Zwitterionic iodonium species afford halogen bond-based porous organic frameworks

Demonstration of π-π Stacking at Interfaces: Synthesis of an Indole-Modified Monodisperse Silica Microsphere SiO2@IN

In the present study, a novel silane coupling agent, designated INSi, was synthesized via a facile synthetic route, incorporating indole-functional moieties. This agent was further employed for the surface modification of homemade silica nanomicrospheres (SMPs). The ensuing nanomicrosphere composite, denoted as SiO2@IN, exemplified pronounced interfacial π-π interactions. Optimization of the reaction conditions was conducted using the response surface optimization technique. Subsequent validation of interfacial π-π interactions was accomplished through a synergistic approach, integrating theoretical calculations and comprehensive analyses of spectral and morphological attributes exhibited by the SiO2@IN.

Hybrid 2D Supramolecular Organic Frameworks (SOFs) Assembled by the Cooperative Action of Hydrogen and Halogen Bonding and π⋯π Stacking Interactions

The cis- and trans-isomers of 6-(3-(3,4-dichlorophenyl)-1,2,4-oxadiazol-5-yl)cyclohex-3-ene-1-carboxylic acid (cis-A and trans-A) were obtained by the reaction of 3,4-dichloro-N'-hydroxybenzimidamide and cis-1,2,3,6-tetrahydrophthalic anhydride. Cocrystals of cis-A with appropriate solvents (cis-A‧½(1,2-DCE), cis-A‧½(1,2-DBE), and cis-A‧½C6H14) were grown from 1,2-dichloroethane (1,2-DCE), 1,2-dibromoethane (1,2-DBE), and a n-hexane/CHCl3 mixture and then characterized by X-ray crystallography. In their structures, cis-A is self-assembled to give a hybrid 2D supramolecular organic framework (SOF) formed by the cooperative action of O-H⋯O hydrogen bonding, Cl⋯O halogen bonding, and π⋯π stacking. The self-assembled cis-A divides the space between the 2D SOF layers into infinite hollow tunnels incorporating solvent molecules. The energy contribution of each noncovalent interaction to the occurrence of the 2D SOF was verified by several theoretical approaches, including MEP and combined QTAIM and NCIplot analyses. The consideration of the theoretical data proved that hydrogen bonding (approx. -15.2 kcal/mol) is the most important interaction, followed by π⋯π stacking (approx. -11.1 kcal/mol); meanwhile, the contribution of halogen bonding (approx. -3.6 kcal/mol) is the smallest among these interactions. The structure of the isomeric compound trans-A does not exhibit a 2D SOF architecture. It is assembled by the combined action of hydrogen bonding and π⋯π stacking, without the involvement of halogen bonds. A comparison of the cis-A structures with that of trans-A indicated that halogen bonding, although it has the lowest energy in cis-A-based cocrystals, plays a significant role in the crystal design of the hybrid 2D SOF. The majority of the reported porous halogen-bonded organic frameworks were assembled via iodine and bromine-based contacts, while chlorine-based systems-which, in our case, are structure-directing-were unknown before this study.

Dioxygen-halogen bonding exemplified by crystalline peroxosolvates of N,N'-bis(haloacetyl) bispidines

