A neutron diffraction study of [N(PPh3)2]+[B2H7]–·CH2Cl2 at 80 K

Abstract

The structure of the [B₂H₇]^– anion, reported by us earlier in an X-ray structure determination, has been analysed more accurately by neutron diffraction. Data were collected at 80 K on a sample of [N(PPh₃)₂]⁺[B₂H₇]^–·CH₂Cl₂ using the Brookhaven High Flux Beam Reactor. The essential results of the X-ray analysis are confirmed, with more accurate molecular parameters. The [B₂H₇]^– anion has a non-crystallographic C_s symmetry, with a bent geometry [B–H–B 127(2)°] and staggered terminal B–H bonds. Average terminal and bridging B–H bond lengths are 1.18(2) and 1.27(6)Å respectively, and the B ⋯ B distance is 2.27(1)Å. There is a slight asymmetry of the B–H–B bridge [B(1)–H 1.32(2), B(2)–H 1.21(2)Å], which is on the borderline of being significant. [N(PPh₃)₂]⁺[B₂H₇]^–·CH₂Cl₂ crystallizes in the triclinic space group P, with a= 9.633(1), b= 10.513(1), c= 16.938(1)Å, α= 90.599(7), β= 93.142(8), γ= 93.744(8)°, and Z= 2 at 80 K. The final R factor is 0.096 for the 1 479 reflections with F_o² > 3σ(F_o²).