A novel convenient synthesis of mixed-valence Ti-III/Ti-IV double phosphates starting with titanium nitride TiN

A new synthetic approach for the low- and mixed-valence double titanium pho sphates starting with titanium nitride, TiN, and based on the controlled ox idation of a low-valent metal in the phosphate melt is presented. The react ion of the system (M2O)-O-I P2O5 - TiN (M-I = Na, K) in air (800-1050 degre es C) leads to loss of nitrogen, N-2, and results in the formation of a num ber of double phosphates: KTiP2O7, (K2TiTiIV)-Ti-III(PO4)(3), KTiOPO4, NaTi P2O7, NaTi2(PO4)(3) and a new mixed-valent diphosphate, (NaTiTiIV)-Ti-III(P 2O7)(2). The mixed-valent species (K2TiTiIV)-Ti-III (PO4)(3) and (NaTiTiIV) -Ti-III(P2O7)(2) were characterized by single crystal X-ray diffraction. Th e described synthetic procedure is proposed as a simple and convenient meth od for the preparation of low- and mixed-valent phosphate materials.