Preparation, crystal structure, and magnetic properties of an oligonuclear complex with 12 coupled spins and an S = 12 ground state

A novel oligonuclear compound, containing six manganese( 11) ions and six nitronyl-nitroxide radicals NITPh (NITPh = 2-phenyl-4,4,5,5-tetramethyl-4,5-dihydr1oH- -imidazolyl- 1- oxy1 3-oxide), [Mn(hfac),NITPh],, was synthesized, and its crystal structure, magnetic properties, and EPR spectra are reported. This cyclohexamer crystallizes in the trigonal system, space group R3, with rhombohedral axes a = b = c = 21.21 (1) A, a = p = y = 116.77 (2)O, and Z = 6. The structure consists of discrete clusters of six radicals and six Mn ( h f a ~ )in~ ,w hich each transition-metal ion is in a distorted octahedral environment. Two oxygen atoms belonging to two different nitronyl-nitroxide radical ligands occupy two cis coordination positions around manganese. The temperature dependence of the magnetic susceptibility in the range 300-5 K indicates that the manganese(I1) and the radical spins are antiferromagnetically coupled to give an S = 12 ground state. The single-crystal EPR spectra of [Mn ( h f a ~ ) ~N1TPshho]w~ both M = 1 and M = 2 transitions. The angular dependence of the line width, which is similar to that of typical onedimensional materials, is discussed within a model considering the zero-field splitting tensors of the populated spin multiplets.