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Amine-linked (C−NH) porous organic cages (POCs) are preferred over the imine-linked (C=N) POCs owing to their enhanced chemical stability. In general, amine-linked cages, obtained by the reduction of corresponding imines, are not shape-persistent in the crystalline form. Moreover, they require multistep synthesis. Herein, a one-pot synthesis of four new amine-linked organic cages by the reaction of 1,3,5-triformylphloroglucinol (Tp) with different analogues of alkanediamine is reported. The POCs resulting from the odd diamine (having an odd number of −CH2 groups) is conformationally eclipsed, while the POCs constructed from even diamines adopt a gauche conformation. This odd–even alternation in the conformation of POCs has been supported by computational calculations. The synthetic strategy hinges on the concept of Schiff base condensation reaction followed by keto–enol tautomerization. This mechanism is the key for the exceptional chemical stability of cages and facilitates their resistance towards acids and bases.

The variation of hardness as a function of the number of carbon atoms in α,ω-alkanedicarboxylic acids, C(N)H(2N-2)O4 (4≤N≤9), was examined by recourse to nanoindentation on the major faces of single crystals. Hardness exhibits odd-even alternation, with the odd acids being softer and the even ones harder; the differences decrease with increasing chain length. These variations are similar to those seen for other mechanical, physical, and thermal properties of these diacids. The softness of odd acids is rationalized due to strained molecular conformations in them, which facilitate easier plastic deformation. Relationships between structural features, such as interplanar spacing, interlayer separation distance, molecular chain length, and signatures of the nanoindentation responses, namely, discrete displacement bursts, were also examined. Shear sliding of molecular layers past each other during indentation is key to the mechanism for plastic deformation in these organic crystals.

A question of both fundamental as well as practical importance is the nature of one-dimensional carbon, in particular whether a one-dimensional carbon allotrope is polyynic or cumulenic, that is, whether bond-length alternation occurs or not. By combining the concept of aromaticity and antiaromaticity with the rule of Peierls distortion, the occurrence and magnitude of bond-length alternation in carbon chains with periodic boundary conditions and corresponding carbon rings as a function of the chain or ring length can be explained. The electronic properties of one-dimensional carbon depend crucially on the bond-length alternation. Whereas it is generally accepted that carbon chains in the limit of infinite length have a polyynic structure at the minimum of the potential energy surface with bond-length alternation, we show here that zero-point vibrations lead to an effective equalization of all carbon-carbon bond lengths and thus to a cumulenic structure.

A new layered zinc phosphate, [Co(NH3)6]3[Zn8(HPO4)8(PO4)2](PO4) (ZnPO-CJ68), has been successfully prepared by using cobalt hexaammine as a template. Single-crystal structure analysis revealed that the structure of ZnPO-CJ68 contains double-sheet layers constructed by strict alternation of Zn- and P-centered tetrahedra. The host framework of the double-sheet layer features unusual 3D microporosity with 8-ring apertures along three directions. The guest Co(NH3)63+ cations are located not only between but also within the host layers. The shape of the guest Co(NH3)63+ cation perfectly matches that of the void within the layered host framework. ZnPO-CJ68 was further characterized by powder X-ray diffraction, thermogravimetric analysis, and inductively coupled plasma spectroscopy.

The structures and stability of F4F6-(BN)n polyhedrons (n = 20–30) with the alternation of B and N atoms were studied with DFT method. The calculation results reveal that the atoms at square–square fusions with large pyramidalization angles are remarkably extruded out of the surfaces of (BN)n polyhedrons. The energetically favorable isomers do not contain square–square bonds and the energies of those isomers containing square–square bonds increase with the number of square–square bonds linearly, demonstrating that the energetically favorable structures of F4F6-(BN)n polyhedrons satisfy the isolated square rule and square adjacency penalty rule. The atom pyramidalization determines the stability of the isomers. The binding energy is fitted to the numbers of vertices formed from different faces and a model is proposed to predict the relative stability of these polyhedral molecules. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Nicht langer obskur: Eine brauchbare Synthese der ersten sechs Mitglieder der fundamentalen Klasse der acyclischen verzweigten Oligoalkene ist gelungen. Auf diesem Weg sind die Zielverbindungen in guten Ausbeuten im Multigramm-Masstab zuganglich. Verbindungen mit einer geraden Zahl an Doppelbindungen sind deutlich stabiler als die mit einer ungeraden Zahl (siehe Bild), und sie unterscheiden sich im Reaktionsverhalten bei Diels-Alder-Reaktionen.

