Cup-shaped E,E-stilbenophane: synthesis,crystal structure and supramolecular chemistry

A new E,E-stilbenophane was synthesised and characterised. The crystal structure of this cyclophane shows that this molecule has a cup-shaped structure, which hosts a phenyl ring of neighbouring molecule as guest in its cavity with a π–π distance of about 3.7 Å. Moreover, the NMR spectra and theoretical analysis (gauge-independent atomic orbitals (GIAO) and quantum theory of atoms in molecules (QTAIM)) suggest that the silver recognition by E,E-stilbenophane host molecules is based on cation–π interactions in which the π-electrons of the double bonds play a major role.     

Facile,high-yielding synthesis of deepened cavitands: a synthetic and theoretical study

A wide variety of 2-methyl-resorcinol-based deepened cavitands were synthesised from readily available reagents in a four-step procedure with overall yields of up to 62%. A systematic variation of the rim was carried out by building up a flexible upper aromatic wall on the rigid cavitand platform through CH₂, CH₂O and CH₂OCH₂ spacers. These aromatic walls were further extended by a Suzuki cross-coupling reaction. Full characterisation of the synthesised cavitands was carried out. The solid-state structure of tetrakis(phenoxymethyl)cavitand was determined by X-ray crystallography. Gas-phase theoretical calculations for this molecule predict the presence of weak T-shaped interactions between the upper phenyl rings. The host–guest complex formation ability of two deepened cavitand hosts towards 4-chloro-benzotrifluoride was proved by photoluminescence method.     

An AM1 semiempirical study of host-guest complexation in hemicarcerand complexes

Semiempirical AM1 calculations have been carried out on host-guest complexes of model hemicarcerands 1a and 2a. The justification for the choice of the AM1 Hamiltonian was based on a comparison between reported X-ray data for the smaller tetrabromocavitand 4a and computational results obtained using several different Hamiltonians. The complexation behavior of hemicarcerands 1a and 2a have been compared with experimental results reported by Cram et al. for the related hemicarcerands 1b and 2b. Based on this comparison, a criterion for predicting guest encapsulation was developed, E(complexation), which relies on the calculation of AM1 heats of formation for host, guest, and hemicarceplex. If E(complexation) is lower than 10 kcal/mol, then a guest will be encapsulated, while if it is greater than 30 kcal/mol, a guest will not be encapsulated. The use of constrained-path AM1 optimizations to determine the energy barriers to guest entry and exit from the host was found to be a useful tool for examining suitable host-guest combinations when the E(complexation) criteria does not hold. We have computed the barriers to exit of N, N-dimethylformamide (dmf) and furan from the hemicarcerand 1a, the former has been compared with the experiment and shows excellent agreement. Based on the success of the above computational methods in predicting which host-guest combinations will form stable hemicarceplexes we have synthesized a new target hemicarceplex 1b.furan.     

Synthesis and crystal structure of a silver(I) 6-methylmercaptopurine riboside complex

Silver nitrate reacts with 6-methylmercaptopurine riboside (6-MMPR) in aqueous solution containing methanol and dimethyl sulfoxide at room temperature to give a colourless crystalline complex, namely, bis(6-methylmercaptopurine riboside-κN⁷)(nitrato-κ²O,O′)silver(I) 2.32-hydrate, [Ag(NO₃)(C₁₁H₁₄N₄O₄S)₂]·2.32H₂O. The crystal structure, determined from synchrotron diffraction data, shows a central Ag^I ion on a crystallographic twofold rotation axis, coordinated in an almost linear fashion by two 6-MMPR ligands via atom N7 (purine numbering), with the nitrate counter-ion loosely coordinated as a bidentate ligand, forming a discrete molecular complex as an approximate dihydrate. The complex and water molecules are connected in a three-dimensional network by hydrogen bonding.     

Monitoring the shape evolution of silver nanoplates: a marker study

Out of the frame: A marker study using gold frames was designed to reveal that silver nanoplates undergo a shape transition during their seeded growth from triangular to circular to hexagonal plates before ultimately returning to triangular structures with an orientation 180° relative to that of the original triangular seeds (see picture, the original gold triangular frame is visible at the center of the silver nanoplate).     

