From 2-D layer to 2-D → 3-D parallel interpenetration: syntheses,structures and luminescent properties

Two new coordination polymers based on 1,1′-(1,4-butanediyl)bis(imidazole) (bbi) and 5-hydroxyisophthalic acid (OH-BDC), [Co₂(HO-BDC)₂(bbi)₂]·H₂O (1) and [Zn(HO-BDC)(bbi)] (2), have been hydrothermally synthesized. The complexes were characterized by single-crystal X-ray diffraction, IR, and elemental analysis. The structure determination reveals that 1 manifests a deeply corrugated 2-D layer with a (4,4) lattice. For 2, there is a highly undulating 2-D (4,4) layer structure. The layers penetrate by each other to give a 2-D → 3-D parallel interpenetrating network. Fluorescence properties and thermal stabilities of 1 and 2 in the solid state have been studied.     

Two new 1-D and 3-D Wells–Dawson structures assisted by alkali metals

Two new Wells–Dawson based compounds containing alkali metals, [Ag(H₂biim)₂]₂·[Ag₅(H₂biim)₁₀Na₂(H₂O)₂(H_3/2P₂W₁₈O₆₂)₂]·12H₂O (1) and [Cd(H₂biim)₂?K(P₂W₁₈O₆₂)_1/2] (2) (H₂biim?=?2,2′-biimidazole), have been synthesized under hydrothermal conditions. In 1, two-supporting Wells–Dawson anions are linked by a [Ag(H₂biim)₂]⁺ subunit to form a dimer. The adjacent dimers are further connected by Na⁺ through (POM)O-Na-O(POM) bonds to build a 1-D chain. In 2, adjacent anions are linked by two [Cd₂(H₂biim)₂]⁴⁺ subunits and a 1-D chain is formed. Furthermore, the anion in the chain is fused by six K⁺ ions and a 3-D framework is obtained. The alkali metals exhibit crucial influence on the conversion of dimensionality assisting anions and Ag-H₂biim subunits to construct 1-D and 3-D frameworks. The electrochemical and photocatalytic properties of 1 and 2 have been investigated.     

Hydrothermal syntheses, crystal structures and properties of 0-D, 1-D and 2-D organic-inorganic hybrid borotungstates constructed from Keggin-type heteropolyanion [α-BW12O40] and transition-metal complexes

Three novel organic-inorganic hybrid borotungstates {[Ni(phen)₂(H₂O)]₂H(α-BW₁₂O₄₀)}·4H₂O (1), [Cu^I(2,2'-bipy)(4,4′-bipy)_0.5]₂{[Cu^I(2,2′-bipy)]₂Cu^I(4,4′-bipy)₂(α-BW₁₂O₄₀)} (2) and {[Cu^I(4,4′-bipy)]₃H₂(α-BW₁₂O₄₀)}·3.5H₂O (3) (phen=1,10-phenanthroline, 2,2′-bipy=2,2′-bipyridine, 4,4′-bipy=4,4′-bipyridine) have been hydrothermally synthesized and structurally characterized by elemental analyses, IR, UV spectra, powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), single-crystal X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and photoluminescence. The structural analysis reveals that 1 consists of a 0-D bisupporting polyoxometalate cluster where two [Ni(phen)₂(H₂O)]²⁺ cations are grafted on the polyoxoanion [α-BW₁₂O₄₀]^5- through two terminal oxygen atoms, 2 shows a 1-D infinite chain constructed from [α-BW₁₂O₄₀]^5- polyoxoanions and {[Cu^I(2,2′-bipy)]₂Cu^I(4,4′-bipy)₂}³⁺ cations by means of alternating fashion, and 3 displays an unprecedented 2D extended structure built by [α-BW₁₂O₄₀]^5- polyoxoanions and -Cu^I-4,4′-bipy- linear chains, in which each [α-BW₁₂O₄₀]^5- polyoxoanion acts as a tetradentate inorganic ligand and provides three terminal oxygen atom and one two-bridging oxygen atom. The presence of Ni^II and W^VI in 1, Cu^I ions and W^VI in 2 and 3 are identified by XPS spectra. The photoluminescence of 2 and 3 are also investigated.     

