Octadecanuclear Gear Wheels by Self‐Assembly of Self‐Assembled “Double Saddle”‐Type Coordination Entities: Molecular “Rangoli”

A series of self‐assembled “double saddle”‐type trinuclear complexes of [Pd₃L′₃ L ₂] formulation have been synthesized by complexation of a series of cis‐protected palladium(II) components with a slightly divergent “E‐shaped” non‐chelating tridentate ligand, 1,1′‐(pyridine‐3,5‐diyl)bis(3‐(pyridin‐3‐yl)urea ( L ). The cis‐protecting agents L′ employed in the study are ethylenediamine (en), tetramethylethylenediamine (tmeda), 2,2′‐bipyridine (bpy), and 1,10‐phenanthroline (phen), for 1 , 2 , 3 , and 4 , respectively. The crystal structures of [Pd₃(tmeda)₃( L )₂](NO₃)₆ ( 2 ), [Pd₃(bpy)₃( L )₂](NO₃)₆ ( 3 ), and [Pd₃(phen)₃( L )₂](NO₃)₆ ( 4 ) unequivocally support the new architecture. Two of the “double saddle”‐type complexes ( 3 and 4 ) are suitably crafted with π surfaces at the strategically located cis‐protecting sites to facilitate intermolecular π–π interactions in the solid state. As a consequence, six units of the 3 (or 4 ) are assembled, by means of six‐pairs of π–π stacking interactions, in a circular geometry to form an octadecanuclear molecular ring of [(Pd₃L′₃ L ₂)₆] composition. The overall arrangement of the rings in the crystal packing is equated with the traditional Indian art form rangoli.     

“Off‐on‐off” Fluorescence pH Switch of Three Trinuclear RuII Complexes Containing Imidazole Rings

Three tripodal ligands H₃L^1–3 containing imidazole rings were synthesized by the reaction of 1,10‐phenanthroline‐5,6‐dione with 1,3,5‐tris[(3‐formylphenoxy)methyl]benzene, 1,3,5‐tris[(3‐formylphenoxy)methyl]‐2,4,6‐trimethylbenzene, and 2,2′,2"‐tris[(3‐formylphenoxy)ethyl]amine, respectively. Trinuclear Ru^II polypyridyl complexes [(bpy)₆Ru₃H₃L^1–3](PF₆)₆ were prepared by the condensation of Ru(bpy)₂Cl₂ · 2H₂O with ligands H₃L^1–3. The pH effects on the UV/Vis absorption and fluorescence spectra of the three complexes were studied, and ground‐ and excited‐state ionization constants of the three complexes were derived. The three complexes act as “off‐on‐off” fluorescence pH switch through protonation and deprotonation of imidazole ring with a maximum on‐off ratio of 5 in buffer solution at room temperature.     

“Half‐Bonds” in an Unusual Coordinated S42− Rectangle

Don′t be square! A rare S₄^2? rectangle bridging two M₂Cp₂(μ₂‐CH₂)₂ (M=Rh, Ir) fragments is found to contain two “half‐bonds” with S? S distances of 2.70 or 2.90 Å. Computational studies explore the connection between these “half‐bonds” and a Jahn–Teller distortion, as well as possible intermediates that form M₄S₄²⁺ clusters having the S₄^2? rectangle rotated by 90°.

     

A “Mitsubishi emblem” tetrauclear aluminum complex containing two unsymmetric N2O2‐ligands and a symmetric NO3‐ligand as initiator for polymerization of rac‐lactide

