A Bowl‐Shaped Circular Trinuclear Helicate Generated from a TiO4N2 Motif by a Multicomponent Self‐Assembly Approach

The synthesis of a bowl‐shaped trinuclear circular titanium‐based helicate is reported. The strategy allowing access to this neutral architecture is based on a multicomponent self‐assembly approach in which the ligands involved in the process are a bis‐biphenol strand and 2,2′‐ bipyrimidine. By reacting the bis‐biphenol ligand and 2,2′‐bipyrimidine with an equimolar amount [Ti(OiPr)₄], a bowl‐shaped architecture is obtained through the formation of 18 new coordination bonds. This aggregate built from three octahedral TiO₄N₂ nodes displays an unusually high stability in solution compared to related species. In addition, by modifying the stoichiometry of the initial components, two assemblies incorporating two titanium centers bridged by a 2,2′‐bipyrimidine ligand are obtained. The crystal structures of these species are reported.     

Two New Lead(II) Coordination Polymers with (Substituted) Bipyridine and Auxiliary Nitrate Ligands

The reaction of lead(II) nitrate with 4,4′‐bipyridine (4,4′‐bpy) and 4,4′‐dimethyl‐2,2′‐bipyridine (4,4′‐dm‐2,2′‐bpy) or 5,5′‐dimethyl‐2,2′‐bipyridine (5,5′‐dm‐2,2′‐bpy) resulted in the fomation of single crystals of [Pb₂(4,4′‐bpy)(5,5′‐dm‐2,2′‐bpy)₂(NO₃)₄] ( 1 ) and [Pb₃(4,4′‐bpy)₂(4,4′‐dm‐2,2′‐bpy)₂(NO₃)₆] ( 2 ). The new compounds have been characterized by single‐crystal X‐ray diffraction structure analysis as well as through elemental analysis, IR, ¹H‐NMR and ¹³C‐NMR spectroscopy and their stability has been studied by thermal analysis. In the crystal structure of ( 1 ) formula‐like dimers are further connected to a 2‐D network through the auxiliary nitrate ligands. The crystal structure of ( 2 ) exhibits two crystallographically independent Pb^II central atoms (in a ratio of 1:2). With the aid of the 4,4′‐bpy and the nitrate ions, a 3‐D polymeric structure is achieved.     

Expanding the Variety of Zirconium‐based Inorganic Building Units for Metal–Organic Frameworks

Two new zirconium‐based metal–organic frameworks with the composition [Zr₆O₄(OH)₄(OAc)₆(BDC)₃] (CAU‐26) and [Zr₅O₄(OH)₄(OAc)₄(BDC)₂] (CAU‐27) are reported, which were synthesized from acetic acid, a rarely utilized but green and sustainable solvent (BDC^2?: 1,4‐benzenedicarboxylate). Structure determination aided by automated electron diffraction tomography revealed that CAU‐26 is composed of layers of well‐known {Zr₆O₈} clusters interconnected by terephthalate ions. In contrast CAU‐27 exhibits a three‐dimensional structure with a so far unknown type of one‐dimensional inorganic building unit (IBU), which can be rationalized as condensed polyhedron‐sharing chains of {Zr₆O₈} clusters. CAU‐26 occurs as an intermediate of the CAU‐27 synthesis and can be isolated easily, when reaction temperature and time are decreased. We were also able to synthesize two isoreticular derivatives of CAU‐27 with extended linker molecules by implementing 4,4′‐biphenyldicarboxylic acid (H₂BPDC) and 5,5′‐dicarboxy‐2,2′‐bipyridine (H₂BIPY). All materials show high thermal and chemical stability as well as permanent microporosity. The excellent stability of CAU‐27‐BIPY was exploited to synthesize a performant iridium‐supported heterogeneous MOF‐based catalyst for the direct C?H borylation of arenes.     