Hydrothermal synthesis,crystal structures,and blue photoluminescence of two 2-D Ag–1,2,4-triazolate coordination polymers with 4462 topology

Two 2-D metal-organic coordination polymers, {[Ag(NH₂–BPT)] · NO₃} _n (1) and {[Ag(BPT)] · H₂O} _n (2), have been synthesized via self-assembly of AgNO₃ and 4-amino-3,5-bis(3-pyridyl)-1,2,4-triazole (NH₂–BPT) under hydrothermal conditions by controlling the reaction temperatures. Lower reaction temperature (140°C) led to formation of 1, which crystallizes in the monoclinic system, space group C2/c, a = 24.001(3), b = 15.844(2), and c = 12.981(3) Å, V = 2996.8(6) ų, Z = 8. When the temperature was increased to 180°C, in situ deaminization of the organic ligand led to crystallization of 2 (space group P₂1 /n, a = 7.3106(10), b = 19.633(2), and c = 9.0596(16) Å, V = 1190.2(3) ų, Z = 4). The NH₂–BPT in 1 and BPT in 2 are μ₄ tetradentate utilizing two triazolyl and two pyridyl nitrogens, generating an unusual 2-D layer, in which binuclear Ag(I) motifs and organic ligands are four-connecting nodes that inter-link in 4⁴6² topology. Adjacent 2-D metal-organic layers are linked by a system of hydrogen bonds to form 3-D supramolecular frameworks. Strong blue fluorescence emissions are observed for 1 and 2 in the solid state at ambient temperature.     

Theoretical studies on the structures and reactivity of stannylenoids I.The structures and isomerization of stannylenoid H_2SnLiF

The structures of singlet stannylenoid H2SnLiF have been examined by ab initio MO theory. Four equilibrium states and three transition states of isomerization reaction are located. The calculation shows that the p-complex 1 is the most stable and experimentally detectable. The other three species, three-membered ring 2, o-complex 3 and tetrahedron 4, are also local minima on the potential energy surface, but are higher in energy.     

Coding and ordering Kekulé structures

The concept of numerical Kekulé structures is used for coding and ordering geometrical (standard) Kekulé structures of several classes of polycyclic conjugated molecules: catacondensed, pericondensed, and fully arenoid benzenoid hydrocarbons, thioarenoids, and [N]phenylenes. It is pointed out that the numerical Kekulé structures can be obtained for any class of polycyclic conjugated systems that possesses standard Kekulé structures. The reconstruction of standard Kekulé structures from the numerical ones is straightforward for catacondensed systems, but this is not so for pericondensed benzenoid hydrocarbons. In this latter case, one needs to use two codes to recover the geometrical Kekulé structures: the Wiswesser code for the benzenoid and the numerical code for its Kekulé structure. There is an additional problem with pericondensed benzenoid hydrocarbons; there appear numerical Kekulé structures that correspond to two (or more) geometrical Kekulé structures. However, this problem can also be resolved.     

Analysis of the hyperfine structures and

From the theories of the nuclear hyperfine structure (HFS) and Λ doubling of diatomic molecules, several brief algebraic equations for interpretation of HFS and Λ doubling of transitions of diatomic molecule have been developed. A few important parameters of HFS and Λ doubling of¹⁵N¹⁶O have been efficiently and accurately obtained from the analysis of the high resolution spectra of¹⁵N¹⁶O (X²∏) observed in our experiments with these equations. This method can provide an effective approach to obtain important hyperfine parameters of novel radicals from their high resolution laser magnetic resonance spectra. Liu Yu-yan, Guo Yuan-qing, Assignments of FIR-LMR spectra of CF X²∏(υ= 1) and MIR-LMR spectra of NO X²∏ (υ =1←0), Spectroscopy and Spectral Analysis (in press).     

Distinct Hydrogen-bonded M^Ⅱ（H2O）8 Clusters as Second Building Units for 1-D, 2-D and 3-D Supramolecular Architectures （M = Cobalt and Nickel）

Two mononuclear metal-organic complexes, [Co（Hmpdc）2（H2O）4]·4H2O 1 and [Ni（Hfmpdc）2（H2O）4]·6H2O 2, were prepared from 2,6-dimethylpyridine-3,5-dicarboxylic acid （Hzmpdc） and 4-furyl-2,6-dimethylpyridine-3,5-dicarboxylic acid （H2fmpdc） with M（NO3）2 salts, respectively, and characterized by single-crystal X-ray diffraction, elemental analyses, IR spectroscopy, and photoluminescent measurement. Complex 1 crystallizes in triclinic, space group P1 with a = 7.634（5）, b = 8.695（5）, c = 10.757（6）A, α = 69.647（7）, β = 69.957（8）, γ = 83.733（7）°, V = 628.9（7）A^3, Dc = 1. 561 g/cm^3,μ（MoKa） = 0.763 mm^-1, F（000） = 309, Z = 1, the final R = 0.0553 and wR = 0.1469 for 1909 observed reflections （Ⅰ 〉 2σ（Ⅰ））. Complex 2 crystallizes in monoclinic, space group P21/n with a = 9.5934（16）, b = 12.422（2）, c = 14.826（3） A, β = 105.201（2）°, V = 1705.0（5）A3, Dc = 1. 479 g/cm^3,μ（MoKa） = 0.655 mm^-1, F（000） = 796, Z = 2, the final R= 0.0351 and wR = 0.0889 for 2387 obsevved reflections （Ⅰ 〉 2σ（Ⅰ））. In the crystal structures of 1 and 2, diverse supramolecular motifs from 1-D chains/ladders to 3-D networks are constructed from corresponding distinct [M^Ⅱ（H2O）8] ion clusters as the second building units, respectively. The solid state compounds of 1 and 2 show similar photoluminescent spectra with emission maximum at ca.     

