Electronic Structure of N₂P₂ Four‐Membered Rings

Abstract

The biradicaloid character of the ground‐state structures of N2P2 rings is studied by using the high‐level ab initio multiconfigurational CASPT2/CASSCF method. In order to obtain accurate descriptors, we combine two criteria: 1) singlet–triplet energy gaps and 2) relative values of the occupation numbers for bonding and antibonding orbitals associated with the radical sites. The singlet–triplet energy gaps, the occupation numbers of antibonding‐like orbitals, and the weights of the main configuration state functions (CSFs) of the ground‐state wavefunctions, that is, Ψ(1A1), are used to derive the biradicaloid character that ranges from 10–15 %.

Electronic Structure of N2P2 Four-Membered Rings and the Effect of Their Ligand Coordination to M(CO)5 (Cr, Mo, and W)

“…However, due to the presence of transition metals and the size of the system, we have optimized the complexes without symmetry constraints in their lowest singlet and triplet states at the B3LYP/6-311+G* level of theory. We have previously demonstrated that singlet–triplet energy gaps are accurately reproduced at this level of theory for unsubstituted P 2 N 2 H 2 rings . Herein we extend this study to substituted P 2 N 2 (CH 3 ) 2 rings 1 and 2 .…”

“…In Figure S1 (see SI), the main geometrical parameters of the S 0 and T 1 structures are collected together with some energetic results. It should be mentioned that the biradicaloid character of compounds 1 and 2 has been previously studied using only the B3LYP singlet–triplet energy gaps . The S 0 optimized geometry of the N 2 P 2 core of compound 1 is almost identical to the experimental core obtained in the X-ray structure of biradicaloid [P(μ-NTer)] 2 in terms of planarity, distances, and angles.…”

“…We have previously demonstrated that singlet−triplet energy gaps are accurately reproduced at this level of theory for unsubstituted P 2 N 2 H 2 rings. 16 Herein we extend this study to substituted P 2 N 2 (CH 3 ) 2 rings 1 and 2.…”

“…These investigations open new perspectives in molecular and materials chemistry. As part of our long-standing interest in small P-heterocycles possessing P–N bonds, − we have recently reported the properties of various biradicaloid N 2 P 2 heterocycles due to their interest in preparative phosphorus–nitrogen chemistry. , Analyzing the electronic structure of several N 2 P 2 -core four-membered rings (CASPT2/CASSCF calculations), we have demonstrated that they show some amount of biradicaloid character. In particular, the [(PH)N] 2 ring (unpaired electrons on the nitrogen atoms) has more biradicaloid character than the [PN(H)] 2 (unpaired electrons on the phosphorus atoms) ring.…”

The Niecke Biradicals and Their Congeners – The Journey from Stable Biradicaloids to Their Utilization for the Design of Nonlinear Optical Properties

“…A peculiarity is presented by the species of type II , which were experimentally prepared by the group of Schulz and summarized in a recent reports . For the latter category interesting calculations appeared, the reader may be referred to this pertinent discussion . Since the aim of this review is a discussion of the Niecke‐type compounds further analysis on the homologues Ia and Ia(P) will not be given here.…”