摘要 : A new trinuclear oxovanadium(V) complex with the anionic dmpp ligand (Hdmpp=3-hydroxyl-1,2-dimethyl-4-pyridinone, [V_3O_6(dmpp)_3(H_2O)] (H_2O_2), was isolated from the reaction of Hdmpp, KOH and sodium metavanadate at Ph 4.5. The... 展开 A new trinuclear oxovanadium(V) complex with the anionic dmpp ligand (Hdmpp=3-hydroxyl-1,2-dimethyl-4-pyridinone, [V_3O_6(dmpp)_3(H_2O)] (H_2O_2), was isolated from the reaction of Hdmpp, KOH and sodium metavanadate at Ph 4.5. The solid state structure of the [V_3O_6(H_2O)(dmpp)_3](H_2O)_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) A, b=16.4107(11) A and c=18.0638(12) A, #beta#=91.1010(10) deg , V=2825.3(3) A~3, Z=4 and R_1(Wr_2) =0.0704 (0.2025). tow to the vanadium atoms (V1 and V3) are sixcoordinated, with distorted octahedral geometries, and the other one (V_2) is five-coordinated with a distorted square pyramidal geometry. The cyclic V_3O_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 corresponding to the [V_3O_6(dmpp)_3(H_2O)+2H~+]~(2+) fragment. ~51V and ~1H NMR spectroscopy were used to study this complex in aqueous solution. The dissolution of the crystalline [V_3O_6(dmpp)_3(H_2O)](H_2O)_2 compound in water, under aerobic conditions at Ph 4.2, gave one intense broad signal at obic conditions at Ph 4.2, gave one intense broad signal at #delta#=-490 in the ~51V NMR spectrum, which is attributed to a major species present in solution. The observation of only one ~51V NMR signal, instead of the three expected for the different chemical environments of each vanadium atom present in solid, is consistent with a fast(in the NMR timescale) dynamic equilibrium equalising their environments. This involves a fast exchange between O8,O10 AND O12 as mono- or bifunctional oxygen atoms, as well as the H_2O molecule, which acts in another fast equilibrium coordinating the vanadium atom that has a dmpp ligand with one bifunctional oxygen atom. The trinuclear oxovandaium(V) complex is relatively stable in water in the pH range 2.5-5.0. However, dissociation of the complex occurs at higher pH, leading to various hydrolysis products, which include mononuclear complex species with 1:1 and 1:2 metal-to-ligand stoichiometries, and monomeric and oligomeric species of free vanadium(V). 收起