A novel μ1,1-azido-, μ2-alkoxo-, and μ2-phenoxo-bridged tetranuclear copper(II) complex with a quinquedentate Schiff-base ligand: magneto-structural and DFT studies

A novel tetranuclear copper(II) complex [Cu4L2(mu(1,1)-N-3)(2)]center dot CH3CN (1) has been synthesized using a symmetrical quinquedentate N2O3-donor Schiff-base ligand H3L (N,N'-(2-hydroxypropane-1,3-diyl)bis(2-hydroxyacetophenimine)) and characterized by elemental analysis, Fourier-transform (FT)-IR, UV-visible, electron paramagnetic resonance spectroscopy, and cyclic voltammetry. The X-ray single-crystal structure of 1 reveals three kinds of bridges among the four metal centres: one from the exogenous azido ligand and two from the phenoxo and alkoxo moieties of the Schiff base. The same structure highlights the remarkable versatility of copper(II) to adopt an array of stereochemistries. Four unusual eight-membered metallacycles exist in 1. The mu(1,1)-azido, mu(2)-alkoxo, and mu(2)-phenoxo bridges among the four copper centres have facilitated interesting magnetic interactions that have been elucidated by variable-temperature magnetic susceptibility measurements and backed up by density functional theory calculations. Detailed analyses have shown that the antiferromagnetic effect through the alkoxo-bridged Cu-II centres combined with the ferromagnetic interaction through the azido-bridged metal centres results in an S = 0 ground state.