CONFORMATIONAL STUDY OF HALOGEN-SUBSTITUTED AND HYDROGEN-SUBSTITUTED POLYTHIONYLPHOSPHAZENES USING DENSITY-FUNCTIONAL THEORY METHOD

The structure and conformational stability of polythionylphosphazenes is investigated by modeling single polymer chains with small mimics. T he model compounds are composed of repeat units of the corresponding p olythionylphosphazenes. Two of the model compounds have hydrogens and two have chlorines as substituents on phosphorus atoms. The substituen ts on sulfur may be either fluorine or chlorine. Fully geometry-optimi zed structures and energies of the stable conformations involving rota tions around the P-N bond near the sulfur are obtained using the densi ty functional theory method. The structural and conformational analyse s indicate that the rotation around the N-P bond leads to variations i n the bond lengths, the SNP bond angle openings, as well as couplings between dihedral angles in different conformations in all model compou nds. In addition, the conformational analysis suggests that the minima on the conformational potential energy surface in these compounds may be located in the vicinity of the following values of the NP-NS dihed ral angle: -50-degrees, 90-degrees (or 60-degrees), 180-degrees, and 2 40-degrees. It was found that the values of the conformational energy differences range between less than 1 to 5 kcal/mol. A comparison is m ade between the structural results obtained using the density function al theory and the ab initio molecular orbital theory for the global mi nimum structures. (C) 1995 John Wiley & Sons, Inc.