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Updated: Aug 20, 2026

Photoelectron Imaging of Anions Illustrated by 310 Nm Detachment of F−
Published on: July 27, 2018
Donor-acceptor properties of isonitriles studied by photoelectron spectroscopy and electron transmission spectroscopy
István Pál Csonka1, László Szepes, Alberto Modelli
1Department of General and Inorganic Chemistry, Eötvös Loránd University, Pázmány Péter sétány 1/a, H-1117 Budapest, Hungary. csip@ludens.elte.hu
Abstract:
Some alkyl and aryl isonitriles, considered as CO analogue sigma-donor and pi-acceptor ligands in transition metal chemistry, were studied by means of HeI photoelectron spectroscopy and electron transmission spectroscopy, in order to evaluate their donor-acceptor properties from the measured ionization energies (IE) and vertical electron attachment energies (VAE). The investigated molecules were 2-propyl, 1-butyl, tert-butyl, 1-pentyl, cyclohexyl, 2,6-dimethylphenyl, 4-methoxyphenyl and 4-chorophenyl isonitrile. By interpreting the spectra on the basis of literature data and quantum chemical calculations, the spectral features associated with the molecular orbitals mainly involved in coordination and back-donation were identified. The results show that the IE (10.62-10.95 eV) of the sigma electron pair (n(c)) responsible for the sigma-donor capability is substantially lower than that of CO. The VAEs of the empty pi* orbitals involved in the d/pi* back-donation indicate that aryl isonitriles are better acceptors (VAE <0.3 eV) than their aliphatic counterparts (VAE >2.7 eV). In the case of aryl derivatives, the pi-donor ability could also play some role in metal-ligand bonding (IE 8.74-9.34 eV). Isonitrile coordination characteristics are also compared with those of CO, N(2) and CH(3)CN.
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