IN-2.24(NCN)(3) AND NAIN(NCN)(2) - SYNTHESIS AND CRYSTAL-STRUCTURES OF NEW MAIN-GROUP METAL CYANAMIDES

Single crystals of In-2.24(NCN)(3) and NaIn(NCN)(2) can be synthesized from a reaction between InBr and NaCN at 400 degrees C, followed by c hemical transport at 400-500 degrees C. The X-ray crystal structure de terminations of In-2.24(NCN)(3) (rhombohedral R ($) over bar 3c, a = 6 06.09(4), c = 2884.4(2) pm, Z = 6) and NaIn(NCN)(2) (orthorhombic Cmcm , a = 961.30(6), b = 716.84(5), c = 603.65(4) pm, Z = 4) reveal ionic layer structures built from sheets of cationic and anionic (cyanamide) motifs. While NaIn(NCN)(2) contains In3+ and Na+ ions, In-2.24(NCN)(3 ) is a mixed-valence compound, incorporating a monovalent In+ ion besi des trivalent indium. The NCN(2-)units of bath In-2.24(NCN)(3) and NaI n(NCN)(2) reflect perfect D-infinity h point group symmetry within the limits of experimental accuracy. Furthermore, an evaluation of all pr esently available crystallographic data on metal cyanamide crystal str uctures manifests that there is no evidence for a non-centrosymmetric description of any of these. Likewise, we propose an alternative centr osymmetric structural model for lead cyanamide, PbNCN, and question th e evidence of the unsymmetrical, non-D-infinity h shaped cyanamide ani on in the latter structure.