A hexanuclear copper(II) Schiff base complex incorporating rare "bicapped cubane" core: structural aspects, magnetic properties and EPR study

The reaction of Cu-2(CH3COO)(4)center dot 2H(2)O with the Schiff base ligand, H4L [(OH)(2)C6H3CH=N-C(CH3)(CH2OH)(2)], yields a novel hexanuclear copper (II) cluster {[Cu-6(HL)(4)]center dot CH3OH center dot 0.5CH(3)CN center dot 6.5H(2)O} (1) with a rare "bicapped cubane" core. Title complex has been characterized by different physico-chemical techniques. Single-crystal X-ray structure reveals that the "bicapped cubane" core was formed by a cubane-like Cu4O4 subcore capped by two copper(II) atoms over opposite faces. The cubane copper(II) atoms are in distorted square pyramidal geometry and connected each other via mu(3)-alkoxo oxygens while two apical copper(II) atoms are in distorted square planar environments and connected to the main cubane subcore by doubly phenoxo bridged oxygen atoms. EPR spectra of the complex reveals overall strong antiferromagnetic behavior, well supported by cryomagnetic susceptibility measurements in the range 2-300 K under the magnetic field of 0.1 T leading different coupling constants: J(1) = +60 cm(-1), J(2) = -45.5 +/- 1 cm(-1); J(3) = -140 +/- 1 cm(-1), using the general Hamiltonian H = -J(S-i-S-j). A plausible magneto-structural correlation has also been established. (C) 2012 Elsevier Ltd. All rights reserved.