A novel hydroxy‐, methoxy‐, and phenoxy‐bridge “Mitsubishi emblem” tetranuclear aluminum complex ( 1 ) is synthesized from an unsymmetric amine‐pyridine‐bis(phenol) N₂O₂‐ligand (H₂L¹) and a symmetric amine‐tris(phenol) NO₃‐ligand (H₂L²). Two same configuration chiral nitrogen atoms are formed in the tetranuclear Al complex upon coordination of the unsymmetric tertiary amine ligand to central Al. Complex 1 initiates controlled ring‐opening polymerization (ROP) of rac‐lactide and afford polylactide (PLA) with narrow molecular weight distributions (M_w/M_n = 1.05–1.19). The analysis of ¹H NMR spectra of the oligomer indicates that the methoxy group is the initiating group and the ring‐opening polymerization of lactide follows a coordination‐insertion mechanism. The Homonuclear decoupled ¹H NMR spectroscopy suggests the isotactic‐rich chains is preferentially formed in PLA. The study on kinetics of the ROP of lactide reveals the homopropagation rate is higher than the cross‐propagation rate, which is in agreement with the observed isotactic selectivity in the ROP of rac‐lactide. The stereochemistry of the polymerization was also supported by activation parameters. The introduction of unsymmetric ligand H₂L¹ has an effect on stereoslectivity of polymerization. This result may be of interest for the design of multinuclear metal complex catalysts containing functionalized ligands. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2084–2091     

Crystal Structures and Photoluminescence Properties of Zinc(II) and Cadmium(II) Coordination Polymers with “Y”‐Shaped Ligands

Three Zn^II and Cd^II complexes with Y‐shaped dicarboxylate ligands, namely [Zn(L₁)(2,2′‐bpy)₂(H₂O)] · 2H₂O ( 1 ), [Zn(L₁)(bpp)(H₂O)] ( 2 ), and [Cd(L₁)(H₂O)] · H₂O ( 3 ) [H₂L₁ = N‐phenyliminodiacetic acid, 2,2′‐bpy = 2,2′‐bipyridine, bpp = 1,3‐bis(4‐pyridyl)propane] were synthesized and characterized by elemental analysis, IR spectroscopy single‐crystal X‐ray diffraction, and thermogravimetric analyses. Compound 1 shows an hydrogen‐bonded 2D network, whereas compound 2 is an infinite 1D wavy chain structure, though O–H ··· O hydrogen‐bonded to form a 2D network. Compound 3 displays a 2D uninodal 3‐connected Shubnikov plane net with the point symbol of (4.8²). Moreover, the solid‐state such as thermal stabilities and fluorescence properties of 1 – 3 were also investigated.     

Solvent‐Dependent Self‐Assembly Behaviour and Speciation Control of Pd6L8 Metallo‐supramolecular Cages

The C₃‐symmetric chiral propylated host‐type ligands (±)‐tris(isonicotinoyl)‐tris(propyl)‐cyclotricatechylene ( L1 ) and (±)‐tris(4‐pyridyl‐4‐benzoxy)‐tris(propyl)‐cyclotricatechylene ( L2 ) self‐assemble with Pd^II into [Pd₆L₈]¹²⁺ metallo‐cages that resemble a stella octangula. The self‐assembly of the [Pd₆( L1 )₈]¹²⁺ cage is solvent‐dependent; broad NMR resonances and a disordered crystal structure indicate no chiral self‐sorting of the ligand enantiomers in DMSO solution, but sharp NMR resonances occur in MeCN or MeNO₂. The [Pd₆( L1 )₈]¹²⁺ cage is observed to be less favourable in the presence of additional ligand, than is its counterpart, where L=(±)‐tris(isonicotinoyl)cyclotriguaiacylene ( L1 a ). The stoichiometry of reactant mixtures and chemical triggers can be used to control formation of mixtures of homoleptic or heteroleptic [Pd₆L₈]¹²⁺ metallo‐cages where L= L1 and L1 a .     

“Click”‐Triggered Self‐Healing Graphene Nanocomposites

Strategies to compensate material fatigue are among the most challenging issues, being most prominently addressed by the use of nano‐ and microscaled fillers, or via new chemical concepts such as self‐healing materials. A capsule‐based self‐healing material is reported, where the adverse effect of reduced tensile strength due to the embedded capsules is counterbalanced by a graphene‐based filler, the latter additionally acting as a catalyst for the self‐healing reaction. The concept is based on “click”‐based chemistry, a universal methodology to efficiently link components at ambient reaction conditions, thus generating a “reactive glue” at the cracked site. A capsule‐based healing system via a graphene‐based Cu₂O (TRGO‐Cu₂O‐filler) is used, acting as both the catalytic species for crosslinking and the required reinforcement agent within the material, in turn compensating the reduction in tensile strength exerted by the embedded capsules. Room‐temperature self‐healing within 48 h is achieved, with the investigated specimen containing TRGO‐Cu₂O demonstrating significantly faster self‐healing compared to homogeneous (Cu(PPh₃)₃F, Cu(PPh₃)₃Br), and heterogeneous (Cu/C) copper(I) catalysts.

