Filling voids : cubic carbodiimide nitride nitridometalates (Ba6Nx)2[MN4][CN2]6 of M = Zr, Hf, Nb, Ta, Mo, and W

Cubic carbodiimide nitride nitridometalates (Ba6Nx)2[MN4][CN2]6 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)2[NbVN4][CN2]6 in space group Im3 as aristotype exhibit site disorder of the [NbN4]7 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)2[NbN4][CN2]6 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)2[HfIVN4][CN2]6 with ordered tetrahedra [HfN4]8. Dark red (Ba6N)2[WVIN4][CN2]6 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.