Strong N−X⋅⋅⋅O−N Halogen Bonds: A Comprehensive Study on N‐Halosaccharin Pyridine N‐Oxide Complexes

Abstract

A study of the strong N−X⋅⋅⋅−O−N+ (X=I, Br) halogen bonding interactions reports 2×27 donor×acceptor complexes of N‐halosaccharins and pyridine N‐oxides (PyNO). DFT calculations were used to investigate the X⋅⋅⋅O halogen bond (XB) interaction energies in 54 complexes. A simplified computationally fast electrostatic model was developed for predicting the X⋅⋅⋅O XBs. The XB interaction energies vary from −47.5 to −120.3 kJ mol−1; the strongest N−I⋅⋅⋅−O−N+ XBs approaching those of 3‐center‐4‐electron [N−I−N]+ halogen‐bonded systems (ca. 160 kJ mol−1). 1H NMR association constants (KXB) determined in CDCl3 and [D6]acetone vary from 2.0×100 to >108 m−1 and correlate well with the calculated donor×acceptor complexation enthalpies found between −38.4 and −77.5 kJ mol−1. In X‐ray crystal structures, the N‐iodosaccharin‐PyNO complexes manifest short interaction ratios (RXB) between 0.65–0.67 for the N−I⋅⋅⋅−O−N+ halogen bond.

Halogen Bonds of Halogen(I) Ions─Where Are We and Where to Go?

“…77 The outcome of the initial studies have been corroborated by further computational 45,78−80 and single-crystal X-ray diffraction 50,63 investigations. Halogen-bond symmetry may be broken using electron donors with different Lewis basicities 49,59,81,82 or through secondary interactions to only one of the two halogen-bonded Lewis bases. 50 If the Lewis basicities of the two coordinating electron donors do not differ drastically, slightly asymmetric complexes with a strong 3c4e bond are formed.…”

“…Complexes with mixed nitrogen/oxygen donor Lewis bases have been studied over the recent years. 81,82 The [N•••I•••O] − halogen-bond complex encompassing N-iodosuccinimide and acetate as Lewis bases has been crystallized and showed a linear geometry with d NI = 2.17 Å (R XB = 0.61) and d OI = 2.30 Å (R XB = 0.66). 101 81,82 The interaction energy was estimated to be up to 120 kJ/mol in CDCl 3 by measuring the association constants by NMR titrations (K a up to 10 8 M).…”

Halogen-Bonded Cocrystals of 1,3,5-Triiodo-2,4,6-trifluorobenzene and Structural Isomers of Benzoylpyridine

“…Most commonly used to date are acceptors containing nitrogen atoms, in particular as a part of an aromatic system, such as pyridine derivatives. 39−42 However, lately, there has been a growing interest in the design of halogen-bond acceptor molecules comprising accessible oxygen atoms such as P-oxides, 43−45 N-oxides, 46,47 cyclic ethers, 48,49 etc. Therefore, the study of halogen-bonding propensity of N,O-ambidentate acceptorsmolecules that contain both nitrogen and oxygen acceptor sitesis of considerable importance.…”

Halogen Bond Motifs in Cocrystals of N,N,O and N,O,O Acceptors Derived from Diketones and Containing a Morpholine or Piperazine Moiety

“…29,30 In recent years, they have been followed by a variety of other, mostly nitrogen or oxygen atom containing species, such as methoxy, 31−33 nitro, 34−37 hydroxyl, 32,33,38 and nitrile 32,39−41 functional groups, and oxygen atoms in Noxides. 42,43 Some recent studies also showcased the promising halogen bond acceptor potential of nitrogen atoms in piperazine 10 and nitrogen and oxygen atoms in morpholine 10,44 as well as the carbonyl oxygen atom. 34,45−48 So far, systematic studies of halogen bonding with these moieties were mainly limited to smaller building blocks.…”