STRUCTURE, SPECTRA, AND REACTION ENERGIES OF THE ALUMINUM-NITROGEN (HAL-NH)(2) AND (H2AL-NH2)(2) RINGS AND THE (HAL-NH)(4) CLUSTER

Rings of four-coordinate aluminum and nitrogen are easily synthesized and well studied, as are clusters of four-coordinate Al and N. Only re cently, however, have rings that are derivatives of the model compound s (HAl-NH)(n) (n = 2, 3) with three-coordinate Al and N been synthesiz ed. Ab initio investigations of the structure, bonding, vibrational sp ectra, and reaction energies for the three-coordinate ring (HAl-NH)2, the four-coordinate ring (H2Al-NH2)(2), and the four-coordinate cluste r (HAl-NH)(4) are presented. Even in the absence of differences in ste ric factors, the four-membered ring has longer Al-N bonds than either the six-membered ring or the unassociated aluminum amide, H2Al-NH2. Th is is due to both rehybridization and pi interactions. Theoretical rea ction energies for formation of the (HAl-NH)(4) cluster from the (H2Al -NH2)(2) ring are consistent with intermolecular loss of hydrogen, or the necessity of surface catalysis.