The magnetic anisotropy of a novel Mn(II)- $[3\times 3]$ grid complex was investigated by means of high-field torque magnetometry. Torque vs field curves at low temperatures demonstrates a ground state with $S>\mathrm{}0\mathrm{}$ and exhibits a torque step due to a field-induced level crossing at $B^{*}\approx 7.5\mathrm{T}$, accompanied by an abrupt change of magnetic anisotropy from easy-axis to hard-axis types. These observations are discussed in terms of a spin Hamiltonian formalism.

• Received 29 May 2001

DOI:https://doi.org/10.1103/PhysRevLett.88.066401