Central bond vibrations in 1,1′-biadamantane

Abstract

Raman (3100–10cm−1) and IR (3100–200cm−1) spectra of solid and dissolved 1,1′-biadamantane were recorded. The molecular structure and vibrational normal modes were calculated using the semi-empirical AM1 Hamiltonian. The distortions from the tetrahedral geometry induced by linking two adamantane units are discussed. The potential barrier of 19.3kJmol−1 for internal rotation of two adamantyl cages around the central bond was determined by calculations of heat of formation for fully relaxed structures at different dihedral angles. The final scaled vibrational force field was obtained by transferring the scale factors from parent adamantane. The normal mode displacements are described in terms of adamantane normal mode displacements using the generalised harmonic mode scrambling approach. The central bond stretching, torsion around the central bond and CCC deformations involving the central bond are genuine 1,1′-biadamantane vibrations. The semi-rigid molecular model is qualitatively applied on lattice dynamics of 1,1′-biadamantane in order to assign two Raman bands observed below 100cm−1.