Evaluation of Concomitant Halogen and Pnictogen Bonds in Cocrystals of Imines Derived from 2-Nitrobenzaldehyde and 4-Haloaniline.

Three imines have been prepared by condensation of 2-nitrobenzaldehyde and 4-haloanilines (halo = Cl, Br, and I) with functionalities that enabled them to act as both halogen and pnictogen bond donors; however, both interactions were found to be absent in the solid state. The prepared imines were further cocrystallized with 1,3-diiodotetrafluorobenzene and 1,3,5-triiodotetrafluorobenzene as halogen bond donors. Six novel cocrystals were prepared by means of liquid-assisted mechanochemical synthesis and by crystallization from solution.

Enhancing the Cation-Binding Ability of Fluorescent Calixarene Derivatives: Structural, Thermodynamic, and Computational Studies.

Novel fluorescent calix[4]arene derivatives and were synthesized by introducing phenanthridine moieties at the lower calixarene rim, whereby phenanthridine groups served as fluorescent probes and for cation coordination. To enhance the cation-binding ability of the ligands, besides phenanthridines, tertiary-amide or ester functionalities were also introduced in the cation-binding site. Complexation of the prepared compounds with alkali metal cations in acetonitrile (MeCN), methanol (MeOH), ethanol (EtOH), -dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) was investigated at 25 °C experimentally (UV spectrophotometry, fluorimetry, microcalorimetry, and in the solid state by X-ray crystallography) and by means of computational techniques (classical molecular dynamics and DFT calculations).

Keggin-Type Anions as Halogen Bond Acceptors.

To study the potential of Keggin-type polyoxometalate anions to act as halogen bond acceptors, we have prepared a series of 10 halogen-bonded compounds starting from phosphomolybdic and phosphotungstic acid and halogenopyridinium cations as halogen (and hydrogen) bond donors. In all the structures, the cations and the anions were interconnected by halogen bonds, more often with terminal M=O oxygen atoms than with bridging oxygen atoms as acceptors. In four structures comprising protonated iodopyridinium cations capable of forming both hydrogen and halogen bonds with the anion, the halogen bond with the anion is apparently favored, whereas hydrogen bonds preferentially involve other acceptors present in the structure.

Semiconductive 2D arrays of pancake-bonded oligomers of partially charged TCNQ radicals.

Multicentre two-electron (mc/2e or 'pancake bonding') bonding between 7,7,8,8-tetra-cyano-quinodi-methane (TCNQ) radical anions was studied on its 14 novel salts with planar organic cations. The formal charges of the TCNQ moieties are -1/2 and -2/3, and they form mc/2e bonded dimers, trimers and tetramers which are further stacked into extended arrays. Multicentre bonding within these oligomers is characterized by short interplanar separations of 2.

Anticooperativity of Multiple Halogen Bonds and Its Effect on Stoichiometry of Cocrystals of Perfluorinated Iodobenzenes.

To investigate influences on the topicity of perfluorinated halobenzenes as halogen bond (XB) donors in the solid state, we have conducted a database survey and prepared 18 novel cocrystals of potentially ditopic (, ) and tritopic () XB donors with 15 monotopic pyridines. shows high tendency to be mono- or ditopic, but with strong bases it can act as a tritopic XB donor. DFT calculations have shown that binding of a single acceptor molecule on one of the iodine atoms of the XB donor reduces the ESP on the remaining iodine atoms and dramatically decreases their potential for forming further halogen bonds, which explains both the high occurrence of crystal structures where the donors do not achieve their maximal topicity and the observed differences in halogen bond lengths.

Isostructural Halogen Exchange and Halogen Bonds: The Case of -(4-Halogenobenzyl)-3-halogenopyridinium Halogenides.