     

Azide/Alkyne‐“Click”‐Reactions of Encapsulated Reagents: Toward Self‐Healing Materials

The successful encapsulation of reactive components for the azide/alkyne‐“click”‐reaction is reported featuring for the first time the use of a liquid polymer as reactive component. A liquid, azido‐telechelic three‐arm star poly(isobutylene) ( = 3900 g · mol⁻¹) as well as trivalent alkynes were encapsulated into micron‐sized capsules and embedded into a polymer‐matrix (high‐molecular weight poly(isobutylene), = 250 000 g · mol⁻¹). Using (Cu^IBr(PPh₃)₃) as catalyst for the azide/alkyne‐“click”‐reaction, crosslinking of the two components at 40 °C is observed within 380 min and as fast as 10 min at 80 °C. Significant recovery of the tensile storage modulus was observed in a material containing 10 wt.‐% and accordingly 5 wt.‐% capsules including the reactive components within 5 d at room temperature, thus proving a new concept for materials with self‐healing properties.

     

Synthesis of a “Masked” Terminal Nickel(II) Sulfide by Reductive Deprotection and its Reaction with Nitrous Oxide

The addition of 1 equiv of KSCPh₃ to [L^RNiCl] (L^R={(2,6‐iPr₂C₆H₃)NC(R)}₂CH; R=Me, tBu) in C₆H₆ results in the formation of [L^RNi(SCPh₃)] ( 1 : R=Me; 2 : R=tBu) in good yields. Subsequent reduction of 1 and 2 with 2 equiv of KC₈ in cold (?25 °C) Et₂O in the presence of 2 equiv of 18‐crown‐6 results in the formation of “masked” terminal Ni^II sulfides, [K(18‐crown‐6)][L^RNi(S)] ( 3 : R=Me; 4 : R=tBu), also in good yields. An X‐ray crystallographic analysis of these complexes suggests that they feature partial multiple‐bond character in their Ni? S linkages. Addition of N₂O to a toluene solution of 4 provides [K(18‐crown‐6)][L^tBuNi(SN?NO)], which features the first example of a thiohyponitrite (κ²‐[SN?NO]^2?) ligand.     

Three novel topologically different metal–organic frameworks built from 3‐nitro‐4‐(pyridin‐4‐yl)benzoic acid

