COMMENT ON THE STRUCTURE OF OSMIUM TETROXIDE-CHITOSAN COMPLEX

Reaction of an aqueous solution of osmium tetroxide with the chitosan polymer model, the oligomer tetradeca(β(1→4)2-amino-2-deoxyglucopyranose)-β(2→5)mannitol, afforded a brown solid, the structure of which was proposed to contain osmium imido groups, −N˭Os. The product showed a new, distinct absorption band at 850 cm−1 in the FTIR spectrum, while the 13C CP-MAS NMR spectrum showed a lower signal relative intensity ratio for C2:C3/5 compared with that in the NMR spectrum of the starting oligosaccharide due to a downfield shift of C2 where allylic to the -N˭Os bond. Results from quantum chemical calculations were used to compare computed properties of the previously described “osmium tetroxide-chitosan complex” in which osmium tetroxide was coordinated to chitosan amino ligands with single dative N→Os bonds, and the product prepared in this study, proposed to have covalently-bonded imido bonds between osmium and nitrogen. The consequences of multiple bonding of two chitosan N to the Os atom in the 5d 3 6s ...