site of Urease

Abstract

The synthesis of the novel asymmetric ligand 1-[bis(2-pyridylmethyl)amino]-3-[2-(2-pyridyl)ethoxy]-2-hydroxypropane (ppepOH) is reported. The ligand is suitable to form asymmetric dinuclear complexes with various transition metal ions. As an example, the synthesis and X-ray structure analysis of the dinickel(II) complex [Ni(2)(ppepO)(C(6)H(5)COO)(2)(CH(3)COOH)]ClO(4).C(4)H(10)O are described. The complex crystallizes in the monoclinic space group P2(1)/n with the following unit cell parameters: a = 13.704(10) Å, b = 14.849(10) Å, c = 22.697(14) Å, beta = 96.80(5) degrees, Z = 4. The nickel(II) ions are bridged by the alkoxy donor of the ligand and two benzoate anions. The hexadentate ligand leaves a free coordination site at one of the nickel(II) ions, which is occupied by a monodentate coordinated acetic acid molecule. The coordination of the neutral acetic acid molecule is selectively stabilized by a strong intramolecular hydrogen bond of the acidic proton to the &mgr;-alkoxo bridge of the dinuclear complex. The asymmetric complex was prepared in order to mimic the substrate uptake in the dinuclear active site of ureases. The magnetic and spectroscopic properties of the complex were determined and related to those of the urease enzymes.