Bent Chain Research Articles

Structure and Properties of Novel Asymmetric Biphenyl Type Polyimides. Homo- and Copolymers and Blends

Asymmetric biphenyl type polyimides (PI) were prepared by thermal imidization of polyamic acids (PAA) derived from 2,3,3‘,4‘-biphenyltetracarboxylic dianhydride (a-BPDA) and p-phenylenediamine (PDA) or 4,4‘-oxydianiline (ODA). The dynamic mechanical properties of these PIs were compared with those of the isomeric PIs derived from symmetric 3,4,3‘,4‘-biphenyltetracarboxylic dianhydride (s-BPDA). a-BPDA/PDA polyimide has a considerably bent chain structure compared to semirigid s-BPDA/PDA. Nevertheless, the a-BPDA/PDA film annealed at 350 °C showed a higher Tg than the s-BPDA/PDA film prepared under the same conditions. When these PIs were annealed at 400 °C, a-BPDA/PDA exhibited an abrupt E‘ decrease at the Tg (=410 °C) as well as the counterpart annealed at 350 °C, whereas s-BPDA/PDA showed no distinct Tg in the E‘ curve. Similar annealing effects were also observed for the ODA systems. The unexpectedly higher Tg's of a-BPDA-based PIs could be explained in terms of the more restricted conformational chang...

Laboratory Detection of Two New C[TINF]5[/TINF]H[TINF]2[/TINF] Isomers

Two new isomers of the C5H2 molecule have been detected in the laboratory, and their microwave spectra have been characterized to high accuracy. Both are good candidates for radio astronomical detection. Like the two isomers previously detected in the laboratory, both are closed-shell carbenes, and both are extremely polar and fairly stable. The first, calculated to lie 0.73 eV above isomer 1, the C5H2 ring-chain ground state, has a bent carbon chain backbone with single, double, and triple bonds; the second, calculated to lie only 0.19 eV higher in energy, is a new type of ring chain formed by adding a pair of doubly bonded carbon atoms to the top of the C3H2 ring, which is one of the most abundant interstellar molecules.

Three-body distribution functions in hard sphere fluids. Comparison of excluded-volume-anisotropy model predictions and Monte Carlo simulation

Hard sphere three-body distribution functions predicted by the recently developed Excluded-Volume-Anisotropy (EVA) model are compared with Monte Carlo computer simulation measurements. Two types of simulations, both based on the Widom insertion method, are performed as a function of solvent density (0.1⩽ρσ3⩽0.8), solute structure (linear, triangular, and bent 3-bead chain), and solute–solvent sphere diameter ratio (0⩽σ/σS⩽3). Comparisons of these results with those of previous studies illustrate the accuracy of the EVA model in predicting multi-body distribution functions near contact separations (and inside of contact), where the Kirkwood-Superposition-Approximation is least accurate.

Monte Carlo Study of Chemically Associating Polymerizing Two-Dimensional Fluids

NVT Monte Carlo simulations are reported for chemically associating two-dimensional fluids which can polymerize for certain interaction energies, due to the presence of two attractive sites per monomeric hard disc. The sites are fixed inside a hard core at a given valence angle and mutual penetration of discs is permitted. The type of products of polymerization depends on the parameters of the model; we observe the formation of small associates, as well as of extended chains, bent chains, and rings with different number of monomers. The values of valence angles and of association energy are of primary importance. The dependence of the structural properties of the model on fluid density and association energy is investigated. We performed detailed analysis of the clusters formed due to association in terms of fractions of singly and doubly bonded particles, of average numbers of chains and rings, and of their size. We also obtain the average end to end distance, the radius of gyration, and the persistent length of the products of polymerization. The pressure is calculated from the density profiles of particles of the polymerizing fluid near a hard “wall.” The data can be used to develop the equation of state for chemically associating two-dimensional fluids.

