Forecasting Columnar Mesophases. Synthesis and Structure of Porphin Derivatives

This paper examines the possibility of columnar mesophase (CM) predictions in a new series of porphin derivatives: polysubstituted phthalocyanines (I) and porphyrins (II, III). In order to reveal discogens, we have calculated the molecular parameters K, K_c, K_s, K_p, M_m, and M_r for 85 molecules, including compounds with few peripheral substituents. Introduction of a new electronic parameter, K_e, defining the electron density distribution from the center to the periphery of the discogen molecule, is discussed. Some of the compounds were synthesized, and their mesomorphism and structure were investigated in order to be able to verify the conclusions concerning CM prediction in the series of compounds under analysis.     

Simple method for determining the critical molecular weight from the loss modulus

The normal concept is that the critical molecular weight (M_C) is about twice as large as the entanglement molecular weight (M_e). However, experimental data have shown considerable deviations from M_C ≈ 2M_e. Furthermore, a determination of M_C requires samples with a wide range of molecular weights, including weights lower than M_C and higher than M_C. In this article, we suggest a simple method for determining M_C from the loss moduli of nearly monodisperse linear polymers with M ? M_C. We consider two characteristic relaxation times, which correspond to the local maximum and minimum of the loss modulus. M_C is determined from the intersection of two phenomenological relaxation times as a function of the molecular weight. The method precisely agrees with M_C ≈ 2M_e, which is not shown by conventional methods. Moreover, our method provides a determination of relaxation time τ_e, at which chain segments first feel the constraints imposed by the conceptual tube, without the measurement of the tube diameter and the monomeric friction coefficient, which may be determined by complicated procedures with a lot of data. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2724–2729, 2004     

Die Kristallstruktur von 1,2-Diferrocenylethanen

X-ray crystal structure analyses of stereoisomeric 1,2-dimethyl and diphenyl 1,2-diferrocenyl ethanes (1,2) as well as of 1,1,2,2-tetraferrocenyl ethane (3) showed that racemic (threo) and meso (erythro)2 adopt conformations with antiperiplanar arrangement of the ethane H-atoms (andC ₂ andC _i symmetry, resp.), whereas1 and3 prefer the synclinal (skew) conformations. In3 the torsional angle between the ethane H-atoms is increased to appr. 90°;3 represents a chiral structure withC ₂ symmetry.For the conformation of tetraferrocenyl ethane (3) in solutionC ₂ symmetry could be deduced from the¹³C-nmr. spectra.The conformations of the diferrocenyl ethanes are discussed and compared with those of corresponding alkyl and aryl ethanes.

Herrn Prof. Dr.E. Ziegler (Graz) mit den besten Wünschen zum 70. Geburtstag gewidmet.     

Explanation for the 3.4-power law for viscosity of polymeric liquids on the basis of the tube model

The viscosity η₀(M) of polymeric liquids of molecular weight M is calculated on the basis of the tube model formulated by Doi and Edwards (ref. 3). The contour length fluctuation of polymers along the tube, which was neglected in ref. 3, is now explicitly taken into account. The result is where M_c = 2M_e, and M_e is the molecular weight between the entanglement points. This result is numerically close to the empirical 3.4-power law, η₀(M) = η₀(M_c)(M/M_c)^3.4, for 10M_c ? M ? 100M_c but approaches the result in ref. 3 for very high molecular weight. We thus conclude that the 3.4-power law is actually an approximate expression for the real curve which slowly approaches the asymptotic form calculated in ref. 3.     

Das unterschiedliche massenspektrometrische Fragmentierungsverhalten von Lysinmethylester und dessen N,N′-Diacetylderivat. 27. Mitteilung über das massenspektrometrische Verhalten von Stickstoffverbindungen

The Different Behaviour of Lysine Methyl Ester and its N,N′-Diacetyl Derivative under Electron Impact The base peak in the spectrum of lysine methyl ester is due to the fragment ion C₅H₁₀N (m/e 84), for which the cyclic structure g (Scheme 1) is deduced. During its formation from the [M-COOCH₃]-ion an equilibration of both nitrogen atoms takes place (ion c , Scheme 1). The cyclic nature of ion m/e 84 is in agreement with the intensity of the corresponding ions in the spectra of homologues of lysine methyl ester (Fig. 1). Although in comparison with lysine methyl ester ( 1 ) N,N′-diacetyl-lysine methyl ester ( 7 ) shows the same general fragmentation pathway with formation of the ions [M-COOCH₃] and [M-COOCH₃-H₂NCOCH₃] (m/e 126), the exact fragmentation mechanism proves to the different. Two mechanisms are discussed for the formation of the ion m/e 126 from 7 (Schemes 2 and 3). The results are based on the spectra of labelled derivatives.     

