Cu2+ and Pt2+ complexes of pyrazole and triazole based dinucleating ligands

Abstract

A series of pyrazole and triazole based dinucleating ligands have been synthesized and their complexation potential for metal ions, which exhibit square planar coordination geometry has been studied. In the case of Cu²⁺ the complexation equilibria in solution have been determined using pH titrations. Species with 1 : 1 stoichiometry [CuLH_n], 2 : 1 stoichiometry [Cu₂LH_m], and of dimeric nature [Cu₂L₂H_p], have been detected and their overall stability constants have been measured. The reactivity of the dinuclear species [Cu₂LH₋₁] towards phosphate ester hydrolysis have shown that the OH-functionality incorporated in some of the ligands does not enhance the hydrolysis rate. Several ligands were reacted with Pt²⁺ to give insoluble dinuclear species [Pt₂LI₃]. One of them was studied by X-ray diffraction and shows that the two Pt²⁺ are bridged by the pyrazolide group and by one I⁻. The remaining two positions are occupied by the amino group in α position of the heterocyclic ring and a terminal I⁻. The nearly planar [Pt₂LI₃] units form sheets in the crystals, which are about 4 Å apart and thus indicate π stacking interactions.