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. By combining the results obtained using the mentioned experimental and computational techniques, an attempt was made to get an as detailed insight into the complexation reactions as possible. The thermodynamic parameters, that is, equilibrium constants, reaction Gibbs energies, enthalpies, and entropies, of the investigated processes were determined and discussed. The stability constants of the 1:1 (metal:ligand) complexes measured by different methods were in very good agreement. Solution Gibbs energies of the ligand and its complexes with Na(+) and K(+) in methanol and acetonitrile were determined. It was established that from the thermodynamic point of view, apart from cation solvation, the most important reason for the huge difference in the stability of these complexes in the two solvents lay in the fact that the transfer of complex species from MeOH to MeCN was quite favorable. That could be at least partly explained by a more exergonic inclusion of the solvent molecule in the complexed calixarene cone in MeCN as compared to MeOH, which was supported by MD simulations. Molecular and crystal structures of the lithium cation complex of L with the benzonitrile molecule bound in the hydrophobic calixarene cavity were determined by single-crystal X-ray diffraction. As far as we are aware, for the first time the alkali-metal cation was found to be coordinated by the solvent nitrile group in a calixarene adduct. According to the results of MD simulations, the probability of such orientation of the benzonitrile molecule included in the ligand cone was by far the largest in the case of LiL(+) complex. Because of the favorable PhCN-Li(+) interaction, L was proven to have the highest affinity toward the lithium ion in benzonitrile, which was not the case in the other solvents examined (in acetonitrile, sodium complex was the most stable, whereas in methanol, complexation of lithium was not even observed). That could serve as a remarkable example showing the importance of specific solvent-solute interactions in determining the equilibrium in solution.

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. The enthalpic and overall stability was the largest in the case of the sodium complex. Molecular and crystal structures of free L, its methanol and MeCN solvates, the sodium complex, and its MeCN solvate were determined by single-crystal X-ray diffraction. The inclusion of a MeCN molecule in the calixarene hydrophobic cavity was observed both in solution and in the solid state. This specific interaction was found to be stronger in the case of metal complexes compared to the free ligand because of the better preorganization of the hydrophobic cone to accept the solvent molecule. Density functional theory calculations showed that the flattened cone conformation (C(2) point group) of L was generally more favorable than the square cone conformation (C(4) point group). In the complex with Na(+), L was in square cone conformation, whereas in its adduct with MeCN, the conformation was slightly distorted from the full symmetry. These conformations were in agreement with those observed in the solid state. The classical molecular dynamics simulations indicated that the MeCN molecule enters the L hydrophobic cavity of both the free ligand and its alkali-metal complexes. The inclusion of MeCN in the cone of free L was accompanied by the conformational change from C(2) to C(4) symmetry. As in solution studies, in the case of ML(+) complexes, an allosteric effect was observed: the ligand was already in the appropriate square cone conformation to bind the solvent molecule, allowing it to more easily and faster enter the calixarene cavity.

Solvent-free Mechanosynthesis of Two Thermochromic Schiff Bases.

Two thermochromic Schiff bases mostly in keto-amine tautomeric form were obtained by means of mechanochemical synthesis. Both Schiff bases Compound 1 and Compound 2, respectively are derived from the same primary amine 2-amino-5-methylphenol. Salicylaldehyde was used as aldehyde component in preparation of 1, and o-vanillin as substituted salicylaldehyde component in synthesis of 2. Powder products of the neat grinding and liquid-assisted grinding syntheses of 1 and 2 were compared with the crystalline products, obtained by recrystallization from a small amount of solvent. Both raw powder and recrystallized products were characterized and compared by means of PXRD, DSC and IR.

Two Ketimine Polymorphs of 2-{1-[(2-Aminophenyl)imino]ethyl}phenol.