Synthesis of Tfmhpncbc with Deuterated Achiral Chain and Study of Extremely Bent Chiral Chain in Antiferroelectric Smectic-IA*

We have synthesized 4-(1-trifluoromethylheptyloxycarbonyl)phenyl-4′-nonylcarbonyloxybiphenyl-4-caboxylate with deuterated achiral chain (TFMHPNCBC-d 19), which enantiotropically exhibits the antiferroelectric hexatic SIA* phase, and studied the orientational structure of the alkyl chains by polarized IR spectroscopy. The extremely bent chiral alkyl chain structure that was already observed in SC* and SA is confirmed even in SIA*. Hence, contrary to the previous conclusion by Neundorf et al. [J. Mater. Chem., 4, 1997 (1995)], the antiferroelectricity both in SCA* and SIA* results from the same type of intermolecular interactions among dipole moments near the smectic layer boundaries.

Role of heteropolar bonds in OCM-2 oligocarbonatemethacrylate

The OCM-2 oligocarbonatemethacrylate was investigated using a HYPERCHEM 4.0 molecular computer package. We have optimized the geometry of the OCM-2 molecule receiving a non-linear structure. Non-uniformly distributed electron charge densities and multipole moments were obtained from ab initio calculations. The heteropolar CO double chemical bonds are transversal with respect to a bent central chain and play an important role in the formation of the optical and non-linear optical features. We have calculated different HOMO-LUMO energy gaps using semiempirical PM3 and ab initio methods for singlet and triplet states and the best agreement with the optical absorption data was observed for the PM3 triplet states. One can expect that the OCM-2 electronic structure properties have strong influence on the solid mixturies, which are formed on basis of the OCM-2 polymer and analogous compounds.

Electronic and Optical Parameters of the TGM-3 Photopolymer

Molecular properties of the TGM-3 photopolymer have been investigated using a HYPERCHEM 4.0 computer package. The geometry of this photopolymer was successfully optimized and the TGM-3 structure obtained shows a very complicated non-linear shape. The total charge density of TGM-3 is strongly nonuniform. C=O double chemical bonds are roughly perpendicular to a bent central chain. We have calculated a value of the HOMO–LUMO energy gap which is not in agreement with our experimental data for the fundamental absorption edge. A possible origin of this difference is suggested. One can expect that the TGM-3 properties have a strong influence on its solid many-component mixtures with other photopolymers.

Palladium-induced rearrangement of a Fe2Sn2 metal core leading to the first Fe–Pd–Sn cluster [(OC)3Fe(μ-SnBun2)(μ-dppm)Pd(μ-dppm)Fe(CO)3

A new tetranuclear FePdFeSn four-membered ring cluster, which could be viewed as a bent chain complex FePdFe bridged by a stannylene ligand, is obtained from a Fe2Sn2 precursor by Ph2PCH2PPh2 (dppm)-assisted palladium incorporation; it provides the first example of a Sn–Fe–Pd linkage.

Synthesis, Structure and Reactions of the Homoleptic Alkyne Nickel(0) Complex (Alkyne)4Ni3 (Alkyne: 2‐methyl‐4‐trimethylsilyl‐3‐butyn‐2‐ol)

AbstractTreatment of (cdt)Ni (cdt: cyclododeca‐1,5,9‐triene) with 2 equivalents of 2‐methyl‐4‐trimethylsilyl‐3‐butyn‐2‐ol leads to the selective formation of the homoleptic complex (alkyne)4Ni3 (compound 3), which can be isolated in excellent yields. The solid‐state structure of 3 exhibits three Ni centers, forming a bent Ni3 chain connected by two bridging alkynes. The other two alkynes are terminally coordinated. Additionally, the trimeric units are stabilized by three intramolecular hydrogen bonds. Two intermolecular hydrogen bonds connect the trimeric units to form a polymer rope. According to the 13C‐ and 1H‐NMR spectra in THF the structure of the complex 3 in solution is very similar to that in the solid state. The reaction of 3 with some alkynediols and with 2,5,5‐trimethylhex‐3‐yn‐2‐ol affords compounds of the type (alkyne)2Ni. Cot (cot: 1,3,5,7‐cyclooctatetraene) converts 3 into [(cot)Ni]2, which in turn reacts with 2,5‐dimethylhex‐3‐yne‐2,5‐diol to form the dimeric complex (alkyne)2Ni2(cot) 6. X‐ray analysis of 6 reveals a very symmetrical structure in which cot connects both Ni(0) centers at opposite sides of the ring system.

