A New Trinuclear Oxovanadium(V) Complex with DMPP Ligands − Synthesis and Structural Characterization in the Solid State and in Aqueous Solution

Abstract

A new trinuclear oxovanadium(V) complex with the anionic dmpp ligand (Hdmpp = 3-hydroxy-1,2-dimethyl-4-pyridinone), [V 3 O 6 (dmpp) 3 (H 2 O)](H 2 O) 2 , was isolated from the reaction of Hdmpp, KOH and sodium metavanadate at pH 4.5. The solid state structure of the [V 3 O 6 (H 2 O)(dmpp) 3 ](H 2 O) 2 complex, investigated by X-ray diffraction methods, was found to contain a cyclic trinuclear metal cluster. This complex crystallises in the monoclinic system: P2 1 /n, a = 9.5324 (7) Å , b = 16.4107(11) Å and c = 18.0638(12) Å , β = 91.1010(10)°, V = 2825.3(3) Å 3 , Z = 4 and R 1 (wR 2 ) = 0.0704 (0.2025). Two of the vanadium atoms (V1 and V3) are sixcoordinated, with distorted octahedral geometries, and the other one (V2) is five-coordinated with a distorted square pyramidal geometry. The cyclic V 3 O 4 framework has one oxygen atom bridging two vanadium atoms in two V−O−V groups, V1−O4−V2 and V2−O5−V3, and two oxygens bridging the V1−V3 atoms, V1−O6−V3 and V1−O12−V3. IR data confirm the crystallographic results, showing the characteristic V=O band in the 973−935 cm −1 frequency range.This compound has three bands corresponding to V=O stretching, indicative of different chemical environments around the vanadium atoms in the solid state. The ES mass spectrum in aqueous solution displays an intense peak cor-

Vanadate complexes of 3-hydroxy-1,2-dimethyl-pyridinone: Speciation, structure and redox properties

“…This complex was observed earlier in the 51 V-NMR spectra (δ = -518 ppm [14,15]). It was suggested to be dinuclear [15] but the protonation state was not identified.…”

“…mononuclear one [(VO 2 )(dhp)]). 1 H-NMR measurements for the mono and bis complexes have also been published [14], but no thermodynamic information was concluded from these measurements.…”

“…Several articles were published about the speciation of the vanadate-dhp system [13][14][15][16], although the conclusions are sometimes contradictory in the different publications and the final picture is still not complete.…”

“…Later X-ray structure for a trinuclear complex [(VO 2 ) 3 (dhp) 3 .H 2 O] has been published [14]. In this cyclic compound, µ-oxygens form bridges between the vanadium centres, the three ligands and the vanadates are not equivalent due to an extra ligand-O-V bound.…”

“…The 51 V-NMR spectral work in the same publication [14] is more detailed, but is still not complete:…”