Field ionization mass spectrometry—IV. Isotopically labeled heptanals

The field ionization (FI) mass spectra of n-heptanal and a series of deuterium labeled analogs have been studied, with the objectives of initiating systematic investigations of reaction mechanisms of FI produced ions and to permit comprison with those found for other ionization processes. It is now recognized that FI ions have: (a) lower average internal energies and (b) shorter residence times than similar ions generated by electron-impact (EI), and the possibility exists of H/D-randomization occuring in ions formed by desorption from the emitter, by unimolecular decomposition close to the emitter and by either ‘fast’ or ‘slow’ metastable decompositions. In this study only the peak shifts of normal ions could be utilized; accurate mass measurements of all major ions revealed elemental compositions similar to EI. A site-specific McLafferty rearrangement gave the base peak at m/e 44 ([C₂H₄O]^+.), although the apparently complementary ion at m/e 70 ([C₅H₁₀]^+.) arose in a less specific process. Ions at m/e 43 ([C₃H₇]⁺) and 71 ([C₅H₁₁]⁺ 80%; [C₄H₇O]⁺ 20%) were apparantly generated without significant H/D-scrambling. Of special interest was the observation of the rearrangement ion at m/e 86 ([C₅H₁₀O]^+.) caused by loss of C-2 and C-3 as C₂H₄, as found for EI. It is concluded that at least in this system, decomposing molecular ions formed: (a) in the gas phase extremely close to the emitter and/or (b) on the emitter surface, have lifetimes sufficiently short to preclude complete H/D randomization. The results also provide evidence for common fragmentation mechanisms for heptanal molecular ions at both the low end and the high end of the energy distribution.     

Rearrangements and fragmentations of [C2H5S]+ ions

[C₂H₅S]⁺ ions (m/e 61) with different initial structures were generated in the mass spectrometer from twelve precursor ions. Abundance ratios of competing metastable ion decompositions were used to determine whether these ions decompose through the same or different reaction channels. It was concluded that all [C₂H₅S]⁺ ions isomerize to a common structure or mixture of structures prior to decomposition in the first field free region. From ¹³C labelling experiments it was concluded that [C₂H₅S]⁺ ions generated from the molecular ions of 2-propanethiol-2-[¹³C], partially rearrange to a symmetrical structure before decomposition to [CHS]⁺ and CH₄, whereas in [C₂H₅S]⁺ ions generated from the the molecular ions of 1,2-bis-(thiomethoxy-[¹³C]) ethane, the two carbon atoms become fully equivalent before CH₄ loss occurs.     

[B(O–C6H4–CN)4]– based Silver and Copper Coordination Polymers

A series of new coordination polymers bearing the [B(O–C₆H₄–CN)₄]^– anion was synthesized. Two new, one dimensional coordination frameworks of the type M[B(O–C₆H₄–CN)₄] (M = Ag, Cu) were obtained by salt metathesis. The reactivity towards organic Lewis‐bases was studied. The reaction with bidentate ligands yielded two dimensional networks with the general formula [M(L)][B(O–C₆H₄–CN)₄] {L = 2,2′‐bipyridine, 4,4′‐bipyridine, 1,2‐bis(pyridyl)ethane, 1,4‐diazabicyclo[2.2.2]octane}. The synthesis, properties and single crystal structure are reported.     