The halogen bonding in molecular crystals and supramolecular assemblies has been widely investigated. Special attention is given to the molecular structures capable of simultaneously exhibiting different types of non-covalent interactions, including conventional hydrogen bonds and halogen bonds. This paper systematically analyzes crystalline peroxosolvates of bispidine-based bis-amide derivatives, containing haloacetic acid residues, namely previously reported 1,1'-(1,5-dimethyl-3,7-diazabicyclo[3.3.1]nonane-3,7-diyl)bis(2-iodooethanone) peroxosolvate C13H20I2N2O2·H2O2 (1) and four new crystalline compounds, 1,1'-(1,5-dimethyl-3,7-diazabicyclo[3.3.1]nonane-3,7-diyl)bis(2-bromoethanone) peroxosolvate C13H20Br2N2O2·H2O2 (2), 1,1'-(9-hydroperoxy-9-hydroxy-1,5-dimethyl-3,7-diazabicyclo[3.3.1]nonane-3,7-diyl)bis(2-iodoethanone) peroxosolvate C13H20I2N2O5·0.5H2O2 (3), 1,1'-(9-hydroperoxy-9-hydroxy-1,5-dimethyl-3,7-diazabicyclo[3.3.1]nonane-3,7-diyl)bis(2-bromoethanone) peroxosolvate C13H20Br2N2O5·H2O2 (4), and 1,1'-(9-hydroperoxy-9-hydroxy-1,5-dimethyl-3,7-diazabicyclo[3.3.1]nonane-3,7-diyl)bis(2-chloroethanone) peroxosolvate C13H20Cl2N2O5·H2O2 (5). Compounds 2-5 were synthesized for the first time and their crystal structures were determined by single-crystal X-ray diffractometry (SCXRD). To the best of our knowledge, 3-5 are unprecedented crystalline hydrogen peroxide adducts of organic hydroperoxides (R-OOH). Short intermolecular contacts between halogen and hydroperoxo oxygen atoms were found in 1-3. The halogen bonding of C-I(Br) fragments with dioxygen species in compounds 1-3 as well as in the previously reported cocrystal of diacetone diperoxide with triodotrinitrobenzene (6) was identified through reduced density gradient analysis, Hirshfeld surface analysis, and Bader analysis of crystalline electron density. The interactions were quantified using the electron density topological properties acquired from the periodic DFT calculations and evaluated to lie in the range of 9-19 kJ mol-1. A distinctive spectral feature was revealed for this type of interaction, involving a red shift of the characteristic O-O stretching vibration by about 6 cm-1, which appeared in IR spectra as a narrow low-intensity band in the region 837-872 cm-1.

A Halogen-Bonded Organic Framework (XOF) Emissive Cocrystal for Acid Vapor and Explosive Sensing, and Iodine Capture

There is a strong and urgent need for efficient materials that can capture radioactive iodine atoms from nuclear waste. This work presents a novel strategy to develop porous materials for iodine capture by employing halogen bonding, mechanochemistry and crystal engineering. 3D halogen-bonded organic frameworks (XOFs) with guest-accessible permanent pores are exciting targets in crystal engineering for developing functional materials, and this work reports the first example of such a structure. The new-found XOF, namely TIEPE-DABCO, exhibits enhanced emission in the solid state and turn-off emission sensing of acid vapors and explosives like picric acid in nanomolar quantity. TIEPE-DABCO captures iodine from the gas phase (3.23 g g-1 at 75 °C and 1.40 g g-1 at rt), organic solvents (2.1 g g-1 ), and aqueous solutions (1.8 g g-1 in the pH range of 3-8); the latter with fast kinetics. The captured iodine can be retained for more than 7 days without any leaching, but readily released using methanol, when required. TIEPE-DABCO can be recycled for iodine capture several times without any loss of storage capacity. The results presented in this work demonstrate the potential of mechanochemical cocrystal engineering with halogen bonding as an approach to develop porous materials for iodine capture and sensing.

Halogen Bond-Involving Self-Assembly of Iodonium Carboxylates: Adding a Dimension to Supramolecular Architecture

We designed 0D, 1D, and 2D supramolecular assemblies made of diaryliodonium salts (functioning as double σ-hole donors) and carboxylates (as σ-hole acceptors). The association was based on two charge-supported halogen bonds (XB), which occurred between IIII sites of the iodonium cations and the carboxylate anions. The sequential introduction of the carboxylic groups in the aryl ring of the benzoic acid added a dimension to the 0D supramolecular organization of the benzoate, which furnished 1D-chained and 2D-layered structures when terephthalate and trimesate anions, correspondingly, were applied as XB acceptors. The structure-directing XB were studied using DFT calculations under periodic boundary conditions and were followed by the one-electron-potential analysis and the Bader atoms-in-molecules topological analysis of electron density. These theoretical methods confirmed the existence of the XB and verified the philicities of the interaction partners in the designed solid-state structures.

