Unique Asymmetric (Cu^II₄) Double-Stranded Helicate from a Hexadentate Piperazine-Based Ligand: Ligand Conformation Isomerism upon Coordination

In methanol, the reaction of Cu(ClO4)2·6H2O and a sterically constrained piperazine imine phenol ligand (H2L), in the presence of NEt3, affords a novel tetranuclear copper(II) complex of formula [CuII4(μ3-L)2(μ-OH)2(H2O)2](ClO4)2·H2O (1). The X-ray structure of this complex shows an elongated Cu4 quasi-tetrahedron coordinated to two hexadentate chair-(e,a)-μ3-piperazine bridging ligands. Variable-temperature magnetic studies show an St = 0 spin ground state resulting from antiferromagnetic interactions between CuII ions within the complex.