A novel pentacoordinated dioxovanadium(v) salicylaldiminate: Solvent specific crystallization of dimorphs with contrasting coordination geometries, ligand conformations and supramolecular architectures

Abstract

The reaction of the tridentate salicylaldimine of 2-picolylamine, C 6H4(OH)CHNCH2C5H4N (HL), with bis(acetylacetonato)oxovanadium(IV) at room temperature under oxygen (or with VOSO4·5H2O plus H2O2) furnished crystalline greenish-yellow α-VO2(L) and green β-VO2(L) from methanol (or ethanol) and acetonitrile (or dichloromethane), respectively. The dimorphs give rise to the same solution species as revealed by spectroscopic data (UV/Vis, 1H and 51V NMR). Both forms react with 3,5-bis(tert-butyl)catechol (H 2dbcat) furnishing the known pseudooctahedral complex VO(L)(dbcat). In the α form the V(L) fragment is planar and the VO3N 2 coordination sphere is distorted trigonal bipyramidal (τ = 0.55) with the two oxo oxygen atoms and the azomethine nitrogen atom defining the trigonal plane. In β-VO2(L) the V(L) moiety, like that in VO(L)(dbcat), is not planar but consists of two planar parts rotated away from each other along the C-N single bond. In this case the coordination sphere is distorted square pyramidal (T = 0.20) with the three donor sites of the L ligand and an oxo oxygen atom defining the tetragonal plane. Both the α and β crystal lattices consist of dimers which associate further to form supramolecules. The noncovalent intradimer and interdimer bonding interactions are predominantly of aromatic π-π stacking (aryl⋯pyridyl and pyridyl⋯pyridyl) and C-H⋯O hydrogen bonding (azomethine⋯oxo and aryl⋯phenolato) types in the α and β dimorphs, respectively. It is proposed that the low polarizability of methanol promotes π-π stacking of planar V(L) fragments, resulting in crystallization of the a form. When the polarizability is relatively high, as in acetonitrile, the β form crystallizes. The geometrically isomeric coordination spheres of the α and β forms are sustained by the respective supramolecular architectures. The Schiff base HL′ of 2-hydroxynapthaldehyde and 2-picolylamine has also afforded two forms of VO2(L′) in the same manner as for VO2(L). © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.