Effect of Ancillary Ligand on Electronic Structure as Probed by V Solid-State NMR Spectroscopy for Vanadium--Dioxolene Complexes.

A series of vanadium(V) complexes with o-dioxolene (catecholato) ligands and an ancillary ligand, (-(salicylideneaminato)ethylenediamine) (hensal), were investigated using V solid-state magic angle spinning NMR spectroscopy (V MAS NMR) to assess the local environment of the vanadium(V). The solid-state V NMR parameters of vanadium(V) complexes with a related potentially tetradentate ancillary ligand (-salicylidene-'-(2-hydroxyethyl)ethylenediamine) (hshed) were previously shown to be associated with the size of the HOMO-LUMO gap in the complex, and as such provide insights on the interaction between metal ion and ligand (P. B. Chatterjee, et al., 50 (2011) 9794). Our results show that the modification of the ancillary ligand does not impact the observed trend between complexes ranging from catechols with electron rich to electron poor substituents. However, the ancillary ligand does impact the size of the HOMO-LUMO separation in the parent complex and thus the solid-state vanadium NMR chemical shift of the unsubstituted vanadium complex. For these complexes significant changes observed in the isotropic shifts and more modest changes detected in the reflect the electronic changes in the complex as the catechol is varied. However, no obvious trend was observed in the chemical shift anisotropies (δ and η) with the variation in the catechol. The electronic changes in the coordination environment of the vanadium can be described using solid-state V NMR spectroscopy.