Role of donor‐acceptor functional groups in N3P3 cyclic‐triphosphazene backbone. Unraveling bonding characteristics from natural orbitals within an extended transition state‐natural orbital for the chemical valence scheme

• Published in: International journal of quantum chemistry 2020-01, Vol.120 (1), p.n/a
• Main Authors: Linares‐Flores, Cristian, Ramirez‐Tagle, Rodrigo, Rojas‐Poblete, Macarena, Arratia‐Perez, Ramiro, Muñoz‐Castro, Alvaro, Guajardo‐Maturana, Raul
• Format: Article
• Language: English
• Subjects: Backbone; Bond strength; Bonding strength; Chemistry; cyclic‐phosphazene; Electrons; ETS‐NOCV; Functional groups; Ligands; Nitrogen dioxide; Organic chemistry; Phosphazene; Physical chemistry; Quantum physics; sigma and pi contributions
• ISSN: 0020-7608; 1097-461X
• DOI: 10.1002/qua.26057

The formation of cyclophosphazenes containing several ligands or substituent groups gives rise to an attractive derivative set, for development of novel applications, with variable properties. Here, it is possible to unravel the role of different functional groups attached to the N3P3 backbone, to reach a better understanding of the bonding character in the cyclic [─P─N─] skeleton. We employed the extended transition state‐natural orbital for the chemical valence scheme to unravel the σ and π orbital kernels that are involved in the assembling of such structures, by varying the acceptor‐donor characteristics of the ─CF3, ─NO2, ─COOH, ─CN, ─NH2, ─OH, and ─OCH3 groups, where ─NO2 behaves as a stronger electron‐withdrawing substituent rather than ─CF3, ─COOH, and ─CN, denoting that the nature of the ligand‐phosphazene interaction contributes to some degree to the bond strength of the cyclic [─P─N─] backbone. Our results reveal that the electron‐withdrawing ─NO2 group leads to higher σ and π [─P─N─] orbital‐energy contributions, which is reflected in a shortening of the [─P─N─] distance, contrasting with the case of electron‐donating groups such as ─NH2, ─OH, and ─OCH3 within the phosphazene set. These insights allow further variation and modulation of the bonding in the [─P─N─] ring. This insight offers the novel interpretation of the molecular structure of the cyclic‐phosphazene compounds. This takes advantage of an energy decomposition scheme that allows for evaluation of the attractor/donating ability of different substituent's groups and their incoming contributions that imply variations in the electronic structure of the phosphazene ring. Such a finding leads to a better understanding of the molecular properties and applications of these interesting systems.