Magnetic properties of a new spin cluster topology with high-spin ground state:: the spin cluster [Mn-4(II)Mn-3(III)(teaH)3(tea)3](ClO4)2•3MeOH

The new spin cluster [(Mn4Mn3III)-Mn-II(teaH)(3)(tea)(3)](ClO4)(2) x 3MeOH realizes a topological structure of mixed-valence manganese clusters which is especially favorable for a high-spin ground state. The magnetic properties of the spin cluster are studied numerically by exact diagonalization of the spin Hamiltonian. By magnetic susceptibility two exchange constants are found: J(1)/k(B) = -1.28 K and J(2)/k(B) = +4.25 K, which lead to a S = 11 high-spin ground state. Electron spin resonance (ESR) measurements at three frequencies 95, 190 and 285 GHz confirm the large spin of the ground state..and reveal, an Ising anisotropy of the ground state which is characterized by the spin Hamiltonian H = alpha(S-z)(2) + beta(S-z)(4) with alpha/h.c. = -0.08 cm(-1) and beta = -2.1 x 10(-4) cm(-1) Ac-susceptibility shows thermally activated relaxation of the magnetization for temperatures above T = 1 K with an activation energy of Delta E/k(B) = -19.5 K and a relaxation time of tau(0) approximate to 10(-8) s.