Discrete and polymeric supramolecular architectures derived from dinuclear oxovanadium(IV) complexes of aryl-linked bis-diketonato ligands and nitrogen donor co-ligands

Abstract

Reaction of vanadyl sulfate in aqueous ethanol in the presence of sodium acetate (as base) with the 1,3-aryl-linked bis-β-diketone H2 L 1 resulted in two dinuclear isomeric complexes of type cis- and trans-[(VO)2 L 2 ]·0.5H2O that differ in the respective orientations of the oxo groups with respect to the main coordination plane in each complex. Hierarchical adduct formation by each isomer was investigated employing pyridine (py), 4,4′-bipyridine (bpy) and pyrazine (pyz) as co-ligands. Recrystallisation of either cis- or trans-[(VO)2(L 1 )2] from pyridine resulted in each case in the corresponding cis bis-pyridine adduct in which both pyridine ligands are coordinated on the same side of the V2 L 2 plane, with the vanadium(IV) centres achieving six-coordination. In contrast, when 4,4′-bipyridine in chloroform was reacted with both isomers and the solutions allowed to evaporate slowly, then a one-dimensional zigzag coordination polymer of type {trans-[(VO)2(L 1 )2(bpy)]·8CHCl3} n was isolated in each case. Each metal centre is again six-coordinate with the oxo groups oriented trans with respect to the mean V2 L 2 plane (with the bound pyridyl groups also positioned trans). In parallel experiments when diethyl ether vapour was allowed to diffuse into the respective chloroform solutions then a different, but structurally related, stepped polymer, {trans-[(VO)2(L 1)2(bpy)]·2CHCl3} n , was isolated. Reaction of either cis- or trans-[(VO)2(L 1 )2] with pyrazine followed by slow evaporation produced the same product, identified as {cis-[(VO)2(L 1 )2(pyz)]}2·4CHCl3·MeCN. In this case two planar dinuclear metallocyclic units are bridged by two pyrazine ligands such that the overall structure is a discrete tetranuclear species.