Atropisomeric [(diphosphine)Au2Cl2] Complexes and their Catalytic Activity Towards Asymmetric Cycloisomerisation of 1,6‐Enynes

X‐ray crystal structures of two [(diphosphine)Au₂Cl₂] complexes (in which diphosphine=P‐Phos and xylyl‐P‐Phos; P‐Phos=[2,2′,6,6′‐Tetramethoxy‐4,4′‐bis(diphenylphosphino)‐3,3′‐bipyridine]) were determined and compared to the reported structures of similar atropisomeric gold complexes. Correlations between the Au???Au distances and torsional angles for the biaryl series of ligands (MeOBIPHEP, SEGPhos, and P‐Phos; BIPHEP=2,2′‐bis(diphenylphosphino)‐1,1′‐biphenyl, SEGPhos=[(4,4′‐bi‐1,3‐benzodioxole)‐5,5′‐diyl]bis[diphenylphosphine]) can be made; these measurements appear to be very dependent upon the phosphorous substituent. Conversely, the same effect was not observed for ligands based on the binaphthyl (BINAP) series. The catalytic activity of these complexes was subsequently assessed in the enantioselective cycloisomerisation of 1,6‐enynes and revealed an over‐riding electronic effect: more‐electron‐rich phosphines promote greater enantioselectivity. The possibility of silver acting as a (co‐)catalyst was ruled out in these reactions.     

Oxygen‐Dependent Photocatalytic Water Reduction with a Ruthenium(imidazolium) Chromophore and a Cobaloxime Catalyst

Detailed investigations of a photocatalytic system capable of producing hydrogen under pre‐catalytic aerobic conditions are reported. This system consists of the NHC precursor chromophore [Ru(tbbpy)₂(RR′ip)][PF₆]₃ (abbreviated as Ru(RR′ip)[PF₆]₃; tbbpy=4,4′‐di‐tert‐butyl‐2,2′‐bipyridine, RR′ip=1,3‐disubstituted‐1H‐imidazo[4,5‐f][1,10]phenanthrolinium), the reduction catalyst Co(dmgH)₂ (dmgH=dimethylglyoximato), and the electron donor ascorbic acid (AA). Screening studies with respect to solvent, cobaloxime catalyst, electron donor, pH, and concentrations of the individual components yielded optimized photocatalytic conditions. The system shows high activity based on Ru, with turnover numbers up to 2000 under oxygen‐free and pre‐catalytic aerobic conditions. The turnover frequency in the latter case was even higher than that for the oxygen‐free catalyst system. The Ru complexes show high photostability and their first excited state is primarily located on the RR′ip ligand. X‐ray crystallographic analysis of the rigid cyclophane‐type ligand dd(ip)₂(Br)₂ (dd(ip)₂=1,1′,3,3′‐bis(2,3,5,6‐tetramethyl‐1,4‐phenylene)bis(methylene)bis(1H‐imidazo[4,5‐f][1,10]phenanthrolinium)) and the catalytic activity of its Ru complex [{(tbbpy)₂Ru}₂(μ‐dd(ip)₂)][PF₆]₆ (abbreviated as Ru₂(dd(ip)₂)[PF₆]₆) suggest an intermolecular catalytic cycle.     

Stabilization of Formate Dehydrogenase in a Metal–Organic Framework for Bioelectrocatalytic Reduction of CO2

The efficient fixation of excess CO₂ from the atmosphere to yield value‐added chemicals remains crucial in response to the increasing levels of carbon emission. Coupling enzymatic reactions with electrochemical regeneration of cofactors is a promising technique for fixing CO₂, while producing biomass which can be further transformed into biofuels. Herein, a bioelectrocatalytic system was established by depositing crystallites of a mesoporous metal–organic framework (MOF), termed NU‐1006, containing formate dehydrogenase, on a fluorine‐doped tin oxide glass electrode modified with Cp*Rh(2,2′‐bipyridyl‐5,5′‐dicarboxylic acid)Cl₂ complex. This system converts CO₂ into formic acid at a rate of 79±3.4 mm h^?1 with electrochemical regeneration of the nicotinamide adenine dinucleotide cofactor. The MOF–enzyme composite exhibited significantly higher catalyst stability when subjected to non‐native conditions compared to the free enzyme, doubling the formic acid yield.     

Single‐Stranded DNA: Replacement of Canonical by Base‐Modified Nucleosides in the Minihairpin 5′‐d(GCGAAGC)‐3′ and Constructs with the Aptamer 5′‐d(GGTTGGTGTGGTTGG)‐3′

