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Innovation in the development of electrochemical energy storage methods is essential if these technologies are to meet the variable needs of the electrical grid. Nonaqueous redox flow batteries represent an underdeveloped area of research in energy storage—one which has seen a recent spike in interest owing to the potential for modular, energy-dense electrochemical energy conversion. Here, we summarize our recent work, focused on the design of polyoxovanadate-alkoxide clusters [V6O7(OR)12] as a new class of charge carrier for nonaqueous energy storage. The synthetic strategies we have employed, including homoleptic ligand substitution, selective ligand functionalization, and heterometal installation, demonstrate the flexibility of this hexametalate platform, and result in significant improvement of molecular properties with relevance to flow battery energy density. The identified homoleptic surface modifications (substituting R = CH3 for R = C2H5) to the polyoxovanadate-alkoxide scaffold yield an increase in stable operating voltage window (from 0.6 V to 1.8 V), as well as an increase in the stoichiometric number of electrons that can be stored at each battery electrode (from 1 to 2). Targeted functionalization at the cluster surface with an ether-based ligand affords [V6O7(OC2H5)9(OCH2)3CCH2OC2H4OCH3], which demonstrates a 12-fold increase in solubility over its homoleptic congener, from 0.05 to 0.60 M in acetonitrile. The substitution of a titanium center into the hexametalate core to generate [V5TiO6(OCH3)13]− further increases the voltage window to 2.3 V, as new heterometal-based redox events are introduced to the profile. Through these studies, we have gained valuable insights into the molecular parameters that determine the energy storage capabilities of multimetallic charge carriers. Collectively, our results highlight new opportunities for polynuclear charge carriers, and emphasize the critical role that synthetic inorganic chemistry plays in the development of effective nonaqueous redox flow battery technologies. [ABSTRACT FROM AUTHOR]

Here we report on a scanning tunnelling microscopy (STM) investigation on the self-assembly of C 3 - and C 2 -symmetric molecules at the solution/graphite interface. 1,3,5-tris(( E )-2-(pyridin-4-yl)vinyl)benzene and 1,1,2,2-tetrakis(4-(pyridin-4-yl)phenyl)ethane are used as model systems. These molecules displayed a concentration dependent self-assembly behaviour on graphite, resulting in highly ordered supramolecular structures, which are stabilized jointly by van der Waals substrate-adsorbate interactions and in-plane intermolecular H-bonding. Denser packing is obtained when applying a relatively high concentration solution to the basal plane of the surface whereas a less dense porous network is observed upon lowering the concentration. We show that the molecular conformation does not influence the stability of the self-assembly and a twisted molecule can pack into dense and porous architectures under the concentration effect. [ABSTRACT FROM AUTHOR]

Non-aqueous redox flow batteries (naRFBs) are promising candidates as high-capacity energy storage devices. Although the wide redox windows associated with the organic solvents used in naRFBs are useful to realize high open circuit voltages, the low solubilities of electrolytes often minimize the energy densities. Strategies have emerged to increase the concentration of active materials employed in naRFBs; however, the dilute conditions typically associated with chronoamperometry and voltammetric experiments are orders of magnitude lower than those found in a working RFB. The electrochemical behavior of non-aqueous electrolytes may differ at high concentrations due to changes in solvation structure, aggregation, solution resistance, and mass transport, which in turn affect the overall cell performance. Accordingly, we studied a series of naRFB systems using ferrocene/TEMPO as a posolyte, and cobaltocenium hexafluorophosphate/N-methylphthalimide as a negolyte, to investigate the effect of concentration on charge-discharge profiles. Cycling studies were performed with four combinations of the above-mentioned catholyte and anolyte materials. Concentration regimes were explored ranging from 10 mM to 1 M depending on the maximum solubility of a given active species. The results indicate that cycling behaviors are concentration dependent. Coulombic efficiencies and voltage efficiencies are calculated for each system. In addition, it was observed that the specific combination of catholyte/anolyte also affects the charge-discharge profiles and that membrane crossover and fouling is a major contributor to performance losses. [ABSTRACT FROM AUTHOR]

We present the formation of a series of chiral metallacycles and metallacages by the use of a BINOL-derived dicarboxylate as a donor that is capable of affording a variety of coordination angles between its two Lewis basic sites. Two squares, two rhomboids, two tetragonal prisms, and one hexagonal prism were successfully formed when the chiral dicarboxylate donor self-assembled with one of four ditopic Pt(II) complexes, including two bimetallic 180° Pt-based acceptors, a 120° bimetallic Pt-based acceptor, and a 90° mononuclear Pt-based acceptor. Their structures were well characterized by 31P{1H} NMR, ESI-MS, CD, and optical rotation analyses. [ABSTRACT FROM AUTHOR]

The article focuses on developments in chemistry of metallacycles and metallacages through metal-ligand coordination. Topics include approaches for structural chemistry of metallacycles including edge-and face-direct assembly, catenanes and covalent stabilization; functional use of metallacycles such as sensors and catalysis; and chemical reaction showing tetranuclear metallacycles.

