51V        solid-state NMR and density functional theory studies of eight-coordinate non-oxo vanadium complexes: oxidized amavadin

Kristopher J. Ooms; Stephanie E. Bolte; Bharat Baruah; Muhammad Aziz Choudhary; Debbie C. Crans; Tatyana Polenova

doi:10.1039/B820383K

⁵¹V solid-state NMR and density functional theory studies of eight-coordinate non-oxo vanadium complexes: oxidized amavadin

Kristopher J. Ooms,^a Stephanie E. Bolte,^a Bharat Baruah,^b Muhammad Aziz Choudhary,^bc Debbie C. Crans*^b and Tatyana Polenova*^a

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* Corresponding authors

^a Department of Chemistry and Biochemistry, 036 Brown Laboratories, University of Delaware, Newark, Delaware
E-mail: tpolenov@mail.chem.udel.edu
Fax: +302 831 6335
Tel: +302 831 1968

^b Department of Chemistry, Colorado State University, Fort Collins, CO
E-mail: crans@lamar.colostate.edu
Fax: +970 491 1801
Tel: +970 491 7635

^c Department of Chemistry, The University of Azad Jammu & Kashmir, Muzaffarabad, Pakistan

Abstract

Using ⁵¹V magic angle spinning solid-state NMR spectroscopy and density functional theory calculations we have characterized the chemical shift and quadrupolar coupling parameters for two eight-coordinate vanadium complexes, [PPh₄][V(V)(HIDPA)₂] and [PPh₄][V(V)(HIDA)₂]; HIDPA = 2,2′-(hydroxyimino)dipropionate and HIDA = 2,2′-(hydroxyimino)diacetate. The coordination geometry under examination is the less common non-oxo eight coordinate distorted dodecahedral geometry that has not been previously investigated by solid-state NMR spectroscopy. Both complexes were isolated by oxidizing their reduced forms: [V(IV)(HIDPA)₂]²⁻ and [V(IV)(HIDA)₂]²⁻. V(IV)(HIDPA)₂²⁻ is also known as amavadin, a vanadium-containing natural product present in the Amanita muscaria mushroom and is responsible for vanadium accumulation in nature. The quadrupolar coupling constants, C_Q, are found to be moderate, 5.0–6.4 MHz while the chemical shift anisotropies are relatively small for vanadium complexes, −420 and −360 ppm. The isotropic chemical shifts in the solid state are −220 and −228 ppm for the two compounds, and near the chemical shifts observed in solution. Presumably this is a consequence of the combined effects of the increased coordination number and the absence of oxo groups. Density functional theory calculations of the electric field gradient parameters are in good agreement with the NMR results while the chemical shift parameters show some deviation from the experimental values. Future work on this unusual coordination geometry and a combined analysis by solid-state NMR and density functional theory should provide a better understanding of the correlations between experimental NMR parameters and the local structure of the vanadium centers.

Dalton Transactions

⁵¹V solid-state NMR and density functional theory studies of eight-coordinate non-oxo vanadium complexes: oxidized amavadin

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⁵¹V solid-state NMR and density functional theory studies of eight-coordinate non-oxo vanadium complexes: oxidized amavadin

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