Structure and magnetism of a mixed-valence octanuclear manganese(ii/iii) cluster derived from carbamoylcyanonitrosomethanide (ccnm)

Abstract

A mixed-valence octanuclear manganese complex of formula [Mn^II₄Mn^III₄O₄(ccnm)₁₂]·4MeCN·7H₂O (1·4MeCN·7H₂O) (ccnm = carbamoylcyanonitrosomethanide) has been synthesized and characterized by single crystal X-ray diffraction, IR spectroscopy, elemental analysis and magnetic measurements. The metal core of 1 adopts a tetra-capped (with Mn^II ions) distorted [Mn^III₄O₄]⁴⁺ cubane topology, with a three-J magnetic analysis indicating that the cluster displays dominant antiferromagnetic interactions. Three equally possible fits were obtained, all leading to a spin ground state of S = 0 with S = 1, 2 and 3 close in energy. Comparisons of the magnetic analysis are made with that published for a related Mn₈ cluster and, more generally, with other Mn^IIIMn^III and Mn^IIIMn^II fragments in clusters of various types.