The minihairpin 5′‐d(GCGAAGC)‐3′ ( 1 ) was modified either in the loop region, in the base‐paired stem, or at the 5′‐terminus by incorporation of base‐modified nucleosides. The thermal melting was correlated to the structural changes induced by the various donor‐acceptor properties of the nucleosides. Overhanging nonpaired nucleosides at the 5′‐terminus stabilized the hairpin, while a reverse of the dG³?dA⁵ sheared base pair to dA³?dG⁵ severely affected the stability. The combination of the minihairpin 5′‐d(GCGAAGC)‐3′ ( 1 ) and the thrombin‐binding aptamer 5′‐d(GGTTGGTGTGGTTGG)‐3′ ( 2 (= 46 )) resulted in the new construct 5′‐d(GGTTGGGCGAAGC GGTTGG)‐3′ ( 43 ) arising by replacement of the 5′‐d(TGT)‐3′ loop of 2 by the minihairpin. The fused oligonucleotide 43 exhibits a two‐phase thermal transition indicating the presence of the two unaltered moieties. According to slight changes of the T_m values of the construct 43 as compared to the separate units 1 and 2 , cooperative distorsions are discussed.     

Synthesis,characterization, and evaluation of biological activities of new 4′‐substituted ruthenium (II) terpyridine complexes: Prospective anti‐inflammatory properties

The synthesis and characterization of Ru (II) terpyridine complexes derived from 4′ functionalized 2,2′:6′,2″‐terpyridine (tpy) ligands are reported. The heteroleptic complexes comprise the synthesized ligands 4′‐(2‐thienyl)‐ 2,2′:6′,2″‐terpyridine) or (4′‐(3,4‐dimethoxyphenyl)‐2,2′:6′,2″‐terpyridine and (dimethyl 5‐(pyrimidin‐5‐yl)isophthalate). The new complexes [Ru(4′‐(2‐thienyl)‐2,2′:6′,2″‐terpyridine)(5‐(pyrimidin‐5‐yl)‐isophthalic acid)Cl₂] ( 9 ), [Ru(4′‐(3,4‐dimethoxyphenyl)‐2,2′:6′,2″‐terpyridine)(5‐(pyrimidin‐5‐yl)‐isophthalic acid)Cl₂] ( 10 ), and [Ru(4′‐(2‐thienyl)‐2,2′:6′,2″‐terpyridine)(5‐(pyrimidin‐5‐yl)‐isophthalic acid)(NCS)₂] ( 11 ) were characterized by ¹H‐ and ¹³C‐NMR spectroscopy, C, H, N, and S elemental analysis, UPLC‐ESI‐MS, TGA, FT‐IR, and UV‐Vis spectroscopy. The biological activities of the synthesized ligands and their Ru (II) complexes as anti‐inflammatory, antimicrobial, and anticancer agents were evaluated. Furthermore, the toxicity of the synthesized compounds was studied and compared with the standard drugs, namely, diclofenac potassium and ibuprofen, using hemolysis assay. The results indicated that the ligands and the complex 9 possess superior anti‐inflammatory activities inhibiting albumin denaturation (89.88–100%) compared with the standard drugs (51.5–88.37%) at a concentration of 500 μg g^?1. These activities were related to the presence of the chelating N‐atoms in the ligands and the exchangeable chloro‐ groups in the complex. Moreover, the chloro‐ and thiophene groups in complex 9 produce a higher anticancer activity compared with its isothiocyanate derivative in the complex 11 and the 3,4‐dimethoxyphenyl moiety in complex 10 . Considering the toxicity results, the synthesized ligands are nontoxic or far less toxic compared with the standard drugs and the metal complexes. Therefore, these newly synthesized compounds are promising anti‐inflammatory agents in addition to their moderate unique broad antimicrobial activity.     

Comparative study on polyimides from isomeric 3,3′‐, 3,4′‐, and 4,4′‐linked bis(thioether anhydride)s

Three isomeric bis(thioether anhydride) monomers, 4,4′‐bis(2,3‐dicarboxyphenylthio) diphenyl ketone dianhydride (3,3′‐PTPKDA), 4,4′‐bis(3,4‐dicarboxyphenylthio) diphenyl ketone dianhydride (4,4′‐PTPKDA), and 4‐(2,3‐dicarboxyphenylthio)‐4′‐(3,4‐dicarboxyphenylthio) diphenyl ketone dianhydride (3,4′‐PTPKDA), were prepared through multistep reactions. Their structures were determined via Fourier transform infrared, NMR, and elemental analysis. Three series of polyimides (PIs) were prepared from the obtained isomeric dianhydrides and aromatic diamines in N‐methyl‐2‐pyrrolidone (NMP) via the conventional two‐step method. The PIs showed excellent solubility in common organic solvents such as chloroform, N,N‐dimethylacetamide, and NMP. Their glass‐transition temperatures decreased according to the order of PIs on the basis of 3,3′‐PTPKDA, 3,4′‐PTPKDA, and 4,4′‐PTPKDA. The 5% weight loss temperatures (T_5%) of all PIs in nitrogen were observed at 504–519 °C. The rheological properties of isomeric PI resins based on 3,3′‐PTPKDA/4,4′‐oxydianiline/phthalic anhydride showed lower complex viscosity and better melt stability compared with the corresponding isomers from 4,4′‐ and 3,4′‐PTPKDA. In addition, the PI films based on three isomeric dianhydrides and 2,2′‐bis(trifluoromethyl)benzidine had a low moisture absorption of 0.27–0.35%. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Phosphanylalanes and Phosphanylgallanes Stabilized only by a Lewis Base

