Novel oxonium compounds of lanthanoids: synthesis of (H_3O)_3La_2F(AsF_6)_8, and syntheses and crystal structures of (H_3O)_8La_2F(AsF_6)_(13) and (H_3O)_4La_2F(AsF_3)_2(AsF_6)_9

摘要

Reactions of Ln_2O_3 with AsF_5 in aHF (Ln = La-Lu, aHF = anhydrous hydrogen fluoride) yield solutions of H_3O~+, solvated Ln~(3+) and AsF_6~- ions. Very similar solutions of these ions may be obtained from combination of various other starting materials, e.g. LnF_3-H_2O-AsF_5-aHF, LnF_x(AsF_6)_(3-x)-H_3OAsF_6-aHF. From such solutions a new type of oxonium compounds with general formula (H_3O)_xLn_yF_z(AsF_6)_(x+3y-z) have been isolated at ambient temperature. (H_3)_3La_2F(AsF_6)_8 was obtained as a white powder from the solution of La_2O_3 dissolved in AsF_5-aHF after pumping off all volatiles at room temperature. Colourless crystals of (H_3O)_8La_2F(AsF_6)_(13) were prepared by slow static evaporation from a solution obtained after solvolysis of solid (H_3O)_3La_2F(AsF_6)_8 in aHF at ambient conditions. Colourless crystals of (H_3O)_4La_2F(AsF_3)_2(AsF_6)_9 were prepared by the reaction of La_2O_3 with AsF_5 and aHF under solvothermal conditions above the critical temperature of AsF_5. Similar reactions of other oxides Ln_2O_3 (Ln = Nd, Sm, Gd, Dy, Ho, Tm) have also been studied. (H_3O)_8La_2F(AsF_6)_(13) crystallises in the monoclinic space group P2_1/c (no. 14) with a = 1079.3(3) pm, b = 2859.0(7) pm, c = 1068.0(3) pm, #beta# = 109.310(8) deg, and Z = 2. (H_3O)_4La_2F(AsF_3)_2(AsF_6)_9 crystallises in the triclinic space group P1 (no. 2) with a = 1064.8(3) pm, b = 1073.3(4) pm, c = 1213.9(3) pm, #alpha# = 75.53(2) deg, #beta# = 64.79(2) deg, #gamma# = 70.07(2) deg, and Z = 1. Both structures are closely related with zig-zag chains of alternating La_2F and AsF_6 units resembling the main feature. Oxonium ions are arranged among such anionic chains.