Preparation and structural characterisation of the trigonal nitridometalate Ba3MoN4

The preparation and structural characterisation of a high temperature trigonal modification of Ba3MoN4 is described and compared to the previously reported orthorhombic form. The trigonal form was prepared by the reaction of barium nitride and molybdenum metal foil at 1393 K for 5 days in sealed stainless steel crucibles under argon. The structure is characterised by the presence of isolated [MoN4](6-) tetrahedra which are stacked along the c axis. The structural analogies and differences between the two forms of Ba3MoN4 are discussed and their relationship to the AMoO(4) (A=Ca, Sr, Ba) compounds with the scheelite structure, which represents the family of oxides most structurally related to the Ba-Mo-N nitrides.