Crystallographic studies of the boron–nitrogen bond in aminoboranes. Part I. The crystal and molecular structure of 1,8,10,9-triazaboradecalin

Abstract

Crystals of 1,8,10,9-triazaboradecalin are monoclinic, a= 18·009, b= 5·134, c= 8·655 Å, β= 93·57°, space group P2₁/n with four molecules in the unit cell. The atomic positions have been determined by least-squares refinement of X-ray diffraction data. The molecular shape is closest to that of a distorted naphthalene. The central part of the molecule comprising the BN₃ group and the carbon atoms in positions 4 and 5 is planar. Atoms 2 and 7 lie 0·2 Å above this plane and atoms 3 and 6 0·5 Å below it, so that the molecular symmetry is close to m(C_s) with the mirror plane containing the B–N bond common to both rings. The mean B–N bond length is 1·421 Å. The molecular structure is discussed in terms of π-bonding between boron and the three nitrogen atoms and a B–N bond order of 1·3 has been deduced from molecular orbital calculations.