Six -(4-halogenobenzyl)-3-halogenopyridinium cations were prepared by reacting -halogenopyridines (Cl, Br, and I) with (4-halogenobenzyl) bromides (Br and I) and were isolated as bromide salts, which were further used to obtain iodides and chlorides. Sixteen compounds (out of 18 possible cation/anion combinations) were obtained; two crystallized as hydrates and 14 as solvent free salts, 11 of which belonged to one isostructural series and 3 to another. All crystal structures comprise halogen-bonded chains, with the anion as an acceptor of two halogen bonds, with the pyridine and the benzyl halogen substituents of two neighboring cations.

Conservation of the Hydrogen-Bonded Pyridone Homosynthon in Halogen-Bonded Cocrystals.

Seven cocrystals of pyridone and perfluorinated halocarbons have been prepared. In all cases pairs of pyridone molecules are connected into dimers by two N-H···O hydrogen bonds, forming the characteristic pyridone homosynthon of R (8) topology. These dimers further act as acceptors of halogen bonds through the two pyridone oxygen atoms, forming two (in six cases) or three (in one case) halogen bonds with the donor molecules.

Evaluation of Halogenopyridinium Cations as Halogen Bond Donors.

We have performed a database survey and a structural and computational study of the potential and the limitations of halogenopyridinium cations as halogen bond donors. The database survey demonstrated that adding a positive charge on a halogenopyridine ring increases the probability that the halogen atom will participate in a halogen bond, although for chloropyridines it remains below 60%. Crystal structures of both protonated and -methylated monohalogenated pyridinium cations revealed that the iodo- and bromopyridinium cations always form halogen-bonding contacts with the iodide anions shorter than the sum of the vdW radii, while chloropyridinium cations mostly participate in longer contacts or fail to form halogen bonds.

Halogen and Hydrogen Bond Motifs in Ionic Cocrystals Derived from 3-Halopyridinium Halogenides and Perfluorinated Iodobenzenes.

Four halopyridinium salts, 3-chloro- and 3-bromopyridinium chlorides and bromides, have been successfully cocrystallized with two ditopic perfluorinated iodobenzenes, 1,4-diiodotetrafluorobenzene and 1,2-diiodotetrafluorobenzene. These halogen bond donor molecules were chosen because the different positionings of halogen bond donor atoms can lead to different supramolecular architectures. In this work, we present insight into the halogen bond acceptor potential of chloride and bromide ions, as well as the halogen bond donor potential of chlorine and bromine atoms substituted on the pyridinium ring when combined with the expectedly very strong hydrogen bonds between halopyridinium ions and free halogenide anions.

Polymorphs of phenazine hexacyanoferrate(II) hydrate: supramolecular isomerism in a 2D hydrogen-bonded network.

The crystal structures of two polymorphs of a phenazine hexacyanoferrate(II) salt/cocrystal, with the formula (Hphen)[HFe(CN)][HFe(CN)]·2(phen)·2HO, are reported. The polymorphs are comprised of (Hphen)[HFe(CN)] trimers and (Hphen)[(phen)(HO)][HFe(CN)] hexamers connected into two-dimensional (2D) hydrogen-bonded networks through strong hydrogen bonds between the [HFe(CN)] and [HFe(CN)] anions. The layers are further connected by hydrogen bonds, as well as through π-π stacking of phenazine moieties.

Cobaloximes as Building Blocks in Halogen-Bonded Cocrystals.

In this work, we explore the halogen-bonded cocrystallization potential of cobaloxime complexes in the synthesis of cocrystals with perhalogenated benzenes. We demonstrate a strategy for synthesizing halogen-bonded metal-organic cocrystals by utilizing cobaloximes whose pendant bromide group and oxime oxygen enable halogen bonding. By combining three well-known halogen bond donor molecules differing in binding geometry and composition with three cobaloxime units, we obtained a total of four previously unreported cocrystals.

A Crystallographic Charge Density Study of the Partial Covalent Nature of Strong N⋅⋅⋅Br Halogen Bonds.