Structure and Properties of Novel Asymmetric Biphenyl Type Polyimides.

Asymmetric biphenyl type polyimides (PI) were prepared by thermal imidization of polyamic acids (PAA) derived from 2, 3, 3′, 4′- biphenyltetracarboxylic dianhydride (a-BPDA) and p-phenylenediamine (PDA) or 4, 4′-oxydianiline (ODA). The degrees of molecular orientation, film densities, and dynamic mechanical properties of these PIs were compared with those of familiar PIs based on symmetric 3, 4, 3′, 4′- biphenyltetracazboxylic dianhydride (s-BPDA). PI(a-BPDA/PDA) cured at 350°C showed a Tg close to that of PI(s-BPDA/PDA) prepared under the same condition in spite of the bent chain structure of the former. Comparison of the PIs cured at 400°C manifested that PI(a-BPDA/PDA) has a Tg at 410°C (abrupt decrease in E′) whereas PI(s-BPDA/PDA) show no distinct Tg. Similar result was also observed for the ODA systems. The unexpectedly high Tgs of a-BPDA-based PIs were explained in terms of the restricted conformational change around the phenyl-phenyl bond in the a-BPDA unit. The difference of the E′ decrement at the Tg for both type of PIs are probably attributed to the difference of the intensity of intermolecular interactions. In PI(a-BPDA/PDA) thin film cured on a substrate, the segments unexpectedly align slightly to the film plane.

Synthetic, Structural, Spectroscopic, and Theoretical Studies of Structural Isomers of the Cluster Pt(3)(&mgr;-PPh(2))(3)Ph(PPh(3))(2). A Unique Example of Core Isomerism in Phosphine Phosphido-Rich Clusters.

Two isomers of the phosphido-bridged platinum cluster Pt(3)(&mgr;-PPh(2))(3)Ph(PPh(3))(2) (2 and 3) have been isolated, and their structures have been solved by single-crystal X-ray diffraction. Compound 2 crystallizes in the orthorhombic space group Cmc2(1) with a = 22.192(10) Å, b = 17.650(9) Å, c = 18.182(8) Å, and Z = 4. Compound 3 crystallizes with 2 molecules of dichloromethane in the monoclinic space group C2/c with a = 21.390(10) Å, b = 18.471(9) Å, c = 19.021(11) Å, beta = 105.27(5) degrees, and Z = 4. The two isomers differ essentially in their metal-metal distances and Pt-(&mgr;-PPh(2))-Pt angles. Thus 2, having an imposed C(s) symmetry, contains a bent chain of metal atoms with two short Pt-Pt distances of 2.758(3) Å and a long separation of 3.586(2) Å. In 3, which has an imposed C(2) symmetry, the metal atoms form an isosceles triangle with two Pt-Pt distances of 2.956(3) Å and one of 3.074(4) Å. These isomers can be smoothly interconverted by changing the crystallization solvents. Solution and solid-state (31)P NMR studies have been performed in order to assign the resonances of the different P nuclei and relate their chemical shifts with their structural environments. Raman spectroscopy was used to assign the nu(Pt-Pt) modes of the two structural isomers. Theoretical studies based on extended Hückel calculations and using the fragment molecular orbital approach show that the isomer with the three medium Pt-Pt distances is slightly more stable, in agreement with earlier theoretical predictions. Cluster core isomerism remains a rare phenomenon, and the present example emphasizes the role and the importance of flexible phosphido bridges in stabilizing clusters as well as the unprecedented features which can be observed in phosphine phosphido-rich metal clusters.