The synthesis and characterization of the first parent phosphanylalane and phosphanylgallane stabilized only by a Lewis base (LB) are reported. The corresponding substituted compounds, such as IDipp?GaH₂PCy₂ ( 1 ) (IDipp=1,3‐bis(2,6‐diisopropylphenyl)‐imidazolin‐2‐ylidene) were obtained by the reaction of LiPCy₂ with IDipp?GaH₂Cl. However, the LB‐stabilized parent compounds IDipp?GaH₂PH₂ ( 3 ) and IDipp?AlH₂PH₂ ( 4 ) were prepared via a salt metathesis of LiPH₂?DME with IDipp?E′H₂Cl (E′=Ga, Al) or by H₂‐elimination reactions of IDipp?E′H₃ (E′=Ga, Al) and PH₃, respectively. The compounds could be isolated as crystalline solids and completely characterized. Supporting DFT computations gave insight into the reaction pathways as well as into the stability of these compounds with respect to their decomposition behavior.     

A one‐dimensional zinc(II) coordination polymer incorporating [1,1′‐biphenyl]‐4,4′‐dicarboxylate and N,N′‐bis(pyridin‐3‐ylmethyl)‐[1,1′‐biphenyl]‐4,4′‐dicarboxamide ligands

In the title compound, catena‐poly[[[N,N′‐bis(pyridin‐3‐ylmethyl)‐[1,1′‐biphenyl]‐4,4′‐dicarboxamide]chloridozinc(II)]‐μ‐[1,1′‐biphenyl]‐4,4′‐dicarboxylato‐[[N,N′‐bis(pyridin‐3‐ylmethyl)‐[1,1′‐biphenyl]‐4,4′‐dicarboxamide]chloridozinc(II)]‐μ‐[N,N′‐bis(pyridin‐3‐ylmethyl)‐[1,1′‐biphenyl]‐4,4′‐dicarboxamide]], [Zn₂(C₁₄H₈O₄)Cl₂(C₂₆H₂₂N₄O₂)₃]_n, the Zn^II centre is four‐coordinate and approximately tetrahedral, bonding to one carboxylate O atom from a bidentate bridging dianionic [1,1′‐biphenyl]‐4,4′‐dicarboxylate ligand, to two pyridine N atoms from two N,N′‐bis(pyridin‐3‐ylmethyl)‐[1,1′‐biphenyl]‐4,4′‐dicarboxamide ligands and to one chloride ligand. The pyridyl ligands exhibit bidentate bridging and monodentate terminal coordination modes. The bidentate bridging pyridyl ligand and the bridging [1,1′‐biphenyl]‐4,4′‐dicarboxylate ligand both lie on special positions, with inversion centres at the mid‐points of their central C—C bonds. These bridging groups link the Zn^II centres into a one‐dimensional tape structure that propagates along the crystallographic b direction. The tapes are interlinked into a two‐dimensional layer in the ab plane through N—H...O hydrogen bonds between the monodentate ligands. In addition, the thermal stability and solid‐state photoluminescence properties of the title compound are reported.     

Synthesis and Characterization of Extended Bis(terpyridine)ruthenium Amino Acids

(Oligopyridine)ruthenium(II) complexes have been widely used in dye sensitized solar cells and other sophisticated optical devices due to their outstanding photophysical properties and their chemical stability. Herein, we describe the longitudinal extension of our previously reported bis(terpyridine)ruthenium(II) amino acid [Ru(tpy–NH₂)(tpy–COOH)]²⁺ (tpy = 4′‐substituted 2,2′:6′,2″‐terpyridine) by insertion of para‐phenylene spacers –C₆H₄– between the terpyridine and the functional groups. The influence of the para‐phenylene spacer on the absorption and emission properties is investigated using UV/Vis absorption and emission spectroscopy and is discussed within a qualitative molecular orbital picture.     

