Central bond vibrations in 1,1 '-biadamantane

Raman (3100-10 cm(-1)) and IR (3100-200 cm(-1)) spectra of solid and dissol ved 1,1'-biadamantane were recorded. The molecular structure and vibrationa l normal modes were calculated using the semi-empirical AM1 Hamiltonian. Th e distortions from the tetrahedral geometry induced by linking two adamanta ne units are discussed. The potential barrier of 19.3 kJ mol(-1) for intern al rotation of two adamantyl cages around the central bond was determined b y calculations of heat of formation for fully relaxed structures at differe nt dihedral angles. The final scaled vibrational force field was obtained b y transferring the scale factors from parent adamantane. The normal mode di splacements are described in terms of adamantane normal mode displacements using the generalised harmonic mode scrambling approach. The central bond s tretching, torsion around the central bond and CCC deformations involving t he central bond are genuine 1,1'-biadamantane vibrations. The semi-rigid mo lecular model is qualitatively applied on lattice dynamics of 1,1'-biadaman tane in order to assign two Raman bands observed below 100 cm(-1) (C) 1999 Elsevier Science B.V. All rights reserved.