RESUMO
A series of rubidium rare earth thiophosphates with the formula Rb4Ln2(P2S6)(PS4)2 (Ln = La, Ce, Pr, Nd, Sm, and Gd) were synthesized using the high temperature molten flux crystal growth method utilizing a RbBr flux. Single crystals of all title compounds, as well as phase pure powders of the La-, Ce-, and Sm-containing compositions, were obtained. Single crystals of the title compounds were characterized by single crystal and powder X-ray diffraction for structure and phase identification. Rb4Ln2(P2S6)(PS4)2 crystallizes in the monoclinic crystal system adopting the P21/n space group for the large rare earths (Ln = La, Ce, Pr) and the C2/c space group for the smaller rare earths (Ln = Nd, Sm, Gd). This Rb4Ln2(P2S6)(PS4)2 series is a rare example of thiophosphates containing both tetrahedral [PVS4]3- and dimeric [PIV2S6]4- thiophosphate units that, in this structural family, link corrugated rare earth sulfide chains into sheets. The band gaps of the materials were determined from UV-Vis data and the fluorescence spectrum of Rb4Ce2(P2S6)(PS4)2 was collected. Optical band gaps were estimated to be 2.9 and 2.4 for the Nd and Sm analogues, respectively.
RESUMO
The stability of the novel Pu(iv) silicate, Cs2PuSi6O15, was predicted from a combination of crystal chemical reasoning and DFT calculations and confirmed by its synthesis via flux crystal growth. Formation enthalpies of the A2MSi6O15 (A = Na-Cs; M = Ce, Th, U-Pu) compositional family were calculated and indicated the Cs-containing phases should preferentially form in the Cmc21 structure type, consistent with previous experimental findings and the novel phases produced in this work, Cs2PuSi6O15 and Cs2CeSi6O15. The formation enthalpies of a second set of compositions, A2MSi3O9, were also calculated and a comparison between the two compositional families correctly predicted A2MSi6O15 to be on average more stable than A2MSi3O9.