[Cu^II₄] clusters from the self-assembly of two imidazolidinyl 2-phenolate-bridged [Cu^II₂] units: The role of the chloride bridge

A new family of tetracopper clusters [Cu₄(μ₄-X)- L₂]ClO₄·nH₂0 (1a-c) [X = Cl, Br, I; n = 12, 2, 2; H₃L = 2-(2′-hydroxyphenyl)-1,3-bis[4-(2- hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine] have been synthesised and characterised. The X-ray crystal structure of 1a reveals that the template action of the spherical Cl^- anion (μ4-Cl^-), which features a unique rectangular planar bridging mode, is responsible for the self-assembly of two [Cu₂L]⁺ units in complex 1a. In this family of complexes the spherical halides serve as templates to assemble the dimeric unit into tetrameric complexes, which gives an insight into the role of the halide bridge in tetranuclear complex formation. The capacity of this bridge to mediate magnetic coupling has been examined by bulk magnetic measurements for complex 1a.