Hydrogen‐bonded two‐ and three‐dimensional polymeric structures in the ammonium salts of 3,5‐dinitrobenzoic acid, 4‐nitrobenzoic acid and 2,4‐dichlorobenzoic acid

The structures of ammonium 3,5‐dinitrobenzoate, NH₄⁺·C₇H₃N₂O₆⁻, (I), ammonium 4‐nitrobenzoate dihydrate, NH₄⁺·C₇H₄NO₄⁻·2H₂O, (II), and ammonium 2,4‐dichlorobenzoate hemihydrate, NH₄⁺·C₇H₃Cl₂O₂⁻·0.5H₂O, (III), have been determined and their hydrogen‐bonded structures are described. All three salts form hydrogen‐bonded polymeric structures, viz. three‐dimensional in (I) and two‐dimensional in (II) and (III). With (I), a primary cation–anion cyclic association is formed [graph set R₄³(10)] through N—H...O hydrogen bonds, involving a carboxylate group with both O atoms contributing to the hydrogen bonds (denoted O,O′‐carboxylate) on one side and a carboxylate group with one O atom involved in two hydrogen bonds (denoted O‐carboxylate) on the other. Structure extension involves N—H...O hydrogen bonds to both carboxylate and nitro O‐atom acceptors. With structure (II), the primary inter‐species interactions and structure extension into layers lying parallel to (001) are through conjoined cyclic hydrogen‐bonding motifs, viz.R₄³(10) (one cation, an O,O′‐carboxylate group and two water molecules) and centrosymmetric R₄²(8) (two cations and two water molecules). The structure of (III) also has conjoined R₄³(10) and centrosymmetric R₄²(8) motifs in the layered structure but these differ in that the first motif involves one cation, an O,O′‐carboxylate group, an O‐carboxylate group and one water molecule, and the second motif involves two cations and two O‐carboxylate groups. The layers lie parallel to (100). The structures of salt hydrates (II) and (III), displaying two‐dimensional layered arrays through conjoined hydrogen‐bonded nets, provide further illustration of a previously indicated trend among ammonium salts of carboxylic acids, but the anhydrous three‐dimensional structure of (I) is inconsistent with that trend.     

Visible‐Light‐Driven Hydrogen Production and Polymerization using Triarylboron‐Functionalized Iridium(III) Complexes

The development of novel iridium(III) complexes has continued as an important area of research owing to their highly tunable photophysical properties and versatile applications. In this report, three heteroleptic dimesitylboron‐containing iridium(III) complexes, [Ir(p‐B‐ppy)₂(N^N)]⁺ {p‐B‐ppy=2‐(4‐dimesitylborylphenyl)pyridine; N^N=dipyrido[3,2‐a:2′,3′‐c]phenazine (dppz) ( 1 ), dipyrido[3,2‐d:2′,3′‐f]quinoxaline (dpq) ( 2 ), and 1,10‐phenanthroline (phen) ( 3 )}, were prepared and fully characterized electrochemically, photophysically, and computationally. Altering the conjugated length of the N^N ligands allowed us to tailor the photophysical properties of these complexes, especially their luminescence wavelength, which could be adjusted from λ=583 to 631 nm in CH₂Cl₂. All three complexes were evaluated as visible‐light‐absorbing sensitizers for the photogeneration of hydrogen from water and as photocatalysts for the photopolymerization of methyl methacrylate. The results showed that all of them were active in both photochemical reactions. High activity for the photosensitizer (over 1158 turnover numbers with 1 ) was observed, and the system generated hydrogen even after 20 h. Additionally, poly(methyl methacrylate) with a relatively narrow molecular‐weight distribution was obtained if an initiator (i.e., ethyl α‐bromophenylacetate) was used. The living character of the photoinduced polymerization was confirmed on the basis of successful chain‐extension experiments.     