Light-emitting materials, especially those with tunable wavelengths, attract considerable attention for applications in optoelectronic devices, fluorescent probes, sensors and so on. Many species evaluated for these purposes either emit as a dilute solution or on aggregation, with the former often self-quenching at high concentrations, and the latter falling dark when aggregation is disrupted. Here we preserve emissive behaviour at both low- and high-concentration regimes for two discrete supramolecular coordination complexes (SCCs). These tetragonal prismatic SCCs are self-assembled on mixing a metal acceptor, Pt(PEt3)2(OSO2CF3)2, with two organic donors, a pyridyl-decorated tetraphenylethylene and one of two benzene dicarboxylate species. The rigid organization of these fluorescence-active ligands imparts an emissive behaviour to dilute solutions of the resulting assemblies. Furthermore, on aggregation the prisms exhibit variable-wavelength visible-light emission, including rare white-light emission in tetrahydrofuran. The favourable photophysical properties and solvent-dependent aggregation behaviour provide a means to tune emission wavelengths. [ABSTRACT FROM AUTHOR]

Oligo(ethylene glycol) (OEG)-decorated supramolecular assemblies are distinguished by their neutral character and macroscopic temperature-sensitive phase transition behavior. OEG functionalization is an emerging strategy to obtain thermoresponsive macrocyclic amphiphiles, although known methods organize the hydrophilic and hydrophobic segments by covalent bonding. Coordination-driven self-assembly offers an alternative route for organizing OEG-functionalized precursors into nanoscopic architectures, resulting in well-defined metallacycle cores surrounded by hydrophilic scaffolds to impart overall amphiphilic character. Here a tri(ethylene glycol)-functionalized thermosensitive amphiphilic metallacycle was prepared with high efficiency by means of the directional-bonding approach. The ensembles thus formed showed good lower critical solution temperature behavior with a highly sensitive phase separation and excellent reversibility. Moreover, the clouding point decreased with increasing metallacycle concentration and addition of K+. [ABSTRACT FROM AUTHOR]

An emerging strategy for the fabrication of advanced supramolecular materials is the use of hierarchical self-assembly techniques wherein multiple orthogonal interactions between molecular precursors can produce new species with attractive properties. Herein, we unify the spontaneous formation of metal-ligand bonds with the host/guest chemistry of crown ethers to deliver a 3D supramolecular polymer network (SPN). Specifically, we have prepared a highly directional dipyridyl donor decorated with a benzo-21-crown-7 moiety that undergoes coordination-driven self-assembly with a complementary organoplatinum acceptor to furnish hexagonal metallacycles. These hexagons subsequently polymerize into a supramolecular network upon the addition of a bisammonium salt due to the formation of [2]pseudorotaxane linkages between the crown ether and ammonium moieties. At high concentrations, the resulting 3D SPN becomes a gel comprising many cross-linked metallohexagons. Notably, thermo- and cation-induced gel-sol transitions are found to be completely reversible, reflecting the dynamic and tunable nature of such supramolecular materials. As such, these results demonstrate the structural complexity that can be obtained when carefully controlling multiple interactions in a hierarchical fashion, in this case coordination and host/guest chemistry, and the interesting dynamic properties associated with the materials thus obtained. [ABSTRACT FROM AUTHOR]

Coordination-driven self-assembly is a process that generates supramolecular architectures from molecular precursors by exploiting the favorable properties of metal–ligand bonding. The discrete supramolecular coordination complexes (SCCs) thus obtained have enjoyed multiple decades of development, focused initially on the design and reactivity of rigid building blocks with specific directionalities and angularities, thereby populating a molecular library of complementary donor and acceptor subunits. More recently, efforts have broadened to encompass pre- and post-self-assembly modifications, which have lead to new routes for obtaining functionalized metallacages and metallacycles, multicomponent assemblies incorporating multiple types of ligands in a single scaffold, and supramolecular transformations that quantitatively alter the structure of a given SCC, furnishing an entirely new architecture. [ABSTRACT FROM AUTHOR]

Metal ions and metal complexes with organic molecules are ubiquitous in nature. Bulk metal ions of Na, K, Mg, and Ca constitute as much as 1% of human body weight. The remaining trace ions, most commonly of Fe, Ni, Cu, Mn, Zn, Co, Mo, and V, make up ∼0.01% by weight, but their importance in biological processes cannot be overstated. [ABSTRACT FROM AUTHOR]

The design of supramolecular coordination complexes (SCCs) is typically predicated on the use of rigid molecular building blocks through which the structural outcome is determined based on the number and orientation of labile coordination sites on metal acceptors, and the angularity of the ligand donors that are to bridge these nodes. Three-component systems extend the complexity of self-assembly by utilizing two different Lewis base donors in concert with a metal that favors a heteroligated coordination environment. The thermodynamic preference for heteroligation provides a new design principle to the formation of SCCs, wherein multicomponent architectures need not employ only rigid donors. Herein, we exploit the self-selection processes of bis(phosphine) PtII metal centers which favor mixed Pt(pyridyl)(carboxylate) coordination spheres over their homoligated counterparts, specifically using alkyl-based dicarboxylate ligands instead of traditionally rigid phenyl, alkenyl, or ethynyl variants. Using this mode of assembly, flexible-based 2D and 3D SCCs containing long alkyl chains were synthesized and characterized. Density functional theory (DFT) and natural population analysis (NPA) calculations were performed on model systems to probe the thermodynamic preference for heteroligated coordination spheres in the experimental systems. [ABSTRACT FROM AUTHOR]

The photophysical properties of bis(phosphine) Pt(II) complexes constructed from 2,6-bis(pyrid-3-ylethynyl) aniline and 2,6-bis(pyrid-4-ylethynyl) aniline vary significantly, even though the complexes differ only in the position of the coordinating nitrogen. By capping the ligands with an aryl bis(phosphine) Pt(II) metal acceptor, the photophysical properties of the two isomeric systems were directly compared, revealing that the low-energy absorption and emission bands of the two systems were separated by 30 nm (1804 cm-1) and 39 nm (1692 cm-1), respectively. From the analysis of time-dependent density functional (TD-DFT) calculations and excited-state lifetime measurements, it was determined that the nature of the Pt-N bond in the HOMO and the sums of the radiative (krad) and nonradiative (knr) rate constants were significantly different in the two systems. As the dominant nonradiative decay pathway in aniline systems is relaxation from the triplet state through intersystem crossing (ISC), the difference in knr can be ascribed to changes in ISC between isomers of the bis(phosphine) Pt(II)-capped 2,6-bis(pyrid-3-ylethynyl) aniline system. It was also determined that the photophysical properties of these capped systems can be altered by functionalizing the aryl capping ligand on the bis(phosphine) Pt(II) metal center, which perturbs the molecular orbitals involved in the observed optical transitions. In addition, an isoelectronic bis(phosphine) Pd(II)-capped system was prepared for comparison with the bis(phosphine) Pt(II) suite of complexes. The Pd(II) system showed significant changes in its low-energy absorption band, but preserved the characteristic emissive properties of its Pt(II) analogue with an even higher quantum yield. [ABSTRACT FROM AUTHOR]

