Synthesis, crystal structures and semiconducting properties of new hexacyanidometallates.

We describe the synthesis, crystal structure and semiconducting properties of a number of hexacyanidometallates with the formula A 2 [MFe(CN) 6 ]· x H 2 O (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 K 2 [MgFe(CN) 6 ] and K 2 [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 K 2 [MgFe(CN) 6 ], K 2 [CaFe(CN) 6 ] and K 2 [BaFe(CN) 6 ]·3H 2 O exhibit positive slopes, which characterizes these compounds as n-type semiconductors.