Methyldisulfide groups enable the direct connection of air-stable metal bis(terpyridine) complexes to gold surfaces

We show that a new terpyridine ligand comprising a directly-connected methyldisulfide group (tpySSMe) can be used to prepare a modular series of metal bis(terpyidine) complexes, [M(tpySSMe)2](PF6)2 (M = Fe, Co, Zn), suitable for the functionalization of metal surfaces. Critically, we find these complexes are air-stable in solution for >7 d, in stark contrast to their thiol-substituted analogues, [M(tpySH)2](PF6)2 (M = Fe, Co), which decompose in <1 d. While CoSH has previously been utilized in several important studies, we explicitly detail its synthesis and characterization here for the first time. We subsequently probe the electrochemical properties of [M(tpySSMe)2](PF6)2 in solution, showing that the (electro)chemical reactions associated with disulfide reduction significantly increase the complexity of the voltammetric response. In preliminary surface voltammetry studies, we confirm that CoSS and FeSS form solution-stable self-assembled monolayers (SAMs) on gold with comparable electrochemical properties to those formed from CoSH. Taken together, this work provides a robust foundation for future studies of this prominent class of complexes as redox-active components of SAMs or single-molecule junctions.

Synthesis and characterization of metallo-supramolecular polymers

The incorporation of metal centers into the backbone of polymers has led to the development of a broad range of organometallic and coordination compounds featuring properties that are relevant for potential applications in diverse areas of research, ranging from energy storage/conversion to bioactive or self-healing materials. In this review, the basic concepts and synthetic strategies leading to these types of materials as well as the scope of available characterization techniques will be summarized and discussed.

Terpyridinyl dibenzo[b,d]furan and dibenzo[b,d]thiophene based tetrameric bismetallo-macrocycles

Dibenzo[b,d]thiophene and dibenzo[b,d]furan based bisterpyridines were prepared. Direct self-assembly with Fe²⁺ led to metallo-macrocyclic mixtures. Utilizing the robust metallo-organic-ligands afforded the pure tetrameric macrocycles.

An iron(ii) spin-crossover metallacycle from a back-to-back bis-[dipyrazolylpyridine]

Iron(ii) and zinc(ii) complexes of bis[2,6-di(pyrazol-1-yl)pyrid-4-yl]disulfide assemble into tetranuclear metallacycles according to ES-MS, DOSY NMR and conductivity data. The iron complex exhibits a thermal spin-state equilibrium in solution, which the iron centres appear to undergo independently of each other.

Tuning Coordination Environments Through Ligand Redox Chemistry: the Thiol - Disulfide Reaction

Oxidative coupling of 6-(pyridin-2-yl)pyridine-2(1H)-thione yields 1,2-bis(2,2′-bipyridin-6-yl)disulfide (4), which can act as a bis(chelate) to a single zinc(ii) centre. The effects on the solid-state structure of introducing a methyl substituent into each 6-position of 4 have been examined. Ligand 4 functions as a bridging ligand in [Cu2(μ-4)(μ-6)]4+ in which ligand 6 is 1,2-bis(2,2′:6′,2″-terpyridin-4′-yl)disulfide; [Cu2(μ-4)(μ-6)]4+ self-assembles from the components according to the preference shown by copper(ii) for a five-coordinate {Cu(bpy)(tpy)} environment. Reaction of 4 with [Cu(NCMe)4][PF6] leads to a product, tentatively formulated as {[Cu(4)][PF6]}n, which, in air, undergoes oxidation of both copper and ligand to yield [Cu(5)2] (H5 = 2,2′-bipyridine-6-sulfonic acid), the solid state structure of which is presented.

Pd-catalyzed diarylation of aniline--a way to a non-linear bis(terpyridyl) ligand providing increased electronic communication

An amine-linked bis(terpyridyl) ligand, prepared via Pd-catalyzed diarylation of aniline, mediates unusually strong metal-metal interaction in its Ru(2) polypyridyl complex.

