STRUCTURAL AND MAGNETIC CHARACTERIZATION OF AN ADAMANTANE-LIKE COMPLEX ION OF CHROMIUM(III) AND 1,3,5-TRIAMINOCYCLOHEXANE, [CR4(TACH)4(OH)6]6+

The synthesis and characterization of a tetranuclear chromium(III) complex of the ligand 1,3,5-triaminocyclohexane, (tach), C6H15N3, are described. The complex [Cr4(tach)4(OH)6](ClO4)n(CF3SO3)6-n, where n refines to approximately 3.57, has been isolated and its structure has been determined from three-dimensional crystallographic data. The complex crystallizes in space group P2(1)/c of the monoclinic system with four tetranuclear species in a cell of dimensions a = 22.365(4), b = 12.581(3), c = 22.508(5) angstrom, beta = 101.75(3)-degrees. The structure has been refined to a final R factor of 0.0737 based on 6023 observed independent reflections. Each chromium(III) center is pseudooctahedrally bonded to the three nitrogen atoms of the ligand and to three hydroxo groups; each hydroxo group acts as a bridge between two chromium atoms. The complex adopts the adamantane structure in which all four chromium atoms are chemically equivalent, as are all six hydroxide groups. The six independent Cr . . . Cr separations in the tetramer are in the narrow range 3.660-3.685 angstrom. The temperature dependence of the magnetic susceptibility of the complex is consistent with the observed structure, the tetranuclear complex exhibiting an antiferromagnetic interaction with a J value of 8.91(2) cm-1. A model is presented which makes it possible to compare the antiferromagnetic interaction in complexes containing different numbers of metal atoms.