Opening the paddlewheel: unusual coordination of [Mo2] dumbbells in the chain structures of A[Mo2(CF3SO3)5]·2CF3SO3H (A = Na, Rb, Cs)

Abstract

The reaction of Mo(II)acetate, concentrated triflic acid and the alkaline metal triflates A(CF₃SO₃) (A = Na, Rb, Cs) in sealed glass ampoules at 110 °C yielded red single crystals of A[Mo₂(CF₃SO₃)₅]·2CF₃SO₃H (A = Na: triclinic, P-1, Z = 4, a = 13.714(1) Å, b = 14.339(1) Å, c = 21.340(2) Å, α = 81.78(1)°, β = 75.21(1)°, γ = 62.65(1)°; A = Rb/Cs: monoclinic, P2₁/m, Z = 2, a = 11.561(1)/11.584(1) Å, b = 14.817(1)/14.9472(8) Å, c = 11.6208(1)/11.744(1) Å, β = 112.38(1)/113.48(1)°). The crystal structures contain dumbbell shaped [Mo₂] moieties surrounded by three chelating and four monodentate triflate anions leading to an opening of the typical paddlewheel fragment at one of its edges. The monodentate triflate anions are connected to further [Mo₂] dumbbells leading to infinite anionic chains according to _∞¹[Mo₂(CF₃SO₃)_3/1(CF₃SO₃)_4/2]⁻. The charge balance is achieved by the alkaline metal ions that are additionally coordinated by triflic acid molecules. Theoretical investigations were preformed on the open paddlewheel fragment and are in good agreement with the experimental findings. According to DTA/TG measurements and the XRD investigations the decomposition of the compounds occurs in multiple steps and leads to MoO₂ and A₂MoO₄.