Alternating charge clusters of side chains: new surface structural invariants observed in calf eye lens gamma-crystallins.

A detailed stereochemical analysis of the oppositely charged side chains of amino acid residues on the surface of calf eye lens protein gamma-crystallin B has been carried out. The refined structural data of very high quality obtained at 1.47 A resolution have been used. Charge-charge interactions were considered to be valuable for all the charged oxygen and nitrogen atoms situated at distances, d, between 2.4 and 7.0 A. This means we consider short contact ion pairs as those with intercharge distances 2.4 < d < or = 4.0 A and distant contact ion pairs as those with distances 4.0 < d < or = 7.0 A. Hydrogen bonding of the charged atomic groups with the structural water molecules also has been considered. We have not looked at the side groups of histidines which are charged only partially at neutral pH. Five clusters of charged side chains which were large enough were observed. The clusters are comprised of four to six residues which compose 54.3% of the total charged residues in the protein. The clusters contain from eight to 12 charged atoms and look like the bent chains of oppositely charged atoms. All clusters are of plane geometry and their maximal linear dimensions are from 11 to 18 A. The root mean square deviations of charged atoms from the cluster plane varied from 0.63 to 0.86 A for four clusters and was only 1.85 A for the largest cluster. All clusters include a number of water molecules situated on the cluster boundary and grouped near the cluster plane. It was shown that the amino acid sequence positions of charged residues are conservative for all the proteins of the gamma-crystallin family of vertebrates including fish, frog, mouse, rat, calf and human. The cluster properties were discussed both in their functional aspect for gamma-crystallins and in other aspects common for globular proteins. As a result, the alternating charge clusters should be considered as newly recognized surface structural invariants. The importance of the charged side chain clusters is claimed for the updated concept of the protein surface.

Ni3(alkyne)4]—The First Homoleptic Alkyne–Metal Oligomer (Alkyne: 2,5,5‐Trimethylhex‐3‐yn‐2‐ol)

Held together by twelve NiC and two NiNi bonds, and stabilized by intra- and intermolecular hydrogen bonds, the title compound 1 is the first member of the hitherto hypothetical series [Mn(alkyne)n+1] (M = d10 system). Complex 1 contains a bent Ni3 chain (118°) and is stable at room temperature.

Thianthrene‐containing polyimides with monomer formation via nucleophilic aromatic substitution

AbstractThianthrene‐2,3,7,8‐tetracarboxylic dianhydride was synthesized via nucleophilic aromatic substitution of N‐phenyle‐4,5‐dichlorophthalimide with thiobenzamide, thioacetamide, and sodium sulfide. This monomer was then polymerized with aromatic diamines by the con‐ventional low temperature technique in N,N‐dimethylacetamide (DMAc) to yield soluble poly(amic acid)s. Polyimides were obtained by thermal cyclization of the poly(amic acid) films. Polymers obtained formed creasable thin films and had excellent thermal stability in air and nitrogen. The bent thianthrene structure limited crystallization and chain packing, as indicated by x‐ray analysis. The amorphous thianthrene‐containing polyimides were only soluble in H2SO4. © 1995 John Wiley &amp; Sons, Inc.

The Thermal Dehydration of Cs 3LnCl 6 · 3H 2O to Cs 3LnCl 6 ( Ln = La-Nd) and Their Crystal Structures