The design and synthesis of metal–organic frameworks (MOFs) have attracted much interest due to the intriguing diversity of their architectures and topologies. However, building MOFs with different topological structures from the same ligand is still a challenge. Using 3‐nitro‐4‐(pyridin‐4‐yl)benzoic acid (HL) as a new ligand, three novel MOFs, namely poly[[(N,N‐dimethylformamide‐κO)bis[μ₂‐3‐nitro‐4‐(pyridin‐4‐yl)benzoato‐κ³O,O′:N]cadmium(II)] N,N‐dimethylformamide monosolvate methanol monosolvate], {[Cd(C₁₂H₇N₂O₄)₂(C₃H₇NO)]·C₃H₇NO·CH₃OH}_n, ( 1 ), poly[[(μ₂‐acetato‐κ²O:O′)[μ₃‐3‐nitro‐4‐(pyridin‐4‐yl)benzoato‐κ³O:O′:N]bis[μ₃‐3‐nitro‐4‐(pyridin‐4‐yl)benzoato‐κ⁴O,O′:O′:N]dicadmium(II)] N,N‐dimethylacetamide disolvate monohydrate], {[Cd₂(C₁₂H₇N₂O₄)₃(CH₃CO₂)]·2C₄H₉NO·H₂O}_n, ( 2 ), and catena‐poly[[[diaquanickel(II)]‐bis[μ₂‐3‐nitro‐4‐(pyridin‐4‐yl)benzoato‐κ²O:N]] N,N‐dimethylacetamide disolvate], {[Ni(C₁₂H₇N₂O₄)₂(H₂O)₂]·2C₄H₉NO}_n, ( 3 ), have been prepared. Single‐crystal structure analysis shows that the Cd^II atom in MOF ( 1 ) has a distorted pentagonal bipyramidal [CdN₂O₅] coordination geometry. The [CdN₂O₅] units as 4‐connected nodes are interconnected by L^? ligands to form a fourfold interpenetrating three‐dimensional (3D) framework with a dia topology. In MOF ( 2 ), there are two crystallographically different Cd^II ions showing a distorted pentagonal bipyramidal [CdNO₆] and a distorted octahedral [CdN₂O₄] coordination geometry, respectively. Two Cd^II ions are connected by three carboxylate groups to form a binuclear [Cd₂(COO)₃] cluster. Each binuclear cluster as a 6‐connected node is further linked by acetate groups and L^? ligands to produce a non‐interpenetrating 3D framework with a pcu topology. MOF ( 3 ) contains two crystallographically distinct Ni^II ions on special positions. Each Ni^II ion adopts an elongated octahedral [NiN₂O₄] geometry. Each Ni^II ion as a 4‐connected node is linked by L^? ligands to generate a two‐dimensional network with an sql topology, which is further stabilized by two types of intermolecular OW—HW…O hydrogen bonds to form a 3D supramolecular framework. MOFs ( 1 )–( 3 ) were also characterized by powder X‐ray diffraction, IR spectroscopy and thermogravimetic analysis. Furthermore, the solid‐state photoluminescence of HL and MOFs ( 1 ) and ( 2 ) have been investigated. The photoluminescence of MOFs ( 1 ) and ( 2 ) are enhanced and red‐shifted with respect to free HL. The gas adsorption investigation of MOF ( 2 ) indicates a good separation selectivity (71) of CO₂/N₂ at 273 K (i.e. the amount of CO₂ adsorption is 71 times higher than N₂ at the same pressure).     

Anion‐directed Silver(I) Coordination Assemblies Based on 1‐(2‐Pyridyl)‐2‐(4‐pyridyl)‐1,2,4‐triazolewith Diverse Supramolecular Networks and Dichromate Removal Capabilities

A series of silver(I) supramolecular complexes, namely, {[Ag(L²⁴)](NO₃)}_n ( 1 ), [Ag₂(L²⁴)(NO₂)₂]_n ( 2 ), and {[Ag_1.25(L²⁴)(DMF)](PF₆)_1.25}_n ( 3 ) were prepared by the reactions of 1‐(2‐pyridyl)‐2‐(4‐pyridyl)‐1,2,4‐triazole (L²⁴) and silver(I) salts with different anions (AgNO₃, AgNO₂, AgPF₆). Single‐crystal X‐ray diffraction indicates that 1 – 3 display diverse supramolecular networks. The structure of dinuclear complex 1 is composed of a six‐membered Ag₂N₄ ring with the Ag ··· Ag distance of 4.4137(3) Å. In complex 2 , the adjacent Ag^I centers are interlinked by L²⁴ ligands into a 1D chain, the adjacent of which are further extended by the bridged nitrites to construct a 2D coordination architecture. Complex 3 shows a 3D (3,4)‐connected framework, which is generated by the linkage of L²⁴ ligands. All complexes were characterized by IR spectra, elemental analysis, and powder X‐ray diffraction. Notably, a structural comparison of the complexes demonstrates that their structures are predominated by the nature of anions. Additionally, 1 and 2 show efficient dichromate (Cr₂O₇^2–) capture in water system, which can be ascribed to the anion‐exchange.     

Walking Metals in d8⋅⋅⋅d8 Hetero‐bimetallic Complexes: An Original Dynamic Phenomenon

