New Cu(ii) complexes based on the hydroxo-bridged dinuclear [Cu(OH)2Cu] units: step-like di- and trimerizations of [Cu(OH)2Cu] units

Abstract

Four new Cu(II) complexes {[Cu₄(bpy)₄(OH)₄(H₂O)₂]}(NO₃)₂(C₇H₅O₂)₂·6H₂O 1, {[Cu₄(bpy)₄(OH)₄(H₂O)₂]}(NO₃)₂(C₅H₆O₄)·8H₂O 2, {[Cu₄(bpy)₄(OH)₄(H₂O)₂]}(C₅H₆O₄)₂·16H₂O 3 and {[Cu₆(bpy)₆(OH)₆(H₂O)₂]}(C₈H₇O₂)₆·12H₂O 4 were synthesized (bpy = 2,2′-bipyridine, H₂(C₅H₆O₄) = glutaric acid, H(C₇H₅O₂) = benzoic acid, H(C₈H₇O₂) = phenyl acetic acid). The building units in 1–3 are the tetranuclear [Cu₄(bpy)₄(H₂O)₂(μ₂-OH)₂(μ₃-OH)₂]⁴⁺ complex cations, and in 4 the hexanuclear [Cu₆(bpy)₆(H₂O)₂(μ₂-OH)₂(μ₃-OH)₄]⁶⁺ complex cations, respectively. The tetra- and hexanuclear cluster cores [Cu₄(μ₂-OH)₂(μ₃-OH)₂] and [Cu₆(μ₂-OH)₂(μ₃-OH)₄] in the complex cations could be viewed as from step-like di- and trimerization of the well-known hydroxo-bridged dinuclear [Cu₂(μ₂-OH)₂] entities via the out-of-plane Cu–O(H) bonds. The complex cations are supramolecularly assembled into (4,4) topological networks via intercationic π⋯π stacking interactions. The counteranions and lattice H₂O molecules are sandwiched between the 2D cationic networks to form hydrogen-bonded networks in 1–3, while the phenyl acetate anions and the lattice H₂O molecules generate 3D hydrogen-bonded anionic framework to interpenetrate with the (4,4) topological cationic networks with the hexanuclear complex cations in the channels. The ferromagnetic coupling between Cu(II) ions in the [Cu₄(μ₂-OH)₂(μ₃-OH)₂] cores of 1–3 is significantly stronger via equatorial-equatorial OH⁻ bridges than via equatorial-apical ones. The outer and the central [Cu₂(OH)₂] unit within the [Cu₆(μ₂-OH)₂(μ₃-OH)₄] cluster cores in 4 exhibit weak ferromagnetic and antiferromagnetic interactions, respectively. Results about i.r. spectra, thermal and elemental analyses are presented.