Origin of the hyperfine anisotropy in a Mn(IV) complex containing paramagnetic ligands

The electronic structure of the manganese complex of the Schiff base, 3,5-di-tert-butyl-1,2-quinone-1-(2-oxo-3,5-di-tert-butyl-3,6-cyclohexadiene)imin radical (SQ-N-BQ; monoanionic form = Cat-N-BQ; dianionic form = Cat-N-SQ) is re-examined on the basis of single-crystal EPR studies on Mn/Zn(Cat-N-BQ)2. It is shown that both possibilities, viz. Mn(Cat-N-BQ)2 (low-spin Mn2+) and Mn(Cat-N-SQ)2 (Mn4+, strongly antiferromagnetically coupled with two S = 12 ligands) can have an anisotropic manganese hyperfine coupling, albeit for different reasons.