Electronic Structures of [Ru^II(cyclam)(Et₂dtc)]⁺, [Ru(cyclam)(tdt)]⁺, and [Ru(cyclam)(tdt)]²⁺: An X-ray Absorption Spectroscopic and Computational Study (tdt = toluene-3,4-dithiolate; Et₂dtc = <i>N</i>,<i>N</i>-diethyldithiocarbamate

The reaction of [RuIII(cyclam)Cl2]Cl with 2 equiv of sodium N,N-diethyldithiocarbamate in methanol afforded [RuII(cyclam)(Et2dtc)](BPh4) (1(BPh4)). The same reaction with only 1 equiv of toluene-3,4-dithiol and a base yielded [Ru(cyclam)(tdt)](PF6) (2(PF6)) which was oxidized by 1 equiv of ferrocenium hexafluorophosphate generating [Ru(cyclam)(tdt)](PF6)2 (2ox(PF6)2). The crystal structures of 1 and 2 have been determined by X-ray crystallography at 100 K. The electronic structures of diamagnetic 1(BPh4), paramagnetic 2(PF6) (S = 1/2), and diamagnetic 2ox(PF6)2 have been studied by magnetochemistry, spectroelectrochemistry, electron paramagnetic resonance spectroscopy, and 1H NMR spectroscopy. X-ray absorption spectroscopy on Ru K- and L-edges as well as S K-edges has been employed. Finally, the molecular and electronic structures of all three species have been calculated by using density functional theory (B3LYP). It is shown that 2ox comprises an electronic structure which is best described by three resonance structures {[RuII(cyclam)(tdt0)]2+ ↔ [RuIII(cyclam)(tdt•)]2+ ↔ [RuIV(cyclam)(tdt2−)]2+} with a closed-shell singlet ground state. This is in stark contrast to the isoelectronic iron species, namely, [FeIII(cyclam)(tdt•)]2+ which is a singlet diradical with a low-spin ferric ion coupled intramolecularly antiferromagnetically to a ligand π radical monoanion (tdt•)−.