pH-controlled assembly of two new supramolecular hybrid compounds based on Keggin polyoxotungstates

Two supramolecular compounds based on Keggin polyoxotungstates, (4,4′-H₂bpy){[Cu(4,4′-bpy)]₂[SiW₁₂O₄₀]} (1) and (4,4′-H₂bpy)₂[SiW₁₂O₄₀]·2H₂O (2) have been synthesized and characterized by elemental analyses, IR, UV, XPS spectra, TG analyses, and single crystal X-ray diffraction analyses. Compound 1 exhibits an infinite 1-D ladder like structure, which is further interconnected into a 3-D supramolecular framework via hydrogen bonding interactions. Compound 2 contains 4,4′-bipyridine (4,4′-bpy), pseudo-Keggin polyoxoanions [SiW₁₂O₄₀]^4?, and water molecules. Polyoxoanions together with water molecules in 2 construct a 3-D inorganic supramolecular network through O···O and O···Ow(1) interactions. The electrochemical behaviors and photocatalytic properties of 1 and 2 have been investigated.     

Efficient phase transfer of pertechnetate with bicyclic guanidinium compounds

Extraction of pertechnetate with bicyclic guanidinium compounds has been studied in the KTcO₄-buffer-H₂O/ligand-trichloromethane system. Extraction data of guanidinium ligands have been compared with trialkylmethylammonium (Aliquat 336), tetraphenylphosphonium and tetraphenylarsonium chloride. The lipophilicity of extractants investigated was determined by RP-HPLC. The efficiency of pertechnetate extraction correlates with the lipophilicity of the guanidinium compounds. 1:1 complex formation in the organic phase was observed. The influence of hydroxide, chloride and bicarbonate on the pertechnetate extraction has been investigated. Pertechnetate is extracted with great preference over OH⁻, Cl⁻ and HCO₃ ⁻, ions.     

5‐n‐Butylpyridine‐2‐carboxylate–copper(II) and –iron(III) complexes

In trans‐bis(5‐n‐butyl­pyridine‐2‐carboxyl­ato‐κ²N,O)­bis­(methanol‐κO)copper(II), [Cu(C₁₀H₁₂NO₂)₂(CH₄O)₂], the Cu atom lies on a centre of symmetry and has a distorted octahedral coordination. The Cu—O(methanol) bond length in the axial direction is 2.596 (3) Å, which is much longer than the Cu—­O(carboxylate) and Cu—N distances in the equatorial plane [1.952 (2) and 1.977 (2) Å, respectively]. In mer‐tris(5‐n‐bu­tyl­pyridine‐2‐carboxyl­ato‐κ²N,O)­iron(III), [Fe(C₁₀H₁₂NO₂)₃], the Fe atom also has a distorted octahedral geometry, with Fe—O and Fe—N bond‐length ranges of 1.949 (4)–1.970 (4) and 2.116 (5)–2.161 (5) Å, respectively. Both crystals are stabilized by stacking interactions of the 5‐n‐butyl­pyridine‐2‐carboxyl­ate ligand, although hydrogen bonds also contribute to the stabilization of the copper(II) complex.     

Different supramolecular assemblies in two 1:1 proton‐transfer compounds of sulfobenzoic acids with aromatic amines

Two 1:1 proton‐transfer complexes of sulfobenzoic acids with aromatic amines, namely 4‐[2‐(4‐pyridyl)ethenyl]pyridinium 2‐carboxybenzenesulfonate, C₁₂H₁₁N₂⁺·C₇H₅O₅S⁻, (I), and 1,10‐phenanthrolin‐1‐ium 4‐carboxybenzenesulfonate dihydrate, C₁₂H₉N₂⁺·C₇H₅O₅S⁻·2H₂O, (II), have very different hydrogen‐bonding patterns compared with reported organic sulfobenzoic acid complexes. In (I), two cations and two anions form a four‐molecule loop, in which π–π interactions occur. In (II), the anions and water molecules form a three‐dimensional hydrogen‐bonding network, while the cations only act as pendant components. The water molecules play a central role in the formation of the abundant hydrogen‐bonding architecture in (II). The relative poorness and richness of hydrogen bonds in (I) and (II), respectively, give rise to novel hydrogen‐bonding patterns.     

Stability of supramolecular compounds under heating

The decomposition of series of supramolecular compounds, namely inclusion compounds, was studied by means of different thermoanalytical methods, i.e., traditional thermogravimetry, quasi-equilibrium thermogravimetry, and thermomechanical analysis. The series of compounds included the intercalates on the base of fluorinated graphite C₂F, the clathrates on the base of carbamide and on the base of coordination compounds and microporous inclusion compounds on the base of coordination compounds. Kinetic parameters of decomposition processes were estimated within the approaches of the non-isothermal kinetics (“model-free” kinetics, linear and non-linear regression methods for the topochemical equation detection). The kinetic stability of the inclusion compounds under heating, the flexibility of the matrix structure, and the thermodynamic stability of the intermediate phases are discussed.     