The article discusses the importance of metal-organic structural frameworks and self-assembled supramolecular coordination chemical complexes in co-ordination chemistry. It mentions that the structural frameworks are beneficial in study of multicomponent chemical assembly and post self assembly chemical modifications. It mentions that the co-ordination chemistry approach is useful in chemical study involving metal ligands.

A series of endohedral and exohedral amine-functionalized ligands were synthesized and used in the construction of supramolecular D2h rhomboids and a D6h hexagon. These supramolecular polygons were obtained via self-assembly of 1200 dipyridyl donors with 180° or 120° diplatinum precursors when combined in 1:1 ratios. Steady-state absorption and emission spectra were collected for each ligand and metallacycle. Density functional theory (DFT) and time-dependent DFT calculations were employed to probe the nature of the observed optical transitions for the rhomboids. The emissive properties of these bis(phosphine) organoplatinum metallacycles arise from ligand-centered transitions involving π-type molecular orbitals with modest contributions from metal-based atomic orbitals. The D211 rhomboid self-assembled from 2,6-bis(4-pyridylethynyl)aniljne and a 60° organoplatinum(ll) acceptor has a low-energy excited state in the visible region and emits above 500 nm, properties which greatly differ from those of the parent 2,6-bis(4-pyridylethynyl)aniline ligand. [ABSTRACT FROM AUTHOR]

The heterobimetallic complexes, PtRh(tfepma)2(CNtBu)X3 (X = Cl, Br), are assembled by the treatment of Pt(cod)X2 (cod =1,5-cyclooctadiene) with {Rh(cod)X}2, in the presence of tert-butylisonitrile (CNtBu) and tfepma (tfepma = bis(trifluoroethoxyl)phosphinomethylamine). The neutral complexes contain Pt-Rh single bonds with metal-metal separations of 2.6360(3) and 2.6503(7) Å between the square planar Pt and octahedral Rh centers for the Cl and Br complexes, respectively. Oxidation of the XPtIRhIIX2 cores with suitable halide sources (PhICl2 or Br2) furnishes PtRh(tfepma)2(CNtBu)X5, which preserves a Pt-Rh bond. For the chloride system, the initial oxidation product orients the platinum-bound chlorides in a meridional geometry, which slowly transforms to a facial arrangement in pentane solution as verified by X-ray crystal analysis. Irradiation of the mer- or fac-Cl3PtIIIRhIICl2 isomers with visible light in the presence of olefin promotes the photoelimination of halogen and regeneration of the reduced ClPtIRhIICl2 core. In addition to exhibiting photochemistry similar to that of the chloride system, the oxidized bromide cores undergo thermal reduction chemistry in the presence of olefin with zeroth-order olefin dependence. Owing to an extremely high photoreaction quantum yield for the fac-ClPtIRhIICl2 isomer, details of the X2 photoelimination have been captured by transient absorption spectroscopy. We now report the first direct observation of the photointermediate that precedes halogen reductive elimination. The intermediate is generated promptly upon excitation (<8 ns), and halogen is eliminated from it with a rate constant of 3.6 × 104 s-1. As M-X photoactivation and elimination is the critical step in HX splitting, these results establish a new guidepost for the design of HX splitting cycles for solar energy storage. [ABSTRACT FROM AUTHOR]

The syntheses and reaction chemistry of two electron mixed-valence diphosphazane-bridged dirhodium and diiridium complexes M20,II(tfepma)2(CNtBu)2Cl2 [M = Rh (1), Ir (2); tfepma = MeN[P(OCH2CF3)2]2, CNtBu = tert-butyl isocyanide] are described. 1 and 2 undergo addition and two-electron oxidation and reduction chemistries. In the presence of CNtBu, the addition product with the stoichiometry M20,II(tfepma)2(CNtBu)3Cl2 [M = Rh (3), Ir (3)] is generated; in the presence of 1 equiv of CNtBu and 2 equiv of bis(pentamethyl-cyclopentadienyl)cobalt(II), 1 and 2 are reduced to furnish M20,0(tfepma)2(CNtBu)3 [M = Rh (5), Ir (6)], which feature both four- and five-coordinate M0 centers. Complexes 1, 2, 5, and 6 all possess coordinatively unsaturated square planar M0 centers that are reactive: (1) 2 reacts with PhICl2 to produce Ir2II,II(tfepma)2(CNtBu)2Cl4 (7); (2) protonation of 2 with HX yields Ir2II,II(tfepma)2(CNtBu)2Cl2HX [X = Cl- (8), OTs- (9)]; (3) protonation of 5 with HOTs produces [Rh2I,I(tfepma)2(CNtBu)3(μ-H)](OTs); and (4) the reversible hydrogenation of 2 proceeds smoothly, furnishing the cis-dihydride complex Ir2II,II(tfepma)2(CNtBu)2(H)2Cl2 (11). Substitution of tfepma in 2 with bis(diphenylphsophino)methane (dppm) yields the orthometalated complex Ir2II,II(dppm)(PPh(o-C6H4)CH2PPh2)(CNtBu)2Cl2H (12). The X-ray crystal structures of 11 compounds are presented and discussed, and spectroscopic characterization by multinuclear and variable temperature NMR provides details about solution structures and in some cases the formation of isomeric products. The electronic spectra of the new complexes are also described briefly, with absorption and emission features derived from the bimetallic core. [ABSTRACT FROM AUTHOR]

The article discusses a study on solar energy supply for the legacy and nonlegacy worlds for an estimated 9.4 billion people by the year 2050. It states that delivering an additional 16 terawatts (TW) is difficult because biomass, nuclear energy, wind energy and other energy sources are insufficient for the increasing global energy consumption. The study noted that sunlight is the preeminent carbon-neutral energy source and that delivering personalized solar energy provides a solution for the world's future energy supply.

