EPR SPECTROSCOPIC STUDY OF THE REACTION OF AL AND GA ATOMS WITH CO2 AND CS2 IN A ROTATING CRYOSTAT

Al and Ga atoms have been allowed to react with CO2, (CO2)-C-13, CS2 a nd (CS2)-C-13 in a rotating cryostat at 77 K. The paramagnetic product s resulting from these reactions have been investigated by electron pa ramagnetic resonance (EPR) spectroscopy. The two main products from th e reaction of Al and CO2 are a mononuclear, mono-ligand complex, Al[CO 2], with a small Al and a large C-13 coupling constant and a species, C, with unresolved Al and C-13 coupling constants. There is also evide nce for the formation of three minor mononuclear complexes, A', A'' an d B, with [a](Al) values of ca. 34, 105 and -71 MHz, respectively. The highly anisotropic nature of the a tenser observed for B (\a(parallel to)(Al)\) < \a(perpendicular to) (Al)\) indicates that a substantial amount (ca. 78%) of the unpaired spin density resides in an Al 3p orbi tal. Ga atoms and CO2 give two mononuclear complexes with unresolved C -13 coupling constants and Ga-69 coupling constants of -282 and 12 MHz , respectively. Both Al and Ga react with CS2 to give species with sma ll metal and unresolved C-13 coupling constants. Structures are propos ed for these complexes, and in the case of Ga and CO2, the spin densit ies obtained from the experimentally derived EPR parameters are compar ed with those obtained by a local spin density functional method.