BA-2(CN2)(CN)(2) AND SR-2(CN2)(CN)(2) - T HE FIRST MIXED CYANAMIDE CYANIDES

The mixed cyanamide-cyanides M(2)(CN2)(CN)(2) (M = Ba, Sr) were synthe sized by the reaction of Ba2N and SrCO3, respectively, with HCN at 630 degrees C. The crystal structure of Ba-2(CN2)(CN)(2) was determined f rom single-crystal X-ray investigations at room temperature and -100 d egrees C; the isostructural Sr-2(CN2)(CN)(2) was refined using powder methods (P6(3)/mmc; Ba-2(CN2)(CN)(2): a= 1066.52(5) pm, c= 696.82(3) p m; Sr-2(CN2)(CN)(2): a = 1035.91(1) pm, c = 664.23(1) pm; Z = 4). The crystal structure is a partially filled defect variant of the anti-NiA s structure type with a distorted hexagonal close packed arrangement o f M(2+)-ions. All CN22- and one quarter of the CN- ions occupy 3/4 of the octahedrally coordinated interstices, the remaining cyanide anions are located at 3/8 of the tetra hedral sites. In the crystal structur e the CN- are coordinated to the cations both end-on and side-on. All anions can be distinguished by vibrational spectroscopy.