The Solid State Structure of [B₁₀H₁₁]^- and Its Dynamic NMR Spectra in Solution

The structure of [PPh3(benzyl)][B10H11] was determined at −123 °C and 24 °C by single-crystal X-ray analyses. The B10 core of [B10H11]- is similar in shape to that of [B10H10]2-. The 11th H atom asymmetrically caps a polar face of the cluster and shows no tendency for disorder in the solid state. Variable temperature multinuclear NMR studies shed light on the dynamic nature of [B10H11]- in solution. In addition to the fluxionality of the cluster H atoms, the boron cage is fluxional at moderate temperatures, in contrast to [B10H10]2-. Multiple exchange processes are believed to take place as a function of temperature. Results of ab initio calculations are presented. Crystal data: [PPh3(benzyl)][B10H11] at −123 °C, P21/c, a = 9.988(2) Å, b = 18.860(2) Å, c = 15.072(2) Å, β = 107.916(8)°, V = 2701.5(7) Å3, Z = 4; [PPh3(benzyl)][B10H11] at 24 °C, P21/c, a = 10.067(5) Å, b = 19.009(9) Å, c = 15.247(7) Å, β = 107.952(9)°, V = 2775(2) Å3, Z = 4.