In the course of our investigations on polymetallic complexes derived from 1,3‐bis(thiophosphinoyl)indene (Ind(Ph₂P?S)₂), we observed original fluxional behavior and report herein a joint experimental/computational study of this dynamic process. Starting from the indenylidene chloropalladate species [Pd{Ind(Ph₂P?S)₂}Cl]^? ( 1 ), the new Pd^II???Rh^I hetero‐bimetallic pincer complex [PdCl{Ind(Ph₂P?S)₂}Rh(nbd)] ( 2 ; nbd=2,5‐norbornadiene) was prepared. X‐ray crystallography and DFT calculations substantiate the presence of a d⁸???d⁸ interaction. According to multinuclear variable‐temperature NMR spectroscopic experiments, the pendant {Rh(nbd)} fragment of 2 readily shifts in solution at room temperature between the two edges of the SCS tridentate ligand. To assess the role of the pincer‐based polymetallic structure on this fluxional behavior, the related monometallic Rh complex [Rh{IndH(Ph₂P?S)₂}(nbd)] ( 3 ) was prepared. No evidence for a metal shift was observed in that case, even at high temperature, thus indicating that inplane pincer coordination to the Pd center plays a crucial role. The previously described Pd^II???Ir^I bimetallic complex 4 exhibited fluxional behavior in solution, but with a significantly higher activation barrier than 2 . This finding demonstrates the generality of this metal‐shift process and the strong influence of the involved metal centers on the associated activation barrier. DFT calculations were performed to shed light onto the mechanism of such metal‐shift processes and to identify the factors that influence the associated activation barriers. Significantly different pathways were found for bimetallic complexes 2 and 4 on one hand and the monometallic complex 3 on the other hand. The corresponding activation barriers predicted computationally are in very good agreement with the experimental observations.     

Pseudohalide‐directed Assembly of Two Zinc(II) Coordination Polymers with a 3,4‐Bis(3‐pyridyl)‐5‐(4‐pyridyl)‐1,2,4‐triazole Tecton

The zinc(II) pseudohalide complexes {[Zn(L³³⁴)(SCN)₂(H₂O)](H₂O)₂}_n ( 1 ) and [Zn(L³³⁴)(dca)₂]_n ( 2 ) were synthesized and characterized using the ligand 3,4‐bis(3‐pyridyl)‐5‐(4‐pyridyl)‐1,2,4‐triazole (L³³⁴) and ZnCl₂ in presence of thiocyanate (SCN^–) and dicynamide [dca, N(CN)₂^–] respectively. Single‐crystal X‐ray structural analysis revealed that the central Zn^II atoms in both complexes have similar octahedral arrangement. Compound 1 has a 2D sheet structure bridged by bidentate L³³⁴ and double μ_N,S‐thiocyanate anions, whereas complex 2 , incorporating with two monodentate dicynamide anions, displays a two‐dimensional coordination framework bridged by tetradentate L³³⁴ ligand. Structural analysis demonstrated that the influence of pseudohalide anions plays an important role in determining the resultant structure. Both complexes were characterized by IR spectroscopy, microanalysis, and powder X‐ray diffraction techniques. In addition, the solid fluorescence and thermal stability properties of both complexes were investigated.     

Formation and Molecular Structure of an Ion Pair Iron (II) Compound Derived from 2,6‐Bis‐ [1‐(2,6‐dibromophenylimino) ‐ethyl] pyridine and 2‐Acetyl‐6‐[1‐(2, 6‐dibromophenylimino)‐ethyl] pyridine

Two novel tridentate ligands of 2,6‐bis‐[l‐(2,6‐dibromophenylimino) ethyl] pyridine (L₁) and2‐acetyl‐6‐[1‐(2,6‐dibromophenylimino) ethyl] pyridine (L2) have been synthesized. The iron(II) complex of L₁ and L₂ has been characterized with the crystal structure of [Fe(L₁)(L₂)]²⁺ [FeCl₄]² CH₂Cl₂ [monoclinic, P2₁ (#11), a = 1.0562(4), b = 2.0928(4), c = 1.2914(2) nm, β = 100.12°, V = 2.810(1) nm³ D_c = 1.879 g/cm³ and Z = 2].     

