YUXIU LEI, JUNG SUP LEE AND DONG-SHENG YANG, Department of Chemistry, University of Kentucky, Lexington, KY 40506-0055.
Al- and Cu-ethylenediamine (C2N2H8) complexes were generated in supersonic molecular beams, and their C-H and N-H stretching modes were measured by resonant infrared-ultraviolet two-photon ionization and depletion spectroscopy. The spectrum of Al-ethylenediamine displayed three C-H stretching frequencies of 2880, 2936, and 2946 cm-1, whereas that of Cu-ethylenediamine exhibited five such vibrations with frequencies of 2880, 2921, 2931, 2951, and 2967 cm-1. In contrast, only two N-H stretches were identified for each of the two complexes, which were 3320 and 3392 cm-1 for Al and 3275 and 3360 cm-1 for Cu. These experimental spectra were compared to the prediction of density functional theory calculations and to the infrared spectrum of the free ligand. From these comparisons, a cyclic bidentate structure was identified for Al-ethylenediamine, and a hydrogen-bonded monodentate structure was determined for the corresponding Cu species. This study was consistent with the previous work of pulsed-field ionization electron spectroscopy of these complexes.