THE MICROWAVE SPECTRUM, STRUCTURE AND DIPOLE MOMENT OF 2,4 DICARBAHEPTABORANE (7)

Author Institution: Space Sciences Division, Jet Propulsion Laboratory, California Institute of Technology; Department of Chemistry, University of Southern CaliforniaThe microwave spectra of all monosubstituted carbon and boron isotopic forms, and one di-substituted boron isotopic form of 2,4-dicarbaheptaborane (7) have been analyzed. The skeletal boron and carbon atomic coordinates determined from the rotational constants show that the molecule is a pentagonal bipyramid with bond distances and angles as follows: [FIGURE]$d[C(2)-B(6) ] 1.5627 {\AA} \pm 0.005\angle [C(2)-B(3)-C(4) ] = 99 52^{\prime} \pm 30' d[C(2)-B(3) ] 1.5455 \angle [B(3)-C(4)-B(5) ] = 116 51^{\prime} d[C(2)-B(1) ] 1.7077 \angle [C(4)-B(5)-B(6) ] = 103 13^{\prime} d[B(5)-B(6) ] 1.6508 \angle [B(1)-B(3)-B(7) ] = 79 42^{\prime} d[B(1)-B(5) ] 1.8146 d[B(1)-B(3) ] 1.8177$ The two carbon atoms lie in the pentagonal base plane and are separated by one boron atom. The two apex boron atoms appear to lie on, or very near to the c axis which is perpendicular to the pentagonal base. The a and b coordinates of these boron atoms are not well determined. The dipole moment, which lies along the a axis in the pentagonal base, is $1.33 \pm 0.03 D$