Hydrogen bonding in 1:1 proton‐transfer compounds of 5‐sulfosalicylic acid with 4‐X‐substituted anilines (X = F,Cl or Br)

The crystal structures of three proton‐transfer compounds of 5‐sulfosalicylic acid (3‐carboxy‐4‐hydroxy­benzene­sulfonic acid) with 4‐X‐substituted anilines (X = F, Cl and Br), namely 4‐fluoro­anilinium 5‐sulfosalicylate (3‐carboxy‐4‐hydroxybenzenesulfonate) monohydrate, C₆H₇FN⁺·C₇H₅O₆S⁻·H₂O, (I), 4‐chloro­anilinium 5‐sulfosalicylate hemihydrate, C₆H₇ClN⁺·C₇H₅O₆S⁻·0.5H₂O, (II), and 4‐bromo­anilinium 5‐sulfosalicylate monohydrate, C₆H₇BrN⁺·C₇H₅O₆S⁻·H₂O, (III), have been determined. The asymmetric unit in (II) contains two formula units. All three compounds have three‐dimensional hydrogen‐bonded polymeric structures in which both the water molecule and the carboxylic acid group are involved in structure extension. With both (II) and (III), which are structurally similar, the common cyclic (8) dimeric carboxylic acid association is present, whereas in (I), an unusual cyclic (8) association involving all three hetero‐species is found.     

A cadmium(II) coordination polymer with both polyrotaxane and polycatenane features constructed by a V‐shaped semi‐rigid ligand: synthesis and fluorescence properties

One of the most interesting phenomena in coordination polymers (CPs) is the co‐existence of different interlaced motifs. However, CPs having two different interlaced motifs at the same time are still rare. Colourless block‐shaped crystals of the two‐dimensional polymer poly[[aqua(μ₂‐naphthalene‐2,6‐dicarboxylato){μ₂‐4,4′‐[oxybis(4,1‐phenylene)]dipyridine}cadmium(II)] monohydrate], {[Cd(C₁₂H₆O₄)(C₂₂H₁₆N₂O)(H₂O)]·H₂O}_n , (I), was synthesized under hydrothermal conditions by the self‐assembly of 4,4′‐[oxybis(4,1‐phenylene)]dipyridine (OPY) with Cd^II in the presence of naphthalene‐2,6‐dicarboxylic acid (H₂ndc). Each Cd^II ion is six‐coordinated by two N atoms from the pyridine rings of two OPY ligands and by four O atoms, three of which are from two ndc²⁻ ligands and one of which is from a water molecule. In (I), every two identical two‐dimensional (2D) 6³ layers are interpenetrated in a parallel fashion, resulting in an interesting 2D→2D framework with both polyrotaxane and polycatenane characteristics. The extension of these sheets into a three‐dimensional supramolecular net is via O—H…O hydrogen bonds. The solid‐state photoluminescence properties of (I) are also discussed.     

Heptametallic,Octupolar Nonlinear Optical Chromophores with Six Ferrocenyl Substituents

New complexes with six ferrocenyl (Fc) groups connected to Zn^II or Cd^II tris(2,2′‐bipyridyl) cores are described. A thorough characterisation of their BPh₄^? salts includes two single‐crystal X‐ray structures, highly unusual for such species with multiple, extended substituents. Intense, visible d(Fe^II)→π* metal‐to‐ligand charge‐transfer (MLCT) bands accompany the π→π* intraligand charge‐transfer absorptions in the near UV region. Each complex shows a single, fully reversible Fe^III/II wave when probed electrochemically. Molecular quadratic nonlinear optical (NLO) responses are determined by using hyper‐Rayleigh scattering and Stark spectroscopy. The latter gives static first hyperpolarisabilities β₀ reaching as high as approximately 10^?27 esu and generally increasing with π‐conjugation extension. Z‐scan cubic NLO measurements reveal high two‐photon absorption cross‐sections σ₂ of up to 5400 GM in one case. DFT calculations reproduce the π‐conjugation dependence of β₀, and TD‐DFT predicts three transitions close in energy contributing to the MLCT bands. The lowest energy transition has octupolar character, whereas the other two are degenerate and dipolar in nature.     

Three‐arm star block copolymers of ε‐caprolactone and acrylic acid: Synthesis and micellization behavior

A series of well‐defined three‐arm star poly(ε‐caprolactone)‐b‐poly(acrylic acid) copolymers having different block lengths were synthesized via the combination of ring‐opening polymerization (ROP) and atom transfer radical polymerization (ATRP). First, three‐arm star poly(ε‐caprolactone) (PCL) (M_n = 2490–7830 g mol^?1; M_w/M_n = 1.19–1.24) were synthesized via ROP of ε‐caprolactone (ε‐CL) using tris(2‐hydroxyethyl)cynuric acid as three‐arm initiator and stannous octoate (Sn(Oct)₂) as a catalyst. Subsequently, the three‐arm macroinitiator transformed from such PCL in high conversion initiated ATRPs of tert‐butyl acrylate (^tBuA) to construct three‐arm star PCL‐b‐P^tBuA copolymers (M_n = 10,900–19,570 g mol^?1; M_w/M_n = 1.14–1.23). Finally, the three‐arm star PCL‐b‐PAA copolymer was obtained via the hydrolysis of the PtBuA segment in three‐arm star PCL‐b‐P^tBuA copolymers. The chain structures of all the polymers were characterized by gel permeation chromatography, proton nuclear magnetic resonance (¹H NMR), and Fourier transform infrared spectroscopy. The aggregates of three‐arm star PCL‐b‐PAA copolymer were studied by the determination of critical micelles concentration and transmission electron microscope. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

