Isonitrile ligand properties as studied by He I/He II photoelectron spectroscopy

A new series of isonitrile-substituted cobalt tricarbonyl nitrosyl (Co(CO)2(NO)CNR, R = Me, Et, nPr, iPr, nBu, nPe, CH2Si(CH3)3) has been synthesized, and their He I ultraviolet photoelectron spectra are reported. The assignment of the bands in the low energy part of the spectra was performed with the aid of DFT calculations. The first vertical ionization energies of the complexes were found to be 7.73 (CNMe), 7.58 (CNEt), 7.59 (CNnPr), 7.70 (CNnBu), 7.67 (CNnPe), 7.77 (CNiPr), and 7.54 ± 0.03 eV (CNCH2Si(CH3)3). In the case of nPr- and CH2Si(CH3)3- substitutions, He II photoelectron spectra were also recorded. The relative importance of electronic and steric effects of the isonitrile ligands, as a function of the size of group –R, is discussed.