The Azideitrate route, a versatile and prolific procedure for the synthesis of alkali oxometalates (Review)

摘要

We review the Azide/Nitrate Route as an alternative access to alkali oxometalates. Along this recently discovered approach appropriate mixtures of the azide and nitrate (or nitrite) of the respective alkali metal are reacted with a binary oxide, in an all-solid-state reaction. The high heats of formation of the azides and nitrates involved provide a substantially increased thermodynamic driving force for the reactions intended to take place. Moreover, the insensitive-to-air starting materials allow to intimately mix them, e.g. by ball milling, which together with the high reactivity of the in-situ formed alkali metal oxide significantly accelerates the kinetics. As a particular further advantage, the oxygen content of the target compound, and thus the oxi-dation state of the countercation, can be precisely adjusted by the azideitrate ratio chosen. Subsequent to a brief description of the procedures, the potential of the synthesis route is validated on three examples, (1) a new family of intrinsically doped sodium cuprates(II/III), featuring first unambiguous manifestations of a Wigner lattice and frustrated magnetic coupling, (2) several new oxocobaltates(III) with cobalt(III) in tetrahedral coordination, which used to be regarded as uncommon, displaying competing magnetic exchange interactions within or between oligomeric cobaltate anions, and (3) alkali oxometalates featuring exotic structural properties.