Study of the Molecular Geometry, Electronic Structure, and Thermal Stability of Phosphazene and Heterophosphazene Rings with ab Initio Molecular Orbital Calculations

Abstract

Ab initio molecular orbital calculations at the MP2/6-31G level of theory have been used to study the molecular geometry, electronic structure, and the thermal stability of six-membered phosphazene and heterophosphazene rings. The studies included the phosphazene ring [NPCl(2)](3), the carbophosphazene ring [(NCCl)(NPCl(2))(2)], and three thionylphosphazene rings [(NSOX)(NPCl(2))(2)] (X = F, Cl) and [(NSOF)(NPF(2))(2)] and their cations [(NPCl)(NPCl(2))(2)](+), [(NC)(NPCl(2))(2)](+), and [(NSO)(NPY(2))(2)](+) (Y = F, Cl). The ring skeleton of the phosphazene ring, the carbophosphazene ring and of all cation rings adopt a planar conformation; the ring skeletons of the thionylphosphazene rings adopt an envelope conformation. The valence electron charge density of the molecules indicates strong charge separations along their skeleton and is in agreement with Dewar's island delocalization model. The electrostatic potential in the vicinity of the neutral heterophosphazene rings which results from their electronic structure, and the position of the HOMO indicate that a heterolytic cleavage of a ligand and the opening of the ring involving a reaction with a electrophilic cation will most likely occur at the nitrogen atoms close to the heteroatom. The thermal stability of the phosphazene ring with respect to a cleavage of chlorine from phosphorus and the thermal stability of the heterophosphazene rings with respect to the cleavage of the halogen ligand bonded to the heteroatom were studied with several model reactions. Most of the reactions are exothermic. A comparison of isodesmic reactions shows that the thionylphosphazenes molecules are the least thermally stable rings with respect to ionization and that the carbophosphazene molecules are the most thermally stable rings with respect to ionization. The energy gains during the ionization reaction of the rings correlate well with the conformational changes which occur during the reactions.

Thin cyclomatrix polyphosphazene films: interfacial polymerization of hexachlorocyclotriphosphazene with aromatic biphenols

“…4,5 Heteroatoms, such as carbon or sulfur, could be introduced into the polymers backbone resulting in polyheterophosphazenes. [6][7][8] Besides linear poly-phosphazes, star, dendritic, block copolymeric, cyclolinear, and cyclomatrix architectures have been synthesized. 9,10 A versatile building block for the preparation of materials based on phosphazenes is the cyclic phosphazene trimer hexachlorocyclotriphosphazene [NPCl 2 ]3, HCCP.…”

Silver Complexes of Cyclic Hexachlorotriphosphazene

“…[8] Cyclic phosphazenes such as P 3 N 3 (OC 6 H 4 CF 3 ) 4 (OC 6 H 4 F) 2 [9] are used as additives to lubricants. [10] Simple (PNX 2 ) 3 phosphazenes (X = H, F, Cl, NH 2 ) were studied by DFT and ab initio calculations, [9,[11][12][13][14][15][16] as well as normal coordinate analyses. [17][18][19][20][21] These investigations were also sparked by the special electronic structure of the phosphazene rings.…”

“…[17][18][19][20][21] These investigations were also sparked by the special electronic structure of the phosphazene rings. [11,13,16,22,23] In the halogen-substituted P 3 N 3 X 6 cyclophosphazenes the basicity of the ring nitrogen atom is very low. Therefore, little is known about the complexing abilities of the P 3 N 3 X 6 halophosphazenes.…”

“…For none of the P 3 N 3 X 6 complexes is a crystal structure known. Nevertheless, Lewis acid-base complexes of hexachlorotriphosphazene are relevant, since they are thought to play a key role in the polymerization to poly(dichlorophosphazene) [2,5,11,14,31] with intermediate formation of the P 3 N 3 Cl 5 + ion. In this work we focused on the reaction of Ag + with P 3 N 3 Cl 6 .…”

Substitution Effects on Reactivity of N-Acyl-2-amino-2-desoxyglucopyranoses. Quantum Chemical Study

“…The N-phthalimidoalkanoyl substitution for 4-8 leads to smaller band gap than N-acetyl, N-ethanoyl substitution for 2 and 3 respectively, since the LUMO energy for 4-8 is lowered more than for compounds with N-acetyl, N-ethanoyl moieties 2, 3. Sella et al and Sawicka et al proposed arguments to explain the observed easier nucleophilic ring opening and cleavage reactions [8][9][10]. One can therefore identify for N-acyl-AGs 2-8 the low-lying LUMO, as a site will be most likely involved in reactions with nucleophiles.…”