The conformations of a cyclic octapeptide built with an alternation of D and L residues are investigated on the basis of 1H n.m.r. and CD data. The cyclooctapeptide can form structures which are specific to the alternating D-L sequence. This peptide can form two types of complexes with cations (peptide 2-cation and peptide-cation complexes) and the binding with monovalent cation is weak. This peptide is able to induce transmembrane ion transfer through both a carrier mechanism and pore formation.

The equilibrium geometries of the cylinder-like lithium hydrocarbon complexes Li[Cn]1 (n = 7–12) are calculated within density functional theory with PBE0 exchange-correlation potential. The 6-31 G* basis was set on carbon and lithium atoms while STO-3G one was chosen for hydrogens. The complexes with odd n possess Cs symmetry for equilibrium structures, and lithium is located near the border of π-electron system of the hydrocarbons. For complexes Li[Cn]1 with even n (n = 8, 10, 12), the lithium position at the center of benzene ring is stable, and the equilibrium geometry has C2v point symmetry. We have observed correlation between the alternation of the equilibrium structure of the complex and degeneracy of boundary MO of isolated hydrocarbons. By using Cnh symmetry, the π-MO of the [Cn]1 are found analytically within Huckel model. The nonbonding orbitals with energy α take place only for hydrocarbons with even n. These MO's are characterized by the density distributions among the terminal carbon atoms with sign alternation of AO's contributions. The solution with energy α with analogous distributions is present for larger hydrocarbons [Cn]q with any finite q and even n. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007

In this work the first samples of polymeric semi-conductors of a new structure are produced. Their electric conductivity is of the order ∼10 -2 Ohm -1 . cm -1 and it increases with temperature. Their synthesis includes a stage of radiation grafting of a matrix-type on stretched polyamide films. Conducting molecular circuits in such materials include fragments with conjugated bonds and metal clusters. The alternation of these fragments is determined by the polyamide matrix.

A less dense packing is observed in the odd-numbered n-alkanes compared to the even-numbered members, which consequently lowers melting temperatures. The reason for this is that the even-numbered n-alkanes have optimal intermolecular interactions at both ends (see the picture on the left), while the odd-numbered ones possess these only at one end-at the other end the intermolecular distances are longer (right).

Donor-acceptor polyenes of various lengths, and that combine aro- matic electron-donating moieties with powerful heterocyclic electron-withdraw- ing terminal groups, have been synthe- sized and characterized as efficient non- linear optical (NLO) chromophores. Their linear and nonlinear optical proper- ties have been investigated, and variations in these properties have been related to ground-state polarization (dipole p) and structure. In particular, unprecedented quadratic hyperpolarizabilities (p) have been achieved (up to p(0) =I500 x 10-30esu) by reduction of the bond- length alternation (BLA) in the polyenic chain. In each series of homologous com

The regiochemistry of a Co-catalyzed 1,4-hydrovinylation reaction can be controlled by alternation of the ligands applied.

Under mild conditions, a linear polymeric (C702- )n fulleride was synthesized as single crystals which allow, for the first time, a complete structural analysis of a polymeric fulleride. Starting from the strongest "disturbance" of the cage geometry at the linkage sites, the pronounced alternation of the bond lengths decreases towards the middle of the C70 units (see Schlegel diagram of the C702- building block; color coding of the bond lengths [A]: blue 1.52).

