Ferromagnetic CuII-CuII exchange interactions in a polyoxomolybdate-based nanocluster

We present initial magnetic properties and a simple Heisenberg model for a recently isolated new member of the {Mo57M6}-type family, a nanometer-sized polyoxomolybdate cluster anion comprising a triangular Cu-6(II) prism. The exchange interactions between the six s=1/2 spin centers are weak compared to the exchange found for other members of the {Mo57M6} cluster family with M=Fe-II, Fe-III, and V-IV but display ferromagnetic exchange interactions of Cu-II-O-Mo-VI-O-Cu-II pairs, i.e., within two equilateral Cu-3(II) triangles. The exchange interaction between the two triangles is antiferromagnetic. The observed temperature dependence of chiT is described well by a Heisenberg model that employs a ferromagnetic intratriangle exchange constant J(1)=1.9 K and antiferromagnetic intertriangle coupling of J(2)=-1.4 K that eventually results in an S=0 ground state. (C) 2003 American Institute of Physics.