A three‐dimensional homochiral metal–organic framework constructed from manganese(II) with S‐carboxymethyl‐N‐(p‐tosyl)‐l‐cysteine and 4,4′‐bipyridine

In the chiral polymeric title compound, poly[aqua(4,4′‐bipyridine)[μ₃‐S‐carboxylatomethyl‐N‐(p‐tosyl)‐l ‐cysteinato]manganese(II)], [Mn(C₁₂H₁₃NO₆S₂)(C₁₀H₈N₂)(H₂O)]_n, the Mn^II ion is coordinated in a distorted octahedral geometry by one water molecule, three carboxylate O atoms from three S‐carboxyatomethyl‐N‐(p‐tosyl)‐l ‐cysteinate (Ts‐cmc) ligands and two N atoms from two 4,4′‐bipyridine molecules. Each Ts‐cmc ligand behaves as a chiral μ₃‐linker connecting three Mn^II ions. The two‐dimensional frameworks thus formed are further connected by 4,4′‐bipyridine ligands into a three‐dimensional homochiral metal–organic framework. This is a rare case of a homochiral metal–organic framework with a flexible chiral ligand as linker, and this result demonstrates the important role of noncovalent interactions in stabilizing such assemblies.     

The coordination complex structures and hydrogen bonding in the three‐dimensional alkaline earth metal salts (Mg,Ca, Sr and Ba) of (4‐aminophenyl)arsonic acid

(4‐Aminophenyl)arsonic acid (p‐arsanilic acid) is used as an antihelminth in veterinary applications and was earlier used in the monosodium salt dihydrate form as the antisyphilitic drug atoxyl. Examples of complexes with this acid are rare. The structures of the alkaline earth metal (Mg, Ca, Sr and Ba) complexes with (4‐aminophenyl)arsonic acid (p‐arsanilic acid) have been determined, viz. hexaaquamagnesium bis[hydrogen (4‐aminophenyl)arsonate] tetrahydrate, [Mg(H₂O)₆](C₆H₇AsNO₃)·4H₂O, (I), catena‐poly[[[diaquacalcium]‐bis[μ₂‐hydrogen (4‐aminophenyl)arsonato‐κ²O :O ′]‐[diaquacalcium]‐bis[μ₂‐hydrogen (4‐aminophenyl)arsonato‐κ²O :O ]] dihydrate], {[Ca(C₆H₇AsNO₃)₂(H₂O)₂]·2H₂O}_n , (II), catena‐poly[[triaquastrontium]‐bis[μ₂‐hydrogen (4‐aminophenyl)arsonato‐κ²O :O ′]], [Sr(C₆H₇AsNO₃)₂(H₂O)₃]_n , (III), and catena‐poly[[triaquabarium]‐bis[μ₂‐hydrogen (4‐aminophenyl)arsonato‐κ²O :O ′]], [Ba(C₆H₇AsNO₃)₂(H₂O)₃]_n , (IV). In the structure of magnesium salt (I), the centrosymmetric octahedral [Mg(H₂O)₆]²⁺ cation, the two hydrogen p‐arsanilate anions and the four water molecules of solvation form a three‐dimensional network structure through inter‐species O—H and N—H hydrogen‐bonding interactions with water and arsonate O‐atom and amine N‐atom acceptors. In one‐dimensional coordination polymer (II), the distorted octahedral CaO₆ coordination polyhedron comprises two trans‐related water molecules and four arsonate O‐atom donors from bridging hydrogen arsanilate ligands. One bridging extension is four‐membered via a single O atom and the other is eight‐membered via O :O ′‐bridging, both across inversion centres, giving a chain coordination polymer extending along the [100] direction. Extensive hydrogen‐bonding involving O—H…O, O—H…N and N—H…O interactions gives an overall three‐dimensional structure. The structures of the polymeric Sr and Ba complexes (III) and (IV), respectively, are isotypic and are based on irregular M O₇ coordination polyhedra about the M ²⁺ centres, which lie on twofold rotation axes along with one of the coordinated water molecules. The coordination centres are linked through inversion‐related arsonate O :O ′‐bridges, giving eight‐membered ring motifs and forming coordination polymeric chains extending along the [100] direction. Inter‐chain N—H…O and O—H…O hydrogen‐bonding interactions extend the structures into three dimensions and the crystal packing includes π–π ring interactions [minimum ring centroid separations = 3.4666 (17) Å for (III) and 3.4855 (8) Å for (IV)].     

