Synthesis, crystal structure and spectroscopic characterization of a novel bis (oxo-bridged) dinuclear vanadium(V)–dipicolinic acid complex

Abstract

The reaction of [VO(dipic)(H 2O) 2] · H 2O with creatinine in a H 2O–CH 3OH mixture yields yellow crystals of a bis(oxo-bridged) binuclear vanadium(V) compound of stoichiometry [CH 3NHC(NH 2) 2] 2[V 2O 4(dipic) 2], (dipic 2− = pyridine 2,6 dicarboxylate; CH 3 NHC ( NH 2 ) 2 + ) = methylguanidinum ). The molecular structure of the compound was determined by X-ray diffraction methods. The binuclear complex crystallizes in the monoclinic space group P2 1/ c with a = 9.557(1), b = 12.363(1), c = 10.466(1) Å, β = 101.56 (2)° and Z = 2. It sits at a crystallographic inversion center with the pair of V(V) atoms in an edge-sharing distorted octahedral environment. In the [VO 2(dipic)] − halves of the dimer, the VO 2 + cation is coordinated to a dipicolinate group acting as a tridentate planar ligand through one oxygen of each carboxylic group and the hetereocyclic nitrogen atom. The oxo ligand lying near the coordination plane bridges through a weak axial V–O bond to the other half of the dimer. This gives rise to a V O2 bond length slightly longer than the other terminal V O1 bond. The infrared and Raman spectra of the compound were recorded and discussed on the basis of its structural data and compared with those of the free acid. The results are also compared with the corresponding results of related structures.