ABSTRACT
Li(7)PS(6) and Li(7)PSe(6) belong to a class of new solids that exhibit high Li(+) mobility. A series of quaternary solid solutions Li(7)PS(6-x)Se(x) (0 < or = x < or = 6) were characterised by X-ray crystallography and magic-angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy. The high-temperature (HT) modifications were studied by single-crystal investigations (both F43m, Z=4, Li(7)PS(6): a=9.993(1) A, Li(7)PSe(6): a=10.475(1) A) and show the typical argyrodite structures with strongly disordered Li atoms. HT-Li(7)PS(6) and HT-Li(7)PSe(6) transform reversibly into low-temperature (LT) modifications with ordered Li atoms. X-ray powder diagrams show the structures of LT-Li(7)PS(6) and LT-Li(7)PSe(6) to be closely related to orthorhombic LT-alpha-Cu(7)PSe(6). Single crystals of the LT modifications are not available due to multiple twinning and formation of antiphase domains. The gradual substitution of S by Se shows characteristic site preferences closely connected to the functionalities of the different types of chalcogen atoms (S, Se). High-resolution solid-state (31)P NMR is a powerful method to differentiate quantitatively between the distinct (PS(4-n)Se(n))(3-) local environments. Their population distribution differs significantly from a statistical scenario, revealing a pronounced preference for P-S over P-Se bonding. This preference, shown for the series of LT samples, can be quantified in terms of an equilibrium constant specifying the melt reaction Se(P)+S(2-) <==>S(P)+Se(2-), prior to crystallisation. The (77)Se MAS-NMR spectra reveal that the chalcogen distributions in the second and third coordination sphere of the P atoms are essentially statistical. The number of crystallographically independent Li atoms in both LT modifications was analysed by means of (6)Li{(7)Li} cross polarisation magic angle spinning (CPMAS).
ABSTRACT
Crystal chemical data of high- (HT) and low-temperature (LT) modifications of lithium argyrodites with the compositions Li(7)PCh(6) (Ch=S, Se), Li(6)PCh(5)X (X=Cl, Br, I), Li(6)AsS(5)Br, and Li(6)AsCh(5)I (Ch=S, Se) based on single-crystal, powder X-ray (113 K
ABSTRACT
A new organic-inorganic two-dimensional hybrid compound, [CuMoO(4)(C(2)H(8)N(2))], has been hydro-thermally synthesized at 443â K. The unit cell contains layers composed of CuN(2)O(4) octa-hedra and MoO(4) tetra-hedra. Corner-sharing MoO(4) and CuN(2)O(4) polyhedra form CuMoO(4) bimetallic sites that are joined together through O atoms, forming an edge-sharing Cu(2)Mo(2)O(4) chain along the c axis. The one-dimensional chains are further linked through bridging O atoms that join the Cu and Mo atoms into respective chains along the b axis, thus establishing layers in the bc plane. The ethyl-enediamine ligand is coordinated to the Cu atom through its two N atoms and is oriented perpendicularly to the two-dimensional -Cu-O-Mo- layers. The average distance between adjacent layers, as calculated by consideration of the closest and furthest distances between two layers, is 8.7â Å. The oxidation states of the Mo and Cu atoms of VI and II, respectively, were confirmed by bond-valence sum calculations.