Using the reversible addition–fragmentation chain transfer process to synthesize core‐crosslinked micelles

Poly(2‐hydroxyethyl acrylate)–poly(n‐butyl acrylate) block copolymers were synthesized with the reversible addition–fragmentation chain transfer (RAFT) process. The block copolymers were synthesized successfully with either poly(2‐hydroxyethyl acrylate) or poly(n‐butyl acrylate) macro‐RAFT agents. The resulting block copolymers had narrow molecular weight distributions (polydispersity index = 1.3–1.4). Copolymer self‐aggregation in water yielded micelles, with the hydrodynamic diameter (D_h) values of the aggregates dependent on the length of both blocks according to D_h ～ N_BA^1.17N_HEA^0.57, where N_BA is the number of repeating units of n‐butyl acrylate and N_HEA is the number of repeating units of 2‐hydroxyethyl acrylate. The micelles were subsequently stabilized via chain extension of the block copolymer with a crosslinking agent. The successful chain extension in a micellar system was confirmed by an increase in the molecular weight, which was detected with membrane osmometry. The crosslinked particles showed noticeably different aggregation behavior in diverse solvent systems. The uncrosslinked micelles formed by the block copolymer (N_HEA = 260, N_BA = 75) displayed a definite critical micelle concentration at 5.4 × 10^?4 g L^?1 in aqueous solutions. However, upon crosslinking, the critical micelle concentration transition became obscure. © 2006Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2177–2194, 2006     

A Convenient Synthetic Route to Spiro[indole‐3,4′‐piperidin]‐2‐ones

Starting from 1‐[(tert‐butoxy)carbonyl]piperidine‐4‐carboxylic acid and 2‐bromoaniline, the spiro[indole‐3,4′‐piperidin]‐2‐one system was obtained in three high‐yielding steps: anilide formation, N(1)‐protection, and intramolecular cyclization under Pd catalysis as the key reaction. The preparation of the corresponding 2‐bromoanilide was studied. In extension, the same sequence was developed with 4‐methyl‐ and 4‐nitro‐2‐bromoaniline. In the key step, the NO₂ group led to a rather diminished yield. The transformation of the protected spiro[indole‐3,4′‐piperidin]‐2‐one to the corresponding unprotected dihydroindoles is discussed.     

A three‐dimensional hydrogen‐bonded framework in 2‐amino‐6‐(N‐methylanilino)pyrimidin‐4(3H)‐one and a ribbon of fused hydrogen‐bonded rings in 2‐amino‐6‐(N‐methylanilino)‐5‐nitropyrimidin‐4(3H)‐one

The molecular dimensions of both 2‐amino‐6‐(N‐methylanilino)pyrimidin‐4(3H)‐one, C₁₁H₁₂N₄O, (I), and 2‐amino‐6‐(N‐methylanilino)‐5‐nitropyrimidin‐4(3H)‐one, C₁₁H₁₁N₅O₃, (II), are consistent with considerable polarization of the molecular–electronic structures. The molecules of (I) are linked into a three‐dimensional framework by a combination of one N—H...N hydrogen bond, two independent N—H...O hydrogen bonds and one C—H...π(arene) hydrogen bond. The molecules of (II) are linked into ribbons containing three types of edge‐fused ring by the combination of two independent three‐centre N—H...(O)₂ hydrogen bonds.     