The key intermediate in dinitrogen cleavage by Mo(N[t-Bu]Ar)3, 1 (Ar = 3,5-C6H3Me2), has been characterized by a pair of single crystal X-ray structures. For the first time, the X-ray crystal structure of (μ-N2)[Mo(N[t-Bu]Ar)3]2, 2, and the product of homolytic fragmentation of the NN bond, NMo(N[t-Bu]Ar)3, are reported. The structural features of 2 are compared with previously reported EXAFS data. Moreover, contrasts are drawn between theoretical predictions concerning the structural and magnetic properties of 2 and those reported herein. In particular, it is shown that 2 exists as a triplet (S = 1) at 20 °C. Further insight into the bonding across the MoNNMo core of the molecule is obtained by the synthesis and structural characterization of the one- and two-electron oxidized congeners, (μ-N2)[Mo(N[t-Bu]Ar)3]2[B(ArF)4], 2[B(ArF)4] (ArF = 3,5-C6H3(CF3)2) and (μ-N2)[Mo(N[t-Bu]Ar)3]2[B(ArF)4]2, 2[B(ArF)4]2, respectively. Bonding in these three molecules is discussed in view of X-ray crystallography, Raman spectroscopy, electronic absorption spectroscopy, and density functional theory. Combining X-ray crystallography data with Raman spectroscopy studies allows the NN bond polarization energy and N-N internuclear distance to be correlated in three states of charge across the MoNNMo core. For 2[B(ArF)4], bonding is symmetric about the μ-N2 ligand and the NN polarization is Raman active; therefore, 2[B(ArF)4] meets the criteria of a Robin-Day class Ill mixed-valent compound. The redox couples that interrelate 2, 2+, and 22+ are studied by cyclic voltammetry and spectroelectrochemistry. Insights into the electronic structure of 2 led to the discovery of a photochemical reaction that forms NMo(N[t-Bu]Ar)3 and Mo(N[t-Bu]Ar)3 through competing NN bond cleavage and N2 extrusion reaction pathways. The primary quantum yield was determined to be Φp = 0.05, and transient absorption experiments show that the photochemical reaction is complete in less than 10 ns. [ABSTRACT FROM AUTHOR]

Review: 93 refs. [ABSTRACT FROM AUTHOR]

The article offers information on a research conducted in order to determine chlorine photoelimination. The research has revealed that photolysis of a Pt2 with ultraviolet (UV) or visible light in the solid state yields chlorine. The research has also revealed energy storage reactivity in the absence of a halogen trap.

Review: 367 refs. [ABSTRACT FROM AUTHOR]

The article describes the preparation and characterization of the first PtAu compound. According to the authors, the d7-d9 complex exhibits a facile two-electron chemically assisted halogen photoelimination that is promoted by visible light. They add the electronic absorption spectrum of platinum compound features a dominant band centered at 338 nm.

Energy-relevant small molecule activations and related processes are often multi-electron in nature. Ferrocene is iconic for its well-behaved one-electron chemistry, and it is often used to impart redox activity to self-assembled architectures. When multiple ferrocenes are present as pendant groups in a single structure, they often behave as isolated sites with no separation of their redox events. Herein, we study a suite of molecules culminating in a self-assembled palladium(II) truncated tetrahedron (TT) with six pendant ferrocene moieties using the iron(III/II) couple to inform about the electronic structure and, in some cases, subsequent reactivity. Notably, although known ferrocene-containing metallacycles and cages show simple reversible redox chemistry, this TT undergoes a complex multi-step electrochemical mechanism upon oxidation. The electrochemical behavior was observed by voltammetric and spectroelectrochemical techniques and suggests that the initial Fc-centered oxidation is coupled to a subsequent change in species solubility and deposition of a film onto the working electrode, which is followed by a second separable electrochemical oxidation event. The complicated electrochemical behavior of this self-assembly reveals emergent properties resulting from organizing multiple ferrocene subunits into a discrete structure. We anticipate that such structures may provide the basis for multiple charge separation events to drive important processes related to energy capture, storage, and use, especially as the electronic communication between sites is further tuned. [ABSTRACT FROM AUTHOR]

The chemistry of zirconium-based metal-organic polyhedra (ZrMOPs) is often limited by their poor solubilities. Despite their attractive features—including high yielding and facile syntheses, predictable topologies, high stability, and tunability—problematic solubilities have caused ZrMOPs to be under-studied and under-applied. Although these cages have been synthesized with a wide variety of carboxylate-based bridging ligands, we explored a new method for ZrMOP functionalization via node-modification, which we hypothesized could influence solubility. Herein, we report ZrMOPs with benzyl-, vinylbenzyl-, and trifluoromethylbenzyl-pendant groups decorating cyclopentadienyl moieties. The series was characterized by 1H/19F NMR, high-resolution mass spectrometry, infrared spectroscopy, and single-crystal X-ray diffraction. The effects of node functionalities on ZrMOP solubility were quantified using inductively coupled plasma mass spectrometry. Substitution caused a decrease in water solubility, but for certain organic solvents, e.g. DMF, solubility could be enhanced by ∼20×, from 16 μM for the unfunctionalized cage to 310 μM for the vinylbenzyl- and trifluoromethylbenzyl-cages. [ABSTRACT FROM AUTHOR]