Cambiarenes: Single-Step Synthesis and Selective Zwitterion Binding of a Clip-Shaped Macrocycle with a Redox-Active Core

A novel macrocyclic host molecule was synthesized that forms in a single step from commercially available starting materials. The core of the macrocycle backbone possesses two quinone rings and, thus, it is redox-active. Host–guest binding involving the clip-shaped cavity indicates selective binding of pyridine N-oxides based on the electron density of and steric bulk around the anionic oxygen.     

Halide ion effect on the chloroform chemical shift in supramolecular complexation studies with tetra-n-butylammonium salts: a 1H NMR and X-ray study

A ¹H NMR spectroscopic study of tetra-n-butylammonium halides (TBAX: X = Cl^? , Br^?  or I^? ) in CDCl₃ solutions was conducted. Complexation studies of TBAX salts with different host molecules using ¹H NMR in CDCl₃ have previously revealed that the reference residual CHCl₃ proton signal had been shifted downfield. The aim of the study was to quantify the extent of these chemical shift changes with TBAX salts. Linear concentration–chemical shift relationships in each case were obtained from the resulting titration plots obtained from the addition of the TBAX salts alone to CDCl₃. Interactions in the solid state as determined by X-ray crystallography support the solution-state investigations indicating halide ion–chloroform proton interactions.     

Synthesis,identification, crystal structure and theoretical study of a Ce(IV) complex

The compound (dienH₃)₂(pydc)_3, 1; dien: diethyltriamine, pydcH₂: pyridine-2,6-dicarboxylic acid, as a proton transfer ligand was applied to synthesize (dienH₃)₂[Ce(pydc)₃]₃·16.75H₂O, 2. The compounds were examined by elemental analysis, IR, UV and NMR spectroscopy. In addition, the compound 2 was studied by TG analysis, single crystal X-ray diffractometry and computational calculations. Geometry optimizations were carried out using B3PW91 hybrid density functional and quasi-relativistic effective core potentials (ECP46MWB) to represent the atomic core of cerium and 6–311G(d, p) basis set that used to describe the electrons of oxygen, nitrogen, carbon and hydrogen atoms. Also, natural bond orbital (NBO) analysis at the B3 PW91/A level gives the natural electron population and the natural charge for each atom. Cerium atom in 2 is nine-coordinated with three (pydc)^2? groups giving an anionic complex which is balanced by (dienH₃)³⁺ in the crystal structure. Several intermolecular interactions including O–H···O and N–H···O hydrogen bonds, face-to-face and edge-to-face stackings are responsible to stabilize the extended structure.     

Synthesis and photophysical,antibacterial studies of some novel molecular tweezers

Zeroth and first generation dendritic wedges with thiophene amide as surface group and 1, 2, 3-triazole as bridging unit which can function as molecular tweezers are synthesised by both convergent and divergent approaches. All the synthesised dendritic wedges displayed the absorbance band between 256 and 294 nm and fluorescence maximum between 357 and 528 nm supporting their self complementary property. Dendritic wedge 5 showed better antibacterial activity than other dendritic wedges in the assay against the human pathogens viz Staphylococcus aureus, Escherichia coli, Bacillus cereus and Klebsiella pneumonia and the dentritic wedge 5 was also effective in the computational molecular docking studies.     

Quinuclidine complex with alpha-cyclodextrin: a diffusion and 13C NMR relaxation study

The stability of an inclusion complex of quinuclidine with alpha-cyclodextrin in solution was investigated by NMR measurements of the translational diffusion coefficient. A 1:1 stoichiometry model yielded an association constant of 35 +/- 3 M(-1). The guest molecules exchange rapidly between the host cavity and the bulk solution. The reorientational dynamics of the guest and host molecules was studied using carbon-13 NMR relaxation at two magnetic fields. The relaxation of the host nuclei showed very little dependence on the guest-host concentration ratio, while the 13C spins in quinuclidine were sensitive to the solution composition. Using mole-fraction data, it was possible to extract the relaxation parameters for the bound and free form of quinuclidine. Relaxation rates of the guest molecule, free in solution, were best described by an axially symmetric model, while the data of the complex species were analyzed using the Lipari-Szabo method. Applying the axially symmetric model to the complexed quinuclidine indicated that the anisotropy of its reorientation in the bound form was increased.     

