Systematic Study of Podand Molecules for Synergistic Halogen and Hydrogen Bond-Driven Anion Recognition in the Solid State.

The increasing demand of species for the efficient capture and sensing of anions benefits from a systematic study of anion binding capabilities in the solid state. This work reports a detailed crystallographic study of ten structurally related podands and shows that these charged receptors bind anions with a combination of charge-assisted halogen and hydrogen bonds. Computational tools helped in highlighting the role of the different involved interaction and afforded possible design principles for the design of improved podands.

Tuning of Ionic Liquid Crystal Properties by Combining Halogen Bonding and Fluorous Effect.

We report halogen-bonded complexes between 1-polyfluoroalkyl-3-alkylimidazolium iodides and mono-iodoperfluoroalkanes of different chain lengths or di-iodoperfluorooctane. F NMR analyses revealed that the preferred stoichiometry between the donors and acceptors is 1 : 1 in the cases of the mono-iodoperfluoroalkanes, and 2 : 1 with di-iodoperfluorooctane, as a result of the monodentate behavior of the iodide anion (halogen bond acceptor). Single crystal X-ray diffraction analyses showed the presence of a perfluorinated superanion, which interdigitates with the cation fluorinated chains, favoring the formation of lamellar structures.

The diiodomethyl-sulfonyl moiety: an unexplored halogen bond-donor motif.

Herein, we report the crystal structures of the antimicrobial agent diiodomethyl-p-tolylsulfone and of three halogen bonded co-crystals demonstrating that the bioactive moiety -SO2CHI2 can function as a quite effective halogen bond based motif in the solid state and in solution, namely demonstrating that α-iodosulfones may become a new entry in the quite small group of alkyl-iodides functioning as reliable halogen bond-donors.

Dicarboxylic Acid Separation by Dynamic and Size-Matched Recognition in Solution and in the Solid State.

Bis(trimethylammonium) alkane diiodides dynamically encapsulate dicarboxylic acids through intermolecular hydrogen bonds between the I anions of the hosts and the carboxylic OH groups of the guests. A selective recognition is realized when the size of the I ⋅⋅⋅HOOC(CH /CF ) COOH⋅⋅⋅I superanion matches the dication alkyl chain length. Dynamic recognition is also demonstrated in solution, where the presence of the size-matching organic salt boosts the acid solubility profile, thus allowing efficient mixture separation.

Connectivity and Topology Invariance in Self-Assembled and Halogen-Bonded Anionic (6,3)-Networks.

We report here that the halogen bond driven self-assembly of 1,3,5-trifluorotriiodobenzene with tetraethylammonium and -phosphonium bromides affords 1:1 co-crystals, wherein the mutual induced fit of the triiodobenzene derivative and the bromide anions (halogen bond donor and acceptors, respectively) elicits the potential of these two tectons to function as tritopic modules (6,3). Supramolecular anionic networks are present in the two co-crystals wherein the donor and the acceptor alternate at the vertexes of the hexagonal frames and cations are accommodated in the potential empty space encircled by the frames. The change of one component in a self-assembled multi-component co-crystal often results in a change in its supramolecular connectivity and topology.

Halogen bonding in hypervalent iodine and bromine derivatives: halonium salts.

Halogen bonds have been identified in a series of ionic compounds involving bromonium and iodonium cations and several different anions, some also containing hypervalent atoms. The hypervalent bromine and iodine atoms in the examined compounds are found to have positive σ-holes on the extensions of their covalent bonds, while the hypervalent atoms in the anions have negative σ-holes. The positive σ-holes on the halogens of the studied halonium salts determine the linearity of the short contacts between the halogen and neutral or anionic electron donors, as usual in halogen bonds.

Halogen bonded Borromean networks by design: topology invariance and metric tuning in a library of multi-component systems.

A library of supramolecular anionic networks showing Borromean interpenetration has been prepared by self-assembly of crypt-222, several metal or ammonium halides, and five bis-homologous α,ω-diiodoperfluoroalkanes. Halogen bonding has driven the formation of these anionic networks. Borromean entanglement has been obtained starting from all the four used cations, all the three used anions, but only two of the five used diiodoperfluoroalkanes.

Proton in a Confined Space: Structural Studies of H ⊂Crypt-111 Iodide and Some Halogen-Bonded Derivatives.