A New Molecular Theory of Non‐Linear Viscoelasticity for Vitrifiable (or Crystallizable) Thermoplastic Polyurethane Elastomers

The molecular theory of non‐linear viscoelasticity for vitrifiable thermoplastic polyurethane elastomers (VTPUE) is a refinement and extension of viscoelastic theory of thermoplastic elastomers and polyurethanes to glassy transition, a structural model and a mechanism of vitrification for glassy polymers were proposed. Five kinds of constituent chains with Nagai chain constraint consisting of soft‐domains, hard‐domains, and entanglements are used as the elementary structural and statistical ensemble units for the correlation of molecular and phase‐domain structures to the static and dynamic mechanical behaviors. So the influences of non‐Gaussian in character, the phase separation of domain, the network topology of structure, the affined deformation of constituent chains, and the thermal history are all taken into account in the constituent chains of the theory. Free energies of deformation for the VTPUE segment copolymer were calculated by the statistical mechanics with the probability distribution functions of the sizes for the five kinds of constituent chains. Then the static constitutive equations and modulus of four types of deformation and the dynamic shear viscosity, modulus and loss tangent of VTPUE are derived from the proposed theory. The theory is successful in relating the molecular chain parameters C₁₀₀, C₀₂₀, and C₂₀₀ to the constitutive equations and modulus under large deformations and the micro‐domain structure to the complex shear viscosity and modulus and the loss tangent. The dynamic shear modulus and loss tangent of VTPUE are related to the domain structures through the fraction of hard segments (W_h), the molecular weight of soft segment (M_ns), and the growth dimensional parameters of hard and soft domains (β). Two series of linear VTPUE copolymers (ES and ET) with different fractions(W_h) of hard segments and molecular weight (M_ns) of soft segments were prepared. Their static and dynamic mechanical properties were studied by uni‐axial extension and dynamic analysis tests. Then the constitutive equation at uni‐axial extension and the expressions of shear modulus and loss tangent are verified by these experimental data, and excellent agreement between the theory and experiments is achieved. It is shown, that the proposed theory can predict the viscoelastic behavior of vitrifiable thermoplastic polyurethanes.     

Preparation of miktoarm star‐block copolymers PSn‐b‐PVAc4‐n via combination of ATRP and RAFT polymerization

Three tetrafunctional bromoxanthate agents (Xanthate₃‐Br, Xanthate₂‐Br₂, and Xanthate‐Br₃) were synthesized. Initiative atom transfer radical polymerizations (ATRP) of styrene (St) or reversible addition fragmentation chain transfer (RAFT) polymerizations of vinyl acetate (VAc) proceeded in a controlled manner in the presence of Xanthate₃‐Br, Xanthate₂‐Br₂, or Xanthate‐Br₃, respectively. The miktoarm star‐block copolymers containing polystyrene (PS) and poly(vinyl acetate) (PVAc) chains, PS_n‐b‐PVAc_4‐n (n = 1, 2, and 3), with controlled structures were successfully prepared by successive RAFT and ATRP chain‐extension experiments using VAc and St as the second monomers, respectively. The architecture of the miktoarm star‐block copolymers PS_n‐b‐PVAc_4‐n (n = 1, 2, and 3) were characterized by gel permeation chromatography and ¹H NMR spectra. Furthermore, the results of the cleavage of PS₃‐b‐PVAc and PVAc₂‐b‐PS₂ confirmed the structures of the obtained miktoarm star‐block copolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Living/controlled radical polymerization of styrene with a new initiating system: DCDPS/FeCl3/PPh3

The living/controlled radical polymerization of styrene was investigated with a new initiating system, DCDPS/FeCl₃/PPh₃, in which diethyl 2,3‐dicyano‐2,3‐diphenylsuccinate (DCDPS) was a hexa‐substituted ethane thermal iniferter. The polymerization mechanism belonged to a reverse atom transfer radical polymerization (ATRP) process. The polymerization was controlled closely in bulk (at 100 °C) or in solution (at 110 °C) with a high molecular weight and quite narrow polydispersity (M_w/M_n = 1.18 ∼ 1.28). End‐group analysis results by ¹H NMR spectroscopy showed that the polymer was ω‐functionalized by a chlorine atom, which also was confirmed by the result of a chain‐extension reaction in the presence of a FeCl₂/PPh₃ or CuCl/bipy (2,2′‐bipyridine) catalyst via a conventional ATRP process. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 101–107, 2000     

Two‐dimensional coordination polymeric structures in caesium complexes with ring‐substituted phenoxyacetic acids

