Interfacing supramolecular and macromolecular chemistry: metallo-supramolecular triple-helicates incorporated into polymer networks

Metallo-supramolecular diiron(II) triple-helical cores based on pyridylimine ligands and decorated with acrylate or methacrylate units are copolymerised with methyl methacrylate (MMA) as major comonomer using AIBN.     

Above room temperature spin transition in a metallo-supramolecular coordination oligomer/polymer

By use of a metallo-supramolecular concept, a linear iron(ii) coordination chain [Fe(II)(L)](n)(BF(4))(2n) (L = 1,4-bis(1,2':6',1'-bispyrazolylpyridin-4'-yl)benzene) was rationally designed and synthesized. The molecular chain shows a reversible spin transition at 323 K with a ca. 10 K wide hysteresis loop.     

A periodic metallo-supramolecular polymer from a flexible building block: self-assembly and photocatalysis for organic dye degradation

A water-soluble metallo-supramolecular polymer MSP-f-6Np, which possesses a regular pore aperture of 1.4 nm, has been assembled from a structurally flexible naphthalene-appended [Ru(bipy)_3]~(2+)complex and cucurbit[8]uril. As the first periodic metallo-supramolecular polymer formed by a flexible building block, MSP-f-6Np exhibits a hydrodynamic diameter of 122 and 164 nm at 0.1 and 2.0 m M of the monomer concentrations. Synchrotron small angle X-ray scattering experiments confirm that MSP-f-6Np possesses porosity periodicity in both the solution and solid states. Compared with a control, the new highly ordered porous system displays enhanced photocatalytic activity for the degradation of organic dyes.     

Novel conductive metallo-supramolecular polymer AIE gel for multi-channel highly sensitive detection of hydrazine hydrate

Hydrazine hydrate (DH) is an important fine chemical intermediate and as fuel for rockets, however, it also has serious toxic for humans and environment. Developing novel materials and methods for sensitive detection of DH in water and air is an important task. In order to effectively detect DH, a novel conductive supramolecular polymer metallogel (PQ-Ag) has been constructed by the coordination of bis-5-hydroxyquinoline functionalized pillar[5]arene (PQ5) with Ag⁺. The metallogel PQ-Ag could realize the multi-channel sensitive detection of DH through naked-eye, fluorescence, and electrochemical methods. The lowest limit of detection (LOD) is 0.1 mg/m³ in air and 2.68 × 10⁻⁸ mol/L in water, which is lower than the standard of the US Environmental Protection Agency (EPA) for DH of maximum allowable concentration in drinking water. More importantly, an electronic device for DH detection based on the metallogel PQ-Ag was designed and prepared, which can realize conveniently and efficiently multi-channel detection and alert of DH through sound and light alarms not only in water but also in air.     

Multistimuli, multiresponsive metallo-supramolecular polymers

The use of metal ion-induced polymerizations of a ditopic ligand offers a facile route to the preparation of organic/inorganic hybrid materials. Such metallo-supramolecular polymers potentially offer the functionality of the metal ion along with the processibility of a polymer. We report, herein, the preparation of gellike metallo-supramolecular polymers prepared from a monomer unit, which consists of a 2,6-bis-(benzimidazolyl)-4-hydroxypyridine unit attached to either end of a polyether chain, mixed with a transition metal ion (e.g., Co(II) or Zn(II)) and a small percentage of a lanthanoid metal (e.g., La(III), Eu(III)). Such materials show dramatic reversible responses to a variety of stimuli, including thermal, mechanical, chemo, and photo. The nature of the response can be controlled by the nature of the combination of transition metal ion and lanthanide metal ion used.     

Spacer directed metallo-supramolecular assemblies of pyridine carboxylates

N,O-donating spacers are members of a class of ambidentate donors used in supramolecular self-assemblies. The skeletal adaptability and coordination flexibility of these ligands enable them to support a myriad of discrete molecular systems and extended network materials. This review focuses on pyridinecarboxylates as a representative of N,O-hetero-donating spacers and describes their recent developments in the coordination assemblies and highlights their functions and potential applications.     

Thin films of cross-linked metallo-supramolecular coordination polyelectrolytes

We report on the synthesis of a new tristerpyridine ligand, tris(2,2':6',2' '-terpyridinyl-4'-oxymethyl)ethane (tritpy), as well as its introduction into metal ion induced self-assembly of cross-linked metallo-supramolecular coordination polyelectrolytes (MEPE). For cross-linking degrees of 9.5% and below, soluble homogeneous networks are obtained. The molar mass of the networks is large and depends on the cross-linking degree. Due to the charges in the MEPE, the soluble networks are suitable for film formation on the basis of layer-by-layer self-assembly and to study the details of film growth. UV-vis spectroscopy, X-ray reflectivity, AFM, and ellipsometry show that the film growth is linear and continuous. The multilayers exhibit no inner structure and have a very low surface roughness. The thickness of the adsorbed layer of MEPE networks is in the range of 3 nm. The important point is that an influence of cross-linking is not seen in multilayers, which is the opposite of what is observed for the MEPE in solution. Our experiments did not reveal an influence of the preparation procedure on the adsorption process, e.g., increasing the layer thickness.     

