The spontaneous interconversion between covalent forces and noncovalent counterparts remains an unexplained mystery to date. Here we have discovered a marvelous transformation between them through halogen bonding using NI3 as a prototype. Our results show that the interaction strength of the NI3 dimer is 7.01 kcal mol-1 , demonstrating that it is a quite strong halogen bond. Molecular orbital analyses indicate that the frontier molecular orbitals result from strong mixing of the fragment orbitals, which may be the electronic structure basis for interconversion. Further studies on a series of NI3 oligomers (5-, 10-, 15-, 20-, 26-, 30-mer) show that the interconversion occurs approximately at 26-mer on the basis on bond distance, ELF, etc.; the interconversion is a gradual transformation and not a sudden one. This study provides more insights into the halogen bonding and the high explosivity of NI3 containing species.
Keywords: NI3; covalent bonds; halogen bonds; localized molecular orbitals; non-covalent interactions.
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