Synthesis and properties of novel polyimides from sulfonated binaphthalene dianhydride for proton exchange membranes

A sulfonated dianhydride monomer, 6,6′‐disulfonic‐4,4′‐binaphthyl‐1,1′,8,8′‐tetracarboxylic dianhydride (SBTDA), was successfully synthesized by direct sulfonation of the parent dianhydride, 4,4′‐binaphthyl‐1,1′,8,8′‐tetracarboxylic dianhydride (BTDA), using fuming sulfuric acid as the sulfonating reagent. A series of sulfonated homopolyimides were prepared from SBTDA and various common nonsulfonated diamines. The resulting polymer electrolytes, which contain ion conductivity sites on the deactivated positions of the aryl backbone rings, displayed high proton conductivities of 0.25–0.31 S cm^?1 at 80 °C. The oxidative stability test indicated that the attachment of the ? SO₃H groups onto the dianhydride units did not deteriorate the oxidative stability of the SPI membranes. The better membranes were achieved by the copolymerization of nonsulfonated diamine, SBTDA, and BTDA. Copolymer membrane synthesized from hexane‐1,6‐diamine, SBTDA, and BTDA displayed excellent water stability of more than 1000 h at 90 °C, while its proton conductivity was still at a high level (comparable to that of Nafion 117). Furthermore, the novel block copolymer ( II‐b ) displayed higher proton conductivity compared with the random one ( II‐r ) obviously, probably due to the slightly higher water uptake and better microphase separated morphology. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2820–2832, 2008     

Molecular Recognition of Bridged Bis （β－cyclodextrin） s Linked by Phenylenediseleno Tether on the Primary or Secondary Side with Fluorescent Dyes

A novel β‐cyclodextrin dimer, 2, 2′‐o‐phenylenediseleno‐bridged bis (β‐cyclodextrin) (2), has been synthesized by reaction of mono‐[2‐O‐(p‐tolylsulfonyl)]‐β‐cyclodextrin and poly(o‐phenylenediselenide). The complexation stability constants (K₂) and Gibbs free energy changes (‐ΔG°) of dimer 2 with four fluorescence dyes, that is, ammonium 8‐anilino‐1‐naphthalenesulfonate (ANS), sodium 6‐(p‐toluidino)‐2‐naphthalenesulfonate (TNS), Acridine Red (AR) and Rhodamine B (RhB) have been determined in aqueous phosphate buffer solution (pH = 7.2, 0.1 mol‐L^?1) at 25 °C by means of fluorescence spectroscopy. Using the present results and the previously reported corresponding data of β‐cyclodextrin (1) and 6, 6′‐o‐phenylenediseleno‐bridged bis (β‐cyclodextrin) (3), binding ability and molecular selectivity are compared, indicating that the bis (β‐cyclodextrin)s 2 and 3 possess much higher binding ability toward these dye molecules than parent β‐cyclodextrin 1, but the complex stability constant for 2 linked from the primary side is larger than that of 3 linked from the secondary side, which is attributed to the more effective cooperative binding of two hydrophobic cavities of host 3 and the size/shape‐fit relationship between host and guest. The binding constant (K₂,) upon inclusion complexation of host 3 and AR is enhanced by factor of 27.3 as compared with that of 1. The 2D ¹H NOESY spectrum of host 2 and RhB is performed to confirm the binding mode and explain the relative weak binding ability of 2.     

Intrinsically microporous polyimides containing spirobisindane and phenazine units: Synthesis,characterization and gas permeation properties