The covalent nature of strong N-Br⋅⋅⋅N halogen bonds in a cocrystal (2) of N-bromosuccinimide (NBS) with 3,5-dimethylpyridine (lut) was determined from X-ray charge density studies and compared to a weak N-Br⋅⋅⋅O halogen bond in pure crystalline NBS (1) and a covalent bond in bis(3-methylpyridine)bromonium cation (in its perchlorate salt (3). In 2, the donor N-Br bond is elongated by 0.0954 Å, while the Br⋅⋅⋅acceptor distance of 2.

The synthesis, structure and catalytic properties of the [MoO(μ-MoO)MoO] anion formed via two intermediate heptamolybdates [Co(en)][NaMoO]Cl·nHO and (HO)[Co(en)][MoO]Cl·9HO.

Ageing a mixture of sodium molybdate, malonic acid, and tris(ethylenediamine)cobalt(iii) chloride using different synthetic routes, namely, solution-based methods at room temperature or 110 °C, and a mechanochemically accelerated vapour-assisted method, yielded the polyoxomolybdate [Co(en)]Na[MoO(μ-MoO)MoO]·nHO (1). The new polyoxomolybdate anion 1 comprised three fragments, namely, two {MoO} units bridged by a {MoO} unit, which were interconnected by the terminal oxygen atoms of MoO octahedra and represent a unique structural motif not yet described in the structurally versatile chemistry of polyoxomolybdates (POMos). The ageing reaction was found to occur via a series of intermediates, two of which were isolated and identified as the heptamolybdate coordination polymer [Co(en)][NaMoO]Cl·nHO (2), comprising {MoO} units bridged by a sodium atom, and the heptamolybdate (HO)[Co(en)][MoO]Cl·9HO (3).

Green and rapid mechanosynthesis of high-porosity NU- and UiO-type metal-organic frameworks.

The use of a dodecanuclear zirconium acetate cluster as a precursor enables the rapid, clean mechanochemical synthesis of high-microporosity metal-organic frameworks NU-901 and UiO-67, with surface areas up to 2250 m2 g-1. Real-time X-ray diffraction monitoring reveals that mechanochemical reactions involving the conventional hexanuclear zirconium methacrylate precursor are hindered by the formation of an inert intermediate, which does not appear when using the dodecanuclear acetate cluster as a reactant.

Pancake Bonding in π-Stacked Trimers in a Salt of Tetrachloroquinone Anion.

The crystal structure of [4-damp]) [Cl Q] (4-damp=4-dimethylamino-N-methylpyridinium, Cl Q=tetrachloroquinone) salt is built up from slipped columnar stacks of quinoid rings composed of closely bound trimers with the intra-trimer separation distance of 2.84 Å and total charge of -2 whereas the inter-trimer distance is 3.59 Å.

Halogen and Hydrogen Bonding between (N-Halogeno)-succinimides and Pyridine Derivatives in Solution, the Solid State and In Silico.

A study of strong halogen bonding within three series of halogen-bonded complexes, derived from seven para-substituted pyridine derivatives and three N-halosuccinimides (iodo, bromo and chloro), has been undertaken with the aid of single-crystal diffraction, solution complexation and computational methods. The halogen bond was compared with the hydrogen bond in an equivalent series based on succinimide. The halogen-bond energies are in the range -60 to -20 kJ mol and change regularly with pyridine basicity and the Lewis acidity of the halogen.

Design of Lead(II) Metal-Organic Frameworks Based on Covalent and Tetrel Bonding.

Three solid materials, [Pb(HL)(SCN)2 ]⋅CH3 OH (1), [Pb(HL)(SCN)2 ] (2), and [Pb(L)(SCN)]n (3), were obtained from Pb(SCN)2 and an unsymmetrical bis-pyridyl hydrazone ligand that can act both as a bridging and as a chelating ligand. In all three the lead center is hemidirectionally coordinated and is thus sterically optimal for participation in tetrel bonding. In the crystal structures of all three compounds, the lead atoms participate in short contacts with thiocyanate sulfur or nitrogen atoms.

Supramolecular stabilization of metastable tautomers in solution and the solid state.

