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Halogen Bonding from a Hard and Soft Acids and Bases Perspective: Investigation by Using Density Functional Theory Reactivity Indices
Author(s) -
Pinter Balazs,
Nagels Nick,
Herrebout Wouter A.,
De Proft Frank
Publication year - 2013
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201202567
Subject(s) - natural bond orbital , hsab theory , chemistry , density functional theory , computational chemistry , non covalent interactions , halogen bond , atomic orbital , valence (chemistry) , fukui function , reactivity (psychology) , halogen , orbital overlap , orbital hybridisation , molecular orbital , crystallography , valence bond theory , molecule , electrophile , organic chemistry , alkyl , quantum mechanics , electron , physics , hydrogen bond , catalysis , medicine , alternative medicine , pathology
Halogen bonds between the trifluoromethyl halides CF 3 Cl, CF 3 Br and CF 3 I, and dimethyl ether, dimethyl sulfide, trimethylamine and trimethyl phosphine were investigated using Pearson’s hard and soft acids and bases (HSAB) concept with conceptual DFT reactivity indices, the Ziegler–Rauk‐type energy‐decomposition analysis, the natural orbital for chemical valence (NOCV) framework and the non‐covalent interaction (NCI) index. It is found that the relative importance of electrostatic and orbital (charge transfer) interactions varies as a function of both the donor and acceptor molecules. Hard and soft interactions were distinguished and characterised by atomic charges, electrophilicity and local softness indices. Dual‐descriptor plots indicate an orbital σ hole on the halogen similar to the electrostatic σ hole manifested in the molecular electrostatic potential. The predicted high halogen‐bond‐acceptor affinity of N‐heterocyclic carbenes was evidenced in the highest complexation energy for the hitherto unknown CF 3 I⋅NHC complex. The dominant NOCV orbital represents an electron‐density deformation according to a n→σ*‐type interaction. The characteristic signal found in the reduced density gradient versus electron‐density diagram corresponds to the non‐covalent interaction between contact atoms in the NCI plots, which is the manifestation of halogen bonding within the NCI theory. The unexpected CX bond strengthening observed in several cases was rationalised within the molecular orbital framework.