A new diamine containing spirobisindane and phenazine units, namely, 3,3,3′,3′‐tetramethyl‐2,2′,3,3′‐tetrahydro‐1,1′‐spirobi[cyclopenta[b]phenazine]‐7,7′‐diamine (TTSBIDA) was synthesized starting from commercially available 5,5′,6,6′‐tetrahydroxy‐3,3,3′,3′‐tetramethyl‐1,1′‐spirobisindane (TTSBI). TTSBI was oxidized to 3,3,3′,3′‐tetramethyl‐2,2′,3,3′‐tetrahydro‐1,1′‐spirobi[indene]‐5,5′,6,6′‐tetraone (TTSBIQ) which was subsequently condensed with 4‐nitro‐1,2‐phenylenediamine to obtain 3,3,3′,3′‐tetramethyl‐7,7′‐dinitro‐2,2′,3,3′‐tetrahydro‐1,1′‐spirobi[cyclopenta[b]phenazine] (TTSBIDN). TTSBIDN was converted into TTSBIDA by reduction of the nitro groups using hydrazine hydrate in the presence of Pd/C as the catalyst. A series of new polyimides of intrinsic microporosity (PIM‐PIs) were synthesized by polycondensation of TTSBIDA with commercially available aromatic dianhydrides. PIM‐PIs exhibited amorphous nature, high thermal stability (T₁₀ > 480 °C) and intrinsic microporosity (BET surface area = 59–289 m²/g). The gas permeation characteristics of films of selected PIM‐PIs were evaluated and they exhibited appreciable gas permeability as well as high selectivity. The CO₂ and O₂ permeability of PIM‐PIs were in the range 185.4–39.2 and 30.6–6.2 Barrer, respectively. Notably, polyimide derived from TTSBIDA and 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (PIM‐PI‐6FDA) exhibited high CO₂ and O₂ permeability of 185.4 and 30.6 Barrer with CO₂/CH₄ and O₂/N₂ selectivity of 43.1 and 5.1, respectively. The data of PIM‐PI‐6FDA for CO₂/CH₄ and O₂/N₂ gas pairs were located near Robeson upper bound. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 766–775     

Hydrazine‐based polyimides from isomeric bis(chlorophthalimide)s

3,3′‐Dichloro‐N,N′‐biphthalimide (3,3′‐DCBPI), 3,4′‐dichloro‐N,N′‐biphthalimide (3,4′‐DCBPI), and 4,4′‐dichloro‐N,N′‐biphthalimide (4,4′‐DCBPI) were synthesized from 3‐ or 4‐chlorophthalic anhydrides and hydrazine in glacial acetic acid. The yield of 3,3′‐DCBPI (90%) was much higher than that of 4,4′‐DCBPI (33%) because of the better stability of the intermediate, 3‐chloro‐N‐aminophthalimide, and 3,3′‐DCBPI. A series of hydrazine‐based polyimides were prepared from isomeric DCBPIs and 4,4′‐thiobisbenzenethiol (TBBT) in N,N‐dimethylacetamide in the presence of tributylamine. Inherent viscosity of these polymers was in the range of 0.51–0.69 dL/g in 1‐methyl‐2‐pyrrolidinone (NMP) at 30 °C. These polyimides were soluble in 1,1,2,2‐terachloroethane, NMP, and phenols. The 5% weight‐loss temperatures (T_5%s) of the polymers were near 450 °C in N₂. Their glass‐transition temperatures (T_gs) determined by dynamic mechanical thermal analysis and differential scanning calorimetry increased according to the order of polyimides based on 4,4′‐DCBPI, 3,4′‐DCBPI, and 3,3′‐DCBPI. The hydrolytic stability of these polymers was measured under acid, basic, and neutral conditions and the results indicated that the order was 3,3′‐DCBPI/TBBT > 3,4′‐DCBPI/TBBT > 4,4′‐DCBPI/TBBT. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4933–4940, 2007     

Lewis Base Sequestered Chalcogen Dihalides: Synthetic Sources of ChX2 (Ch=Se,Te; X=Cl,Br)

The synthesis and comprehensive characterization of a series of base‐stabilized ChX₂ (Ch=Se, Te; X=Cl, Br) is reported using aryl‐substituted diazabutadiene and 2,2′‐bipyridine (bipy) as the ligands. In stark contrast to free ChX₂ the complexes display excellent thermal stability. Their use as viable ChX₂ reagents that may be stored for later use is demonstrated in principle. The syntheses are simple and high‐yielding from commercially available or easily synthesized reagents. The bipy complexes are exceedingly rare examples of this ubiquitous ligand being utilized within Group 16 chemistry; the Se examples are the first to be characterized by X‐ray crystallography, and the Te species are only the second.     

