Polymorphism Driven by π–π Stacking and van der Waals Interactions: Preparation and Characterization of Polymorphic Vanadium Crystals of [V^VO(Hacshz)(OEt)] and [V^IV(Hacshz)₂]

Abstract

Polymorphic mono-oxo mono-alkoxo square-pyramidal [V V O(Hacshz)(OEt)] (where Hacshz 2-is a doubly deprotonated dianionic acetylacetosalicylhydrazone; thick plateshaped dark-greenish-brown crystals for 1a and blockshaped dark-reddish-brown crystals for 1b) and mononuclear trigonal-prismatic [V IV (Hacshz) 2 ] (block-shaped dark-bluishbrown crystals for 2a and triangular-shaped dark-violet crystals for 2b) were synthesized and characterized. The crystals were prepared by simple addition of vanadium(III) acetylacetonate to an ethanol solution of salicylhydrazide (H 3 shz). Depending on the ratio of the ligand to the metal ion, the extent of exposure to molecular oxygen, and the filtration of the intermediate, various polymorphs could be obtained as both mixtures and pure forms. A common π-π stacked dimeric

Vanadium, niobium and tantalum

“…16 These di-and tri-peptide compounds were reacted with [VO] 21 sources in aqueous solution, and studied under various pH regimes. Related hydrazone-based ligands also featured prominently in the coordination chemistry of vanadium, [17][18][19][20] in which they predominantly form dianionic tridentate O,N,Oligands. The reaction between N-hexanoylsalicylhydrazide and V III acetylacetone afforded the trinuclear mixed valence V V /V IV /V V complex in which the initially trivalent vanadium centres have been 'air-oxidized' to their final state.…”