The Disordered Crystal Structures of Zn(CN)2 and Ga(Cn)3

The structure of Zn(CN)(2) has been reexamined using neutron time-of-flight diffraction and has been determined to have symmetry Pn (3) over bar m, a=5.9227 (1) Angstrom at 14 K and 5.8917 (1) Angstrom at 305 K (negative thermal "expansion"). The CN groups are disordered in contrast to the ordered arrangement with symmetry p4 (3) over bar m assumed in earlier X-ray diffraction experiments. Zn is tetrahedrally surrounded with average Zn-(C,N)=1.9697(3) and C-N=1.1897(1) Angstrom. Ga(CN)(3) has been examined for the first time, X-ray powder diffraction shows it to have a cubic Prussian blue framework structure, symmetry Pm (3) over bar m, a=5.295(2) Angstrom, also with CN disorder. Ga is octahedrally surrounded with average Ga-(C, N) distance=2.072(2) Angstrom and C-N=1.148(1) Angstrom. (C) 1997 Academic Press.