Mono‐, bis‐ and tris‐piperidine fused imidazolinium salts: their in situ catalytic applications for C?C bond formation in aqueous solutions

The 1,5,6,7,8,8a‐hexahydroimidazo[1,5‐a]pyridine, 3, was quaternized with 2‐(bromomethyl‐1,3,5‐trimethylbenzene, 1,4‐bis(bromomethyl)‐2,3,5,6‐tetramethylbenzene, 2,4‐bis(bromomethyl)‐1,3,5‐trimethylbenzene, 1,3,5‐tris(bromomethyl)‐2,4,6‐trimethylbenzene and 1,3,5‐tris(bromomethyl)‐2,4,6‐triethylbenzene to obtain mono‐, bis‐ and tris‐imidazolinium salts (4–7) which were characterized by elemental analysis and NMR spectroscopy. In order to understand the effects of these changes on the N‐substituent and how they translate to catalytic activity, these new salts (4–7) with Pd(OAc)₂ were applied as in situ catalysts for Suzuki‐Miyaura and Heck‐Mirozoki cross‐coupling reactions of aryl chlorides and aryl bromides, respectively. The tris‐imidazolinium salts (7) were found to be more efficient than the related analogs 4–6. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and Supramolecular Assemblies of Tripodal 1,3,5‐Tris(phenoxymethyl)‐2,4,6‐triethylbenzene Analogues

Tripodal 1,3,5‐tris(phenoxymethyl)‐2,4,6‐triethylbenzene analogues have been synthesized and structurally characterized by IR, ¹H NMR and ¹³C NMR spectroscopy and HRMS, and additionally, the single crystal structures of compounds bearing ortho‐ ( 7 ), meta‐ ( 9 ) and para‐hydroxymethyl ( 11 ) functions have been determined by X‐ray diffraction analysis. The structural study revealed that compounds 7 , 9 , and 11 do not adopt the expected 1,3,5‐alternate conformation in the solid state. The packing diagrams of compounds 7 , 9 , and 11 revealed that six hydrophilic hydroxymethyl groups from six individual molecules ( 7 , 9 and 11 ) were arranged in close contact via intermolecular hydrogen‐bond interactions. For compounds 7 and 9 , the six hydroxyl groups formed a distorted hexagonal ring; however, formation of such a hexagonal ring was not clear in the case of compound 11 . Compounds 9 and 11 were found to form hydrophobic cavities via intermolecular hydrogen‐bond interactions in the solid state, and the cavities were occupied by two ethyl groups from the two cavity‐forming molecules.     

Stimuli‐Responsive Metallogels for Synthesizing Ag Nanoparticles and Sensing Hazardous Gases

A newly synthesized bis‐pyridyl ligand having a diphenyl ether backbone ( LP6 ) displayed the ability to form crystalline coordination polymers ( CP1‐CP6 ) which were fully characterized by single crystal X‐ray diffraction. Most of the resulting polymers were lattice‐occluded crystalline solids—a structural characteristic reminiscent to gels. The reactants of the coordination polymers produced metallogels in DMSO/water confirming the validity of the design principles with which the coordination polymers were synthesized. Some of the metallogels displayed material properties like in situ synthesis of Ag nanoparticles and stimuli‐responsive gel–sol transition including sensing hazardous gases like ammonia and hydrogen sulfide.     

Rheoreversible Metallogels Derived from Coordination Polymers

A series of mixed‐ligand‐based Cd^II/Co^II coordination polymers (CPs) that were derived from two bis(pyridyl)–bis(amide) ligands, 4,4′‐oxybis(N‐(pyridin‐3‐yl)benzamide) ( LP ) and 4,4′‐oxybis(N‐(pyridin‐4‐yl)benzamide) ( LP1 ), and a variety of dicarboxylates isophthalates, terephthalates, 1,2‐carboxytranscinamates, and 1,3‐ and 1,4‐phenylene dicarboxylates were synthesized based on a rationale that they would occlude solvate guests inside their crystal lattice, thereby rendering these CPs suitable as metallogelators. The CPs were characterized by using single‐crystal X‐ray diffraction, elemental analysis, powder X‐ray diffraction (PXRD), FTIR spectroscopy, and thermogravimetric analysis (TGA). Structural analyses revealed that the majority of the CPs were lattice‐occluded molecular solids, which provided us with an opportunity to study their gelation behavior. We observed that, out of eight CPs that were tested, seven were able to produce metallogels. A thorough study of the rheological behavior of the metallogels was performed and CPG1 , CPG2 , CPG4 , and CPG5 were found to exhibit rheoreversible behavior, which was further confirmed by rheological experiments. Interestingly, ligand LP was found to form an aqueous gel, which was exploited to produce silver nanoparticles.     

