The XXI International Scientific Conference of Young Scientists and Specialists (AYSS-2017)

ISOPOLYMOLYBDATE- AND ISOPOLYVANADATE ANIONS IN AQUEOUS DIMETHYLFORMAMIDE MEDIUM AND IN SALTS

3 Oct 2017, 16:30

1h 50m

2-nd and 3-rd floor (International conference hall)

Poster Poster session

Speaker

Ms Violetta Kravchenko (Donetsk National University)

Description

According to the data of pH-potentiometric titration, the complexation processes in Na2MoO4 – HCl – NaCl – C3H7ON – H2O and Na3VO4 – HCl – NaCl – C3H7ON (10-40 vol.%) – H2O (Cv = 0.01 - 0.1 mol/L; μ = 0.5 mol/L) and the concentration formation constants of isopolymolybdate- and isopolyvanadate-anions were calculated according to the CLINP 2.1 program; the diagrams of isopolyanion distribution are plotted as a function of acidity and concentration, and schemes for their transformation in aqueous dimethylformamide medium are proposed. The pH (acidity) zones of the dominance of isopolymolybdates and isopolyvanadates are established as a function of the concentration of MoO42 , and VO43-- ions; the C3H7ON and H2O ratios in the systems. According to the results of mathematical modeling in aqueous media at a concentration of molybdenum С£0,05 M in the acidity range Z = 0,5-2,5 the tetraiones of the two compositions Mo4O132- and Mo4O144- dominate in the solution, and the protonated hexamolybdates HMo6O215- and H2Mo6O214- are in minor amounts. In the dimethylformamide medium the effect of increasing the concentration of organic solvent on the composition and distribution of isopolymolybdate-anions is shown, namely: protonated hepta- and octa-ions are formed in dilute solutions, unlike aqueous systems, and octa- and tetramolybdate-anions dominate in decimolar solutions with negligible the content of the other ions Мо2О72-, Мо6О216-, Мo4O144-, НМо7О245-. To confirm the stabilizing effect of dimethylformamide (DMF) on the formation of tetra-, hexa- and octa- molybdate-anions, the synthesis of salts with tetraethylammonium cation in decimolar systems and 25% DMF content was carried out. The composition of crystalline products was determined by chemical, X-ray phase analysis and IR spectroscopy and showed that in the acidity range Z = 1,14 – 1,80 white crystals of octamolybdate [N(C2H5)4]4Mo8O26·nC3H7ON·mH2O precipitate after the separation of white crystals of tetramolybdate [N(C2H5)4]2Mo4O13·nC3H7ON·mH2O at Z = 1.50 and yellow hexamolybdate crystals [N(C2H5)4]2Mo6O19·nC3H7ON·mH2O at Z = 1.80. Salts with hexa-, tetra- and octamolybdate anion, which do not precipitate from water solutions, were obtained from the medium with DMF by precipitation with a cation of the inorganic nature – barium. In the system with vanadium in the aqueous organic medium, as well as in the aqueous medium, it was possible to detect the existence of three-(V3O93-) and tetrametavanadates (HV4O123-) in a narrow range of concentrations (0,01-0,1 mol/L). The decavanadate anion V10O286- is fixed at Z = 2,50, which is marked by an inflection point on the potentiometric titration curve. There are no tetravanadates of composition V4O124- and V4O136-. In the decimolar solution of sodium orthovanadate such polyoxoanions dominate: V4O124-, HV4O135- and V10O286- with an insignificant amount of protonated decavanadate H3V10O283- and V3O93- . With an increase in the DMF concentration of up to 25% by volume, the formation of the unprotonated form of decavanadate anion is stabilized in the system, with the formation of aprotic three- and tetravanadates in larger amounts at Z> 2,5. Crystals of composition: [N(C4H9)4]5V3O10·4H2O·C3H7ON, [N(C4H9)4]4V4O12·4H2O·2C3H7ON, [N(C4H9)4]6V10O28·4H2O·4C3H7ON; In4(V4O12)3·7H2O·3C3H7ON; In2V10O28·5H2O·5C3H7ON were obtained.