The two‐dimensional polymeric structures of the caesium complexes with the phenoxyacetic acid analogues (4‐fluorophenoxy)acetic acid, (3‐chloro‐2‐methylphenoxy)acetic acid and the herbicidally active (2,4‐dichlorophenoxy)acetic acid (2,4‐D), namely poly[[μ₅‐(4‐fluorophenoxy)acetato][μ₄‐(4‐fluorophenoxy)acetato]dicaesium], [Cs₂(C₈H₆FO₃)₂]_n, (I), poly[aqua[μ₅‐(3‐chloro‐2‐methylphenoxy)acetato]caesium], [Cs(C₉H₈ClO₃)(H₂O)]_n, (II), and poly[[μ₇‐(2,4‐dichlorophenoxy)acetato][(2,4‐dichlorphenoxy)acetic acid]caesium], [Cs(C₈H₅Cl₂O₃)(C₈H₆Cl₂O₃)]_n, (III), are described. In (I), the Cs⁺ cations of the two individual irregular coordination polyhedra in the asymmetric unit (one CsO₇ and the other CsO₈) are linked by bridging carboxylate O‐atom donors from the two ligand molecules, both of which are involved in bidentate chelate O_carboxy,O_phenoxy interactions, while only one has a bidentate carboxylate O,O′‐chelate interaction. Polymeric extension is achieved through a number of carboxylate O‐atom bridges, with a minimum Cs...Cs separation of 4.3231 (9) Å, giving layers which lie parallel to (001). In hydrated complex (II), the irregular nine‐coordination about the Cs⁺ cation comprises a single monodentate water molecule, a bidentate O_carboxy,O_phenoxy chelate interaction and six bridging carboxylate O‐atom bonding interactions, giving a Cs...Cs separation of 4.2473 (3) Å. The water molecule forms intralayer hydrogen bonds within the two‐dimensional layers, which lie parallel to (100). In complex (III), the irregular centrosymmetric CsO₆Cl₂ coordination environment comprises two O‐atom donors and two ring‐substituted Cl‐atom donors from two hydrogen bis[(2,4‐dichlorophenoxy)acetate] ligand species in a bidentate chelate mode, and four O‐atom donors from bridging carboxyl groups. The duplex ligand species lie across crystallographic inversion centres, linked through a short O—H...O hydrogen bond involving the single acid H atom. Structure extension gives layers which lie parallel to (001). The present set of structures of Cs salts of phenoxyacetic acids show previously demonstrated trends among the alkali metal salts of simple benzoic acids with no stereochemically favourable interactive substituent groups for formation of two‐dimensional coordination polymers.     

Cationic,neutral and anionic metal(II) complexes derived from 4‐oxo‐4H‐pyran‐2,6‐dicarboxylic acid (chelidonic acid)

The structures of five metal complexes containing the 4‐oxo‐4H‐pyran‐2,6‐dicarboxylate dianion illustrate the remarkable coordinating versatility of this ligand and the great structural diversity of its complexes. In tetraaquaberyllium 4‐oxo‐4H‐pyran‐2,6‐dicarboxylate, [Be(H₂O)₄](C₇H₂O₆), (I), the ions are linked by eight independent O—H...O hydrogen bonds to form a three‐dimensional hydrogen‐bonded framework structure. Each of the ions in hydrazinium(2+) diaqua(4‐oxo‐4H‐pyran‐2,6‐dicarboxylato)calcate, (N₂H₆)[Ca(C₇H₂O₆)₂(H₂O)₂], (II), lies on a twofold rotation axis in the space group P2/c; the anions form hydrogen‐bonded sheets which are linked into a three‐dimensional framework by the cations. In bis(μ‐4‐oxo‐4H‐pyran‐2,6‐dicarboxylato)bis[tetraaquamanganese(II)] tetrahydrate, [Mn₂(C₇H₂O₆)₂(H₂O)₈]·4H₂O, (III), the metal ions and the organic ligands form a cyclic centrosymmetric Mn₂(C₇H₂O₆)₂ unit, and these units are linked into a complex three‐dimensional framework structure containing 12 independent O—H...O hydrogen bonds. There are two independent Cu^II ions in tetraaqua(4‐oxo‐4H‐pyran‐2,6‐dicarboxylato)copper(II), [Cu(C₇H₂O₆)(H₂O)₄], (IV), and both lie on centres of inversion in the space group P; the metal ions and the organic ligands form a one‐dimensional coordination polymer, and the polymer chains are linked into a three‐dimensional framework containing eight independent O—H...O hydrogen bonds. Diaqua(4‐oxo‐4H‐pyran‐2,6‐dicarboxylato)cadmium monohydrate, [Cd(C₇H₂O₆)(H₂O)₂]·H₂O, (V), forms a three‐dimensional coordination polymer in which the organic ligand is coordinated to four different Cd sites, and this polymer is interwoven with a complex three‐dimensional framework built from O—H...O hydrogen bonds.     