We report the electrocatalytic Oxygen Reduction Reaction on a rigid Co(II) porphyrin prism scaffold bridged by Ag(I) ions. The reactivity of this scaffold differs significantly from previous prism catalysts in that its selectivity is similar to that of monomer (∼35% H2O) yet it displays sluggish kinetics, with an order of magnitude lower ks of ∼0.5 M−1 s−1. The deleterious cofacial effect is not simply due to metal–metal separation, which is similar to our most selective prism catalysts. Instead we conclude the structural rigidity is responsible for these differences. [ABSTRACT FROM AUTHOR]

Herein we report the first study of the oxygen reduction reaction (ORR) catalyzed by a cofacial porphyrin scaffold accessed in high yield (overall 53%) using coordination-driven self-assembly with no chromatographic purification steps. The ORR activity was investigated using chemical and electrochemical techniques on monomeric cobalt(II) tetra(meso-4-pyridyl)porphyrinate (CoTPyP) and its cofacial analogue [Ru8(η6-iPrC6H4Me)8(dhbq)4(CoTPyP)2][OTf]8 (Co Prism) (dhbq = 2,5-dihydroxy-1,4-benzoquinato, OTf = triflate) as homogeneous oxygen reduction catalysts. Co Prism is obtained in one self-assembly step that organizes six total building blocks, two CoTPyP units and four arene-Ru clips, into a cofacial motif previously demonstrated with free-base, Zn(II), and Ni(II) porphyrins. Turnover frequencies (TOFs) from chemical reduction (66 vs 6 h-1) and rate constants of overall homogeneous catalysis (kobs) determined from rotating ring-disk experiments (1.1 vs 0.05 h-1) establish a cofacial enhancement upon comparison of the activities of Co Prism and CoTPyP, respectively. Cyclic voltammetry was used to initially probe the electrochemical catalytic behavior. Rotating ring-disk electrode studies were completed to probe the Faradaic efficiency and obtain an estimate of the rate constant associated with the ORR. [ABSTRACT FROM AUTHOR]

Review: 964 refs. [ABSTRACT FROM AUTHOR]

Herein, we describe the synthesis of tetraphenyl -ethylene (TPE)-based di-Pt(ll) acceptors as shown by X-ray analysis, which are subsequently used to construct pure TPE-based 2D hexagonal metallacycles and 3D drumlike metallacages with three different counteranions via coordination-driven self-assembly.The metallacycles possess alternating TPE donor and acceptor 6 units that arrange 12 pendant phenyl rings along the outer perimeter that provide the basis for the observed aggregation induced emission (ALE) behavior. The metallacages are similarly 2 constructed from TPE-based building blocks, specifically two donors and four acceptors, resulting in eight freely rotating phenyl rings decorating the prismatic core. The fluorescence of these cages in dilute solution is intensified when hexane is added to CH2C12 solutions, indicative of aggregation-induced enhanced emission (ALEE). The influence of the counteranions on the photophysics of the assemblies was investigated. The molar absorption coefficients (ε), fluorescence emission intensities, and quantum yield (ΦF) values of the SCCs with different counteranions in CH2C12 follow the order PF6- > OTf- > N03-. The same trend also applies to the AIE characteristics of the SCCs in the aggregated state. The metal-organic materials developed here not only enrich a newly emerging library of self-assembly AIE metallacycles and cages that are promising candidates for turn-on fluorescent sensors and advanced optical devices but also provide an understanding of how structural factors affect the photophysics of AIE-active SCCs. [ABSTRACT FROM AUTHOR]

Here we present a method for the construction of functionalizable supramolecular polymers by controlling three orthogonal interactions within a single system: (i) coordination-driven self-assembly; (ii) H-bonding; and (iii) host--guest interactions between crown ether and dialkylammonium substrates. Three unique molecules constitute the supramolecular construct, including a 2-ureido-4-pyrimidinone (UPy)-functionalized rigid dipyridyl donor and a complementary organo-platinum(II) acceptor decorated with a crown ether moiety that provide the basis for self-assembly and polymerization. The final host--guest interaction is demonstrated by using one of two dialkylammonium molecules containing fluorophores that bind to the benzo-21-crown-7 (B21C7) groups of the acceptors, providing a spectroscopic handle to evaluate the functionalization. An initial coordination-driven self-assembly yields hexagonal metallacycles with alternating UPy and B21C7 groups at their vertices. The assembly does not interfere with H-bonding between the UPy groups, which link the discrete metallacycles into a supramolecular network, leaving the B21C7 groups free for functionalization via host--guest chemistry. The resultant network results in a cavity-cored metallogel at high concentrations or upon solvent swelling. The light-emitting properties of the dialkylammonium substrates were transferred to the network upon host-guest binding. This method is compatible with any dialkylammonium substrate that does not disrupt coordination nor H-bonding, and thus, the unification of these three orthogonal interactions represents a simple yet highly efficient strategy to obtain supramolecular polymeric materials with desirable functionality. [ABSTRACT FROM AUTHOR]

Coordination-drivenself-assembly can be used to construct metallacyclesdecorated with saccharide functionalities by combining organoplatinumacceptor building blocks with glycosylated dipyridyl donors. We describehere the synthesis of a suite of donors encoded with 120° directionality.The 1,3-bis(pyridin-4-ylethynyl)benzene cores contain one of fourpendant saccharide groups, resulting in a glucose-, galactose-, mannose-,and lactose-variant. The angularity of these donors makes them suitablefor the self-assembly of [2 + 2] rhomboids and [3 + 3] hexagons containingtwo and three saccharide groups on combination with a 60 or 120°acceptor, respectively. The synthesis and characterization of eightsuch metallacycles are described, supported by multinuclear NMR andelectrospray mass spectrometry data that confirm clean, highly symmetricproducts with the expected stoichiometries of formation. This workillustrates the use of coordination-driven self-assembly to obtainnanoscopic metallacycles with biologically relevant functionalitiesin high yields and facile synthetic methods. [ABSTRACT FROM AUTHOR]