C10H6N2O4, Mr = 218.2, triclinic, P1, a = 7.5552 (8), b = 7.763 (1), c = 9.073 (1) A, alpha = 110.742 (9), beta = 99.570 (9), gamma = 100.309 (9) degrees, V = 474.1 (2) A3, D chi = 1.528 g cm-3, Z = 2, Cu K alpha (lambda = 1.54178 A, graphite monochromator) mu = 10.5 cm-1, F(000) = 224, T = 293 K, final R = 0.064, wR = 0.092 for 1213 reflections with I greater than 3 sigma (I). The naphthalene ring is planar with an average deviation of 0.004 A from the ten-atom least-squares plane. The C-C distances show the typical naphthalene alternation: C1-C2, C3-C4, C5-C6 and C7-C8 average 1.359 A; C2-C3 and C6-C7 average 1.391 A. The C1 nitro group is twisted out of the ring plane by approximately 37 degrees to relieve non-bonded interactions between an oxygen and the C8-H8 region.

The Mo4 tetrahedral metal clusters observed in the crystal structure of GaMo4S8-type compounds are described as arising from the deformation of a highly symmetrical structure with MoS6 octahedral local stoichiometry. Then Mo4 clusters occur at the crossing of MoS4 distorted linear chains made of MoS6 octahedra sharing their opposite edges. The main factors (orbital interactions and electron counts) governing the pairing distortions, which lead to a metal—metal alternation phenomenon and then to cluster formation, are analysed through extended Huckel molecular orbital calculations. It is shown that the tetrahedral clustering corresponds to a multidirectional Peierls distortion in an extended network.

A new mixed-valent monophosphate Sr2V2O(PO4)3 has been synthesized. Its 4-fold superstructure has been refined using the 4D formalism for modulated structures and using X-ray single-crystal diffraction data. The average structure can be described as a stacking of [V2P3O13]∞ layers and [Sr2]∞ layers. In these layers, the VO6 octahedra, occupied by V(III), the VO5 trigonal bipyramids, occupied by V(IV), and the PO4 tetrahedra form chains running along b. The 4D description allows us to give a better description of the measured intensities in reciprocal space (main and first order satellite reflections) and particularly to explain why the second order satellite reflections are not observed using a classical X-ray source. The corresponding structural mechanism consists of an alternation of disordered ribbons of VO5 bipyramids and PO4 tetrahedra in two enantiomorphic configurations, separated by displacively modulated ribbons of VO6 octahedra and PO4 tetrahedra. Crystal data: monoclinic, superstructure space ...

Under mild conditions, a linear polymeric (C702- )n fulleride was synthesized as single crystals which allow, for the first time, a complete structural analysis of a polymeric fulleride. Starting from the strongest "disturbance" of the cage geometry at the linkage sites, the pronounced alternation of the bond lengths decreases towards the middle of the C70 units (see Schlegel diagram of the C702- building block; color coding of the bond lengths [A]: blue 1.52).

Na10(Na,Mn)7Mn43(PO4)36 (sodium manganese phosphate) was synthesized hydrothermally at 873 K and 0.35 GPa. The complex crystal structure is almost identical to that of natural fillowite-type phosphates and can be described as a hexagonal packing of three types of rods parallel to the c axis. The rods are constituted by an alternation of five- to seven-coordinated Mn sites [average Mn-O = 2.243 (3) A], of six- to nine-coordinated Na sites [average Na-O = 2.590 (3) A], of PO4 tetrahedra [average P-O = 1.548 (3) A] and of cation vacancies.

