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| The planar tetracoordinate nitrogen (ptN) has been successfully extended as a new branch of planar chemistry in both theory and experiment. As the simplest ptN, the penta-atomic species, i.e., pptN (e.g., NAl4-), is known to have the "delocalized" molecular environment with the single bonding between the central N and the ligand. In this paper, through the extensive isomeric search of a series of group V-based systems NXAl3+ (X=N, P and As) in both singlet and triplet electronic states at the B3LYP/6-311+G(d) level, we report a class of novel pptN with unique chemical bonding, i.e., the central nitrogen and the connected ligand X (X=N, P and As) effectively form a highly "localized" N-X multiple bonding, as confirmed by the aug-cc-pVTZ-B3LYP and MP2 calculations. The high-level CCSD(T)/aug-cc-pVTZ energetic calculations show that the three pptN species each have appreciable kinetic stability against structural transformation and fragmentation, which is confirmed by the Born-Oppenheimer molecular dynamics calculations. In particular, the pptN isomer with X=P, i.e., NPAl3+, is the corresponding global minimum. Thus, we propose that the three pptN isomers can be realized via the mass spectroscopic techniques. Possible formation pathways of the three pptNs are discussed. The present work demonstrates that the frequently used concept "localization vs delocalization" in organic chemistry can also be transplanted to the exotic planar chemistry like pptN. |
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| Keywords:planar tetracoordinate nitrogen;localization;multiple bonding |
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