DYNAMICS OF MOLECULAR-HYDROGEN IN THE COMPLEX TRANS-[FE(ETA-2-H-2)(H)(PPH2CH2CH2PPH2)2]BF4 IN THE SOLID-STATE AS REVEALED BY NEUTRON-SCATTERING EXPERIMENTS

The vibrational spectrum of the Fe(η2-H2)H fragment in trans-[FeH(H2)(PPh2CH2CH2PPh2)2]BF4 has been obtained by inelastic neutron scattering in the range 200–1000 cm−1. High-resolution neutron spectroscopy was also utilized to observe the rotational tunnel splitting of the librational ground state of the dihydrogen ligand at 2.1 cm−1. This and the torsional transitions assigned at 225 and 255 cm−1 are consistent with a modulated double-minimum potential for rotation with one angular degree of freedom. The resulting barrier to rotation of about 2.3 kcal/mol is discussed in terms of its origin in electronic and steric factors and compared with similar results on other molecular hydrogen complexes. © 1990, American Chemical Society. All rights reserved.