New trinuclear copper(II) species

Abstract

Bidentate isonitrosoketimine ligands containing the functions −C(NOH)C(NR)− (abbreviated as HinkR) and −C(NOH)C(NAr)− (HinkAr) readily yield trinuclear copper(II) species [Cu₃O- (inkR)₃]ClO₄ and [Cu₃OH(inkAr)₃](ClO₄)₂ which have been characterized using solution electrical conductivity, electronic and infrared spectra and variable temperature magnetic susceptibility. The complexes uniformly have magnetic moments of ∼1.8 BM per molecule (∼ BM per copper) over the temperature range 80–380 K. The species are thus strongly antiferromagnetic in nature and only doublet states are populated. The lower limit of the exchange integral ∣J∣ is set at ∼350 cm⁻¹. Structures containing a central Cu₃O or Cu₃OH core held by peripheral oximato bridge is strongly indicated by the experimental data taken collectively with some known structural information. The superexchange mechanism has been investigated. Results of EHT calculation on the Cu₃O⁴⁺ core is presented. It is shown that the O bridge can bring about considerable antiferromagnetic interaction. However on the basis of experimental and theoretical results concerning the role of oximato bridge in bringing about exchange, it is suggested that the peripheral oxime bridge plays a dominant role. A new system which is most probably trinuclear and contains the Cu3 core held only by oximato group (no central oxygen) also has S = 1/2, thus showing the pivotal importance of the oximato bridges in relation to the strong magnetic coupling.