Stability and structure of mono- and dinuclear Cu(II), Ni(II) and Zn(II) complexes of pyrazole and triazole bridged bis-macrocycles

The two ligands L1 and L2, consisting of two 1,4,7-triazacyclononane rings bridged by a pyrazole or a triazole group, form with Cu2+, Ni2+ and Zn2+ a series of mononuclear [MLHn](n+ 2)+(n=–3, –2, –1, 0, 1, 2) and dinuclear species [M2LHm](m+ 4)+(m= 0, –1, –2, –3), the stabilities of which have been determined by potentiometric titrations. The triazole bridged ligand L1 forms complexes which are more stable than those of the pyrazole bridged system L2. It also shows a higher tendency to form dinuclear species compared to L2. In addition two dinuclear species [Cu2(L2H–1)(mu-Ph2PO2)](ClO4)2·MeCN and [Cu4(L2H–1)2(mu4-PO4)](ClO4)3·MeCN·H2O have been isolated as solids and their X-ray structures have been determined. In the first complex we find a dinuclear Cu2+ species which is bridged by the pyrazolide group as well as by the exogenous diphenyl phosphinate. In the second case a mu4-phosphate ion bridges two dinuclear units, resulting in a tetranuclear species.