Control over structural transformations in supramolecular entities by external stimuli is critical for the development of adaptable and functional soft materials. Herein, we have designed and synthesized a dipyridyl donor containing a central Z-configured stiff-stilbene unit that self-assembles in the presence of two 180° di-Pt(ll) acceptors to produce size-controllable discrete organoplatinum(ll) metallacycles with high efficiency by means of the directional-bonding approach. These discrete metallacycles undergo transformation into extended metallosupramolecular polymers upon the conformational switching of the dipyridyl ligand from Z-config-ured (0°) to E-configured (180°) when photoirradiated. This transformation is accompanied by interesting morphological changes at nanoscopic length scales. The discrete metallacycles aggregate to spherical nanoparticles that evolve into long nanofibers upon polymer formation. These fibers can be reversibly converted to cyclic oligomers by changing the wavelength of irradiation, which reintroduces Z-configured building blocks owing to the reversible nature of stiff-stilbene photoisomerization. The design strategy defined here represents a novel self-assembly pathway to deliver advanced supramolecular assemblies by means of photocontrol. [ABSTRACT FROM AUTHOR]

We describe the efficient preparation of rhomboidal metallacycles that self-assemble upon mixing a donor decorated with 2-ureido-4-pyrimidinone (UPy) with acceptors containing pendant [G1]-[G3] dendrons. The formed rhomboids subsequently polymerize into dendronized organoplatinum(II) metallacyclic polymers through H-bonding UPy interfaces, which possess the structural features of conventional dendronized polymers as well as the dynamic reversibility of supramolecular polymers. Preservation of both properties in a single material is achieved by exploiting hierarchical self-assembly, namely the unification of coordination-driven self-assembly with H-bonding, which provides facile routes to dendronized metallacycles and subsequent high ordering. The supramolecular polymerization defined here represents a novel method to deliver architecturally complex and ordered polymeric materials with adaptive properties. [ABSTRACT FROM AUTHOR]

Metallacyclic cores provide a scaffold upon which pendant functionalities can be organized to direct the formation of dimensionally controllable nanostructures. Because of the modularity of coordination-driven self-assembly, the properties of a given supramolecular core can be readily tuned, which has a significant effect on the resulting nanostructured material. Herein we report the efficient preparation of two amphiphilic rhomboids that can subsequently order into 0D micelles, 1D nanofibers, or 2D nanoribbons. This structural diversity is enforced by three parameters: the nature of the hydrophilic moieties decorating the parent rhomboids, the concentration of precursors during self-assembly, and the reaction duration. These nanoscopic constructs further interact to generate metallohydrogels at high concentrations, driven by intermolecular hydrophobic and π-π interactions, demonstrating the utility of coordinationdriven self-assembly as a first-order structural element for the hierarchical design of functional soft materials. [ABSTRACT FROM AUTHOR]

Supramolecular coordination complexes (SCCs) have been proposed for applications necessitating photon emitting properties; however, two critical characteristics, facile tunability and high emission quantum yields, have yet to be demonstrated on SCC platforms. Herein, a series of functionalized D2h [D2A2] rhomboids (D = 2,6-bis(4-ethynylpyridine)aniline-based ligands; A = 2,9-bis[trans-Pt(PEt3)2NO3]phenanthrene) is described with emission wavelengths spanning the visible region (Λmax = 476-581 nm). Tuning was achieved by simple functional group modifications para to the aniline amine on the donor building block. Steady-state absorption and emission profiles were obtained for each system and are discussed. When the Hammett spara constants for the functional groups σpara to the aniline amine were plotted versus the wavenumber (cm-1) for the Λmax of the emission profile, a linear relationship was observed. By utilizing this relationship, the emission wavelength of a given rhomboid can be predetermined on the basis of the Hammett constant of the functionality employed on the donor precursor. This range of visible light emission for a suite of simple rhomboids along with the predictive nature of the wavelength of emission is unprecedented for these types of systems. [ABSTRACT FROM AUTHOR]

In this work, spectroscopic techniques and quantum chemistry calculations were used to investigate the photophysical properties of various multinuclear platinum complexes with different conformational geometries. This suite of complexes includes a Pt–pyridyl square, a Pt–carboxylate triangle, and a mixed Pt–pyridyl–carboxylate rectangle, as well as two mononuclear Pt model complexes. Studying the individual molecular precursors in the context of larger assemblies is important to provide a complete understanding of the factors governing the observed photophysical properties of a given system. The absorption and emission bands of the parent linear dipyridyl donor (ligand 1) are largely preserved in the [4 + 4] square and the multicomponent [4 + 2 + 2] rectangle (3 and 4, respectively), with significant red shifts. The [3 + 3] Pt–carboxylate triangle containing p-phthalic acid is nonemissive. Phosphorescence and nanosecond transient spectroscopy on 3 and 4 reveal that the introduction of platinum atoms enhances spin–orbital coupling, thereby increasing the rate of intersystem crossing. This phenomenon is consistent with the low fluorescence quantum yields and short fluorescence lifetimes of 3 and 4. Moreover, the electronic structures for the ground state and low-lying excited states of these compounds were studied using quantum chemistry calculations. The fluorescent states of the platinum complexes are local excited states of ligand-centered π-π* transition features, whereas the nonfluorescent states are intramolecular charge-transfer states. These low-lying intramolecular charge-transfer states are responsible for the nonemissive nature of small molecules 1 and 2 and triangle 5. As the interactions between these components determine the properties of their corresponding assemblies, we establish novel excited-state decay mechanisms which dictate the observed spectra. [ABSTRACT FROM AUTHOR]

