Abstract
Hexamethylenetetramine (HMTA) and N-haloimides form two types of short (imide)X···N and X–X···N (X = Br, I) halogen bonds. Nucleophilic substitution or ligand-exchange reaction on the peripheral X of X–X···N with the chloride of N-chlorosuccinimide lead to Cl–X···N halogen-bonded complexes. The 1:1 complexation of HMTA and ICl manifests the shortest I···N halogen bond [2.272(5) Å] yet reported for an HMTA acceptor. Two halogen-bonded organic frameworks are prepared using 1:4 molar ratio of HMTA and N-bromosuccinimide, each with a distinct channel shape, one possessing oval and the other square grid. The variations in channel shapes are due to tridentate and tetradentate (imide)Br···N coordination modes of HMTA. Density Functional Theory (DFT) studies are performed to gain insights into (imide)X···N interaction strengths (ΔEint). The calculated ΔEint values for (imide)Br···N (−11.2 to −12.5 kcal/mol) are smaller than the values for (imide)I···N (−8.4 to −29.0 kcal/mol). The DFT additivity analysis of (imide)Br···N motifs demonstrates Br···N interaction strength gradually decreasing from 1:1 to 1:3 HMTA:N-bromosuccinimide complexes. Exceptionally similar charge density values ρ(r) for N–I covalent bond and I···N non-covalent bond of a (saccharin)N–I···N motif signify the covalent character for I···N halogen bonding.
Highlights
Halogen bonding, an attractive interaction between the electrophilic region associated with a halogen [X] and a nucleophile [B] forming X···B non-covalent interaction (Desiraju et al, 2013), was recognized by Colin over one and a half centuries ago (Colin, 1814)
HMTA and five different N-haloimides, namely Nchlorosuccinimide (NCS), N-bromosuccinimide (NBS), N-iodosuccinimide (NCS), N-bromophthalimide (NBP), and Niodosaccharin (NISac), were used to prepare 13 halogen-bonded complexes 1–13 of composition types [HMTA]·[dihalogen]n and [HMTA]·[N-haloimide]n (Scheme 1). [HMTA]·[dihalogen]n is of two types: complexes 1, 3, and 5, which contain homo-halogen X–X···N (X = Br, I) motifs, and complexes 2, 4, and 6 comprising hetero-halogen Y–X···N (Y = Cl, X = Br, I) motifs
We investigated Y–X···N (X = Br, I and Y = N, Cl, Br, I) halogen bonds in 13 X-ray crystal structures obtained from HMTA and N-haloimides
Summary
An attractive interaction between the electrophilic region associated with a halogen [X] and a nucleophile [B] forming X···B non-covalent interaction (Desiraju et al, 2013), was recognized by Colin over one and a half centuries ago (Colin, 1814). Crystal engineering studies help promote a better understanding of the X···N(sp2) X-bonding, and their structures have applications ranging from chemical and optical (Christopherson et al, 2018; Zhuo et al, 2018; Huang et al, 2019; Li et al, 2020) to the preparation of intriguing topologies. The control over the bidentate mode depends on the HMTA itself while the tetradentate relies heavily on the donor, solvents, hydrogen bonds (HBs), and packing forces (Lemmerer, 2011). Crystallization experiments involving HMTA and dihalogens, e.g., iodine, often generate an acidic solvent medium yielding undesired HB complexes of the sort [HMTA-H]+·I−n rather than desired halogen-bonded structures [HMTA]·[I2]n (Tebbe and Nagel, 1995b). Many other fundamental structural features of HMTA are unknown, and their synthetic and structural rationale could provide useful groundwork in self-assembly design and even pave the way to the rational design of materials
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