New uranyl vanadates A3(UO2)7(VO4)5O (M=Li (1), Na (2), Ag (3)) have been synthesized by solid-state reaction and their structures determined from single-crystal X-ray diffraction data for 1 and 3. The tetragonal structure results of an alternation of two types of sheets denoted S for ∞2[UO2(VO4)2]4− and D for ∞2[(UO2)2(VO4)3]5− built from UO6 square bipyramids and connected through VO4 tetrahedra to ∞1[U(3)O5-U(4)O5]8− infinite chains of edge-shared U(3)O7 and U(4)O7 pentagonal bipyramids alternatively parallel to a- and b-axis to construct a three-dimensional uranyl vanadate arrangement. It is noticeable that similar ∞[UO5]4− chains are connected only by S-type sheets in A2(UO2)3(VO4)2O and by D-type sheets in A(UO2)4(VO4)3, thus A3(UO2)7(VO4)5O appears as an intergrowth structure between the two previously reported series. The mobility of the monovalent ion in the mutually perpendicular channels created in the three-dimensional arrangement is correlated to the occupation rate of the sites and by the geometry of the different sites occupied by either Na, Ag or Li. Crystallographic data: 293 K, Bruker X8-APEX2 X-ray diffractometer equipped with a 4 K CCD detector, MoKα, λ=0.71073 A, tetragonal symmetry, space group P4¯m2, Z=1, full-matrix least-squares refinement on the basis of F2; 1, a=7.2794(9) A, c=14.514(4) A, R1=0.021 and wR2=0.048 for 62 parameters with 782 independent reflections with I⩾2σ(I); 3, a=7.2373(3) A, c=14.7973(15) A, R1=0.041 and wR2=0.085 for 60 parameters with 1066 independent reflections with I⩾2σ(I).

TcBr3 (1) and TcBr4 (2) were synthesized by reaction of Tc metal with elemental bromine at 400 °C. Single crystal XRD measurements indicate that TcBr3 crystallizes in the orthorhombic space group Pmmn (a = 11.0656(2) A, b = 5.9717(1) A, c = 6.3870(1) A). The structure consists of infinite chains of face-sharing TcBr6 octahedra with a regular alternation of short and long Tc−Tc distances (2.8283(4) A, 3.1434(4) A). TcBr4 crystallizes in the orthorhombic space group Pbca (a = 6.3237(5) A, b = 12.1777(9) A, c = 14.7397(11) A). TcBr4 contains infinite chains of edge-sharing TcBr6 octahedra with no apparent metal−metal bond (Tc−Tc = 3.7914(4) A). Technetium tribromide is isomorphous with RuBr3 and MoBr3, while TcBr4 is isomorphous with PtBr4 and OsBr4.

A new two-dimensional-layered fluoroaluminophosphate (C4H11NOH)(3.5)[Al-4(PO4)(5)F]center dot 0.5H(3)O (denoted as AlPO-CJ20) with an Al/P ratio of 4:5 has been synthesized solvothermally by using 2-amino-2-methyl-1-propanol as the structure-directing agent. Its structure was determined by single-crystal X-ray diffraction analysis and further characterized by solid-state NMR techniques, including Al-27, F-19 -> Al-27 cross-polarization, and P-31 magic angle spinning NMR. The alternation of Al-centered tetrahedra (AlO4 and AlO3F) and PO3(O) tetrahedra gives rise to a new type of 4.6.16-net sheet. The inorganic sheets are stacked in an ABAB sequence along the [010] direction and further held together through strong H bonds between protonated template molecules and PO groups in the inorganic layers. Except for Mu-4, AlPO-CJ20 is the second layered aluminophosphate with an Al/P ratio of 4:5, and it contains the largest pore opening of 16-rings in the known layered aluminophosphates. Furthermore, the coordination of Al and P of fluoroaluminophosphates is summarized. Crystal data: (C4H11NOH)(3.5)[Al-4(PO4)(5)F]center dot 0.5H(3)O, monoclinic, C2/c (No. 15), a = 32.678(7) angstrom, b = 12.956(3) angstrom, c = 21.045(4) angstrom, beta = 115.17(3)degrees, V = 8064(3) angstrom(3), Z = 8, R1 = 0.0837 [I > 2 sigma(I)], and wR2 = 0.2428 (all data).