Hydrothermal syntheses and characterizations of two new hydrogen bond-supported supramolecular compounds based on polyoxometalates

Two new polyoxometalates [HN(C₂H₅)₃]₃[PMo₁₂O₄₀] (1) and [NH₂(C₂H₄NH₃)₂]₂[Mo₅P₂O₂₃] (2) have been hydrothermally synthesized and characterized by IR, UV-Vis, XPS spectra, TG analyses, and single crystal X-ray diffraction. Crystal data for 1: monoclinic, space group C2/c, a = 24.651(5) Å, b = 10.822(2) Å, c = 22.413(5) Å, β = 120.37(3)°, and V = 5158.7(18) ų; for 2: triclinic, space group P-1, a = 9.821(2) Å, b = 9.948(2) Å, c = 14.687(3) Å, α = 95.490(3)°, β = 98.870(3)°, γ = 95.710(3)°, and V = 1401.7(5) ų. The crystal structure analyses reveal complex hydrogen bonds in both 1 and 2 in 3-D supramolecular arrays constructed from different polyoxoanions and organic ligands.     

Inter‐ring and endo anomeric effects,and hydrogen‐bonded supramolecular motifs in two 2,4,6,8‐tetraazabicyclo[3.3.0]octane derivatives

In 2,4,6,8‐tetrakis(4‐chlorophenyl)‐2,4,6,8‐tetraazabicyclo[3.3.0]octane, C₂₈H₂₂Cl₄N₄, the imidazolidine rings adopt envelope conformations, which are favoured by two equal endo anomeric effects. The molecule lies on a crystallographic twofold axis and molecules are linked into a three‐dimensional framework via two C—H...Cl hydrogen bonds. In 2,4,6,8‐tetrakis(4‐methoxyphenyl)‐2,4,6,8‐tetraazabicyclo[3.3.0]octane, C₃₂H₃₄N₄O₄, one of the methyl groups is disordered over two sets of sites and the same methyl group participates in an intermolecular C—H...O hydrogen bond, which in turn causes a considerable deviation from the preferred conformation. There are two unequal inter‐ring anomeric effects in the N—C—N groups. Molecules are linked into corrugated sheets by one C—H...π hydrogen bond and two independent C—H...O hydrogen bonds involving methoxy groups.     

Carboxylic acid–pyridine supramolecular heterocatemer in a co-crystal

Robustness of carboxylic acid–pyridine supramolecular heterosynthon was examined in three 1:2 binary co-crystals of 4,4′-bipyridine with monocarboxylic acids, (4,4′-bipyridine)·(dl-hydroxyphenylacetic acid)₂, 1; (4,4′-bipyridine)_0.5·(4-bromonaphthalene-1-carboxylic acid), 2 and (4,4′-bipyridine)_0.5·(4-methylbenzoic acid), 3. All the three co-crystals form “two-component supermolecules” (consisting of one molecule of 4,4′-bipyridine and two molecules of the relevant carboxylic acid) stabilized through carboxylic acid–pyridine heterosynthons. Co-crystals 1 and 2 exhibits the expected carboxylic acid–pyridine dimer (heterodimer I) whereas co-crystal 3 forms a novel carboxylic acid–pyridine catemer (heterocatemer II).     

Assembly of ethylzincate compounds into supramolecular structures

Sodium and potassium triethylzincate were isolated by Wanklyn in 1858, and are corner stones in the history of organometallic chemistry. Crystallisation of organozincates from neat dialkylzinc, in the absence of a coordinating solvent, can be expected to result in assembly of supramolecular structures, rather than formation of discrete molecules in the crystalline state. This inspired us to reinvestigate Wanklyn’s classical compounds. Crystallisation of sodium triethylzincate from benzene led to metallation of benzene and the formation of diethylphenylzincate anions. The compound is a two-dimensional network where Na⁺ ions link the zincate anions by coordination to both ethyl- and phenyl groups. We have also, accidently, isolated crystals of the two-dimensional coordination network [K₂(ZnEt₂)₄O]_n, displaying a rare oxo-centred core with an octahedral oxide ion surrounded by four zinc atoms and two potassium atoms.     

Solid-state supramolecular structures of resorcinol-arylboronic acid compounds

[structure: see text] An X-ray crystallographic study of unique hydrogen-bonded supramolecular solid-state networks comprised of a tetraarylboronic acid resorcinarene is described. When 1 is recrystallized from 9:1 MeOH:EtOH, partial esterification takes place to give compound 2, the corresponding half methyl ester, which forms an infinite two-dimensional array. Each molecule participates in 12 hydrogen bonds with other macrocycles. These hydrogen bonds are both B-OH- - - OH (phenolic) and OH (phenolic)- - -OH (phenolic).     