The First Metal‐Carbon Bond β‐Isomer Paddlewheel Pd24+ Compounds

The first metal‐carbon bond β‐form paddlewheel complexes containing a Pd₂⁴⁺ core, [Pd(η²‐dithio)]₂(μ‐dppa)( μ‐SCNMe₂) (dithio = S₂P(OEt)₂, 2 ; S₂COEt, 3 ; S₂CNC₄H₈, 4 ), were prepared by the reactions of the α‐form paddlewheel‐type Pd₂⁺⁴ dipalladium complex [Pd₂ (μ‐Hdppa)₂(μ‐SCNMe₂)₂][Cl]₂, 1 with various dithio‐ligands, [NH₄][S₂P(OEt)₂], [K][S₂COEt] and [NH₄][S₂CNC₄H₈], in methanol at ambient temperature (Hdppa = bis(diphenylphosphino)amine). Electronic spectra and two X‐ray structures of the Pd₂⁺⁴ species have been determined.     

One‐Step Versus Multistep Equilibrium of Carbazole‐Bridged Dinuclear Zinc(II) Complex Formation: Metal‐Assisted π‐Association and ‐Dissociation Processes

This work demonstrates a selection criteria that determines whether molecular assembly occurs through a one‐step or stepwise manner in ligand‐bridged dinuclear zinc(II) (Zn²⁺) complex formation, which is associated with the π stacking of building blocks. The building blocks of carbazole ligands ( L¹ and L⁴ ) that contain two imidazole moieties at the 3,6‐positions form 4:2 complexes (i.e., [ L ]₄?(Zn²⁺)₂) at a molar ratio of 0.50 ([Zn²⁺]/[ L ]₀=0.50), thereby providing π stacking between the carbazole ligands. At the molar ratio of 0.67 ([Zn²⁺]/[ L ]₀=0.67), the 4:2 complexes change to 3:2 complexes (i.e., [ L ]₃?(Zn²⁺)₂) with no π‐stacked carbazole unit. In contrast, when the imidazole groups in L¹ are replaced with benzoimidazole groups ( L³ ), L³ also yields the 4:2 complex [( L³ )₄?(Zn²⁺)₂] at a molar ratio of 0.50. However, there is no structural transition from ( L³ )₄?(Zn²⁺)₂ to other complex species above a molar ratio of 0.50. Similarly, when two imidazole groups are introduced into the carbazole ring at 2,7‐positions ( L⁵ ), L⁵ also gives the 4:2 complex [( L⁵ )₄?(Zn²⁺)₂] that shows no structural transition to other complex species at a higher molar ratio.     

Strontium Vanadium Oxide–Hydrides: “Square‐Planar” Two‐Electron Phases

A series of strontium vanadium oxide–hydride phases prepared by utilizing a low‐temperature synthesis strategy in which oxide ions in Sr_n+1V_nO_3n+1 (n=∞, 1, 2) phases are topochemically replaced by hydride ions to form SrVO₂H, Sr₂VO₃H, and Sr₃V₂O₅H₂, respectively. These new phases contain sheets or chains of apex‐linked V³⁺O₄ squares stacked with SrH layers/chains, such that the n=∞ member, SrVO₂H, can be considered to be analogous to “infinite‐layer” phases, such as Sr_1?xCa_xCuO₂ (the parent phase of the high‐T_c cuprate superconductors), but with a d² electron count. All three oxide–hydride phases exhibit strong antiferromagnetic coupling, with SrVO₂H exhibiting an antiferromagnetic ordering temperature, T_N>300 K. The strong antiferromagnetic couplings are surprising given they appear to arise from π‐type magnetic exchange.     

Selective Detection of Multicarboxylate Anions based on “Turn on” Electron Transfer by Self‐Assembled Molecular Rectangles

