Filling voids : cubic carbodiimide nitride nitridometalates (Ba6Nx)2MN4CN26 of M = Zr, Hf, Nb, Ta, Mo, and W

Cubic carbodiimide nitride nitridometalates (Ba6Nx)2MN4CN26 of M = Zr, Hf, Nb, Ta, Mo, and W are synthesized by various high-temperature reactions and their respective crystal structures were investigated using X-ray diffraction. Red transparent crystals (Ba6N5/6)2NbVN4CN26 in space group Im3 as aristotype exhibit site disorder of the NbN47 anion and an about 42% occupation of a further nitride ion site for charge balance. Upon reduced nitrogen content on the latter site, dark gray (Ba6Nx)2NbN4CN26 with x=0.55(7) crystallizes in the direct subgroup I23 with fully ordered tetrahedra. This structure is also observed for crystals of red (Ba6N2/3)2HfIVN4CN26 with ordered tetrahedra HfN48. Dark red (Ba6N)2WVIN4CN26 with enlarged nitride content balancing the higher charge of the transition metal in oxidation state þ6 crystallizes in the different direct subgroup Pn3, and shows an unlike site order for the nitride ions. Depending on the (dis)order of the nitride ions, the nitridometalate ions (dis)order in different patterns. Powder diffraction data of microcrystalline samples indicate identical structures of the zirconium and hafnium compounds in I23, but realization of space group Pn3 of the red compounds of not only molybdenum and tungsten but also niobium and tantalum. The IR spectra corroborate the identity of the carbodiimide anion.