Synthesis,crystal structure and biological properties of Cd and Zn coordination polymers based on a flexible tripodal ligand

Two new coordination polymers, namely poly[[hexathiocyanatotetrakis{μ₃‐2,4,6‐trimethyl‐1,3,5‐tris[(triazol‐1‐yl)methyl]benzene}tricadmium(II)] 3.5‐hydrate], {[Cd₃(SCN)₆(C₁₈H₂₁N₉)₄]·3.5H₂O}_n ( 1 ), and poly[[hexathiocyanatotetrakis{μ₃‐2,4,6‐trimethyl‐1,3,5‐tris[(triazol‐1‐yl)methyl]benzene}trizinc(II)] 3.5‐hydrate], {[Zn₃(SCN)₆(C₁₈H₂₁N₉)₄]·3.5H₂O}_n ( 2 ), have been synthesized under hydrothermal conditions and characterized by elemental analysis, IR spectroscopy and single‐crystal X‐ray diffraction analysis. From the X‐ray analysis, it is noteworthy that polymers 1 and 2 are isostructural, with their three‐dimensional structures composed of three kinds of four‐connection metal ions and two kinds of three‐connection 2,4,6‐trimethyl‐1,3,5‐tris[(triazol‐1‐yl)methyl]benzene (TTTMB) ligand nodes. Each metal ion is six‐coordinated in a slightly distorted octahedral geometry. The antioxidant activity against DPPH (2,2‐diphenyl‐1‐picrylhydrazyl) and the antidiabetic activity against α‐amylase of the synthesized compounds were evaluated in vitro. The results of the DPPH free‐radical scavenging assay showed that polymers 1 and 2 exhibited strong antioxidant effects, with IC₅₀ values of 3.81 and 2.56 mg ml^?1, respectively. The IC₅₀ value in the antidiabetic studies of polymer 1 was 3.94 mg ml^?1, while polymer 2 exhibited no antidiabetic activity. Polymers 1 and 2 revealed different inhibitory activities on DPPH and α‐amylase, which indicated that the metal ions play important roles in the biological activity of coordination polymers. In addition, the solid‐state photoluminescence properties and thermal stability of 1 and 2 have been investigated.     

A new lanthanum coordination polymer built from a semi‐rigid tripodal carboxylic acid ligand: synthesis,crystal structure and properties

By employing the semi‐rigid multidentate carboxylic acid ligand 4,4′,4′′‐{[(2,4,6‐trimethylbenzene‐1,3,5‐triyl)tris(methylene)]tris(oxy)}tribenzoic acid (denoted H₃L), a new lanthanum coordination polymer, namely poly[[bis(dimethylformamide)(μ₆‐4,4′,4′′‐{[(2,4,6‐trimethylbenzene‐1,3,5‐triyl)tris(methylene)]tris(oxy)}tribenzoato)lanthanum(III)] dimethylformamide tetrasolvate 0.25‐hydrate], {[La(C₃₃H₂₇O₉)(C₃H₇NO)₂]·4C₃H₇NO·0.25H₂O}_n or {[La(L)(DMF)₂]·4(DMF)·0.25(H₂O)}_n (DMF is dimethylformamide) ( 1 ), was prepared and characterized by single‐crystal X‐ray diffraction, elemental analysis, thermogravimetric analysis, IR spectroscopy and photoluminescence studies. The asymmetric unit contains one La^III cation, one anionic L^3? ligand, two coordinated DMF molecules, four free DMF molecules and one‐quarter of a free water molecule. Compound 1 possesses (3,6)‐connected two‐dimensional kgd topology sheets consisting of secondary building units of La₂ clusters and L^3? ligands, which further stack into three‐dimensional supramolecular networks through π–π interactions. Compound 1 exhibits a photoluminescence emission at room temperature, with a peak at 410 nm, owing to a ligand‐centred excited state.     

