A quantum chemical ab initio study of the polymerization to polyhydridophosphazenes

Quantum chemical ab initio calculations on the polymerization to polyhydridophosphazenes were carried out using mainly Møller-Plesset perturbation theory. Considering finite clusters of increasing size modeling the infinite system suggests that the isolated polyhydridophosphazenes prefer helical structures. A small bond alternation of 0.02 Å was found, whereas amino substituted hydridophosphazenes show a little larger bond alternation of 0.04 Å. Our study suggests that a substituent on the phosphorus atom with an electronegativity of about 3, e.g. amino substituents, makes the polymerization energetically favorable. This agrees excellently with the experiments on the polymerization of trisaminophosphines to polyhydridophosphazenes. The theoretical investigations also support a recently proposed polymerization mechanism.