Two new large molecular rectangles ( 4 and 5 ) were obtained by the reaction of two different dinuclear arene ruthenium complexes [Ru₂(arene)₂(O O)₂Cl₂] (arene=p‐cymene; O O=2,5‐dihydroxy‐1,4‐benzoquinonato ( 2 ), 6,11‐dihydroxy‐5,12‐naphthacene dionato ( 3 )) with the unsymmetrical amide (N‐[4‐(pyridin‐4‐ylethynyl)phenyl]isonicotinamide) donor ligand 1 in methanol in the presence of AgO₃SCF₃, forming tetranuclear cations of the general formula [Ru₄(arene)₄( )₂(O O)₂]⁴⁺. Both rectangles were isolated in good yields as triflate salts and were characterized by multinuclear NMR, ESI‐MS, UV/Vis, and photoluminescence spectroscopy. The crystal structure of 5 was determined by X‐ray diffraction. Luminescent rectangle 5 was used for anion sensing with an amide ligand as a hydrogen‐bond donor and an arene–ruthenium acceptor as a signaling unit. Rectangle 5 strongly bound multicarboxylate anions, such as oxalate, tartrate, and citrate, in UV/Vis titration experiments in 1:1 ratios, in contrast to monoanions, such as F^?, Cl^?, NO₃^?, PF₆^?, CH₃COO^?, and C₆H₅COO^?. The fluorescence titration experiment showed a large fluorescence enhancement of 5 upon binding to multicarboxylate anions, which could be attributed to blocking of the photoinduced electron transfer process from the arene–ruthenium moiety to the amidic donor in 5 ; this was likely to be a result of hydrogen bonding between the ligand and the anion. On the other hand, rectangle 5 was not selective towards any other anions. To the naked eye, multicarboxylate anions in a solution of 5 in methanol appear greenish upon irradiation with UV light.     

“Push‐pull” supramolecular chromophores supported on cyclopolymers

Well‐defined macromolecules have been obtained through free‐radical cyclopolymerization and cyclocopolymerization of difunctional and acrylic‐like monomers, which contained “push‐pull” supramolecular chromophores, able to form 1:1 complexes with Eu³⁺ ions in solution. The monomeric molecular modules are built around bismalonate crown ethers in a convergent fashion, in which one of the malonate moiety is derivatized as the ylidene malonate push‐pull fragment, and the other malonate moiety is elaborated to introduce two polymerizable and acrylic‐like substituents. The free‐radical induced cyclopolymerization of these monomers, or their cyclocopolymerization with UV/Vis “silent” but structurally related monomers, afforded macromolecular architectures characterized by GPC, NMR and DSC techniques. UV/Vis titration studies, performed with Eu(OTf)₃ as the supramolecular probe, revealed how adjacent chromophores within the polymeric backbone are virtually independent from each other, and how the binding ability towards the probe of these multivalent, highly packed cyclopolymeric architectures, although reduced, is still clearly detectable. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5202–5213, 2008     

Synthesis and clustering of supramolecular “graft” polymers

The synthesis and melt rheology of supramolecular poly(isobutylene) polymers bearing statistically distributed hydrogen‐bonding moieties is reported, aiming at understanding the formation of the underlying supramolecular networks for self‐healing polymers. Two different hydrogen bonds were incorporated into a poly(isobutylene) (PIB) copolymer, one based on a (weak) pyridinium/pyridine interaction, the other based on a (stronger) 2,6‐diaminotriazine/thymine interaction. A direct copolymerization based on living cationic polymerization of isobutene and the comonomers 1 , 2 , and 4 in amounts of 1 mol % lead to the copolymers PIB‐ 1 , PIB‐ 2 , and PIB‐ 4 with a content of ～1 mol % of comonomer and molecular weights ranging from ～2000 to 19,000 g mol^?1 (M_w/M_n ～ 1.2–1.5). Subsequent azide/alkyne “click” chemistry enabled the attachment of 2,6‐diaminotriazine‐ and thymine‐moieties to yield the copolymers PIB‐ 5 , PIB‐ 6 , and PIB‐ 7 . Proof of the statistical incorporation of ～1 mol % of hydrogen‐bonding moieties was achieved by ¹H NMR spectroscopy and matrix‐assisted laser desorption ionization measurements. The true presence of a supramolecular network in PIB‐ 1 (pyridinium/pyridine interaction) as well as with 1/1 blends of PIBs interacting via the 2,6‐diaminotriazine/thymine interaction (PIB‐ 5 /PIB‐ 6 ) was proven via the increasing plateau modulus with increasing molecular weights (5.5k, 9.9k, 12.4k, 16k, and 19k). Dynamics of the hydrogen bonds in the melt state was investigated by determining the effective cluster lifetime ( τ ) observing a clear difference in the (weaker) pyridinium/pyridine interaction ( τ ～ 1 s) to the 2,6‐ (stronger) diamintriazine/thymine interaction ( τ ～ 100 s). The so‐generated materials will be useful as a basis for self‐healing polymers, as dynamics plays a major role in such polymers. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012