Two New Solvent‐modulated Zinc(II) Metal‐Organic Hybrid Materials based on Rigid Tripodal Carboxylate Ligand and 2,2′‐Bipy Co‐ligand: Crystal Structures and Luminescent Properties

The zinc(II) coordination polymers [Zn(Htatb)(2,2′‐bipy) · (NMP) · H₂O] ( 1 ) and [Zn₃(tatb)₂(2,2′‐bipy)₃ · H₂O] ( 2 ) (H₃tatb = 4,4′,4′′‐s‐triazine‐2,4,6‐triyl‐tribenzoic acid; 2,2′‐bipy = 2,2′‐bipyridyl, NMP = N‐methyl‐2‐pyrrolidon), were synthesized hydrothermally, and characterized by infrared spectroscopy (IR), powder X‐ray diffraction (PXRD), and single‐crystal X‐ray diffraction. Both compounds 1 and 2 possess expectant low dimensional coordination structures, which further connected into interesting 3D networks by hydrogen bond and strong π–π interactions. Moreover, the thermal stabilities and fluorescent properties of 1 and 2 were investigated.     

A self‐penetrated three‐dimensional zinc(II) coordination framework based on 4,4′,4′′‐(1,3,5‐triazine‐2,4,6‐triyl)tribenzoic acid and 1,3‐bis[(imidazol‐1‐yl)methyl]benzene ligands: synthesis,structure and properties

With the rapid development of metal–organic frameworks (MOFs), a variety of MOFs and their derivatives have been synthesized and reported in recent years. Commonly, multifunctional aromatic polycarboxylic acids and nitrogen‐containing ligands are employed to construct MOFs with fascinating structures. 4,4′,4′′‐(1,3,5‐Triazine‐2,4,6‐triyl)tribenzoic acid (H₃TATB) and the bidentate nitrogen‐containing ligand 1,3‐bis[(imidazol‐1‐yl)methyl]benzene (bib) were selected to prepare a novel Zn^II‐MOF under solvothermal conditions, namely poly[[tris{μ‐1,3‐bis[(imidazol‐1‐yl)methyl]benzene}bis[μ₃‐4,4′,4′′‐(1,3,5‐triazine‐2,4,6‐triyl)tribenzoato]trizinc(II)] dimethylformamide disolvate trihydrate], {[Zn₃(C₂₄H₁₂N₃O₆)₂(C₁₄H₁₄N₄)₃]·2C₃H₇NO·3H₂O}_n ( 1 ). The structure of 1 was characterized by single‐crystal X‐ray diffraction, IR spectroscopy and powder X‐ray diffraction. The properties of 1 were investigated by thermogravimetric and fluorescence analysis. Single‐crystal X‐ray diffraction shows that 1 belongs to the monoclinic space group Pc. The asymmetric unit contains three crystallographically independent Zn^II centres, two 4,4′,4′′‐(1,3,5‐triazine‐2,4,6‐triyl)tribenzoate (TATB^3?) anions, three complete bib ligands, one and a half free dimethylformamide molecules and three guest water molecules. Each Zn^II centre is four‐coordinated and displays a distorted tetrahedral coordination geometry. The Zn^II centres are connected by TATB^3? anions to form an angled ladder chain with large windows. Simultaneously, the bib ligands link Zn^II centres to give a helical Zn–bib–Zn chain. Furthermore, adjacent ladders are bridged by Zn–bib–Zn chains to form a fascinating three‐dimensional self‐penetrated framework with the short Schläfli symbol 6⁵·7·8¹³·9·10. In addition, the luminescence properties of 1 in the solid state and the fluorescence sensing of metal ions in suspension were studied. Significantly, compound 1 shows potential application as a fluorescent sensor with sensing properties for Zr⁴⁺ and Cu²⁺ ions.     