We describe the formation of a suite of [3]catenanes via multicomponent coordination-driven self-assembly and host–guest complexation of a rectangular scaffold comprising a 90° Pt-based acceptor building block with a pseudorotaxane bis(pyridinium)ethane/dibenzo-24-crown-8 linear dipyridyl ligand and three dicarboxylate donors. The doubly threaded [3]catenanes are formed from a total of 10 molecular components from four unique species. Furthermore, the dynamic catenation process is reversible and can be switched off and on in a controllable manner by successive addition of KPF6 and 18-crown-6, as monitored by 1H and 31P NMR spectroscopy. [ABSTRACT FROM AUTHOR]

The 90° and 60° bimetallic platinum complexeswith specialstructures are widely used in coordination-driven self-assembled metallosupramoleculararchitectures, and these complexes are the key components of triangular,rectangular, and polygonal metallacycle and metallocage supramolecules.Therefore, spectroscopic techniques and quantum chemistry calculationswere employed in this article to investigate the photophysical propertiesof these bimetallic platinum complexes. Compared with spectra forthe ligands, the absorption spectra of these Pt complexes are red-shifted,and the fluorescence spectra become wider and are also red-shifted.Moreover, the reasons for the low fluorescence quantum yields andshort fluorescence lifetimes of these compounds were investigatedusing quantum chemistry calculations. We demonstrate that the fluorescentstates of the bimetallic platinum complexes can be considered as localexcited states, and that they possess a ligand-centered π–π*transition feature. Meanwhile, the platinum metals act as perturbationfor these transitions, whereas the nonfluorescent states are classifiedas intramolecular charge-transfer states. Furthermore, a new fluorescencemodulation mechanism is developed to explain the different emissionprocesses of these complexes with different ligands. [ABSTRACT FROM AUTHOR]

A novel, interlocked, self-assembled (M2L2)2 molecular architecture was constructed from an arene-Ru acceptor and a 1,4-di(pyridin-4-yl)buta-1,3-diyne donor. Two M2L2 units, with cavities of ∼7.21 Å, spontaneously interlock, with one unit encapsulating a twin in a non-catenane fashion. The dimeric host-guest complex thus formed is unique among two-dimensional self-assemblies and is stabilized by π-π interactions between the M2L2 units. [ABSTRACT FROM AUTHOR]

A new approach for the construction of functionalized metallosupramolecular tetragonal prisms via multicomponent, coordination-driven, template-free self-assembly is described. The combination of tetra-(4-pyridylphenyl)ethylene, a 90° Pt(II) acceptor, and ditopic bipyridine or carboxylate ligands functionalized with hydroxyl or amine groups, hydrophobic alkyl chains, or electrochemically active ferrocene, yields a suite of seven self-assembled tetragonal prisms under mild conditions. These three-dimensional metallosupramolecules were characterized by multinuclear NMR (31P and ¹H) and mass spectrometry. Their shapes and sizes were established using Merck Molecular Force Field (MMFF) simulations. In addition, their approximate sizes were further supported by pulsed-field-gradient spin-echo (PGSE) NMR experiments. [ABSTRACT FROM AUTHOR]

Among the many challenges in medicine, the treatment and cure of cancer remains an outstanding goal given the complexity and diversity of the disease. Nanotheranostics, the integration of therapy and diagnosis in nanoformulations, is the next generation of personalized medicine to meet the challenges in precise cancer diagnosis, rational management and effective therapy, aiming to significantly increase the survival rate and improve the life quality of cancer patients. Different from most conventional platforms with unsatisfactory theranostic capabilities, supramolecular cancer nanotheranostics have unparalleled advantages in early-stage diagnosis and personal therapy, showing promising potential in clinical translations and applications. In this review, we summarize the progress of supramolecular cancer nanotheranostics and provide guidance for designing new targeted supramolecular theranostic agents. Based on extensive state-of-the-art research, our review will provide the existing and new researchers a foundation from which to advance supramolecular cancer nanotheranostics and promote translationally clinical applications. [ABSTRACT FROM AUTHOR]

A series of new polymer-inorganic composites has been synthesized from poly(amic acid) (PAA) and various M-MOF-74 (M = Mg, Mn, Co, Ni, Zn) frameworks using a postsynthetic ligand exchange strategy, wherein ligand moieties built into the PAA backbone are exchanged with MOF-bound ligands. The reaction is monitored by UV-vis spectroscopy in order to compare exchange rates for different metal ions, and the resulting composites are characterized by powder X-ray diffraction and scanning electron microscopy. This method of polymer-ligand exchange (PLE) hybridization has only been previously demonstrated using Zn2+-carboxylate and Zn2+-imidazolate frameworks; therefore, this work further reveals the versatility of PLE by showing that exchange is possible for several additional metal ions, as well as frameworks containing 2,5-dihydroxyterephthalate ligands. [ABSTRACT FROM AUTHOR]

Abstract: We report a suite of coordination‐driven self‐assembled prisms for heterogeneous electrocatalytic oxygen reduction (ORR) differing in the molecular clips linking two porphyrin faces in a cofacial arrangement. ORR activities and selectivities of monomeric CoTPyP along with cofacial prisms Ox‐Co, Oxa‐Co, and Benzo‐Co were probed using cyclic voltammetry and rotating ring‐disk techniques. All species were immobilized as heterogeneous catalysts on glassy carbon electrodes using a Nafion ink method. The selectivities of Ox‐Co, Oxa‐Co, and Benzo‐Co prisms towards H2O as determined by RRDE were 87, 97, and 75 %, respectively. The current density of the Oxa‐Co plateaus at five times that of Pt/C when normalized per Co/Pt. The high synthetic yield (79 %), competitive overpotential (η ≈800 mV) and high selectivity (%H2O ≈97 %) of the Oxa‐Co highlights how self‐assembly can be used to address multi‐electron multi‐proton transformations using polynuclear catalysts. [ABSTRACT FROM AUTHOR]

