Novel oxonium compounds of lanthanoids: synthesis of (H3O)3La2F(AsF6)8, and syntheses and crystal structures of (H3O)8La2F(AsF6)13 and (H3O)4La2F(AsF3)2(AsF6)9

Abstract Reactions of Ln 2 O 3 with AsF 5 in aHF (Ln=La–Lu, aHF=anhydrous hydrogen fluoride) yield solutions of H 3 O + , 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 2 O–AsF 5 –aHF, LnF x (AsF 6 ) 3− x –H 3 OAsF 6 –aHF. From such solutions a new type of oxonium compounds with general formula (H 3 O) x Ln y F z (AsF 6 ) x +3 y − z have been isolated at ambient temperature. (H 3 O) 3 La 2 F(AsF 6 ) 8 was obtained as a white powder from the solution of La 2 O 3 dissolved in AsF 5 –aHF after pumping off all volatiles at room temperature. Colourless crystals of (H 3 O) 8 La 2 F(AsF 6 ) 13 were prepared by slow static evaporation from a solution obtained after solvolysis of solid (H 3 O) 3 La 2 F(AsF 6 ) 8 in aHF at ambient conditions. Colourless crystals of (H 3 O) 4 La 2 F(AsF 3 ) 2 (AsF 6 ) 9 were prepared by the reaction of La 2 O 3 with AsF 5 and aHF under solvothermal conditions above the critical temperature of AsF 5 . Similar reactions of other oxides Ln 2 O 3 (Ln=Nd, Sm, Gd, Dy, Ho, Tm) have also been studied. (H 3 O) 8 La 2 F(AsF 6 ) 13 crystallises in the monoclinic space group P 2 1 / c (no. 14 ) with a =1079.3(3) pm, b =2859.0(7) pm, c =1068.0(3) pm, β =109.310(8)°, and Z =2. (H 3 O) 4 La 2 F(AsF 3 ) 2 (AsF 6 ) 9 crystallises in the triclinic space group P 1 (no. 2) with a =1064.8(3) pm, b =1073.3(4) pm, c =1213.9(3) pm, α =75.53(2)°, β =64.79(2)°, γ =70.07(2)°, and Z =1. Both structures are closely related with zig-zag chains of alternating La 2 F and AsF 6 units resembling the main feature. Oxonium ions are arranged among such anionic chains.