Solvent‐Controlled Construction of Two 3D Manganese(II) Coordination Polymers Based on Flexible Tripodal Multicarboxylate Linker and Rod‐Shaped SBUs

To further explore the coordination possibilities of the flexible tripodal ligand, 4,4′,4′′‐(benzene‐1,3,5‐triyl‐tris(oxy))tribenzoic acid (H₃BTTB), two solvent‐controlled three‐dimensional (3D) manganese(II) coordination polymers, [Mn₃(BTTB)₂(H₂O)₄](H₂O)₂ ( 1 ) and [Mn₃(BTTB)₂(DMF)₂](DMF)₂ ( 2 ), were synthesized and characterized. Single crystal X‐ray diffraction analysis indicates that in the Mn^II complexes the BTTB ligands exhibit two coordination modes, which have not been reported previously. Complexes 1 and 2 involve different one‐dimensional (1D) rod‐shaped metal–carboxylate secondary building units (SBUs). The 1D SBUs are further extended to afford two different three‐dimensional (3D) frameworks with similar flu topology via linkage of the BTTB ligands. The results demonstrate that the reaction solvent as well as conformation and coordination mode of BTTB ligands play key roles on the formation of the final framework structures. Additionally, their luminescent properties were investigated.     

Synthesis and Crystal Structure of a New 2D Honeycomb—like Cadmium （Ⅱ） Complex with Tripodal Ligand

A new cadmium (II) coordination polymer, [Cd(TTTMB)₂]‐(SO₄) · 21H₂O, where TTTMB =1,3, 5‐tris (imidazol‐1‐yl‐methyl)‐2,4,6‐trimethylbenzene, was obtained by self‐assembly of tripodal ligand TTTMB with CdSO₄·2.7H₂O in acetonitrile, and characterized by X‐ray crystallography. The crystal data belongs to monoclinic space group C_c with cell parameters a = 1.16891(4) nm, b=2.06671(6) nm, c = 2.48185(7) nm, β = 97.8560(10)°, R = 0.0487, wR = 0.1211. The results of structure analysis indicate that each TTTMB ligand coordinates three metal atoms and in turn each Cd(II) atom with octahedral coordination geometry connects six nitrogen atoms of imidazole group from six different TTTMB ligands to produce a 2D honeycomb network structure. There are a lot of water molecules linked by hydrogen bonds and occupied the channels formed intra‐ and inter‐sheets.     

Rational Approach Towards Designing Metallogels From a Urea‐Functionalized Pyridyl Dicarboxylate: Anti‐inflammatory,Anticancer, and Drug Delivery

A structural rationale was adopted to design a series of metallogels from a newly synthesized urea‐functionalized dicarboxylate ligand, namely, 5‐[3‐(pyridin‐3‐yl)ureido]isophthalic acid ( PUIA ), that produces metallogels upon reaction with various metal salts (Cu^II, Zn^II, Co^II, Cd^II, and Ni^II salts) at room temperature. The gels were characterized by dynamic rheology and transmission electron microscopy (TEM). The existence of a coordination bond in the gel state was probed by FTIR and ¹H NMR spectroscopy in a Zn^II metallogel (i.e., MG2 ). Single crystals isolated from the reaction mixture of PUIA and Co^II or Cd^II salts characterized by X‐ray diffraction revealed lattice inclusion of solvent molecules, which was in agreement with the hypothesis based on which the metallogels were designed. MG2 displayed anti‐inflammatory response (prostaglandin E₂ assay) in the macrophage cell line (RAW 264.7) and anticancer properties (cell migration assay) on a highly aggressive human breast cancer cell line (MDA‐MB‐231). The MG2 metallogel matrix could also be used to load and release (pH responsive) the anticancer drug doxorubicin. Fluorescence imaging of MDA‐MB‐231 cells treated with MG2 revealed that it was successfully internalized.     