The first two low-dimensional beryllium phosphates, [C5H14N2]2[Be3(HPO4)5].H2O (BePO-CJ29) and [C6H18N2]0.5[Be2(PO4)(HPO4)OH].0.5 H2O (BePO-CJ30), have been successfully synthesized under mild hydrothermal/solvothermal conditions. BePO-CJ29 is built up from strict alternation of BeO4 and HPO4 tetrahedra forming a unique one-dimensional double chains with 12-ring apertures. There are pseudo-10-ring apertures enclosed by two double chains through H-bonds. BePO-CJ29 can also be viewed as a pseudo 2-D layered structure stabilized by strong H-bonds. The diprotonated 2-methylpiperazium cations are located at three positions (i.e., inside the 12-ring aperture, inside the pseudo-10-ring aperture, and in the interlayer of the inorganic pseudo-layers. BePO-CJ30 is constructed by the alternation of Be-centered tetrahedra (including BeO4 and HBeO4) and P-centered tetrahedra (including PO4 and HPO4) resulting in a two-dimensional layered structure parallel to the (0 1 1) direction. The complex layer is composed of coupled 4.8 net sheets. The diprotonated 1,6-hexandiamine cations and water molecules reside in the interlayer regions and interact with the inorganic layers through H-bonds. Crystal data are as follows: [C5H14N2]2[Be3(HPO4)5].H2O (BePO-CJ29), triclinic, P1 (No. 2), a = 8.1000(9) A, b = 8.4841(14) A, c = 19.665(2) A, alpha = 89.683(10) degrees, beta = 78.182(8) degrees, gamma = 87.932(9) degrees, V = 1321.9(3) A3, Z = 2, R1 = 0.0523 (I2sigma(I)), and wR2 = 0.1643 (all data); [C6H18N2]0.5[Be2(PO4)(HPO4)OH].0.5 H2O (BePO-CJ30), orthorhombic, Pccn (No. 56), a = 26.01(4) A, b = 8.431(12) A, c = 9.598(13) A, V = 2105(5) A3, Z = 8, R1 = 0.0833 (I2sigma(I)), and wR2 = 0.2278 (all data).

The cover picture shows the molecular structure of the helically extended angular [8]phenylene. An unprecedented cobalt-catalyzed triple cyclization of an appropriate nonayne was successful in assembling the largest crystallographically characterized helical phenylene (heliphene). Its properties are intriguing; the heliphene is unusually configurationally labile and has a strongly attenuated bathochromic increment in the UV spectrum, shielding of the terminal rings as a result of spatial overlap, and alternating ring-current intensities along the angular frame. The X-ray crystallographic data detail the helical and σ–π distortive features. Most surprisingly, the remarkable flexibility of the heliphene provided an unusually low barrier (ΔG≠ (−4.5 °C) = 13.4±0.4 kcal mol−1) for enantiomerization. The 1H NMR spectrum was consistent with the alternation of cyclohexatrienoid and aromatic character; the terminal rings are the most diatropic and the penultimate ones the least. Further details about this chiral polycyclic benzenoid hydrocarbon are described by K. P. C. Vollhardt, et al. on p 3227 ff.

The cholesteric-nematic phase change under tilted surface alignment is investigated. An alternation of the transition behaviour with increasing twist angle can be observed. Additionally, the results are influenced by the ratio between the cell thickness and the helical pitch. In cholesteric systems with a pitch undisturbed by the surface the voltage of unwinding increases linear with the increase of this ratio. Der cholesterin-nematische Phasenwechsel wird bei angekippter Oberflachenausrichtung untersucht. Es kann ein Alternieren im Ubergangsverhalten bei anwachsendem Verdrillungswinkel beobachtet werden. Auserdem werden die Ergebnisse vom Verhaltnis zwischen Zellendicke und helikaler Ganghohe beeinflust. In cholesterinen Systemen mit einer von der Oberflache nicht gestorten Ganghohe wachst die Spannung, die fur das Aufwinden notwendig ist, linear mit der Vergroserung dieses Verhaltnisses an.

In terms of the pseudopotential method the Hume-Rothery electron phase stability is studied. Unlike the previous studies here the effects related to the nonsphericity of the Fermi surface are taken into account. The numerical calculations are carried out for the CuZn system. It is shown that the theory results in a phase alternation which is observed at rather high temperatures. The conclusion is made that the account of real Fermi surface is in principle necessary in analyzing the electron phase stability. [Russian Text Ignored].

