Testing the Limits of the 18-Electron Rule: The Gas-Phase Carbonyls of Sc+ and Y

Scandium and yttrium carbonyl cations produced in the gas phase via laser vaporization are mass selected and studied with infrared laser spectroscopy in the C–O stretching region. Mass spectra, ion fragmentation behavior, and infrared spectra, complemented by computational chemistry, establish the coordination numbers and structures of these complexes. Sc+ does not form the eight-coordinate 18-electron complex but instead produces a 16-electron seven-coordinate species. However, Y+ forms the anticipated eight-coordinate structure. Density functional theory computations provide structures and corresponding vibrational spectra for these complexes. Sc(CO)7 + has a C3v capped octahedral structure, while Y(CO)8 + forms a D4d square antiprism. The C–O stretches at 2086 and 2087 cm–1 for Sc(CO)7 + and Y(CO)8 +, respectively, are among the most red-shifted frequencies measured for any transition metal carbonyl cation.