A novel tetranuclear [CrIII2MnIII2(µ3-O)2]8+ core with an ST= 0 spin ground state

Abstract

The reaction of [Cr^IIIL(MeOH)₃]³⁺ ions with Mn^III(salox) units (L = 1,4,7-trimethyl-1,4,7-triazacyclononane; salox = salicylaldehyde oxime) produced in situ in methanol, yielded, in the presence of a small amount of triethylamine and NaClO₄, the complex [L₂Cr^III₂(µ-OMe)₂(µ₃-O)₂(salox)₂Mn^III₂][ClO₄]₂·3H₂O. It has been characterized on the basis of elemental analysis, IR spectroscopy and variable-temperature (4–278 K) magnetic susceptibility measurements. The molecular structure established by X-ray diffraction consists of a [Cr^III₂(µ₃-O)₂Mn^III₂]⁸⁺ butterfly core with the chromium(III) ions representing the wing-tips, and high-spin manganese(III) ions the ‘body’ ions in the tetranuclear core. The magnetic susceptibility measurements revealed a diamagnetic (S_T= 0) ground state with antiferromagnetic exchange interactions J_CrMn=–11.7 cm^–1 and J_MnMn=–13.0 cm^–1. The ground state is the result of spin frustration of the ‘body’ manganese(III) ions. In other words, owing to the topology of the tetranuclear complex, which can be viewed as being made up of two edge-shared triangular units, the ground state represents the lowest possible spin state for this electronic configuration when both interactions are antiferromagnetic.