The spectrophotometric study of a fluorescence‐enhanced inclusion complex threaded with β‐cyclodextrin: Synthesis and characterization

A novel achiral monomer end‐capped with a phenyl‐[1,3,4]oxadiazolyl group and threaded through β‐cyclodextrin was synthesized to investigate the host‐guest interactions in the inclusion complex. ¹H NMR studies revealed that one or two cyclodextrin molecules were threaded onto the synthesized achiral monomer, leading to the formation of a fibrous construction of self‐assembled inclusion complexes. The formation of a self‐assembled inclusion complex was identified using SEM and TEM. The highly ordered alignment of self‐assembled supramolecules was confirmed using polarized optical microscopy. We demonstrate an easy process for the fabrication of nano‐structured self‐assembled inclusion complexes in pyridine/ethanol (1 mL/10 mL) as well as the enhancement of photo‐induced fluorescence via monomers end‐capped with a phenyl‐[1,3,4]oxadiazolyl moiety threaded with β‐cyclodextrins. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3368–3374, 2010     

2-吡嗪羧酸银的合成、晶体结构及热化学性质

以二次蒸馏水为溶剂,合成了2-吡嗪羧酸银(Ag(pyza)(s)),并利用X-射线单晶衍射法表征了其晶体结构.根据晶体结构数据计算得到2-吡嗪羧酸银的晶格能为554.10 kJ/mol.利用TG/DSC热分析技术研究了该化合物的热分解过程;用精密自动绝热热量计测量了其在78~378 K温区的低温热容;通过最小二乘法拟合得到了摩尔热容随折合温度变化的多项式方程,利用此方程计算出该化合物的舒平热容和各种热力学函数.通过设计合理的热化学循环,利用等温环境溶解-反应热量计分别测定了所设计热化学反应的反应物和产物在选定溶剂中的溶解焓,通过计算得到反应的反应焓为:?(31.919±0.526)kJ/mol.利用Hess定律计算出2-吡嗪羧酸银的标准摩尔生成焓为:?(243.659±1.298)kJ/mol.利用紫外-可见光谱仪对反应物和产物溶解所得溶液分别进行测量,从而证实了所设计热化学循环的可靠性.     

Covalently assembled resorcin[4]arenes and molecular tweezers: a chiral recognition rationale by NMR

Chiral diamides and tetramidic resorcin[4]arenes deriving from (R,R)-1,2-diaminocyclohexane and (S,S)-1,2-diphenylethylendiamine, and a valine containing resorcin[4]arene have been compared by NMR in the enantiodiscrimination of mandelic acid. The relevance of cooperation between side arms and external surface of resorcin[4]arene core has been ascertained.     

Synthesis,crystal structure and complexation behaviour of a thiacalix[4]arene bearing 1,2,3-triazole groups

The structure and complexation behaviour of 1,3-alternate-1,2,3-triazole based on thiacalix[4]arene,1,3-alternate-1 and 2 have been determined by means of X-ray analysis, fluorescence and ¹H NMR spectroscopy. The X-ray results suggested that the nitrogen atom N3 on triazole ring can act as hydrogen bond acceptors in the self-assembly of a supramolecular structure. The fluorescence spectra changes indicated that the thiacalix[4]arene bearing 1,2,3-triazole groups were highly selective for Ag⁺ in comparison with other tested metal ions by enhancement of the monomer emission of pyrene. The ¹H NMR results suggested that Ag⁺ can be strongly bonded by the triazole groups with the cooperation of the ionophoric cavity formed by the two inverted benzene rings and the sulfur atoms of the thiacalix[4]arene.     

Synthesis and crystal structure of a novel luminescent cadmium complex

A novel cadmium complex Cd(IPA)₂(phen)₂ (IPAH?=?isophthanic acid, phen?=?1,10-phenanthroline) was synthesized by hydrothermal methods and characterized structurally by X-ray diffraction. The complex possesses a monomeric molecular structure. Cd(IPA)₂(phen)₂ is orthorhombic, space group Aba2, with a?=?14.670(7), b?=?22.876(8), c?=?9.473(6)?Å, V?=?3179(3)?ų, D _c?=?1.573?Mg?m^?3, Z?=?4, F(000)?=?1520, GOF?=?1.027, R1?=?0.0299, wR2?=?0.0617. Photophysical properties (fluorescence excitation and emission spectra) are reported.     

