Characterisation of the torsion potential for ethylene ligands using inelastic neutron scattering

The inelastic neutron spectra of Zeise's salt K[PtCl3(C2H4)], H2O, Zeise's Dimer Pt2Cl4(C2H4)2, Cs[PtCl3(C2H4)] and Pd2Cl4(C2H4)2 have been measured and the principal feature in each case is assigned to the torsion of the ethylene group. The results from inelastic neutron scattering are compared with those from n.m.r. studies on related compounds and evidence is adduced for a metastable potential well in addition to the ground state well.Using certain approximations this paper presents the first experimentally determined energy values for the metastable and the ground state well depths in these salts. The torsion vibrations also reflect changes in the π-electron donor capacities of the metal atoms in the above salts.