Electrochromic properties of a metallo-supramolecular polymer derived from tetra(2-pyridyl-1,4-pyrazine) ligands integrated in thin multilayer films

The electrochromic behavior of iron complexes derived from tetra-2-pyridyl-1,4-pyrazine (TPPZ) and a hexacyanoferrate species in polyelectrolytic multilayer adsorbed films is described for the first time. This complex macromolecule was deposited onto indium-tin oxide (ITO) substrates via self-assembly, and the morphology of the modified electrodes was studied using atomic force microscopy (AFM), which indicated that the hybrid film containing the polyelectrolyte multilayer and the iron complex was highly homogeneous and was approximately 50 nm thick. The modified electrodes exhibited excellent electrochromic behavior with both intense and persistent coloration as well as a chromatic contrast of approximately 70%. In addition, this system achieved high electrochromic efficiency (over 70 cm(2) C(-1) at 630 nm) and a response time that could be measured in milliseconds. The electrode was cycled more than 10(3) times, indicating excellent stability.     

Functionalized nanoporous thin films from metallo-supramolecular diblock copolymers

A polystyrene-[Ni(2+)]-poly(ethylene oxide) metallo-supramolecular block copolymer (PS-[Ni(2+)]-PEO), where -[ is a terpyridine, is used to create nanoporous thin films with free terpyridine ligands homogenously distributed on the pore walls. The PS-[Ni(2+)]-PEO block copolymer is synthesized by a two step assembly process, and is then self-assembled into a thin film in order to obtain PEO cylinders oriented perpendicularly to the film surface. The supramolecular junction is opened by exposing the film to an excess of a competing ligand, and the free PEO block is then rinsed away by a selective solvent. The presence of the terpyridines on the pore walls is evidenced by fluorescence spectroscopy after formation of a fluorescent complex with an europium salt.     

Synthesis and optical properties of metallo-supramolecular polymers

Metal-ligand interactions between metal ions, such as Zn2+, and ditopic low-molecular weight conjugated monomers, which utilize the 2,6-bis(1'-methylbenzimidazolyl)pyridine ligand, lead to the formation of supramolecular conjugated polymers with interesting optical properties.     

Structure and temperature behavior of metallo-supramolecular assemblies

A detailed structural analysis of a Langmuir-Blodgett (LB) multilayer composed of a polyelectrolyte-amphiphile complex (PAC) is presented. The PAC is self-assembled from metal ions, ditopic bis-terpyridines, and amphiphiles. The vertical structure of the LB multilayer is investigated by X-ray reflectometry. The multilayer has a periodicity of 57 A, which corresponds to an architecture of flat lying metallo-supramolecular coordination polyelectrolyte (MEPE) rods and upright-standing amphiphiles (dihexadecyl phosphate, DHP). In-plane diffraction reveals hexagonal packing of the DHP molecules. Using extended X-ray absorption fine structure (EXAFS) experiments, we prove that the central metal ion is coordinated to the terpyridine moieties in a pseudo-octahedral coordination environment. The Fe-N bond distances are 1.82 and 2.0 A, respectively. Temperature resolved measurements indicate a reversible phase transition in a temperature range up to 55 degrees C. EXAFS measurements indicate a lengthening of the average Fe-N bond distance from 1.91 to 1.95 A. The widening of the coordination cage upon heating is expected to lower the ligand field stabilization, thus giving rise to spin transitions in these composite materials.     

Aggregation of metallo-supramolecular architectures by metallo-assembled hydrogen bonding sites

Metal-ligand interactions are used not only to design metallo-supramolecular architectures but also to assemble multiple hydrogen bond sites at the periphery of these architectures. The hydrogen bond sites aggregate the architectures into polymeric arrays with the selection of anion determining whether this is self H-bond aggregation or anion-mediated H-bond aggregation.     

Electron capture dissociation mass spectrometry of metallo-supramolecular complexes

The electron capture dissociation (ECD) of metallo-supramolecular dinuclear triple-stranded helicate Fe₂L₃⁴⁺ ions was determined by Fourier transform ion cyclotron resonance mass spectrometry. Initial electron capture by the di-iron(II) triple helicate ions produces dinuclear double-stranded complexes analogous to those seen in solution with the monocationic metal centers Cu^I or Ag^I. The gas-phase fragmentation behavior [ECD, collision-induced dissociation (CID), and infrared multiphoton dissociation (IRMPD)] of the di-iron double-stranded complexes, (i.e., MS³ of the ECD product) was compared with the ECD, CID, and IRMPD of the Cu^I and Ag^I complexes generated from solution. The results suggest that iron-bound dimers may be of the form Fe₂^IL₂²⁺ and that ECD by metallo-complexes allows access, in the gas phase, to oxidation states and coordination chemistry that cannot be accessed in solution.     

