Structural features and molecular assembly of amorphous phosphazenic materials in the bulk-combined theoretical and experimental techniques: Tris-(2,2 '-dioxy-1,1 '-binaphthyl)cyclotriphosphazene

The structure and the assembly of tris-(2,2'-dioxy-binaphthyl)cyclotriphosp hazene {(+)-[N3P3(O2C20H12)(3)], DBNP, in the solid amorphous state was stu died using molecular dynamics (MD) including ad hoc quantum mechanically de rived force field (FF) parameters, in combination with the energy dispersiv e X-ray diffraction (EDXD) technique. The atom-atom radial distribution fun ction (RDF) curve obtained through the EDXD experiment revealed low intensi ty peaks not attributable to the intramolecular distances of the single mol ecule, but clearly featuring a low energy state of long-distance three-dime nsional assembly. The radial distribution functions (RDF) were calculated f or various models of DBNP submitted to theoretical MD simulations. Based on the comparison of theoretically calculated RDFs and those obtained from th e EDXD experiment, the predominant structural motif of the material in the bulk was found to have DBNP molecules laid one upon the other to form tubul ar nanostructures. These contain eight DBNP units each (length ca. 46 Angst rom) with two and three of these units aligned in parallel and held togethe r. The material can be represented as a bulk of tubular snake-like chains u ndergoing distortions with a step of eight DBNP units. The bending angles, that vary randomly, attain limited values sufficient to induce disorder and thus nonperiodic structure. The present application of MD simulations comb ined with EDXD data appear to be a general approach to solve for the first time otherwise intractable issues concerning structural features and assemb ly of molecular materials in the bulk.