Experimental observations and modeling data are reported on the solid-state structural features of crypt- 111⋅HI (1) and the three-component co-crystals that 1 forms with α,ω-diiodoperfluoroalkanes 2 a-d. X-ray analyses indicate that, in all five systems and at low temperature, the caged proton is covalently bonded to a single nitrogen atom and is involved in a network of intramolecular hydrogen bonds. In contrast, room-temperature, solid-state N NMR spectroscopy suggests magnetic equivalency of the two N atoms of crypt-111 in both 1 and co-crystals of 1 with diiodoperfluoroalkanes.

Superfluorinated Ionic Liquid Crystals Based on Supramolecular, Halogen-Bonded Anions.

Unconventional ionic liquid crystals in which the liquid crystallinity is enabled by halogen-bonded supramolecular anions [Cn F2 n+1 -I⋅⋅⋅I⋅⋅⋅I-Cn F2 n+1 ](-) are reported. The material system is unique in many ways, demonstrating for the first time 1) ionic, halogen-bonded liquid crystals, and 2) imidazolium-based ionic liquid crystals in which the occurrence of liquid crystallinity is not driven by the alkyl chains of the cation.

The Halogen Bond.

The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

Dynamic Characterization of Crystalline Supramolecular Rotors Assembled through Halogen Bonding.

A modular molecular kit for the preparation of crystalline molecular rotors was devised from a set of stators and rotators to gain simple access to a large number of structures with different dynamic performance and physical properties. In this work, we have accomplished this with crystalline molecular rotors self-assembled by halogen bonding of diazabicyclo[2.2.

Halogen bond: a long overlooked interaction.

Because of their high electronegativity, halogen atoms are typically considered, in most of their derivatives, as sites of high electron density and it is commonly accepted that they can form attractive interactions by functioning as the electron donor site (nucleophilic site). This is the case when they work as hydrogen bond acceptor sites. However, the electron density in covalently bound halogens is anisotropically distributed.

The 1:1 co-crystal of triphen-yl(2,3,5,6-tetra-fluoro-benz-yl)phospho-nium bromide and 1,1,2,2-tetra-fluoro-1,2-di-iodo-ethane.

The title compound, C25H18F4P(+)·Br(-)·C2F4I2, is a 1:1 co-crystal of triphen-yl(2,3,5,6-tetra-fluoro-benz-yl)phospho-nium (TTPB) bromide and 1,1,2,2-tetra-fluoro-1,2-di-iodo-ethane (TFDIE). The crystal structure consists of a framework of TTPB cations held together by C-H⋯Br inter-actions. In this framework, infinite channels along [100] are filled by TFDIE mol-ecules held together in infinite ribbons by short F⋯F [2.

Azobenzene-based difunctional halogen-bond donor: towards the engineering of photoresponsive co-crystals.

Halogen bonding is emerging as a powerful non-covalent interaction in the context of supramolecular photoresponsive materials design, particularly due to its high directionality. In order to obtain further insight into the solid-state features of halogen-bonded photoactive molecules, three halogen-bonded co-crystals containing an azobenzene-based difunctional halogen-bond donor molecule, (E)-bis(4-iodo-2,3,5,6-tetrafluorophenyl)diazene, C12F8I2N2, have been synthesized and structurally characterized by single-crystal X-ray diffraction. The crystal structure of the non-iodinated homologue (E)-bis(2,3,5,6-tetrafluorophenyl)diazene, C12H2F8N2, is also reported.

(4,7,13,16,21,24-Hexaoxa-1,10-di-aza-bicyclo-[8.8.8]hexa-cosa-ne)sodium iodide-1,1,2,2,tetra-fluoro-1,2-diiodo-ethane (2/3).

The title complex (CX1), [Na(C18H36N2O6)]I·1.5C2F4I2, is a three-component adduct containing a [2.2.

Multinuclear Solid-State Magnetic Resonance as a Sensitive Probe of Structural Changes upon the Occurrence of Halogen Bonding in Co-crystals.

Although the understanding of intermolecular interactions, such as hydrogen bonding, is relatively well-developed, many additional weak interactions work both in tandem and competitively to stabilize a given crystal structure. Due to a wide array of potential applications, a substantial effort has been invested in understanding the halogen bond. Here, we explore the utility of multinuclear ((13)C, (14/15)N, (19)F, and (127)I) solid-state magnetic resonance experiments in characterizing the electronic and structural changes which take place upon the formation of five halogen-bonded co-crystalline product materials.

Memory of chirality approach to the enantiodivergent synthesis of chiral benzo[d]sultams.

The "memory of chirality" stereodivergent synthesis of polyfluorobenzo[d]sultams has been developed. The interest of this protocol resides in the possibility of using the chirality of a starting sulfonamide single enantiomer to synthesize the target sultams in both absolute configurations, by using different base systems, under homogeneous conditions.

