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

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journal contribution
posted on 2015-02-16, 00:00 authored by Mingyue Li, Jenna Yehl, Guangjin Hou, Pabitra B. Chatterjee, Amir Goldbourt, Debbie C. Crans, Tatyana Polenova
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.