Asymmetry in endogenously bridged binuclear copper(ii) and zinc(ii) complexes formed by 1,2-bis[1,4,7-triazacyclonon-1-yl]propan-2-ol

Abstract

Endogenously bridged binuclear copper(II) and zinc(II) complexes of singly deprotonated 1,2-bis[1,4,7-triazacyclonon-1-yl]propan-2-ol (T₂PrOH) have been prepared by reacting the ligand hexabromide salt with appropriate metal salts. An X-ray structural analysis of the Cu(II) complex, [Cu₂(T₂PrO)Br₂]Br·2H₂O (1), confirmed the presence of a complex cation, [Cu₂(T₂PrO)Br₂]⁺, which consists of Cu(II) centres linked by an endogenous alkoxo bridge. Three N donors from the tacn macrocycle and a bromo ligand complete the coordination sphere. The two Cu(II) centres are in slightly different distorted square pyramidal (SPY) Cu(II) geometries. A magnetic susceptibility study of 1 revealed the presence of moderately strong antiferromagnetic coupling between the Cu(II) centres (J = −86 cm⁻¹), as found for other binuclear Cu(II) complexes bridged by endogenous alkoxo groups. The molecular structure of the Zn(II) complex, [Zn₂(T₂PrO)Br(H₂O)₂](ClO₄)₂ (2), apart from confirming that the two Zn(II) were bridged by an endogenous alkoxo group, revealed coordination asymmetry in the two Zn(II) centres. One Zn(II) centre is six-coordinate and pseudo-octahedral with the coordination sphere occupied by three tacn nitrogens, the bridging oxygen, one bromo and one water ligand, while the other is five-coordinate and pseudo-square pyramidal, lacking the bromo ligand.