SYNTHESIS,CHARACTERIZATION AND ELECTROCHEMICAL STUDIES OF MONO- AND DINUCLEAR COMPLEXES OF NICKEL(II) AND COBALT(II) WITH HEXADENTATE LIGANDS HAVING N2P4 DONOR ATOMS. CRYSTAL STRUCTURE OF [Ni(BDPE)]ClO4)2. CH2Cl2

Abstract

A series of mono- and dinuclear complexes of Ni(II) and Co(II) with two hexadentate ligands α,α′-bis(bis(2-(diphenylphosphino)ethyl)amino)ethane(BDPE) and α,α′-bis(bis(2-(diphenylphosphino)ethyl)-amino)-m-xylene (BDPX) were synthesized and chracterized by means of elemental analyses, molar conductance, magnetic susceptibilities, infrared, electronic and ³¹P NMR data. The molecular structure of a mononuclear Ni(II) complex, [Ni(BDPE)](CIO₄)₂.CH₂Cl₂, was established by single-crystal X-ray diffraction methods. Crystal data: C₅₉H₆₂NiCl₄N₂O₈P₄, M = 1250.98, orthorhombic, space group Pbca, V= 11834.3(7) Å3, Z= 8, a= 10.817(1), b = 31.683(7), c=34.538(1) Å, final R 0.055 (R w = 0.057) for 3118 observed reflections. The Ni(II) ion exists in a slightly distorted square planar geometry, the coordination sites being two phosphorous and two tertiary nitrogen atoms of the ligand. Electrochemical studies of the complexes were also carried out.     

Microstructure and rheological properties of polybutadienes

The viscosities, rubbery deformations, densities, and their dependence on temperature have been measured for several series of polybutadienes with molecular weights ranging from 5,000 to 400,000 and differing in proportions of cis and trans structures (cis content from 40 to 95%). On the basis of the viscosity measurements the critical molecular weight M_c has been determined, corresponding to a sharp change in the nature of the viscosity versus molecular weight dependence. Rubbery deformations are displayed pronouncedly in specimens with M > M_c and are closely related to the appearance of non-Newtonian flow. The value of M_c depends on the relative content of cis and trans forms. When M > M_c, the initial viscosity is a parameter sensitive to the microstructure of polybutadienes, so that with at a single molecular weight, depending on the ratio of cis and trans units, the viscosity may vary over a more than tenfold range. The glass transition temperature and activation energy of viscous flow rise regularly with increasing trans content in the polymer chain, these parameters becoming independent of the molecular weight for specimens with M > M_c within a series of polybutadienes of equal microtacticity. Thermomechanical investigations of polybutadienes also made it possible to define more accurately the boundaries of the crystallization region and the dependence of the melting point on the microtacticity. The results obtained are discussed on the basis of modern ideas of polymer structure.     

Cooperative chain relaxation in miscible polymer blends

Orientation relaxation of dissimilar chains in the molten miscible blends, poly(methyl methacrylate)/poly(vinylidene fluoride) and poly(methyl methacrylate)/poly(vinylidene fluoride-co-trifluoroethylene), were investigated by measuring (1) the change of infrared dichroic ratio with time after the uniaxial stretching of film specimens, (2) the shear stress relaxation spectrum, and (3) birefringence relaxation in shear. The dissimilar polymers showed an identical time variation of the normalized Hermans orientation function. The blend showed a relaxation spectrum with a single characteristic relaxation time τ_c, depending on the blend composition. The birefringence relaxed monotonically, remaining positive. These results suggest that the dissimilar polymers do not relax independently but cooperatively. This behavior may be induced by a constraint due to the specific interactions between the dissimilar polymers, e.g., weak hydrogen bonding. For the cooperative chain relaxation, a third power relationship was found; τ_c/τ_e vprop; (M/M_e),³ where τ_e and M_e are the relaxation time and molecular weight of entanglement strand, respectively, and M is the number average molecular weight in the blend.     

Extraction and sorption studies using linear polymer chains and model networks

Model networks have been prepared by tetrafunctionally endlinking linear polydimethylsiloxane (PDMS) chains having molecular weights M_n in the range 2000–15,000 g mole^?1. The first series of networks were prepared from mixtures containing known amounts of unreactive linear PDMS chains with molecular weights M_d between 1000 and 16,000 g mole^?1. Rates of extraction were used to estimate diffusion coefficients; as expected, they were found to increase with increase in molecular weight M_c = M_n between crosslinks, but to decrease with increase in M_d. The ease with which all of such a diluent could be removed showed the same dependence on M_c and M_d. A second series of networks was prepared from the same reactive PDMS chains without diluents. Sorption and extraction studies using the same diluents were then carried out. The diffusion coefficients for sorption were found to be in the range (1.7–15.0) × 10^?12 m² s^?1 and depended on both M_c and M_d. The amount of diluent absorbed at equilibrium was between 10 and 70%, which is in good agreement with predictions from the Flory equation for dilation in networks, with account of constraints on crosslink fluctuations.     