Two and three-dimensional halogen-bonded frameworks: self-assembly influenced by crystallization solvents

In this paper, two types of solid phase 2D and 3D XBOFs were selectively constructed from identical building blocks of tetraphenylmethane tetrapyridine derivative and 1,4-diiodotetrafluorobenzene by changing the crystallization solvent. This 3D XBOF is a novel hybrid supramolecular organic framework with the synergistic control of hydrogen and halogen bonds.

Noncovalent Chelation by Halogen Bonding in the Design of Metal-Containing Arrays: Assembly of Double σ-Hole Donating Halolium with CuI-Containing O,O-Donors

Five new copper(I) complexes─composed of the paired dibenzohalolium and [CuL₂]^- (L = 1,2,4-oxadiazolate) counterions in which O,O-atoms of the anion are simultaneously linked to the halogen atom─were generated and isolated as the solid via the three-component reaction between [Cu(MeCN)₄](BF₄), sodium 1,2,4-oxadiazolates, and dibenzohalolium triflates (or trifluoroacetates). This reaction is different from the previously reported Cu^I-catalyzed arylation of 1,2,4-oxadiazolones by diaryliodonium salts. Inspection of the solid-state X-ray structures of the complexes revealed the strong three-center X···O,O (X = Br, I) halogen bonding occurred between the oxadiazolate moieties and dibenzohalolium cation. According to performed theoretical calculations, this noncovalent interaction (or noncovalent chelation) was recognized as the main force in the stabilization of the copper(I) complexes. An explanation for the different behavior of complexes, which provide either chelate or nonchelate binding, is based on the occurrence of additional -CH₃···π interactions, which were also quantified.

Ligand-free Ullmann-type arylation of oxazolidinones by diaryliodonium salts

The arylation of azaheterocycles can be considered as one of the most important processes for the preparation of various biologically active compounds. In the present work, we describe a method for the copper-catalyzed N-arylation of hindered oxazolidinones using diaryliodonium salts. The method succeeds in good to excellent yields for the arylation of 4-alkyloxazolidinones, including sterically hindered isopropyl- and tert-butyl-substituted. The efficiency of the method was demonstrated for a wide range of diaryliodonium salts - symmetric and unsymmetric as well as ortho-substituted derivatives. The developed approach will provide an important contribution in the development and preparation of novel drugs and bioactive molecules containing oxazolidinone moieties.

The importance of tetrel bonding interactions with carbon in two arrestive iso-structural Cd(ii)-Salen coordination complexes: a comprehensive DFT overview in crystal engineering

In this article, we describe the serendipitous synthesis of two remarkable iso-structural Cd(ii)-Salen complexes [L₂Cd₄(OAc)₂(NCS)₂] in the presence of H₂L and NaSCN {where L = L¹ (N,N'-bis(3-methoxysalicylidene)-1,2-diaminopropane) and L = L² (N,N'-bis(3-methoxysalicylidene)-ethylenediamine) in 1 and 2, respectively}. The complexes were characterized by using elemental analysis, SEM-EDX, PXRD, spectroscopy, and X-ray crystallography. The X-ray crystal structure revealed that both complexes crystallize in the orthorhombic space group Pbcn, with unit cell parameters: a = 20.758(6), b = 11.022(3), c = 21.396(6) Å, V = 4895(2) ų, and Z = 4. The inner N₂O₂ and outer O₄ compartments are essentially occupied by two different Cd(ii) metal ions resulting from the de-protonated form of the ligand (L^2-) with the Cd(1) metal ions adopting a capped octahedral geometry. At the same time, Cd(2) assumes a distorted trigonal prismatic geometry. The solid-state crystal structure involves various non-covalent supramolecular interactions delineated by Hirshfeld Surface and 2D fingerprint plot analysis. Noteworthily, interesting S⋯H, O⋯H, and N⋯H contacts were observed, which have identical percentages in both complexes. The sparse tetrel bonding interactions in the complex, involving the CH₃ group, were evaluated in a new dimension of DFT. We observed this privileged bonding landscape that leads to the formation of self-assembled dimers in the crystal complexes. DFT-based MEP, RDG surface, NBO, and QTAIM/NCI plot investigation quantified such unique tetrel bonding interactions.