Effect of ancillary ligand on electronic structure as probed by 51V solid-state NMR spectroscopy for vanadium–o-dioxolene complexes

Abstract

A series of vanadium(V) complexes with o-dioxolene (catecholato) ligands and an ancillary ligand, (N-(salicylideneaminato)ethylenediamine) (hensal), were investigated using ⁵¹V solid-state magic angle spinning NMR spectroscopy (⁵¹V MAS NMR) to assess the local environment of vanadium(V). The solid-state ⁵¹V NMR parameters of vanadium(V) complexes with a related potentially tetradentate ancillary ligand (N-salicylidene-N′-(2-hydroxyethyl)ethylenediamine) (h₂shed) 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., Inorg. Chem., 2011, 50, 9794). Our results show that the modification of the ancillary ligand does not affect the observed trend between complexes ranging from catechols with electron-rich to electron-poor substituents. However, the ancillary ligand does affect 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 C_Q reflect the electronic changes in the complex as the catechol is varied. However, no obvious trend was observed in the chemical shift anisotropies (δ_σ and η_σ) with the variation in the catechol. The electronic changes in the coordination environment of the vanadium can be determined using solid-state ⁵¹V NMR spectroscopy.