Two polymorphic structures of the Schiff base 2-1-[(2-aminophenyl)imino]ethylphenol, compound (1), C14H14N2O are reported. Depending on the solvent used for recrystallization it crystallizes as either a monoclinic or an orthorhombic polymorph. The monoclinic form, polymorph [1] contains three, while the orthorhombic polymorph [2] contains only one molecule in the asymmetric unit. In both polymorphs, a strong intramolecular O-H•••N hydrogen bond is present from the stereochemical reason due to the rigidity of the chelate ring. Weak intermolecular N-H•••O interactions appearing in both structures combine the molecules in the form of infinite columns by the graph-set motif C22(7).

2-[1-(3-Amino-phenyl-imino)-eth-yl]phenol.

The title compound, C(14)H(14)N(2)O, exists as the enol-imine tautomer. A strong intra-molecular hydrogen bond between O and N atoms forms a six-membered ring with an S(6) graph-set motif, which is approximately coplanar with the phenol ring, the inter-planar angle being 3.4 (3)°. In the crystal, inter-molecular C-H⋯O hydrogen bonds and N-H⋯π inter-actions link the mol-ecules into infinite chains along [100].

2,2'-[1,5-Bis(4-amino-phen-yl)-1,5-dihydro-benzo[1,2-d;4,5-d']diimidazole-2,6-di-yl]diphenol.

The title mol-ecule, C(32)H(24)N(6)O(2), has a crystallographic inversion centre in the middle of the benzodiimidazole core. It exists as the enol-imine tautomeric form and exhibits a strong intra-molecular O-H⋯N hydrogen bond. The dihedral angles between the planes of the 2-hy-droxy-phenyl and 4-amino-phenyl substituents and the plane of the benzodiimidazole unit [12.69 (8) and 84.71 (8)°, respectively] differ significantly due to steric reasons. In the crystal, mol-ecules are linked by C-H⋯π inter-actions, forming a two-dimensional network.

2-{[(4-{[(2-Hy-droxy-phen-yl)(phen-yl)methyl-idene]amino}-phen-yl)imino](phen-yl)meth-yl}phenol.

The title mol-ecule, C(32)H(24)N(2)O(2), has a crystallographically imposed inversion centre and exists in the crystal as an enol-imine tautomer. The mol-ecular structure is stabilized by two strong intra-molecular O-H⋯N hydrogen bonds. The dihedral angles between the central benzene ring and the mean planes of the phenyl substituents are 59.99 (1) and 62.79 (2)°. In the crystal, the mol-ecules are arranged into (010) layers via C-H⋯π inter-actions.

1,1'-[m-Phenyl-enebis(nitrilo-methanylyl-idene)]dinaphthalen-2-ol-1,1'-[m-phenyl-enebis(imino-methanylyl-idene)]dinaphthalen-2(1H)-one (0.58/0.42).

In the solid state the title Schiff base, 0.58C(28)H(20)N(2)O(2)·0.42C(28)H(20)N(2)O(2), exists both as the keto-imino and as the enol-amino tautomer, which is manifested in the disorder of the H atom in the intra-molecular hydrogen-bonded ring. The naphthalene ring systems show some distortion, which is consistent with the quinoid effect. The ratio of the enol form refined to 58 (5)%. The mol-ecule has crystallographically imposed symmetry: a twofold axis passes through the central benzene ring. Crystals are built up of layers parallel to (010). Stacking interactions between the layers involve only standard van der Waals attraction forces between apolar groups. The alignment of the aromatic rings in neighbouring layers shows a herringbone motif. A weak C-H⋯O inter-action is observed.

1-[(4-{[(2-Oxo-1,2-dihydro-naphthalen-1-yl-idene)meth-yl]amino}-anilino)methyl-idene]naphthalen-2(1H)-one dihydrate.

The title compound, C(28)H(20)N(2)O(2)·2H(2)O, comprises a Schiff base mol-ecule with an imposed inversion centre in the middle of p-phenyl-enediamine unit and water mol-ecules of crystallization. In the structure, the Schiff base mol-ecule is present as the keto-amino tautomer with a strong intra-molecular N-H⋯O hydrogen bond. The Schiff base mol-ecules and water mol-ecules of crystallization create infinite [010] columns through O-H⋯O hydrogen bonds. Inter-molecular attractions within columns are through additional π-π inter-actions [centroid-centroid distance = 3.352 (1) Å] between parallel Schiff base mol-ecules. The columns are joined into infinite (011) layers through weak C-H⋯O hydrogen bonds. The layers pack in an assembly by van der Waals attractions, only being effective between bordering non-polar naphthalene ring systems.

