Molecular structure and scaled quantum mechanical force fields of bis(dimethylamino)chloroborane, [(CH3)2N]2BCl, determined by gas-phase electron diffraction and molecular orbital calculations; and supplementary computations for [(CH3)2N]3B, (CH3)2NBCl2,

The molecular structure of bis(dimethylamino)chloroborane, [(CH3)2N]2BCl, has been determined by gas-phase electron diffraction (GED) at 320 K and by molecular orbital (MO) calculations at the HF, MP2, B3LYP, and B3PW91/6-311þþG** levels of theory. Vibrational analyses were carried out resulting in refined scaled quantum mechanical force fields based on literature data with some reassignments. B3PW91/6-311þþG** results were used for interplay with the GED structural investigation. All results were consistent with C2 molecular symmetry with slightly non-planar B-NC2 groups. The final results were obtained with shrinkage corrections for the skeletal non-bond distances. The two types of carbon atoms are identified by E and Z subscripts, referring to C–N–B–N, and the results with effects from correlation in the data and uncertainty in the s-scale (0.1%) included in the standard deviations, are: ra(B–Cl) ¼ 180.9(3) pm, ra(B–N) ¼ 142.6(3) pm, ra(N–CE) ¼ ra(N–CZ) þ 0.04 pm ¼ 145.6(2) pm, /N–B–N ¼ 124.7(3)8, /B–N–CE ¼ 123.0(5)8, /B–N–CZ ¼ 123.8(4)8, u (N–B–N–CE) ¼ 2161.2(12)8, and DuZ ¼ 187.2(16)8 giving u (N–B–N–CZ) ¼ DuZ þ u (N–B–N–CE) ¼ 26.4(11)8. This GED structure has a difference D(NC–BN) ¼ 3.0(3) pm. The locations of the hydrogen atoms relied heavily on MO-constraints using only one distance and one valence angle variable to give kraðC–HÞl ¼ 111:1ð2Þ pm; and k/N–C–Hl ¼ 110.6(4)8, and two independent torsional angles that in the final refinement were fixed to the computational values of u (B–N–CE–H) ¼ 8.08 and u (B–N–CZ–H) ¼ 6.08. The experimental and computational results are compared with literatureGEDresults for the three additional compounds in the [(CH3)2N]32nBCln ðn ¼ 0–3Þ series of molecules and own results from compatible computations for these molecules. The bond-length variations are discussed in relation to different possibilities for p back donation to the electron deficient trivalent boron atom and strengthening of the s-bond as the number of electronegative ligands attached to the central atom increases. q2003 Elsevier B.V. All rights reserved.