Syntheses and crystal structures of two magnesium–tetrazole compounds in salt and polymeric forms

Two alkaline earth–tetrazole compounds, namely catena‐poly[[[triaquamagnesium(II)]‐μ‐5,5′‐(azanediyl)ditetrazolato‐κ³N¹,N^1′:N⁵] hemi{bis[μ‐5,5′‐(azanediyl)ditetrazolato‐κ³N¹,N^1′:N²]bis[triaquamagnesium(II)]} monohydrate], {[Mg(C₂HN₉)(H₂O)₃][Mg₂(C₂HN₉)₂(H₂O)₆]_0.5·H₂O}_n, (I), and bis[5‐(pyrazin‐2‐yl)tetrazolate] hexaaquamagnesium(II), (C₅H₃N₆)[Mg(H₂O)₆], (II), have been prepared under hydrothermal conditions. Compound (I) is a mixed dimer–polymer based on magnesium ion centres and can be regarded as the first example of a magnesium–tetrazolate polymer in the crystalline form. The structure shows a complex three‐dimensional hydrogen‐bonded network that involves magnesium–tetrazolate dimers, solvent water molecules and one‐dimensional magnesium–tetrazolate polymeric chains. The intrinsic cohesion in the polymer chains is ensured by N—H...N hydrogen bonds, which form R₂²(7) rings, thus reinforcing the propagation of the polymer chain along the a axis. The crystal structure of magnesium tetrazole salt (II) reveals a mixed ribbon of hydrogen‐bonded rings, of types R₂²(7), R₂²(9) and R₂⁴(10), running along the c axis, which are linked by R₂⁴(16) rings, generating a 4,8‐c flu net.     

The (6–4) Dimeric Lesion as a DNA Photosensitizer

The front cover artwork is provided by Miguel A. Miranda and co‐workers at Instituto de Tecnología Química (UPV‐CSIC). The image shows that (6–4) photoproducts, primary UVB dimeric lesions, act as photosensitizers of cyclobutane pyrimidine dimers that are produced as secondary DNA lesions. Read the full text of the article at 10.1002/cphc.201600154 .     

A polymorph of butobarbital with two distinct hydrogen‐bonding motifs

N—H...O bonding in a form of 5‐butyl‐5‐ethylbarbituric acid (systematic name: 5‐butyl‐5‐ethyl‐1,3‐diazinane‐2,4,6‐trione), C₁₀H₁₆N₂O₃, produces two distinct one‐dimensional motifs, viz. tape and ladder. Both are different from the ribbon chain motif observed in two previously reported polymorphs of the same compound.     

Stereochemistry of the citrate anion in compounds containing guanidinium and citrate ions

Journal of Structural Chemistry - An analysis is presented for the results obtained in the studies initiated by A. E. Shvelashivili, Corresponding Member, Academy of Sciences of Georgia, and...     

Self-assembly of supramolecular architectures and polymers by orthogonal metal complexation and hydrogen-bonding motifs

A modular construction kit with two orthogonal noncovalent binding sites for self-assembly of supramolecular architectures is presented. The heteroditopic building blocks contain a terpyridine (tpy) unit for coordination of metal ions and a Hamilton receptor for multiple H-bonding of cyanuric acid derivatives. The association constants of ligand binding of M(II) complexes (M=Ru, Zn, Fe, and Pt) with a dendritic end cap were determined to be in the range of 10(2) and 10(4) L mol(-1) in chloroform. The capabilities for binding of metal ions were investigated by (1)H NMR and UV/Vis spectroscopy. The Fe complexes are most appropriate for the generation of discrete and high-ordered architectures due to their strong tendency to form FeL(2) complexes. Superstructures are readily formed in a one-pot procedure at room temperature. No mutual interactions between the orthogonal binding motifs were observed, and this demonstrates the highly specific nature of each binding process. Decomplexation experiments were carried out to examine the reversibility of Fe-tpy coordination. Substitution of the terminal end cap with a homoditopic bis-cyanurate linkage leads to formation of an iron-containing supramolecular strand. Formation of coordination polymers was confirmed by viscosity measurements. The supramolecular polymer strands can be reversibly cleaved by addition of a terminating cyanuric acid building block, and this proves the dynamic nature of this noncovalent polymerization process.     

Tin–halide compounds. IV

The mol­ecules of the title compound, [Sn(C₄H₉)Cl₃], adopt an eclipsed conformation with respect to the C and Cl atoms, and possess crystallographic C_s symmetry. The molecular structure and geometric parameters are comparable with those of related organotin trihalides.     

Antenna behavior of donor–acceptor dye‐loaded novel supramolecular framework hosts

New guest dye cations within the channel cavities of supramolecular hosts are studied. The guest organic dyes are intercalated in the supramolecular hosts by a coprecipitation reaction to give new dye‐sensitizer coordination polymers. The absorption spectra for the dye molecules within the supramolecular hosts show intense bands in the region from 500 to 700 nm due to the presence of the dyes within the parallel channels in the monomeric forms. The properties of the resulting colored polymers were investigated by IR, UV–vis, fluorescence spectra and X‐ray powder diffraction, indicating the excitation energy transfer from neutral red or pyronine as donors to methylene blue or thionine as acceptors within a supramolecular system filled with a mixture of both dyes. The wide‐ranging tenability of these highly organized materials offers fascinating new possibilities for exploring excitation energy transfer phenomena, and challenges for developing new photonic devices. Copyright © 2005 John Wiley & Sons, Ltd.