The synthesis of single crystals of Sr2NiN2 has been accomplished in a liqu
id sodium flux from strontium or strontium nitride, nickel, and sodium azid
e. The decomposition of sodium azide provides additional nitrogen for the s
ynthesis. The structure of Sr2NiN2 is derived from the Na2HgO2 structure ty
pe. However, Sr2NiN2 forms with a twinned superstructure. Single crystal X-
ray diffraction was used to determine the structure of the tetragonal subce
ll: I4/mmm, a = 3.8874(3) Angstrom, c = 13.992(2) Angstrom, Z = 2, R(F) = 5
.2%, and R-w(F) = 5.0% with the Ni and N positions split into two sites, ea
ch half occupied. The superstructure can be modeled as a 2 x 1 x 1 ordering
of the subcell in Pnma. The physical properties are unusual since Sr2NiN2
displays metallic conductivity and Pauli paramagnetism even though it is co
mprised of isolated NiN2 units. In addition, Sr2NiN2 possesses a Ni2+ forma
l charge, whereas the oxidation states for nickel nitrides are typically Ni
+ and Ni-0. (C) 2000 Academic Press.