Synthesis and Sweetness of Pseddo-β-D and L-Frdctopyranose

Abstract

Pseudo-β-D (D-2) and L-fructopyranose (L-2), 1(S) and (1R)-(1,2/-3,4)-4-C-hydroxymethyl-1,2,3,4-cyclohexanetetrol, have been synthesized, starting from optically active endo-adducts of furan and acrylic acid, following the modified procedure used for the preparation of the racemic modification. It has been demonstrated that the D and L-enantiomers are nearly as sweet as D-fructose, and the former is somewhat sweeter than the latter.     

1-D and 2-D coordination polymers of lead(II) thiocyanate with substituted 2,2′-bipyridine ligand

Two lead(II)-thiocyanato coordination polymers with 5,5′-dimethyl-2,2′-bipyridine (5,5′-dm-2,2′-bpy) and 4,4′-dimethoxy-2,2′-bipyridine (4,4′-dmo-2,2′-bpy) as chelating ligands were synthesized and characterized by elemental analysis, IR and ¹H-NMR spectroscopy, thermal behavior, and X-ray crystallography. These complexes have formulas [Pb(5,5′-dm-2,2′-bpy)(NCS)₂] _n (1) and [Pb(4,4′-dmo-2,2′-bpy)(NCS)₂] _n (2). The coordination numbers of Pb^II in 1 and 2 are four, PbN₄, with “stereo-chemically active” electron pairs and hemidirected coordination spheres. Considering Pb···S as weak bonds, 1 and 2 are 1- and 2-D coordination polymers, respectively. The supramolecular features in these complexes are guided/controlled by weak directional intermolecular interactions.     

Valence bond description for structures of O_3, SO2 and NO_2~-

A modern valence bond approach, namely bonded tableau unitary group approach, isapplied to ozone, sulphur dioxide and nitrite systems, respectively. It is shown that the biradicalstructure is in the primary position in descrbing the molecular structure of ozone. Thus threeinstead of two resonance structures are needed to describe the ground state of ozone. The caseof sulphur dioxide is similar to that of ozone. It is found that, however, for the nitrite anion fourresonance structures are needed.     

Formation of 1-D ladder- and 2-D sheet-like networks due to stereospecific π–π stacking and hydrogen bonding between enantiomeric sulfur-bridged dinuclear complexes of penicillaminates

Reaction of trans(N)-[Co(D-pen)₂]^? (pen = penicillaminate) or trans(N)-[Co(L-pen)₂]^? with [MCl₂(L)] {M = Pd or Pt, L = 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen)} in the presence of tetrafluoroborate stereoselectively gave an optically active S-bridged dinuclear complex, [M(L){Co(D-pen)₂}]BF₄ · 2H₂O or [M(L){Co(L-pen)₂}]BF₄ · 2H₂O. The mixture of equimolar amounts of these enantiomers in H₂O crystallizes as [M(L){Co(D-pen)₂}]_0.5[M(L){Co(L-pen)₂}]_0.5BF₄ · 4H₂O (DLbpyM · 4H₂O, DLphenM-A · 4H₂O), in which the enantiomeric complex cations are included by the ratio of 1 : 1. In crystals of DLbpyM · 4H₂O and DLphenM-A · 4H₂O, [M(L){Co(D-pen)₂}]⁺ and [M(L){Co(L-pen)₂}]⁺ interact stereospecifically with each other through π-conjugated systems to form dimeric structures. Other racemic crystals with the same chemical compositions as DLphenM-A · 4H₂O, DLphenM-B · 4H₂O, were obtained from equimolar amounts of [M(phen){Co(D-pen)₂}]⁺ and [M(phen){Co(L-pen)₂}]⁺ in aqueous acetonitrile solution. In the crystals of DLphenM-B · 4H₂O, [M(phen){Co(D-pen)₂}]⁺ and [M(phen){Co(L-pen)₂}]⁺ are arranged alternately while overlapping phen planes, and the π electronic systems of phen interact with each other. Although stereospecific hydrogen bonds between the coordinated ?NH₂ and ?COO^? groups are formed in both DLphenM-A · 4H₂O and DLphenM-B · 4H₂O, their bonding modes differ noticeably from each other. As a result, DLphenM-A · 4H₂O builds up 1-D ladder-like networks due to the stereospecific π–π stackings and hydrogen bondings between enantiomers, while 2-D sheet-like networks are established for DLphenM-B · 4H₂O.     

