The study reported herein focused on the electronic structure of the {Ru(NO)} 6 fragment and characterization of the oxidation state of ruthenium in mer,trans- [RuCl 3 (Hind) (3) were experimentally and theoretically investigated as reference compounds. A complete active space SCF calculation was performed to estimate the extent of antiferromagnetic spin-spin coupling in 1. We found that the closed-shell structure {Ru III (NO) 0 } 6 fits better to the physical/ spectroscopic properties of 1, although {Ru II (NO) + } 6 is formally still suitable for describing the oxidation state of Ru in this entity.