Physical nature of interactions in ZnII complexes with 2,2′-bipyridyl : quantum theory of atoms in molecules (QTAIM), interacting quantum atoms (IQA), noncovalent interactions (NCI), and extended transition state coupled with natural orbitals for chemical valence (ETS-NOCV) comparative studies

摘要

In the present account factors determining the stability of ZnL, ZnL2, ZnL3 complexes (L = bpy,2,2-bipyridyl) were characterized based on various techniques: the Quantum Theory of Atoms inMolecules (QTAIM), energy decomposition schemes based on Interacting Quantum Atoms(IQA) and Extended Transition State coupled with Natural Orbitals for Chemical Valence (ETSNOCV).Finally, the Non-covalent Interactions (NCI) index was also applied. All methodsconsistently indicated that the strength of the coordination bonds, Zn–O, Zn–N, decreases fromZnL to ZnL3. Importantly, it has been identified that the strength of secondary intramolecularheteropolar hydrogen bonding interactions, CH•••O, CH•••N, increases when going from ZnL toZnL3. A similar trend appeared to be valid for the π -bonding as well as electrostatic stabilization.In addition to the above leading bonding contributions, all techniques suggested the existence ofvery subtle, but non-negligible additional stabilization from the CH•••HC electronic exchangechannel; these interactions are the weakest among all considered here. From IQA it was foundthat the local diatomic interaction energy, H,Hint E , amounts at HF to –2.5, –2.7 and –2.9 kcal mol–1for ZnL, ZnL2 and ZnL3, respectively (–2.1 kcal mol–1 for ZnL at MP2). NOCV-baseddeformation density channels showed that formation of CH--HC contacts in Zn-complexescauses significant polarization of (C–H) bonds, which accordingly leads to chargeaccumulation in the CH•••HC bay region. Charge depletion from (C–H) bonds were alsoreflected in the calculated spin-spin 1J(C–H) coupling constants, which decrease from 177.06 Hz(ZnL) to 173.87 Hz (ZnL3). This last result supports our findings of an increase in the localelectronic CH•••HC stabilization from ZnL to ZnL3 found from QTAIM, IQA, and ETS-NOCV.Finally, this work unites for the first time the results from four methods that are widely used fordescription of chemical bonding.