Fourth-order zero-field splitting parameters of [Mn(cyclam)Br2]Br determined by single-crystal W-band EPR

Single-crystal W-band (95 GHz) electron paramagnetic resonance (EPR) studies have been performed at 20 K and at room temperature on a tetragonal Mn(III) compound with potential application as a building block for high-spin clusters. The observed EPR spectra correspond to an anisotropic high-spinS = 2 ground state and have been attributed to equivalent centers related by four-fold symmetry. Accurate values for the spin Hamiltonian parameters were obtained from the analysis of the data at both temperatures. At 20 K the contribution of fourth-order zero-field splitting terms was shown to be significant, with parameter values B ₄ ⁰ = 0.0009(3) cm^?1, B ₄ ² = 0.0006(2) cm^?1 and B ₄ ⁴ = 0.0017(3) cm^?1, to be considered together with the second-order parametersD = ?1.1677(7) cm^?1 andE= ?0.0135(6) cm^?1.