Three different fluoro‐ or chloro‐substituted 1′‐deoxy‐1′‐phenyl‐β‐D‐ribofuranoses

Crystal structures are reported for three fluoro‐ or chloro‐substituted 1′‐deoxy‐1′‐phenyl‐β‐D‐ribofuranoses, namely 1′‐deoxy‐1′‐(2,4,5‐trifluorophenyl)‐β‐D‐ribofuranose, C₁₁H₁₁F₃O₄, (I), 1′‐deoxy‐1′‐(2,4,6‐trifluorophenyl)‐β‐D‐ribofuranose, C₁₁H₁₁F₃O₄, (II), and 1′‐(4‐chlorophenyl)‐1′‐deoxy‐β‐D‐ribofuranose, C₁₁H₁₃ClO₄, (III). The five‐membered furanose ring of the three compounds has a conformation between a C2′‐endo,C3′‐exo twist and a C2′‐endo envelope. The ribofuranose groups of (I) and (III) are connected by intermolecular O—H...O hydrogen bonds to six symmetry‐related molecules to form double layers, while the ribofuranose group of (II) is connected by O—H...O hydrogen bonds to four symmetry‐related molecules to form single layers. The O...O contact distance of the O—H...O hydrogen bonds ranges from 2.7172 (15) to 2.8895 (19) Å. Neighbouring double layers of (I) are connected by a very weak intermolecular C—F...π contact. The layers of (II) are connected by one C—H...O and two C—H...F contacts, while the double layers of (III) are connected by a C—H...Cl contact. The conformations of the molecules are compared with those of seven related molecules. The orientation of the benzene ring is coplanar with the H—C1′ bond or bisecting the H—C1′—C2′ angle, or intermediate between these positions. The orientation of the benzene ring is independent of the substitution pattern of the ring and depends mainly on crystal‐packing effects.     

A Dynamic Crystal‐to‐Amorphous Transformation Microporous ZnII Mixed Neutral‐ligand Metal‐organic Polymer {[Zn(bpp)2(μ‐4,4′‐bipy)(H2O)2](ClO4)2·H2O}n

A new rarely reported Zn^II mixed‐polypyridine coordination polymer with both rigid and flexible spacers, {[Zn(bpp)₂(μ‐4,4′‐bipy)(H₂O)₂](ClO₄)₂ · H₂O}_n ( 1 ), has been synthesized and characterized by elemental analysis, IR‐, ¹H NMR‐, ¹³C NMR spectroscopy and single‐crystal X‐ray diffraction. The thermal stability of compound 1 was studied by thermal gravimetric (TG) and differential thermal analyses (DTA). The single‐crystal X‐ray structure of 1 shows that the complex has been formed from a 1D polymer as a result of bridging by the 4,4′‐bipy ligands. Solution and solid‐state luminescent spectra of the compound 1 indicate intense fluorescent emissions at ca. 353.6 and 468.8 nm, respectively. Removal of the interstitial water guest molecules results in a loss of crystallinity, but exposure to water vapor reestablishes the original structure, thus constituting 1 as a third‐generation porous framework.     

Oligodeoxynucleotide Duplexes Containing (5′S)‐5′‐C‐Alkyl‐Modified 2′‐Deoxynucleosides: Can an Alkyl Zipper across the DNA Minor‐Groove Enhance Duplex Stability?

A series of oligonucleotides containing (5′S)‐5′‐C‐butyl‐ and (5′S)‐5′‐C‐isopentyl‐substituted 2′‐deoxyribonucleosides were designed, prepared, and characterized with the intention to explore alkyl‐zipper formation between opposing alkyl chains across the minor groove of oligonucleotide duplexes as a means to modulate DNA‐duplex stability. From four possible arrangements of the alkyl groups that differ in the density of packing of the alkyl chains across the minor groove, three (duplex types I – III , Fig. 2) could experimentally be realized and their duplex‐forming properties analyzed by UV‐melting curves, CD spectroscopy, and isothermal titration calorimetry (ITC), as well as by molecular modeling. The results show that all arrangements of alkyl residues within the minor groove of DNA are thermally destabilizing by 1.5–3°/modification in T_m. We found that, within the proposed duplexes with more loosely packed alkyl groups (type‐ III duplexes), accommodation of alkyl residues without extended distorsion of the helical parameters of B‐DNA is possible but does not lead to higher thermodynamic stability. The more densely packed and more unevenly distributed arrangement (type‐ II duplexes) seems to suffer from ecliptic positioning of opposite alkyl groups, which might account for a systematic negative contribution to stability due to steric interactions. The decreased stability in the type‐ III duplexes described here may be due either to missing hydrophobic interactions of the alkyl groups (not bulky enough to make close contacts), or to an overcompensation of favorable alkyl‐zipper formation presumably by loss of structured H₂O in the minor groove.