NMR Crystallography for Structural Characterization of Oxovanadium(V) Complexes: Deriving Coordination Geometry and Detecting Weakly Coordinated Ligands at Atomic Resolution in the Solid State

NMR crystallography is an emerging method for atomic-resolution structural analysis of ubiquitous vanadium­(V) sites in inorganic and bioinorganic complexes as well as vanadium-containing proteins. NMR crystallography allows for characterization of vanadium­(V) containing solids, based on the simultaneous measurement of ⁵¹V–¹⁵N internuclear distances and anisotropic spin interactions, described by ¹³C, ¹⁵N, and ⁵¹V chemical shift anisotropy and ⁵¹V electric field gradient tensors. We show that the experimental ⁵¹V, ¹³C, and ¹⁵N NMR parameters are essential for inferring correct coordination numbers and deriving correct geometries in density functional theory (DFT) calculations, particularly in the absence of single-crystal X-ray structures. We first validate this approach on a structurally known vanadium­(V) complex, (¹⁵N-salicylideneglycinate)-(benzhydroxamate)­oxovanadium­(V), VO¹⁵NGlySalbz. We then apply this approach to derive the three-dimensional structure of (methoxo)­(¹⁵N-salicylidene-glycinato)­oxovanadium­(V) with solvated methanol, [VO­(¹⁵NGlySal)­(OCH₃)]­·(CH₃OH). This is a representative complex with potentially variable coordination geometry depending on the solvation level of the solid. The solid material containing molecules of CH₃OH, formally expressed as [VO­(¹⁵NGlySal)­(OCH₃)]­·(CH₃OH), is found to have one molecule of CH₃OH weakly coordinated to the vanadium. The material is therefore best described as [VO­(¹⁵NGlySal)­(OCH₃)­(CH₃OH)] as deduced by the combination of multinuclear solid-state NMR experiments and DFT calculations. The approach reported here can be used for structural analysis of systems that are not amenable to single-crystal X-ray diffraction characterization and which can contain weakly associated solvents.