This work presents a successful application of a recently reported supramolecular strategy for stabilization of metastable tautomers in cocrystals to monocomponent, non-heterocyclic, tautomeric solids. Quantum-chemical computations and solution studies show that the investigated Schiff base molecule, derived from 3-methoxysalicylaldehyde and 2-amino-3-hydroxypyridine (ap), is far more stable as the enol tautomer. In the solid state, however, in all three obtained polymorphic forms it exists solely as the keto tautomer, in each case stabilized by an unexpected hydrogen-bonding pattern.

The effect of specific solvent-solute interactions on complexation of alkali-metal cations by a lower-rim calix[4]arene amide derivative.

Complexation of alkali-metal cations with calix[4]arene secondary-amide derivative, 5,11,17,23-tetra(tert-butyl)-25,26,27,28-tetra(N-hexylcarbamoylmethoxy)calix[4]arene (L), in benzonitrile (PhCN) and methanol (MeOH) was studied by means of microcalorimetry, UV and NMR spectroscopies, and in the solid state by X-ray crystallography. The inclusion of solvent molecules (including acetonitrile, MeCN) in the calixarene hydrophobic cavity was also investigated. The classical molecular dynamics (MD) simulations of the systems studied were carried out.

An Integrated approach (thermodynamic, structural, and computational) to the study of complexation of alkali-metal cations by a lower-rim calix[4]arene amide derivative in acetonitrile.

The calix[4]arene secondary-amide derivative L was synthesized, and its complexation with alkali-metal cations in acetonitrile (MeCN) was studied by means of spectrophotometric, NMR, conductometric, and microcalorimetric titrations at 25 °C. The stability constants of the 1:1 (metal/ligand) complexes determined by different methods were in excellent agreement. For the complexation of M(+) (M = Li, Na, K) with L, both enthalpic and entropic contributions were favorable, with their values and mutual relations being quite strongly dependent on the cation.

N-Benzyl-3-nitro-aniline.

The mol-ecule of the title compound, C(13)H(12)N(2)O(2), has a bent conformation with a torsion angle about the central C-N bond of 72.55 (19)°. In the crystal, the mol-ecules are connected via classical N-H⋯O and non-classical C-H⋯O hydrogen bonds into chains along [10[Formula: see text]].

Comparative refinement of correct and incorrect structural models of tetrabutylammonium tetrabutylborate - pitfalls arising from poor-quality data.

This paper demonstrates how numerical parameters usually used to assess the quality of a crystal structure solution (R, wR and S) may be misleading when studying a model refined against poor-quality data. Weakly diffracting crystals of tetrabutylammonium tetrabutylborate, a low-density organic salt comprising isoelectronic cations and anions, were measured using Cu and Mo Kalpha radiation. Along with the correct structural model, six erroneous structural models were constructed and refined against the same data.

(R,S)-3-Carb-oxy-2-(isoquinolinium-2-yl)propanoate monohydrate.

The title compound, C(13)H(11)NO(4)·H(2)O, is a monohydrate of a betaine exhibiting a positively charged N-substituted isoquino-line group and a deprotonated carboxyl group. In the crystal, mol-ecules are connected via short O-H⋯O hydrogen bonds between protonated and deprotonated carboxyl groups into chains of either R or S enanti-omers along [001]. These chains are additionally connected by hydrogen bonding between water mol-ecules and the deprotonated carb-oxy groups of neighbouring mol-ecules.

Partial ordering of tripivaloylmethane at 110 K.

Tripivaloylmethane [systematic name: 4-(2,2-dimethylpropanoyl)-2,2,6,6-tetramethylheptane-3,5-dione], C(16)H(28)O(3), is known to crystallize at room temperature in the space group R3m with three molecules in the unit cell. The molecules are conformationally chiral and pack so that each molecular site is occupied with equal probability by the two enantiomers. Upon cooling to 110 K, the structure partially orders; two molecules in the unit cell order into two different conformations of opposite chirality, while the third remains disordered.