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The structure and properties of Na 3 O͑CN͒ have been studied using parameter-free model calculations based on density functional theory. The results suggest that, unlike in pure alkalicyanides, the CN anions are orientationally disordered in the ground-state structure. The calculations show that in the fully disordered structure, the global strain is minimized.

More than a dozen minerals and some synthetic compounds (arsenates, vanadates, silicates, and molybdates) are known to belong to the adelitedescloizite structure type. The double salts are formed by two cations featuring distinct environments. The cation A is in a [7]-or [8]-coordination (Na, Ca, Pb atoms) whereas the cation B is octahedrally [6] or tetragonal bipyramidally [4 plus 2] coordinated to O atoms (Mg, Mn, Fe, Co, Ni, Cu, Zn atoms). All compounds crystallize orthorhombic. The parental structure is centrosymmetric and exhibits a mono-capped trigonal prism for the coordination polyhedron around the A atoms (descloizite type). An acentric structure variant is known (adelite type); the main difference is the [8] coordination of the A atoms in form of a square antiprism. Further deviations from the centrosymmetric parental structure are moderate. A tendency is observed that the centrosymmetric symmetry goes along with lead-vanadates whereas calcium, arsenate and silicate favour the acentric symmetry. The system Cd(II)-Cu(II)arsenate(V) system was investigated under hydrothermal conditions; as a result, a new Cd-member was synthesized. Single-crystal X-ray structure investigations proved that this compound is a centrosymmetric Pnam member of the adelite-descloizite group: a = 7.415(1), b = 9.016(2), c = 5.890(1) Å; NONIUS four-circle diffractometer, CCD detector, capillary-optics collimator, Mo tube, graphite monochromator; R1 = 0.020, wR2 = 0.046, total 772 reflections (689 observed reflections); for non-hydrogen atoms anisotropic displacement parameters were refined; the H atom was found from a difference Fourier map and refined isotropically. The [4 plus 2] coordinated Cu atoms are located in an inversion centre; they are linked by O-O edges to chains parallel to [001]: Cu-O = 1.8967(14), 2x / 2.0533(16), 2x / 2.3083(16) Å, 2x. Each of the arsenate tetrahedra link two such chains to a three-dimensional network , the average As-O bond distance is 1.6908 Å. Cavities house the A = Cd atoms: Cd-O is 2.224(2) to 2.542(3) Å. The hydrogen bond O-H … O is 2.622(4) Å. Despite similar ionic radii of Ca and Cd atoms, the Ca compound crystallizes acentric.