[n + n]-Heterometallomacrocyclic complexes (n ≥ 2) prepared from platinum(ii)-centred ditopic 2,2′:6′,2″-terpyridine ligands: dimensional cataloguing by pulsed-field gradient spin-echo NMR spectroscopy

The reaction of 4'-(2-propyn-1-oxy)-2,2':6',2''-terpyridine (HC[triple bond]CCH2Oterpy) with trans-[PtI2(PR3)2] (R = Et, (n)Bu, Ph) results in the regioselective formation of the metalloditopic ligands trans-[Pt(C[triple bond]CCH2Oterpy)2(PR3)2], crystallographic data for which are presented. Each ditopic ligand reacts with FeCl(2).4H(2)O to give heterometallomacrocycles, the smallest of which is a [2 + 2] macrocycle, confirmed structurally for R = Et. The NMR spectroscopic data confirm the formation of symmetrical species, i.e. macrocyclic and not polymeric species. The distribution of products has been investigated using pulsed-field gradient spin-echo (PGSE) diffusion NMR spectroscopy, and indicates that the kinetic products from the reactions of 1, 2 or 3(L) with iron(II) are [Fe(n)L(n)](2n+) with n = 2, 3 or 4. For L = 1 and 2, these mixtures of products convert in solution to the thermodynamically favoured [Fe(2)L(2)](4+).

2,2':6',2''-terpyridines: from chemical obscurity to common supramolecular motifs

This tutorial review describes the use of 2,2':6',2''-terpyridine (tpy) metal-binding domains in supramolecular chemistry. The origins of tpy chemistry are described and the reasons for its current importance in supramolecular chemistry are explained. Examples of tpy compounds in a wide variety of supramolecular chemistry are presented. The content will be of interest to organic, inorganic, supramolecular and nanoscale chemists.

Structural Development of Free or Coordinated 4′-(4-Pyridyl)-2,2′:6′,2′′-terpyridine Ligands through N-Alkylation: New Strategies for Metallamacrocycle Formation

A series of N-alkylated derivatives of [Ru(pytpy)(2)]2+ (pytpy=4'-(4-pyridyl)-2,2':6',2''-terpyridine) has been synthesised and characterised. These include both model and functionalised complexes that complement previously reported iron(II) analogues. Reaction of [Ru(pytpy)(2)]2+ with bis[4-(bromomethyl)phenyl]methane leads to the formation of a [2+2] ruthenamacrocycle. Related ferramacrocycles could not be accessed by this route, and instead were prepared in two steps by first reacting bis[4-(bromomethyl)phenyl]methane or 4,4'-bis(bromomethyl)biphenyl with two equivalents of pytpy, and then treating the resulting bis(N-alkylated) product with iron(II) salts.

Design, synthesis and photoelectrochemical properties of hexagonal metallomacrocycles based on triphenylamine: [M6(4,4′-bis(2,2′:6′,2″-terpyridinyl)triphenylamine)6(X)12]; [M = Fe(ii), PF6−and Zn(ii), BF4−]

Synthesis of a novel bis(terpyridine) ligand, 4,4'-bis(2,2':6',2''-terpyridinyl)triphenylamine, utilizing triphenylamine, as a specific angle controller, has led to the self-assembly of a unique hexagonal metallomacrocycle family, [Fe6(2)6(PF6)12] and [Zn6(2)6(BF4)12], utilizing terpyridine-metal(II)-terpyridine connectivity. The crystal structure of the novel ligand shows that the angle between the two terpyridinyl moieties is 119.69 degrees , which enabled the formation of the hexagonal-shaped macrocycles. The crystal packing architectures of this starting ligand revealed channels induced by solvent encapsulation. Following complexation of this ligand with transition metals [Fe(II) or Zn(II)] in a one-pot reaction, the resultant structures were characterized by (1)H and (13)C NMR, UV/Vis and mass spectroscopies. The expected metal-to-ligand charge transfer (MLCT; lambda(max) = 582 nm) and emission (lambda(em) = 575 nm) characteristics were exhibited by both [Fe6(2)6(PF6)12] and[Zn6(2)6(BF4)12]. The photoelectrochemical characteristics of these hexagonal metallomacrocycles demonstrate that they can be used as sensitizers in dye-sensitized solar cells.