The crystal structure of Cs 3LaCl 6 · 3H 2O has been determined by X ray single crystal analysis. The compound crystallizes from aqueous solution by evaporation at 50°C in the arthorhombic space group Pnma ( a = 2124.2(7) pm, b = 865.8(2) pm, and c = 852.3(2) pm, Z = 4). The coordination polyhedra of lanthanum are slightly distorted trigonal prisms triply capped by water molecules. The prisms are connected by common edges forming bent chains [LaCl 2Cl 4/2(H 2O) 3] - ∞. The three different coordination polyhedra around cesium are associated in three dimensions. The compounds with Ln = Ce, Pr, and Nd are isotypic. Upon heating these compounds to 130°C they decompose in one step to Cs 3 LnCl 6. Cs 3 LaCl 6 and Cs 3CeCl 6 crystallize into the Cs 3BiCl 6 type. Cs 3PrCl 6 and Cs 3NdCl 6 belong to another type; its structure was determined from X ray single-crystal data of Cs 3NdCl 6 (space group Pbcm, a = 828.2(2) pm, b = 1322.5(4) pm, c = 2673.0(10) pm, Z = 8). The NdCl 6 octahedra are slightly distorted, and the cesium cations are coordinated with 11 or 8 chlorine atoms. Using the notation of "layers of close-packed octahedra" the stacking frequency is compared with those of the Cs 3BiCl 6, K 3MoCl 6, and Rb 3BiBr 6 types. When annealing the compounds for several days at 280°C they transform irreversibly into the Cs 3BiCl 6 structure.

A New Type of Trinuclear Oxoiron(III) Cluster

A bent Fe3 chain in which the central Fe atom has two cis oxo bridges is the distinguishing feature of complex 1 (structure on the right). The resulting strong antiferromagnetic interactions between the metal atoms are evident in interesting magnetic and spectroscopic properties.

Diagonal Two-Particle-Hole Tamm-Dankoff Approximation Green's Function Simulation of the Valence X-ray Photoelectron Spectra of Cycloalkanes: Theoretical Search for Signatures of the Molecular Structure

With the aim of searching for conformational signatures and investigating the influence of cyclic connectivity in the valence XPS spectra of cycloalkane compounds ranging from C 5 H 10 to C 10 H 20 , the XPS spectra of optimized model structures are simulated by means of the direct Green's function approach. Calculations are performed using the minimal STO-3G basis set and a self-energy expansion derived at the level of the diagonal two-particle-hole Tamm-Dankoff approximation (2ph-TDA). A bent n-alkane chain is used to decouple roughly the combined effects of the cyclic connectivity and the torsional constraints imposed by such a connectivity

About the Crystal Structure of CuNb(OH, F) 7 · 3H 2O

Single crystals of CuNb(OH, F) 7 · 3H 2O have been grown from aqueous HF solutions. Their crystal structure is isotypic with that of CuTiF 6 · 4H 2O and consists of bent chains of trans-F-linked alternate Cu(H 2O, OH, F) 6 and Nb(OH, F) 6 octahedra, running along the [101] direction of the monoclinic unit cell ( P2 1/ c, a = 5.590(1) Å, b = 9.978(4) Å, c = 7.544(1) Å, and β = 103.36(1)°; R = 0.0272 and R w = 0.0272 for 459 reflections and 58 parameters). Bond valence calculations reveal a partial disorder between OH -, F -, and water molecules on all the nonbridging anionic sites. The Cu X 6 octahedra are classically distorted by the Jahn-Teller effect. A network of O-H ... F hydrogen bonds ensures the tridimensional cohesion of the structure.

Physics of tightly curved semiflexible polymer chains

A deflection length determines the statistical physics of a tightly bent wormlike chain because the undulations of the chain must follow its «classical» path. The deflection length which is proportional to the square of the radius of the classical path and inversely proportional to the persistence length, is interpreted to be a critical scale. By comparing it to the usual deflection length for a wormlike chain confined by various forces, we can distinguish regimes of weak and strong bending. A scaling analysis is given of various problems: DNA packed in tori and phages, worms wound around cylinders, adsorption on spheres, hairpin and disclination defects in polymer nematics

Metachromasia and Circular Dichroism induced by ATP and ADP : Evidence in Favour of Bent Phosphate Chain

Metachromasia and Circular Dichroism induced by ATP and ADP : Evidence in Favour of Bent Phosphate Chain