Synthesis, crystal structures and semiconducting properties of new hexacyanidometallates

Abstract

We describe the synthesis, crystal structure and semiconducting properties of a number of hexacyanidometallates with the formula A₂[MFe(CN)₆]·xH₂O (A = Na, K; M = Mg, Ca, Sr and Ba). All crystal structures were studied via single-crystal or powder X-ray diffraction. The unexpectedly low-symmetric structures in these ferrocyanides are described and contrasted with analogous transition-metal compounds which have been reported to be strictly or nearly cubic. The amount of crystal water in the structure for powder samples was determined by the thermogravimetric analysis (TGA), supported by IR and Raman spectroscopy. Electronic-structure calculations of K₂[MgFe(CN)₆] and K₂[CaFe(CN)₆] are compared with experimental UV-Vis measurements. The large band gaps by advanced theory indicate that the smaller experimental band gaps are due to surface effects of impurity states. Mott–Schottky curves of K₂[MgFe(CN)₆], K₂[CaFe(CN)₆] and K₂[BaFe(CN)₆]·3H₂O exhibit positive slopes, which characterizes these compounds as n-type semiconductors.