INTRAMOLECULAR ANTIFERROMAGNETISM IN [CR- 2(MU-NH2)(3)(NH3)(6)]I-3

The magnetism of [Cr-2(mu-NH2)(3)(NH3)(6)]I-3 which consists of binucl ear cations with NH2--bridged face-sharing octahedral coordination pol yhedra and a metal-metal separation of 264.9 pm can be explained by an tiferromagnetically exchange coupled Cr-III-3d(3) pairs. The magnetoch emical analysis in the temperature range 5 K-295 K on the basis of the isotropic Heisenberg model (spin Hamiltonian ($) over cap H = -2J ($$ $) over cap S-1 .($) over cap S-2) leads to the parameter value J = -9 8(3)cm(-1). Compared to the exchange coupling in corresponding binucle ar chromium compounds with OH- bridges and identical metal-metal separ ation the strength of the coupling is significantly enhanced (J(NH2)/J (OH) approximate to 1.6).