(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.

One-pot mechanosynthesis with three levels of molecular self-assembly: coordination bonds, hydrogen bonds and host-guest inclusion.

Liquid-assisted grinding (LAG) was used to combine three levels of molecular self-assembly into a one-pot mechanochemical approach for the construction of metal-organic materials. The approach was applied for the construction of three adducts of cobalt(II) dibenzoylmethanate with isonicotinamide, nicotinamide and imidazole, to screen for their inclusion compounds. The one-pot process consists of: i) The coordination-driven binding of addends to the equatorially-protected metal ion, resulting in "wheel-and-axle"-shaped complexes; ii) self-assembly of resulting complexes by way of hydrogen-bonded synthons to form metal-organic inclusion hosts; iii) in situ inclusion of the grinding liquid in the resulting host. This approach provided quantitatively and within 20 min the known inclusion compounds of the bis(isonicotinamide) adduct in a single synthetic step. Changing the liquid phase in LAG was used to explore the inclusion behaviour of new wheel-and-axle adducts with nicotinamide and imidazole, revealing several inclusion compounds, as well as two polymorphs, of the bis(nicotinamide) host. Preliminary results suggest that one-pot LAG is superior to solution synthesis in screening for metal-organic inclusion compounds. The difference between the methods is rationalised in terms of reactant solubility and solvent competition. In contrast to the nicotinamide adduct, the bis(imidazole) adduct did not form inclusion compounds. The difference in the inclusion properties of the two adducts is rationalised by structural information gathered by single crystal and powder X-ray diffraction.

Interactions between dimers of {1,1'-[o-phenylenebis(nitrilomethylidyne)]di-2-naphtholato-kappa4O,N,N',O'}nickel(II).

In the title compound, [Ni(C(28)H(18)N(2)O(2))], the Ni(II) centre has a square-planar coordination geometry in which the Schiff base ligand acts as a cis-O,N,N',O'-tetradentate ligand. The crystal structure is built up of centrosymmetric dimer units stacked into chains along the [010] direction. Adjacent chains associate via C-H...O hydrogen bonding only, leading to a two-dimensional sheet-like structure consisting of layers parallel to (101). The cofacial dimeric complex contains an Ni...Ni contact of 3.291 (4) A.

Hydrogen-bonding motifs in 3-carboxyanilinium bromide and iodide.

In the title compounds, C(7)H(8)NO(2)(+).Br(-), (I), and C(7)H(8)NO(2)(+).I(-), (II), the asymmetric unit contains a discrete 3-carboxyanilinium cation, with a protonated amine group, and a halide anion. The compounds are not isostructural, and the crystal structures of (I) and (II) are characterized by different two-dimensional hydrogen-bonded networks. The ions in (I) are connected into ladder-like ribbons via N-H...Br hydrogen bonds, while classic cyclic O-H...O hydrogen bonds between adjacent carboxylic acid functions link adjacent ribbons to give three characteristic graph-set motifs, viz. C(2)(1)(4), R(4)(2)(8) and R(2)(2)(8). The ions in (II) are connected via N-H...I, N-H...O and O-H...I hydrogen bonds, also with three characteristic graph-set motifs, viz. C(7), C(2)(1)(4) and R(4)(2)(18), but an O-H...O interaction is not present.

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. The symmetry of the resulting crystal is P3, with each of the molecules lying about a different threefold rotation axis. This paper describes an unusual case of order-disorder phase transition in which the structure partially orders by changes of molecular conformation in the single crystals. Such behaviour is of interest in the study of phase transitions and molecular motion in the solid state.

Hydrogen bonding in the bromide salts of 4-aminobenzoic acid and 4-aminoacetophenone.