Low‐dimensional coordination polymeric structures in alkali metal complex salts of the herbicide (2,4‐dichlorophenoxy)acetic acid (2,4‐D)

The Li, Rb and Cs complexes with the herbicide (2,4‐dichlorophenoxy)acetic acid (2,4‐D), namely poly[[aqua[μ₃‐(2,4‐dichlorophenoxy)acetato‐κ³O¹:O¹:O^1′]lithium(I)] dihydrate], {[Li(C₈H₅Cl₂O₃)(H₂O)]·2H₂O}_n, (I), poly[μ‐aqua‐bis[μ₃‐(2,4‐dichlorophenoxy)acetato‐κ⁴O¹:O^1′:O^1′,Cl²]dirubidium(I)], [Rb₂(C₈H₅Cl₂O₃)₂(H₂O)]_n, (II), and poly[μ‐aqua‐bis[μ₃‐(2,4‐dichlorophenoxy)acetato‐κ⁵O¹:O^1′:O^1′,O²,Cl²]dicaesium(I)], [Cs₂(C₈H₅Cl₂O₃)₂(H₂O)]_n, (III), respectively, have been determined and their two‐dimensional polymeric structures are described. In (I), the slightly distorted tetrahedral LiO₄ coordination involves three carboxylate O‐atom donors, of which two are bridging, and a monodentate aqua ligand, together with two water molecules of solvation. Conjoined six‐membered ring systems generate a one‐dimensional coordination polymeric chain which extends along b and interspecies water O—H...O hydrogen‐bonding interactions give the overall two‐dimensional layers which lie parallel to (001). In hemihydrate complex (II), the irregular octahedral RbO₅Cl coordination about Rb⁺ comprises a single bridging water molecule which lies on a twofold rotation axis, a bidentate O_carboxy,Cl‐chelate interaction and three bridging carboxylate O‐atom bonding interactions from the 2,4‐D ligand. A two‐dimensional coordination polymeric layer structure lying parallel to (100) is formed through a number of conjoined cyclic bridges, including a centrosymmetric four‐membered Rb₂O₂ ring system with an Rb...Rb separation of 4.3312 (5) Å. The coordinated water molecule forms intralayer aqua–carboxylate O—H...O hydrogen bonds. Complex (III) comprises two crystallographically independent (Z′ = 2) irregular CsO₆Cl coordination centres, each comprising two O‐atom donors (carboxylate and phenoxy) and a ring‐substituted Cl‐atom donor from the 2,4‐D ligand species in a tridentate chelate mode, two O‐atom donors from bridging carboxylate groups and one from a bridging water molecule. However, the two 2,4‐D ligands are conformationally very dissimilar, with one phenoxyacetate side chain being synclinal and the other being antiperiplanar. The minimum Cs...Cs separation is 4.4463 (5) Å. Structure extension gives coordination polymeric layers which lie parallel to (001) and are stabilized by intralayer water–carboxylate O—H...O hydrogen bonds.     

Cyclic heterotetrameric and low‐dimensional hydrogen‐bonded polymeric structures in the morpholinium salts of ring‐substituted benzoic acid analogues

The morpholinium (tetrahydro‐2H‐1,4‐oxazin‐4‐ium) cation has been used as a counter‐ion in both inorganic and organic salt formation and particularly in metal complex stabilization. To examine the influence of interactive substituent groups in the aromatic rings of benzoic acids upon secondary structure generation, the anhydrous salts of morpholine with salicylic acid, C₄H₁₀NO⁺·C₇H₅O₃⁻, (I), 3,5‐dinitrosalicylic acid, C₄H₁₀NO⁺·C₇H₃N₂O₇⁻, (II), 3,5‐dinitrobenzoic acid, C₄H₁₀NO⁺·C₇H₃N₂O₆⁻, (III), and 4‐nitroanthranilic acid, C₄H₁₀NO⁺·C₇H₅N₂O₄⁻, (IV), have been prepared and their hydrogen‐bonded crystal structures are described. In the crystal structures of (I), (III) and (IV), the cations and anions are linked by moderately strong N—H…O_carboxyl hydrogen bonds, but the secondary structure propagation differs among the three, viz. one‐dimensional chains extending along [010] in (I), a discrete cyclic heterotetramer in (III), and in (IV), a heterotetramer with amine N—H…O hydrogen‐bond extensions along b, giving a two‐layered ribbon structure. With the heterotetramers in both (III) and (IV), the ion pairs are linked though inversion‐related N—H…O_carboxylate hydrogen bonds, giving cyclic R₄⁴(12) motifs. With (II), in which the anion is a phenolate rather than a carboxylate, the stronger assocation is through a symmetric lateral three‐centre cyclic R₁²(6) N—H…(O,O′) hydrogen‐bonding linkage involving the phenolate and nitro O‐atom acceptors of the anion, with extension through a weaker O—H…O_carboxyl hydrogen bond. This results in a one‐dimensional chain structure extending along [100]. In the structures of two of the salts [i.e. (II) and (IV)], there are also π–π ring interactions, with ring‐centroid separations of 3.5516 (9) and 3.7700 (9) Å in (II), and 3.7340 (9) Å in (IV).     