Aggregation of imine-based metallo-supramolecular architectures through pi-pi interactions

The design of supramolecular architectures based on isoquinoline-imine ligand systems is described. The isoquinoline affords an extended pi surface and the use of this surface to obtain self-recognition and consequent pi-pi aggregation is investigated. The approach is effective in that each of four complexes is observed to aggregate through these interactions. Other pi-pi interactions can interfere with the aggregation indicating that a larger pi-surface may be required to obtain complete control over the aggregation of the units.     

Thermodynamics and selectivity of two-dimensional metallo-supramolecular self-assembly resolved at molecular scale

We investigated the thermodynamic processes of two-dimensional (2D) metallo-supramolecular self-assembly at molecular resolution using scanning tunneling microscopy and variable-temperature low-energy electron diffraction. On a Au(111) substrate, tripyridyl ligands coordinated with Cu in a twofold Cu-pyridyl binding mode or with Fe in a threefold Fe-pyridyl binding mode, forming a 2D open network structure in each case. The network structures exhibited remarkable thermal stability (600 K for the Cu-coordinated network and 680 K for the Fe-coordinated network). The Fe-pyridyl binding was selected thermodynamically as well as kinetically in self-assembly involving both modes. The selectivity can be effectively suppressed in a specifically designed self-assembly route.     

Design and DNA binding of an extended triple-stranded metallo-supramolecular cylinder

A new tetracationic triple-stranded supramolecular cylinder is prepared from a bis(pyridylimine) ligand containing a diphenylmethane and two ketimine groups in the spacer. The cylinder is longer and slightly wider than the corresponding cylinder containing just diphenylmethane spacers. Inter-strand CH...pi interactions are not observed and this affects the relay of the chiral information within the cylinder; a mixture of rac and meso isomers results, with the meso isomer being the dominant solution species and characterised in the solid state by crystallography. This new cylinder does bind to DNA as confirmed by induced circular dichroism signals in both the metal-to-ligand charge transfer (MLCT) and in-ligand bands of the cylinder. Flow linear dichroism demonstrates that the cylinder binds to DNA in a specific orientation(s) and is consistent with (major) groove-binding as seen for the shorter cylinder. Some DNA bending/coiling is observed but the effect is much less dramatic than observed for the cylinder with diphenylmethane spacers confirming that coiling is not solely a consequence of the tetracationic charge, but rather is related to the precise size and shape of the cylinder.     

Structural basis for vapoluminescent organoplatinum materials derived from noncovalent interactions as recognition components

The spectroscopic properties and crystal structures of a series of platinum(II) complexes bearing functionalized sigma-alkynyl groups, namely [(tBu(2)bpy)Pt(C triple bond CAr)(2)] (tBu(2)bpy = 4,4'-bis-tert-butyl-2,2'-bipyridine, Ar = 4-pyridyl, 1; 3-pyridyl, 2; 2-pyridyl, 3; 4-ethynylpyridyl, 4; 2-thienyl, 5; pentafluorophenyl, 6) have been studied. Solid-state emissions of 1 and 6 are dependent on their crystallinity. Reversible and selective vapoluminescence was observed for 1 and 6 in the presence of chlorocarbon vapors. For solid 1, dramatic enhancement of green luminescence is observed upon sorption of CH(2)Cl(2) or CHCl(3) vapor. The excimeric orange emission for solid 6 is switched to monomeric green emission upon exposure to CH(2)Cl(2) vapor. The luminescent responses of a thin film of 1 towards various organic vapors have also been examined. In the crystallographically determined structure of 1.CH(2)Cl(2), the bis(acetylide) moiety acts as the receptor berth for a CH(2)Cl(2) molecule through concerted C-H.pi(C triple bond C) interactions, while Cl.Cl interactions connect the CH(2)Cl(2) molecules into infinite linear chains. The observed crystal lattices are arranged into scaffolds of varying porosity by weak C-H...N(py) (1.CH(2)Cl(2), 1.CH(3)CN, 4.DMF) and C-H...F-C (6, 6.CH(3)CN) interactions. The correlation between the crystal structures of 1.CH(2)Cl(2), 1.CH(3)CN, 2, 4.DMF, 5, 6, and 6.CH(3)CN and their vapoluminescence suggests that weak nonconventional hydrogen-bonding interactions preside over the reversible sensing and signalling processes.