Distorted cubic tetranuclear vanadium(iv) phosphonate cages: double-four-ring (D4R) containing transition metal ion phosphonate cages

Abstract

The reaction of VCl₃ with 3,5-dimethylpyrazole (3,5-Me₂PzH) and trichloromethylphosphonic/tert-butylphosphonic acid in the presence of triethylamine as a hydrogen chloride scavenger afforded the tetranuclear V(IV) assemblies, [(VO)₄(3,5-Me₂PzH)₈(CCl₃PO₃)₄] (1) and [(VO)₄(3,5-Me₂PzH)₄(t-BuPO₃)₄] (2). Both of these compounds possess a distorted cubic framework structures containing V(IV) ions and phosphorus atoms in the alternate corners of the cube. The edges of the cube contain oxygen atoms derived from the phosphonate ligand. The phosphonate ligand in both of these compounds is dianionic and helps to bind to three V(IV) centers. The faces of the cubic ensembles contain puckered V₂P₂O₄ eight-membered rings. The V(IV) center in 1 is six-coordinate in a distorted octahedral geometry while in 2 it is five-coordinate in a distorted square-pyramidal geometry. Magnetic studies carried out on 1 and 2 reveal that the V(IV) centers are anti-ferromagnetically coupled to each other, albeit weakly, through the mediation of the phosphonate ligands.