In the title compounds, 4-carboxyanilinium bromide, C(7)H(8)NO(2)(+) x Br(-), (I), and 4-acetylanilinium bromide, C(8)H(10)NO(+) x Br(-), (II), each asymmetric unit contains a discrete cation with a protonated amino group and a halide anion. Both crystal structures are characterized by two-dimensional hydrogen-bonded networks. The ions in (I) are connected via N-H...Br, N-H...O and O-H...Br hydrogen bonds, with three characteristic graph-set motifs, viz. C(8), C(2)(1)(4) and R(3)(2)(8). The centrosymmetric hydrogen-bonded R(2)(2)(8) dimer motif characteristic of carboxylic acids is absent. The ions in (II) are connected via N-H...Br and N-H...O hydrogen bonds, with two characteristic graph-set motifs, viz. C(8) and R(4)(2)(8). The significance of this study lies in its illustration of the differences between the supramolecular aggregations in two similar compounds. The presence of the methyl group in (II) at the site corresponding to the hydroxyl group in (I) results in a significantly different hydrogen-bonding arrangement.

3-Acetylanilinium bromide, nitrate and dihydrogen phosphate: hydrogen-bonding motifs in one, two and three dimensions.

In the title compounds, namely 3-acetylanilinium bromide, C(8)H(10)NO(+) x Br(-), (I), 3-acetylanilinium nitrate, C(8)H(10)NO(+) x NO(3)(-), (II), and 3-acetylanilinium dihydrogen phosphate, C(8)H(10)NO(+) x H(2)PO(4)(-), (III), each asymmetric unit contains a discrete cation, with a protonated amino group, and an anion. In the crystal structure of (I), the ions are connected via N-H...Br and N-H...O hydrogen bonds into a chain of spiro-fused R(2)(2)(14) and R(2)(4)(8) rings. In compound (II), the non-H atoms of the cation all lie on a mirror plane in the space group Pnma, while the nitrate ion lies across a mirror plane. The crystal structures of compounds (II) and (III) are characterized by hydrogen-bonded networks in two and three dimensions, respectively. The ions in (II) are connected via N-H...O hydrogen bonds, with three characteristic graph-set motifs, viz. C(2)(2)(6), R(2)(1)(4) and R(4)(6)(14). The ions in (III) are connected via N-H...O and O-H...O hydrogen bonds, with five characteristic graph-set motifs, viz. D, C(4), C(1)(2)(4), R(3)(3)(10) and R(4)(4)(12). The significance of this study lies in its illustration of the differences between the supramolecular aggregations in the bromide, nitrate and dihydrogen phosphate salts of a small organic molecule. The different geometry of the counter-ions and their different potential for hydrogen-bond formation result in markedly different hydrogen-bonding arrangements.

(1,10-Phenanthroline-κN,N')bis-(2,2,6,6-tetra-methyl-heptane-3,5-dionato-κO,O')nickel(II).

The title compound, [Ni(C(11)H(19)O(2))(2)(C(12)H(8)N(2))], was obtained from the reaction of bis-(2,2,6,6-tetra-methyl-heptane-3,5-dionato)nickel(II), [Ni(dpm)], and 1,10-phenanthroline (phen). The Ni(II) ion is coordinated by four O atoms from two dpm ligands and two N atoms from a phen ligand in a slightly distorted octa-hedral environment. The methyl C atoms of two of the tert-butyl groups are disordered over two sites, having approximate occupancies of 0.85 and 0.15 for the two components. In the crystal structure, there are no direction-specific inter-actions. Thermal studies showed that the title complex is stable to 623 K.

Effect of atmosphere on solid-state amine-aldehyde condensations: gas-phase catalysts for solid-state transformations.

The presence of water or organic solvent vapour accelerates the solid-state condensation of solid aromatic amines and aromatic aldehydes into Schiff bases; we show the important role of catalytic triethylamine in the vapour phase in such vapour digestion synthesis, as well as in the liquid phase in synthesis via liquid-assisted grinding.

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. For both data sets it was found that models based on an incorrect unit-cell choice give lower values of R and wR than the correct one, thus apparently being in better agreement with measured data. Closer inspection of the measured data shows that this is in fact not the case.