Synthesis and Crystal Structure of Two Lanthanide Complexes with Benzenecarboxylic Derivatives

Two novel lanthanide coordination polymers, [La(tpaa)₃(H₂O)₂] ( 1 ) and [Eu₂(BDC)₃(DMF)₂(H₂O)₂] ( 2 ) (Htpaa = terephthalamic acid, H₂BDC = 1,4‐benzenedicarboxylic acid, DMF = N,N‐dimethylformamide), were hydro(solvo)thermally synthesized by reactions of the corresponding lanthanide nitrate salts with 1,3,5‐triazine‐2,4,6‐tri(4‐benzenecarboxylate) ( L ), in which a simultaneous hydrolysis of the ligand L occurred. Single‐crystal X‐ray analysis revealed that complex 1 comprises one‐dimensional chains that are further interlinked via hydrogen bonds, resulting in a two‐dimensional network; while complex 2 is a three‐dimensional interpenetrated coordination architecture.     

Anion and Additive Effects on the Structure of Mercury(II) Halides Complexes with Tripodal Ligand

The metal complexes [Hg₂(tbim)₂Br₄]·2DMF ( 1 ) and [Hg₂(tbim)I₄]·1.5DMF ( 2 ) were prepared by reactions of 1,3,5‐tris(benzimidazol‐1‐ylmethyl)‐2,4,6‐trimethylbenzene (tbim) with HgBr₂, HgI₂, respectively, and [Hg₂(tbim)I₄]·0.5(FeCp₂)·H₂O ( 3 ) was obtained by the same method with addition of ferrocene (FeCp₂) as additive. Their structures were determined by X‐ray crystallographic analyses. Complex 1 has a macrocyclic binuclear structure with one benzimidazole arm of the ligand free of coordination and the binuclear units are further connected by C‐H···N hydrogen bonds to give an infinite zigzag chain. Complexes 2 and 3 have a 2D network structure in which tbim serves as a tridentate ligand. The results showed that the halides of bromide and iodide have remarkable impact on the structure of the complexes. The FeCp₂ molecules are trapped in the voids of framework 3 .     

Linear π‐conjugated polymers containing 2,4,6‐tris(thiophen‐2‐yl)‐1,3,5‐triazine unit: Synthesis and optical properties

Some linear π‐conjugated polymers containing 2,4,6‐tris(thiophen‐2‐yl)‐1,3,5‐triazine unit were synthesized via Sonogashira or Suzuki reaction for the first time and characterized by IR, NMR, and GPC. Because of the introduction of 2,4,6‐tris(thiophen‐2‐yl)‐1,3,5‐triazine unit into π‐conjugated system, all polymers exhibited good thermal stability with high decomposition temperature. Their optical and electrochemical properties were investigated. Based on the 2,4,6‐tris(thiophen‐2‐yl)‐1,3,5‐triazine unit linked with different aromatic rings, the polymers showed the tunable fluorescence from blue to blue‐green emission with satisfied quantum yield. Cyclic voltammetry measurement indicated that the LUMO and HOMO levels of the polymers could be adjustable through the main‐chain structural modification. All polymers had low LUMO level (?2.86 to ?3.06 eV) due to the high‐electron affinity of triazine unit. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 702–712, 2008     

Unique Hydrogen‐Bonded Complex of Hydronium and Hydroxide Ions

H₃O⁺ and OH^?, formed by the self‐ionization of two coordinating water molecules during the crystal growing of a host molecule [1,3,5‐tris(hydroxymethyl)2,4,6‐triethylbenzene ( 1 )], could be effectively stabilized by hydrogen‐bonding interactions with the preorganized hydroxy groups of three molecules of 1. The binding motifs observed in the complex ( 1 )₃?H₃O⁺?HO^? show remarkable similarity to those postulated for the hydrated hydronium and hydroxide ion complexes, which play important roles in various chemical, biological, and atmospheric processes, but their molecular structures are still not fully understood and remain a subject of intensive research.     

