Interligand communication in a metal mediated LL′CT system - a case study

• Published in: RSC advances Vol. 11; no. 39; pp. 24381 - 24386
• Main Authors: Dille, Sara A, Colston, Kyle J, Ratvasky, Stephen C, Pu, Jingzhi, Basu, Partha
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 12.07.2021; The Royal Society of Chemistry
• Subjects: Benzene; Charge density; Charge transfer; Chemistry; Crystallography; Density functional theory; Electron density; Electronic structure; Hydrocarbons; Ligands; Molecular orbitals; Molecular structure; Oxidation; Quinoxalines; Toluene
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/d1ra04716g

A series of oxo-Mo( iv ) complexes, [MoO(Dt 2− )(Dt 0 )] (where Dt 2− = benzene-1,2-dithiol (bdt), toluene-3,4-dithiol (tdt), quinoxaline-2,3-dithiol (qdt), or 3,6-dichloro-benzene-1,2-dithiol (bdtCl 2 ); Dt 0 = N , N ′-dimethylpiperazine-2,3-dithione (Me 2 Dt 0 ) or N , N ′-diisopropylpiperazine-2,3-dithione ( i Pr 2 Dt 0 )), possessing a fully oxidized and a fully reduced dithiolene ligand have been synthesized and characterized. The assigned oxidation states of coordinated dithiolene ligands are supported with spectral and crystallographic data. The molecular structure of [MoO(tdt)( i Pr 2 Dt 0 )] ( 6 ) demonstrates a large ligand fold angle of 62.6° along the S S vector of the Dt 0 ligand. The electronic structure of this system is probed by density functional theory (DFT) calculations. The HOMO is largely localized on the Dt 2− ligand while virtual orbitals are mostly Mo and Dt 0 in character. Modeling the electronic spectrum of 6 with time dependent (TD) DFT calculations attributes the intense low energy transition at ∼18 000 cm −1 to a ligand-to-ligand charge transfer (LL′CT). The electron density difference map (EDDM) for the low energy transition depicts the electron rich Dt 2− ligand donating charge density to the redox-active orbitals of the electron deficient Dt 0 ligand. Electronic communication between dithiolene ligands is facilitated by a Mo-monooxo center and distortion about its primary coordination sphere. The interligand communication between non-innocent dithiolene ligands of different oxidation states has been described in a Mo system. The fully reduced ene-dithiolate (Dt 2− ) acts as a donor moiety to the oxidized dithione (Dt 0 ) in an LL′CT process.