Structural and compositional tuning of layered subnitrides; new complex nitride halides

New quaternary bimetallic nitride halides and the first examples of quintinary nitride mixed halides have been synthesised in the phase system Ca - Sr - N - Cl - Br. The variation in structure with composition has been investigated by powder X- ray and powder neutron diffraction techniques. All compounds crystallise in the R-3m spacegroup, with the anti-alpha-NaFeO2 structure. The layered compounds exhibit unprecedented coexistent disorder of both cations and anions in which only nitride solely occupies a discrete crystallographic position. [N(Ca,Sr)(2)](+) layers alternate with halide ions (Cl, Br)(-), which fill the octahedral voids between the positively charged sheets. A dual cationic-anionic substitution approach allows all aspects of the anisotropic structure to be controlled, including the thickness of the ionic layers and the [N(Ca,Sr)(2)](+) interlayer spacing