Tetra-phenyl-phospho-nium iodide-1,3,5-tri-fluoro-2,4,6-tri-iodo-benzene-methanol (3/4/1).

The crystallization of a 1:1 molar solution of 1,3,5-tri-fluoro-2,4,6-di-iodo-benzene (TFTIB) and tetra-phenyl-phosponium iodide (TPPI) from methanol produced tetra-gonal needles of pure TPPI and tabular pseudo-hexa-gonal truncated bipyramids of the title compound, 3C24H20P(+)·3I(-)·4C6F3I3·CH4O or (TPPI)3(TFTIB)4·MeOH. The asymmetric unit is composed of six TPPI mol-ecules, eight TFTIB mol-ecules and two methanol mol-ecules, overall 16 constituents. The formation of the architecture is essentially guided by a number of C-I⋯I(-) halogen bonds (XB), whose lengths are in the range 3.

(Tris{2-[2-(2,3,5,6-tetra-fluoro-4-iodo-phen-oxy)eth-oxy]eth-yl}amine)-potassium iodide.

The title adduct, [K(C30H24F12I3NO6)]I, gives an extended tape of cations linked through I⋯I(-) halogen bonds (XBs), two of them being quite short and one quite long. In the structure, the cation is hosted in a cavity formed by the arms of the podand which presents a closed conformation wherein two tetra-fluoro-iodo-benzene rings are near parallel [dihedral angle = 15.8 (4)°; centroid-centroid distance = 3.

[5,11,17,23-Tetra-tert-butyl-25,27-(3,6-dioxaoctan-1,8-di-oxy)-26,28-bis-(pyridin-2-ylmeth-oxy)calix[4]arene]sodium iodide-1,2,4,5-tetra-fluoro-3,6-diiodo-benzene-methanol (2/3/4).

The title compound, [Na(C62H76N2O6)]I·1.5C6F4I2·2CH3OH, is composed of five components: a calix[4]arene derivative (hereinafter C4), a sodium cation, an iodide anion, a 1,2,4,5-tetra-fluoro-3,6-diiodo-benzene (tFdIB) mol-ecule and a methanol mol-ecule in a 1:1:1:1.5:2 ratio.

1,3-Bis(2,3,5,6-tetra-fluoro-4-iodo-phen-oxy)-2,2-bis-[(2,3,5,6-tetra-fluoro-4-iodo-phen-oxy)meth-yl]propane.

In the crystal structure of the title compound, C29H8F16I4O4, short I⋯I and I⋯F contacts, which can be understood as halogen bonds (XBs), represent the strongest inter-molecular inter-actions, consistent with the presence of I and F atoms, and the absence of H atoms, at the periphery of the mol-ecule. In addition, π-π stacking inter-actions between tetra-fluoro-iodo-phenyl (TFIP) groups and five short F⋯F inter-actions are present.

Halogen bonding and pharmaceutical cocrystals: the case of a widely used preservative.

3-Iodo-2-propynyl-N-butylcarbamate (IPBC) is an iodinated antimicrobial product used globally as a preservative, fungicide, and algaecide. IPBC is difficult to obtain in pure form as well as to handle in industrial products because it tends to be sticky and clumpy. Here, we describe the preparation of four pharmaceutical cocrystals involving IPBC.

The halogen-bonded adduct 1,4-bis(pyri-din-4-yl)buta-1,3-diyne-1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8-hexa-deca-fluoro-1,8-diiodo-octane (1/1).

In the crystal structure of the title compound, C8F16I2·C14H8N2, the mol-ecules form infinite chains parallel to [2-11] through two symmetry-independent C-I⋯N halogen bonds (XBs). As commonly found, the perfluoro-alkyl mol-ecules segregate from the hydro-carbon ones, forming a layered structure. Apart from the XBs, the only contact below the sum of van der Waals radii is a weak H⋯F contact.

Steric and electronic effects on the configurational stability of residual chiral phosphorus-centered three-bladed propellers: tris-aryl phosphanes.

A series of tris-aryl phosphanes, structurally designed to exist as residual enantiomers or diastereoisomers, bearing substituents differing in size and electronic properties on the aryl rings, were synthesized and characterized. Their electronic properties were evaluated on the basis of their electrochemical oxidation potential determined by voltammetry. The configurational stability of residual phosphanes, evaluated by dynamic HPLC on a chiral stationary phase or/and by dynamic (1)H and (31)P NMR spectroscopy, was found to be rather modest (barriers of about 18-20 kcal mol(-1)), much lower than that shown by the corresponding phosphane oxides (barriers of about 25-29 kcal mol(-1)).