Syntheses, crystal structures, and solid state NMR investigations of K_4M_2P_6S_(25) and K_3M_2P_5S_(18) (M = Ti, Sn)

摘要

Reaction of K_2S_5 with P_4S_(10) and Ti at 450 deg C results in the formation of K_4Ti_2P_6S_(25), a new titanium thiophosphate, whose crystal structure was solved by single-crystal X-ray diffraction. The title compound crystallizes in the orthorhombic space group Fdd2, with the lattice constants a = 33.819(7), b = 35.508(7), and c = 6.251(1) A (Z = 8). The structure contains a layered arrangement of crosslinked quasi-one-dimensional Ti_2P_6S_(25)~(4-) chains. The K~+ ions are situated between the layers. The Ti atoms within the chains are octahedrally coordinated by P_2S_7~(4-) and P_2S_9~(4-) ligands. Reaction of K_2S with P_4S_(10), S and Ti at 600 deg C results in the formation of K_3Ti_2P_5S_(18), a novel titanium thiophosphate, which crystallizes in the monoclinic space group C2/c, with a = 22.739(5), b = 6.058(1), c = 20.440(4) A, and beta = 105.41(3) deg (Z = 4). The structure contains linear Ti_2P_5S_(18)~(3-) chains with the K~+ ions situated between the chains. The Ti atoms within the chains are octahedrally coordinated by PS_4~(3-) and P_2S_7~(4-) ligands. Reaction of K_2S with P_4S_(10), S and Sn at 600 deg C results in the formation of the isostructural compound K_3SnP_5S_(18), a novel tin thiophosphate, with the lattice parameters a = 23.303(7), b = 6.023(2), c = 20.888(6) A, and beta = 106.18(2) deg. The spectroscopic characteristics of the thiophosphate groups, in particular that of the novel P_2S_9~(4-) entity are examined by UV-VIS, FT-IR and ~(31)P one- and two-dimensional magic-angle spinning (MAS-) NMR studies. The NMR experiments illustrate the utility of double-quantum coherence techniques as a unique tool of site assignments based on ~(31)P-~(31)P spatial proximity, allowing a spectroscopic distinction of the P_2S_7~(4-) and the P_2S_9~(4-) groups can be differentiated based on their different chemical shift anisotropies.