The crystal and molecular structures of [In(η5-P2C3But3)] are reported. He I and He II photoelectron (PE) spectra of [In(η5-P3C2But2)] and of [In(η5-P2C3But3)] are assigned by comparison with related systems and with the aid of density functional calculations of the ionisation energies (IE). In both cases the first PE band comprises ionisation from the ring π levels together with an ionisation from a Pσ orbital. The second band is due to ionisation from an In-ring antibonding orbital with In s character. Other Pσ ionisation bands lie at higher IE. Substitution of CBut by P within the five membered aromatic ring increases the IE of related bands. Geometry optimisation of the parent complexes [In(η5-P3C2H2)] and [In(η5-P2C3H3)] gave structural parameters in good agreement with the X-ray data. Attempts to find an energy minimum corresponding to η1-coordination were unsuccessful, the structures reverting to the η5-coordination mode. Bonding of the ring is principally due to overlap of the two upper occupied π orbitals with the In 5p orbitals. Some rehybridisation at the P atoms assists this overlap. Mulliken population analysis shows the In 5p occupation to be ca. half an electron in both cases.
