Rotational spectrum of thiophene center dot center dot center dot ClF and the role of thiophene as a pi- or n-electron pair donor in weakly bound complexes

Rotational constants, centrifugal distortion constants and all five indepen dent components chi(aa), chi(bb) - chi(cc), chi(ab), chi(ac) and chi(bc) of the Cl nuclear quadrupole coupling tensor chi(alpha beta) have been determ ined for thiophene ... (ClF)-Cl-35 and thiophene ... (ClF)-Cl-37. A method for determining the geometry of this complex of C-1, symmetry is presented which uses the direction cosines theta(az), theta(bz) and theta(cz) (z is t he ClF axis), determined by diagonalisation of the chi(alpha beta) tensor, in combination with principal moments of inertia. Four geometries of thioph ene ... ClF are consistent with the observed quantities, but each has ClF i nteracting with the pi-electron system on one face of the thiophene ring. ( C) 1998 Elsevier Science B.V. All rights reserved.