Chemistry and Structure of an Inorganic Analogue of a Carboxylic Acid: Hydroxobis (8-quinolinato) oxovanadium (V)

Abstract

Basic hydrolysis, under mild conditions, of (~-oxo)bis[bis(8-quinolinato)oxovanadium(V)], [(Q2VO)20]( Q = 8-quinolinato anion), obtained by a one-step synthesis, gave a dioxovanadium(V) complex, [Q2V02]-, containing the V02- unit. The structure of this anionic species was determined by an X-ray analysis carried out on the corresponding salts ( [Q2V02Na(H20)2]2(pDMF)()V I) and ([Q2V02(]n -Bu4N).H201( VII). The VQ2 unit has similar structural characteristics in both complexes, with the two N donor atoms trans to the oxo groups, which have a cis configuration. The V-N bonds, as a consequence, have the longest distances so far encountered (V-Na, = 2.33 A). Complex VI is a dimer, where two V02 units are bridged by two Na' ions sharing the oxygen of a DMF molecule. In complex VI1 the oxygen is only weakly bonded to a H20 molecule, via hydrogen bonding. In both complexes the structural data concerning the V02 units are very close, with a V-0-V angle varying from 105.7 (2)' in complex VI to 106.1 (5)' in com lex VII, while the V-0 bond distances have a double-bond character [1.647 (4) and 1.628 (2) 8, in complex VI; 1.62 (1) 1in complex VII]. The 0-0 bite values are 2.610 (4) A (complex VI) and 2.58 (1) A (complex VII). These results invite comparison of the V02- unit with the carboxylato group RCOC. The relationship between other vanadium(V) derivatives and organic functional groups related to a carboxylic acid is reported. The inorganic analogue of a carboxylic acid itself is obtained on acidifying an aqueous solution of [Q2VOz]-. [QzV(O)(OH)], which is a very well-known analytical reagent for organic compounds, was found to be a weak acid with a pKA of 6.3. Crystallographic details for ([Q2V02Na(H20)2]2(p-DMF)}:s pace group Pbcn (orthorhombic); a = 30.245 (2), b = 9.744 (l), c = 14.167 (1) A; V = 4175.1 A,; Z = 4. The final R factor was 4.7% for 2867 observed data. Crystallographic details for ( [QzV02](n-Bu4N).H20]}: space group Z42d (tetragonal); a = b = 19.04 (3), c = 19.486 (3) A; V = 7064.1 .A3; Z = 8. The final R factor was 5.9% for 568 observed data.