A mixed-valence octanuclear manganese complex of formula [Mn(II)(4)Mn(III)(4)O(4)(ccnm)(12)]·4MeCN·7H(2)O (1·4MeCN·7H(2)O) (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(III)(4)O(4)](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 Mn(8) cluster and, more generally, with other Mn(III)Mn(III) and Mn(III)Mn(II) fragments in clusters of various types.