Analytical application of ion-molecule reactions. Reactions of various substituted cyclopropane molecular ions with ammonia

By ion cyclotron resonance it is found that various substituted cy clopropanes after ionization react with ammonia to give products which allow identification of the degree and kind ofsubstitution on the cyclopropl ring. For example, cyclopropyle reacts to give [CH₂NH₂]⁺ (m/e 30), methylcyclopropane gives [CH₂NH₂]⁺ (m/e 30) and the ethyl substituted [CH(C₂H₃)NH₂]⁺ (m/e 44) and ethylopropane gives [CH₂NH₂]⁺ (m/e 30) and the ethyl substituted [CH(C₂H₅)NH₂]⁺ (m/e 58). It is suggested that reactions of stable molecular ions with reagent neutrals may be a source of highly specific structural information for organic compounds.     

The structure of the [C2H5O]+ ion in the mass spectrum of diethyl ether

The structure of the [C₂H₅O]⁺ ion in the spectrum of diethyl ether was examined by use of deuterated ether, CH₃CD₂OCH₂CH₃. The results show that, at all electron energies from threshold to 70 eV, the predominant ion is a rearrangement ion, probably protonated acetaldehyde, with very little of the [C₂H₅O]⁺ being formed by direct carbon-oxygen bond cleavage. Appearance potential measurements made on the m/e 45, m/e 46 and m/e 47 ions in the deuterated ether show that the threshold structure of the rearrangement ion is protonated acetaldehyde.     

Characterization of moisture-cured polyurethane films

A series of polyurethanes (PU) prepolymers with NCO/OH ratios of 2.1:1 and 1.9:1 were prepared by reacting hydrogenated methylene di-p-phenyl diisocyanate (HMDI) with triol mixtures of TP740 (molecular weight 740) and TP1540 (molecular weight 1540). Stress–strain (S/S) and swelling equilibrium measurements were performed using thin-film samples prepared by moisture-curing the prepolymer at room temperature. The swollen PU networks gave an S/S curve which is fully described by rubber elasticity theory. The Mooney-Rivlin constant C₁ (swollen) was found to increase directly while the molecular weight between crosslinks M_c decreases as the number of branches per cubic centimeter is increased. The solvent—polymer interaction parameter χ determined in benzene was 0.077 + 0.97_vr, where v_r is the volume fraction of rubber in the swollen network. The crosslink density v′, and M_c were calculated from the relations v′ = pNB and M_c = 0.667 B^?1, where B denotes moles of branches per gram, and were found to be in good agreement with v′ and M_c established from S/S and swelling-equilibrium measurements. In calculating v′ and M_c, the water-PU crosslinking reaction at room temperature was assumed to occur mainly through the formation of a urea linkage.     

Chromium‐based clinopyroxene‐type germanates NaCrGe2O6 and LiCrGe2O6 at 298 K

The structure analyses of sodium chromium digermanate, NaCrGe₂O₆, (I), and lithium chromium digermanate, LiCrGe₂O₆, (II), provide important structural information for the clinopyroxene family, and form part of our ongoing studies on the phase transitions and magnetic properties of clinopyroxenes. (I) shows C2/c symmetry at 298 K, contains one Na, one Cr (both site symmetry 2 on special position 4e), one Ge and three O‐atom positions (on general positions 8f) and displays the well known clinopyroxene topology. The basic units of the structure of (I) are infinite zigzag chains of edge‐sharing Cr³⁺O₆ octahedra (M1 site), infinite chains of corner‐sharing GeO₄ tetrahedra, connected to the M1 chains by common corners, and Na sites occupying interstitial space. (II) was found to have P2₁/c symmetry at 298 K. The structure contains one Na, one Cr, two distinct Ge and six O‐atom positions, all on general positions 4e. The general topology of the structure of (II) is similar to that of (I); however, the loss of the twofold symmetry makes it possible for two distinct tetrahedral chains, having different conformation states, to exist. While sodium is (6+2)‐fold coordinated, lithium displays a pure sixfold coordination. Structural details are given and chemical comparison is made between silicate and germanate chromium‐based clinopyroxenes.