Solid state and solution characterization of a new dinuclear nickel (II) complex: The search for synthetic models for urease

The X-ray molecular structure and, magnetic, and spectroscopic properties, as well as the analysis of the structural behavior in solution of a novel nickel (II) complex [Ni2(HBPClNOL)2(OAc)](ClO4) 1 are reported. Complex 1 was prepared by the reaction between the ligand H2BPClNOL (N-(2-hydroxybenzyl)-N-(2-pyridylmethyl)[(3-chloro)(2-hydroxy)]propylamine), [Ni(H2O)6](ClO4)2 and sodium acetate. Magnetic measurements indicate the presence of a weak antiferromagnetic coupling between the Ni(II) ions in 1, resulting in J = −4.23 cm−1. Mass spectrometric characterization of the complex 1 was also performed via ESI-MS and ESI-MS/MS experiments and reveals that there are at least three different cations in solution, one mononuclear [Ni(H2BPClNOL)(OAc)]+ and two dinuclear [Ni2(HBPClNOL)2(OAc)]+ and [Ni2(HBPClNOL)2(ClO4)]+ cations, as well as likely a fourth one [Ni(HBPClNOL)]+. Potentiometric titration experiments confirm that under acid conditions, the dinuclear unit is broken. However, under neutral/basic pH values the dinuclear unit is stable and shows the presence of two water molecules coordinated to the nickel ions, resulting in the cation [Ni2(HBPClNOL)2(H2O)2]2+. This cation shows two protonation/deprotonation equilibriums with pKa values of 9.68 and at 10.29, which are related to the aquo/hydroxo equilibrium associated with the water molecules coordinated to the metal ions.