Nuclear quadrupole coupling in an EPR investigation of a low-spin cobalt(II) system

The nuclear quadrupole coupling constants for a low-spin square planar cobalt(II) compound were determined by EPR spectroscopy. Oriented single crystals and powders of Co-doped [(C2H5)4N]2Ni(S2C4N2)2 were examined and their EPR spectra interpreted with the following spin Hamiltonian: H = βB·g·S + hI·A·S − gnβnB·I + hQD(Iz2 − 634) + hQE(Iz2 − Iy2) with parameters gx = 2.7822, gy = 2.0130, gz = 1.9815, Ax = 131.8 MHz, Ay = 69.0 MHz, Az = 59.5 MHz, QD = -0.9 MHz, and QE = 0.2 MHz, where the principal axis systems for A and Q coincide with that of g. The quadrupole coupling parameters are compared with other available examples and the general absence of quadrupolar effects in the EPR of other low-spin cobalt(II) single crystals discussed.