Stishovite's Relative: A Post‐Coesite Form of Phosphorus Oxonitride

Phosphorus oxonitride (PON) is isoelectronic with SiO₂ and may exhibit a similar broad spectrum of intriguing properties as silica. However, PON has only been sparsely investigated under high‐pressure conditions and there has been no evidence on a PON polymorph with a coordination number of P greater than 4. Herein, we report a post‐coesite (pc) PON polymorph exhibiting a stishovite‐related structure with P in a (5+1) coordination. The pc‐PON was synthesized using the multianvil technique and characterized by powder X‐ray diffraction, solid‐state NMR spectroscopy, TEM measurements and in situ synchrotron X‐ray diffraction in diamond anvil cells. The structure model was verified by single‐crystal X‐ray diffraction at 1.8 GPa and the isothermal bulk modulus of pc‐PON was determined to K₀=163(2) GPa. Moreover, an orthorhombic PON polymorph (o‐PON) was observed under high‐pressure conditions and corroborated as the stable modification at pressures above 17 GPa by DFT calculations.     

Three New Lanthanide Coordination Polymers Built from H2bpdc Ligands: Syntheses,Structures, and Properties

Three new lanthanide‐organic coordination polymers, {[Ln₂(bpdc)₂(H₂O)₆(NO₃)] · NO₃} [Ln = La ( 1 ), Ce ( 2 ), Pr ( 3 )] (H₂bpdc = 2, 2′‐bipyridine‐6, 6′‐dicarboxylic acid) were synthesized under hydrothermal conditions and structurally characterized by elemental analysis, IR spectroscopy as well as single‐crystal and powder X‐ray diffraction. Single‐crystal X‐ray diffraction analysis revealed that compounds 1 – 3 are isostructural, composed of two dimensional honeycomb network linked by bpdc ligands. The magnetic property of compound 3 was investigated.     

Redetermination of the trigonal prismatic complex tris­(cis‐1,2‐diphenyl­ethyl­ene‐1,2‐dithiol­ato)rhenium

The first trigonal prismatic mol­ecular compound characterized by single‐crystal X‐ray diffraction, [Re(C₁₄H₁₀S₂)₃], has been redetermined using modern laboratory equipment. The new experiment reaffirms the results of the original. Since then, numerous tris‐dithiol­ene complexes have been structurally characterized, having geometries ranging from trigonal prismatic to nearly octa­hedral. An examination of the coordination geometries of these structures is included.     

Spontaneous Phosphorus‐Halogen Bond Cleavage in N‐Heterocyclic Halogenophosphanes Revisited: The Case of P–Br and P–I Bonds

P‐bromo‐ and P‐Iodo‐substituted N‐heterocyclic phosphanes (NHP) were synthesized by halogen exchange starting from the P‐chloro compound and characterized by spectroscopic data and X‐ray diffraction studies. Whereas the Br‐NHP still forms a molecular crystal, the solid‐state structure of the I‐derivative consists of ion‐pairs which assemble via secondary P···I interactions to form one‐dimensional coordination polymers. Computational studies indicate that the bond dissociation is due to a combination of intramolecular stabilisation (aromatisation of the phosphenium cation formed) and intermolecular Lewis‐acid/base interactions. Reaction of the I‐NHP with I₂ proceeded under complete P–I bond cleavage to give an ionic phosphenium triiodide whose single‐crystal X‐ray diffraction study revealed a unique supramolecular structure.     

Synthesis and characterization of iron‐ and nitrogen‐functionalized graphene catalysts for oxygen reduction reaction

Iron‐ and nitrogen‐functionalized graphene (Fe‐N‐G), as well as iron‐ and nitrogen‐functionalized oxidized graphene (Fe‐N‐Gox) catalysts were synthesized as non‐noble metal electrocatalysts for oxygen reduction reaction (ORR). The physical properties of the resultant catalysts were characterized using nitrogen adsorption measurements, X‐ray diffraction, Raman and X‐ray photoelectron spectroscopies and transmission electron microscopy. Subsequently, ORR activities of the catalysts were determined electrochemically using a conventional three‐electrode cell via cyclic voltammetry with a rotating disc electrode, the results of which indicated that the synthesized catalysts had a marked electrocatalytic activity towards ORR in acid media. Among the synthesized catalysts, that functionalized using 2,4,6‐tris(2‐pyridyl)‐1,3,5‐triazine as nitrogen source had the highest electrocatalytic activity with the highest onset potential (0.98 V/SHE) and limiting current density (5.12 mA cm⁻²). The findings are particularly important to determine a non‐precious metal catalyst for ORR activity in fuel cells.