Nitroxide‐Mediated Polymerization of Bio‐Based Farnesene with a Functionalized Methacrylate

Farnesene (Far) is a bio‐based terpene monomer that is similar in structure to commercially used dienes like butadiene and isoprene. Nitroxide‐mediated polymerization (NMP) is adept for the polymerization of dienes, but not particularly effective at controlling the polymerization of methacrylates using commercial nitroxides. In this study, Far is statistically copolymerized with a functional methacrylate, glycidyl methacrylate (GMA), by NMP using N‐succinimidyl modified commercial BlocBuilder (NHS‐BB) initiator. Reactivity ratios are determined to be r _Far = 0.54 ± 0.04 and r _GMA = 0.24 ± 0.02. The ability of the poly(Far‐stat‐GMA) chains to reinitiate for chain extension with styrene showed a clear shift in molecular weight and monomodal distribution. Copolymerizations using a new alkoxyamine, Dispolreg 007 (D7), is explored as it is shown to homopolymerize methacrylates, but not yet reported for statistical copolymerizations. Bimodal molecular weight distributions are observed when an equimolar ratio of Far and GMA is copolymerized with D7 due to slow decomposition of the initiator, but chain ends are active as shown by successful chain extension with styrene. Both NHS‐BB and D7 initiators are used to synthesize poly[Far‐b‐(GMA‐stat‐Far)] and poly(Far‐b‐GMA) diblock copolymers. While the NHS‐BB initiated polymer chains have lower dispersity, D7 exhibits more linear polymerization kinetics and maintains more active chain ends.     

The Structural Characterization of Folded Peptides Containing the Conformationally Constrained β‐Amino Acid Residue β2,2Ac6c

Backbone alkylation has been shown to result in a dramatic reduction in the conformational space that is sterically accessible to α‐amino acid residues in peptides. By extension, the presence of geminal dialkyl substituents at backbone atoms also restricts available conformational space for β and γ residues. Five peptides containing the achiral β^2,2‐disubstituted β‐amino acid residue, 1‐(aminomethyl)cyclohexanecarboxylic acid (β^2,2Ac₆c), have been structurally characterized in crystals by X‐ray diffraction. The tripeptide Boc‐Aib‐β^2,2Ac₆c‐Aib‐OMe ( 1 ) adopts a novel fold stabilized by two intramolecular H‐bonds (C₁₁ and C₉) of opposite directionality. The tetrapeptide Boc‐[Aib‐β^2,2Ac₆c]₂‐OMe ( 2 ) and pentapeptide Boc‐[Aib‐β^2,2Ac₆c]₂‐Aib‐OMe ( 3 ) form short stretches of a hybrid αβ C₁₁ helix stabilized by two and three intramolecular H‐bonds, respectively. The structure of the dipeptide Boc‐Aib‐β^2,2Ac₆c‐OMe ( 5 ) does not reveal any intramolecular H‐bond. The aggregation pattern in the crystal provides an example of an extended conformation of the β^2,2Ac₆c residue, forming a ‘polar sheet’ like H‐bond. The protected derivative Ac‐β^2,2Ac₆c‐NHMe ( 4 ) adopts a locally folded gauche conformation about the C_β? C_α bonds (θ=?55.7°). Of the seven examples of β^2,2Ac₆c residues reported here, six adopt gauche conformations, a feature which promotes local folding when incorporated into peptides. A comparison between the conformational properties of β^2,2Ac₆c and β^3,3Ac₆c residues, in peptides, is presented. Backbone torsional parameters of H‐bonded αβ/βα turns are derived from the structures presented in this study and earlier reports.