Star hexacarboxylate: Synthesis,crystal structure and luminescent properties of its terbium complex

A new star host, hexakis (carboxylphenyl-2-thiolmethyl)benzene (1H6), has been synthesized by a simple one-step condensation procedure with the high yield. Crystal structure of the DMSO adduct 1H6.6DMSO (2) reveals it to be rhombohedral crystal system, space group R-3, with a =b=2.4129(2), c= 1.1576(3) nm, α=β= 90°γ = 120°?V=5.837(2) nm3,Z=3. The six arms of side benzole acid rings and the H-bonded DMSO molecules are located alternatively above and below the central benzene plane with "1,3,5-up/2,4,6-down" conformation. Terbium complex (Tb21)2Py.9H2O (3) was prepared in hot pyridine, which shows bright characterized Tb(Ⅲ) emission with a longer lifetime and higher luminescent intensity than that of the corresponding terbium benzoate in solid state. These observations suggest that host 1 is a good antenna for sensitizing TbⅢ emission.     

Urea Derivatives as Functional Molecules: Supramolecular Capsules,Supramolecular Polymers,Supramolecular Gels,Artificial Hosts,and Catalysts

Urea, which has both hydrogen bond acceptor and donor moieties, is an ideal structure for a supramolecular synthon. Various supramolecules having ureido group(s) have been widely developed. This article summarizes recent developments of urea derivatives that exhibit various functions: i) supramolecular capsules that form discrete urea–urea intermolecular hydrogen bonds, ii) supramolecular polymers that form continuous urea–urea intermolecular hydrogen bonds, iii) supramolecular gels that form continuous urea–urea intermolecular hydrogen bonds, iv) artificial host molecules based on the molecular recognition ability of the ureido group, and v) catalytic reactions developed by utilizing the molecular recognition ability of the ureido group.     

Synthesis, crystal structure, and catalytic properties of MgCo6Ge6

The ternary compound MgCo6Ge6 represents a novel member of the RM6X6 phases, which contains a graphite-type Ge network, Kagomé nets of Co atoms, and Ge2 dumbbells with an unexpected short Ge-Ge contact in the range of a localized Ge-Ge single bond. The title compound shows a large variety of chemical bonding, which ranges from metallic to multicenter and covalent bonding. The role of polar intermetallic alloys as promising candidates for the application as catalysts for the selective hydrogenation of alpha,beta-unsaturated aldehydes is discussed. MgCo6Ge6 possesses a remarkable activity and selectivity for the hydrogenation of cis/trans-citral to geraniol and nerol.     

A highly distorted hexacoordinated silver(I) complex: synthesis,crystal structure,and DFT studies

A new highly distorted hexacoordinated silver(I) complex [AgL₂NO₃] with 2-(bis(methylthio)methylene)-1-phenylbutane-1,3-dione (L) as ligand is synthesized and characterized using elemental analysis, FTIR, NMR, and X-ray single-crystal structure analysis. The ligand (L) and the nitrate group act as bidentate ligands. The geometry around the silver ion has an intermediate configuration between a trigonal prism (TP) and an octahedron (OCT). Continuous shape measure (CShM) analysis indicated a closer configuration to TP than OCT. Experimentally and theoretically, the Ag–S bonds are shorter than any of the Ag–O bonds, indicating a stronger interaction between Ag⁺ (soft metal) and S-atom as a softer site than oxygen. Natural bond orbital (NBO) analyses showed higher interaction energies between the S-atom lone pairs and the Ag–antibonding NBO (8.61–31.39 kcal/mol) than LP(O)→Ag (3.48–11.46 kcal/mol). The acceptor antibonding NBO of the Ag atom has mainly s-orbital character. The Ag atom has a natural charge of +0.7579 e at the experimental structure, suggesting that negative charge was transferred from the ligand (0.0666 e) and nitrate (0.1090 e) to the Ag ion. Using Hirshfeld surface analysis, the important intermolecular interactions between molecular units within the crystal lattice of the ligand and its Ag-complex were analyzed and compared.