Helical secondary structures in 2:1 and 1:2 α/γ-peptide foldamers

Oligomers containing both α- and γ-amino acid residues in a 1:1 alternating pattern have recently been shown by several research groups to adopt helical secondary structures. We have begun to explore the folding behavior of oligomers with different α-residue/γ-residue backbone patterns. Previously we reported that the γ-amino acids bearing a cyclohexyl constraint at the C_β–C_γ bond and a variable side chain at C_α strongly promote a helical conformation containing 12-atom CO(i)?H–N(i+3) hydrogen bonds for 1:1 α:γ backbones. Here we report synthesis and crystallographic analysis of 2:1 and 1:2 α/γ-peptides that adopt CO(i)?H–N(i+3) hydrogen-bonded helical conformations.     

Electronic structures and stabilities of GeC n and Ge2C n in Hückel theory

Some recent results about Ge _p C _n ⁺ ions (p=1, 2;n < 6) produced in laser microprobe mass analyser experiments (LAMMA) show very marked alternations in the emission intensities I(Ge _p C _n ⁺ ) as a function of then andp parities. I(Ge _p C _n ⁺ ) are maxima for evenn. Thus, intensity maxima occur when the total atom numberm of the aggregates is odd for GeC _n ⁺ (m=n+1) and even for Ge₂C _n ⁺ (m=n+2). As a result, GeC _n ⁺ ions seem to behave as C _m ⁺ ions, whereas the behaviour of Ge₂C _n ⁺ ions is quite similar to that of Ge _p ⁺ ions formed in SIMS or vaporization experiments on pure germanium. It is well known (correspondence rule) that the parity effect in the emissions corresponds to alternations in the ion stabilities. These results are analysed from a model built in Hückel approximation with hybridization. Forp=1, the clusters are assumed to be insp hybridization as for C _m ⁺ ions, hence with linear shapes, and forp=2, they would rather be insp ² orsp ³ hybridization as for Ge _p ⁺ ions. Relative stabilities and distributions of the energy levels of the aggregates are then calculated. The relative stabilities given for Ge _p C _n ⁺ by this model show maxima for evenn as in experiments, and we have thus a good agreement between our calculation results and the experimental data. Moreover, we found that Ge₂C _n ⁺ would rather be insp ³ hybridization, that is under three dimensional shapes.     

Formation of a 1-D metal–water chain and a 2-D water–sulfate layer containing cyclic water octamers in a 3-D supramolecular network

A new tetranuclear complex, {[Cu(phen)(OH)]₄(H₂O)₂}?·?(SO₄)₂?·?8H₂O (1) (phen = 1,10-phenanthroline), has been synthesized and characterized by elemental analysis, UV-Vis, IR, TG, and single-crystal X-ray diffraction. Complex 1 exhibits a 3-D supramolecular network with a 1-D metal–water chain consisting of tetranuclear hydroxo-bridged copper(II) clusters and water octamers and a 2-D water–sulfate layer containing cyclic water octamers with five types of O–H?···?O hydrogen-bonding motifs. The free ligand and its complex were screened for antibacterial activity against Gram-positive and Gram-negative bacteria.     

Elastic properties and electronic structures of typical Al–Ce structures from first-principles calculations

The elastic property and electronic structure of three typical Al–Ce structures have been studied by means of first-principles calculations within GGA approximation. The optimized structural parameters for these precipitates agree very well with experimental data. The obtained negative cohesive energy and formation enthalpy show that all of these precipitates have strong structural stability. Elastic constants as well as other mechanical parameters such as bulk modulus B, shear modulus G, Young’s modulus E and Poisson’s ratio ν for these phases are computed and discussed. The calculated electronic densities of state and charge distribution show the covalent features of Ce–Ce and Al–Ce bonding in three phases, which reveals the underlying mechanism for the elastic properties of these Al–Ce structures.     