A novel method has been developed for the determination of the extent of alternation in copolymers in which one of the comonomers contains a fluorescent chromophore capable of intramolecular excimer formation. The ratio of excimer to monomer fluorescence intensity is linearly correlated with the fraction of adjacent fluorescent chromphores to isolated fluophores on the chain. The method is illustrated for the case of styrene-acrylonitrile copolymers.

Analyses of masses and relative kinetic energies for metastable peaks may be achieved by the use in alternation of two types of linked scans of the electric sector voltage and magnetic field. The method is demonstrated by an appraisal of hydrogen exchange in molecular ions of 2-methyl-[2H3]-benzoic acid.

Within the framework of the LCAO-MO theory, a novel sign-alternation rule has been found empirically for the lowest excited ππ* triplet state in the alternant aromatic system. This rule can be applied to identify the phosphorescent state.

This is a study of the structural arrangement in a polymer which is on a size level larger than the crystallite but smaller than the spherulite. It is based on the data from x-ray diagrams at small angles, combined with crystallite dimensions measured from wide-angle x-ray patterns. The earlier interpretations of polymer texture by Hess and Kiessig which describe alternating regions of order and disorder appear to be most probable. However, those earlier interpretations are extended by showing that oriented crystalline polymers can be thought of as having aligned elementary fibrils which consist along their length of a regular alternation of bulky and condensed regions. The width of these elementary fibrils is proportional to the width of the crystallites. The amount of regularity of crystallite positions along an elementary fibril and the length of the repeat period are both variable; they depend on the manner of original nucleation and the thermal treatment after nucleation. The length of the long period is a function of the length of the crystallites. These elementary fibrils can pack closely to form a higher state of ordered texture. The amount of close packing is variable; it is optimal after a relaxation treatment. Elongated voids exist between the elementary fibrils. The difference between the effects of original nucleation and thermal after-treatment is emphasized. Elementary fibrils are proposed as a basic unit of aggregation in polymer melts, solutions, and fibers.

X-ray analyses of chain-shaped and of coupled polymethines show an enlargement of the bond angles of the positively charged methine atoms and a contraction of the bond angles of the negatively charged methine atoms. The bond angle alteration can be explained by deviations from the trigonal hybridisation of the methine atoms. There exists a simple linear function between the square of the hybridisation parameter λ and the total charge densities calculated by means of the CNDO/2 method: λ2 ≅ 2 – Q.

Description de l'application du concept d'alternance de charge a la distribution de charge dans les diions de molecules mono- et polycycliques. Determination de la densite de charge par etude theorique et experimentale (RMN 13 C)

The concept of stabilization of polyanionic and polycationic compounds by charge alternation was introduced to explain the course of polymetalation of hydrocarbons and enolates. This concept is generalized to the positional stabilization of polar compounds containing two or more donor or acceptor groups and reconciled with the different known stabilizations of compounds containing a donor and an acceptor group. Various properties of other classes of compounds such as relative acidities and basicities of heterocyclic compounds, charge distribution in cyanines, mesocyanines,oxonoles and aromatic dianions, as well as the regioselectivity of some reactions seem also to obey the rules based on this concept.

4,10b-Methano-8H-benzo[ab]cyclodecen-8-one (C14H10O), a stable derivative of so-called 1,6-methano[10]annulene, forms reddish orange crystals of the space group Pbca, with eight molecules in a unit cell with dimensions of a=16.567, b=14.090, and c=8.418 A. The structure was solved by the symbolic addition method and refined by the block-diagonal least-squares method. The final R factor was 0.080 for the 1386 independent observed reflections. The lengths of the peripheral bonds of the [10]annulene nucleus do not exhibit any apparent alternation. The peripheral eight atoms are approximately coplanar. The C–O distance (1.236 A) is longer than those in quinones and tropones, and it is consistent with the large dipole moment and high basicity of the present molecule.