NMe4V3O7: critical role of pH in hydrothermal synthesis of vanadium oxides

Hydrothermal Synthesis and Characterization of (H3N(CH2)4NH3)[V6O14]

“…At high pH values, vanadium is only four-fold coordinated in the oxide. However, as the pH decreases, the vanadium coordination increases to five (square pyramids) at pHE7 until six (octahedra) at pHo2 (6). The title compound has been synthesized at a pH close to nine which is consistent with the presence of [VO 5 ] square pyramids and [VO 4 ] tetrahedra in the structure.…”

“…2 A similar structure was already described in several layered vanadium oxides as the V 3 O 7 structure is one of the most prevalent of those found (6,(12)(13)(14). The square pyramids share edges to form zigzag chains, connected by corner-sharing tetrahedra (see Fig.…”

“…The (H 3 N(CH 2 ) 4 NH 3 )[V 6 O 14 ] compound reported in this paper exhibits the [V 3 O 7 ] structure already described in several layered vanadium oxide compounds (6,(12)(13)(14). Several parameters are important in the synthesis, the pH of the aqueous solution, the ratio of the reactants, the nature of the ions and the temperature.…”

“…Several parameters are important in the synthesis, the pH of the aqueous solution, the ratio of the reactants, the nature of the ions and the temperature. In particular, Whittingham et al pointed out the importance of the pH on vanadium coordination and consequently on the structure of the inorganic framework [1,6]. At high pH values, vanadium is only four-fold coordinated in the oxide.…”

“…They all exhibit a layered structure in which protonated amines are inserted between negatively charged vanadium oxide planes. It has been shown that the structure of the layers and particularly the coordination of vanadium centers are strongly dependent on the pH of the aqueous solution (1,6). At a pH close to 7, vanadium oxide layers are currently built of [VO 4 ] tetrahedra and [VO 5 ] square pyramids and vanadium may exhibit both V IV 4 ] tetrahedra (5, 4(a)).…”