A New Family of High Oxidation State Antiperovskite Nitrides: La 3 MN 5 (M=Cr, Mn and Mo).

Three new nitrides La 3 MN 5 (M=Cr, Mn, and Mo) have been synthesized using a high pressure azide route. These are the first examples of ternary Cs 3 CoCl 5 -type nitrides, and show that this (MN 4 )NLa 3 antiperovskite structure type may be used to stabilise high oxidation-state transition metals in tetrahedral molecular [MN 4 ] n- nitridometallate anions. Magnetic measurements confirm that Cr and Mo are in the M 6+ state, but the M=Mn phase has an anomalously small paramagnetic moment and large cell volume. Neutron powder diffraction data are fitted using an anion-excess La 3 MnN 5.30 model (space group I4/mcm, a=6.81587(9) Å and c=11.22664(18) Å at 200 K) in which Mn is close to the +7 state. Excess-anion incorporation into Cs 3 CoCl 5 -type materials has not been previously reported, and this or other substitution mechanisms may enable many other high oxidation state transition metal nitrides to be prepared.