Analysis of why boron avoids sp2 hybridization and classical structures in the BnHn+2 series

We performed global minimum searches for the B(n) H(n+2) (n=2-5) series and found that classical structures composed of 2c-2e B-H and B-B bonds become progressively less stable along the series. Relative energies increase from 2.9?kcal?mol(-1) in B(2) H(4) to 62.3?kcal?mol(-1) in B(5) H(7). We believe this occurs because boron atoms in the studied molecules are trying to avoid sp(2) hybridization and trigonal structure at the boron atoms, as in that case one 2p-AO is empty, which is highly unfavorable. This affinity of boron to have some electron density on all 2p-AOs and avoiding having one 2p-AO empty is a main reason why classical structures are not the most stable configurations and why multicenter bonding is so important for the studied boron-hydride clusters as well as for pure boron clusters and boron compounds in general.     

Hydrothermal syntheses and crystal structures of crystalline catalysts based on 3-D Ln3+–pdc2− frameworks and [BW12O40]5− and their heterogeneous photocatalytic oxidation of thiophene

Five [BW₁₂O₄₀]^{5 ?} -containing metal-organic frameworks (MOFs), {K[Ln(H₂O)₄(pdc)]₄}[BW₁₂O₄₀]·2H₂O (Ln=La 1 and Ce 2, H₂pdc = pyridine-2,6-dicarboxylate) and {K[Ln(H₂O)₃(pdc)]₄}[BW₁₂O₄₀]·6H₂O (Ln=Tb 3, Dy 4 and Er 5), are synthesized hydrothermally. Ln³⁺ and pdc^2? are built into 3-D MOF segments containing large channels and cavities which are occupied by [BW₁₂O₄₀]^{5 ?} . Herein, we report MOF-containing polyoxometalates (POMs) as photocatalysts to oxidize thiophene with O₂ as the oxidant. Photo-excited state species ([BW₁₂O₄₀]^5??) are generated under UV irradiation and then H₂O is oxidized into OH˙ radicals and O₂ is reduced into O₂ ^2?. The active oxygen species (O₂ ^2?, OH˙) oxidize thiophene in the presence of photocatalysts and SO₃, CO₂, and H₂O are obtained as photoproducts. ESR measurements provide evidence that OH˙ species are generated during photocatalysis.     

Synthesis and structures of α-lithiated vinyl ethers

The structures of α-lithiated vinyl ethers were explored on the basis of a combined computational and NMR study. Calculations (M06/6-31 + G(d)) on free energies of aggregate formation for a series of α-lithiated vinyl ethers indicated that the tetramer is generated preferentially in both the gas phase and THF solution, except for cyclohexylidene derivatives. (1-(Methoxymethoxy)vinyl)lithium, (2,2-difluoro-1-(methoxymethoxy)vinyl)lithium, and (1-butoxyvinyl)lithium were prepared in NMR tubes by the deprotonation of alkyl/alkoxylalkyl vinyl ethers or by the transmetalation of tin compounds. The NMR spectra of these lithium species in THF solution showed that in each species one aggregate is primarily present at 173 K, which is consistent with the preference of the tetramer.     

Syntheses,weak interactions,and 3-D network structures of two salts based on [Ni(i-mnt)2]2− (i-mnt2−=iso-maleonitriled-ithiolate) anion with substituted pyridinium cation

Two new salts, [2-NaMePy]₂[Ni(i-mnt)₂] (1) and [2-NaMe-4-MePy]₂[Ni(i-mnt)₂] (2) ([2-NaMePy]⁺ = 1-(2′-naphthylmethyl)pyridinium, [2-NaMe-4-MePy]⁺ = 1-(2′-naphthylmethyl)-4-methylpyridinium and i-mnt^2? = iso-maleonitriledithiolate), have been prepared and characterized by elemental analyses, UV, IR, molar conductivity, and single crystal X-ray diffraction. The anions in 1 form a 1-D chain through short C ··· N interactions between the anions, while the cations in 2 stack a 1-D column via C–H ··· π and π ··· π stacking interactions between the cations. The effect of weak intramolecular interactions such as C–H ··· N, C–H ··· S, C–H ··· Ni hydrogen bonds, and π ··· π stacking interactions between the cations and the anions further generate a 3-D network structure. The change of the molecular topology of the countercation when the 4-substituted group in the pyridine ring is changed from H atom to CH₃ group results in different crystal system, space group, and the stacking mode of the cations and anions of 1 and 2.