Discrete metal–organic polyhedra (MOPs) containing copper(ii), palladium(ii), and iron(ii) nodes were synthesized as fillers for mixed-matrix materials (MMMs) with a polyvinylidine fluoride (PVDF) polymer phase and contrasted against an MMM containing a metal–organic framework, MOF-5. When a given MOP was soluble in the precursor solutions, the resulting MMMs were thin, flexible, and homogeneous based on microscopy and SEM imaging. Analogous MMM formation using either insoluble MOPs or the inherent insoluble MOF-5 showed a higher degree of phase separation and inhomogeneity. Even when a MOP was not fully soluble, a significant particle size decrease was observed in contrast to the MOF-5 materials wherein the crystallites remained largely intact. This is a consequence of solubilizing the MOP fillers into the polymer solvent. The crystallinity and thermal stabilities of the MMMs were compared to pure PVDF using powder X-ray diffraction, and differential scanning calorimetry, indicating that the incorporation of MOPs both decreased overall crystallinity as well as increased thermal stability. In addition, MMMs containing PdMOP and FeMOP showed improved gas permeabilities relative to pure PVDF for H2, N2, CH4, and CO2, with the 10 wt% FeMOP membrane more selective for CO2 over N2 and H2. [ABSTRACT FROM AUTHOR]

Light-emitting supramolecular coordination complexes (SCCs) have been widely studied for applications in the chemical and biological sciences. Herein, we report the coordination-driven self-assembly of two highly emissive platinum(II) supramolecular triangles (1 and 2) containing BODIPY-based bridging ligands. The metallacycles exhibit favorable anticancer activities against HeLa cells (IC50 of 6.41 and 2.11 µM). The characteristic ~570 nm fluorescence of the boron dipyrromethene (BODIPY) moieties in the metallacycles permits their intracellular visualization using confocal microscopy. Additionally, the BODIPY fluorophore is an excellent photodynamic agent, making the metallacycles as ideal therapeutics for photodynamic therapy (PDT) and chemotherapy. In vitro studies demonstrate that the combination indexes against HeLa cells are 0.56 and 0.48 for 1 and 2, respectively, confirming their synergistic anticancer effect. More importantly, these SCCs also exhibit superior anticancer efficacy toward cisplatin-resistant A2780cis cell line by combining PDT and chemotherapy, showing promise in overcoming drug resistance. This study exploits a multicomponent approach to self-assembled metallacages that enables design of effective theranostic agents wherein the platinum acceptors are toxic chemotherapeutics and the BODIPY donors are imaging probes and photosensitizers. Since each piece may be independently tuned, i.e., Pt(II) polypyridyl fragment swapped for Pt(II) phosphine, the activity may be optimized without a total redesign of the system. [ABSTRACT FROM AUTHOR]

A reversible Fe3+/Fe2+ redox couple of an azamacrocyclic complex is evaluated as an electrolyte with a pH-tunable potential range for aqueous redox-flow batteries (RFBs). The FeIII complex is formed by 1,4,7-triazacyclononane (TACN) appended with three 2-methyl-imidazole donors, denoted as Fe(Tim). This complex exhibits pH-sensitive redox couples that span E1/2(Fe3+/Fe2+)=317 to −270 mV vs. NHE at pH 3.3 and pH 12.8, respectively. The 590 mV shift in potential and kinetic inertness are driven by ionization of the imidazoles at various pH values. The Fe3+/Fe2+ redox is proton-coupled at alkaline conditions, and bulk electrolysis is non-destructive. The electrolyte demonstrates high charge/discharge capacities at both acidic and alkaline conditions throughout 100 cycles. Given its tunable redox, fast electrochemical kinetics, exceptional stability/cyclability, this complex is promising for the design of aqueous RFB catholytes and anolytes that utilize the earth-abundant element iron. [ABSTRACT FROM AUTHOR]

The coordination of a bis(dipyrrin) ligand (LH2) to Re(CO)5Cl delivers a dirhenium salt that serves as a precursor to a dinuclear phosphine compound or as a component of a metallacycle when combined with 4,4'-bipyridine (bpy) to furnish a tetranuclear [{(CO)3Re}4L2(bpy)2] complex. The distorted nature of the metallacycle was determined by single-crystal X ray diffraction revealing that the Re-bpy-Re edges are twisted by approximately 119° and the Re-L-Re edges are twisted by approximately 88° from the idealized rectangular plane. The ReI metallacycle exhibits luminescence (λfluo. = 592 nm; λphos. = 731 nm) in CH2Cl2 at 77 K. [ABSTRACT FROM AUTHOR]

The emission of platinum-alkynyl complexes with terminal pyridyl moieties changes upon simple alkylation reactions. Due to growing interest in photovoltaics, photocatalysis, and light-emitting devices, understanding the nature of these changes is important to develop simple synthetic pathways for the rational design of photophysically active molecules. Herein, the choice of ligand isomer, methylation, and Pt-coordination environment on phosphorescent quantum yields, lifetimes, and associated radiative and non-radiative rate constants of eight organometallic complexes were studied. Single-crystal X-ray diffraction experiments and computational studies provide evidence for stabilization of metallo-cumulene resonance forms whose increased rigidities manifest in the observed photophysical changes. This effect is more pronounced for 4-ethynylpyridyl complexes over 3-ethynylpyridyl variants since the metallo-cumulene form shifts electron density to the electronegative N-atom at the para site. Furthermore, the use of σ-donating N-heterocyclic carbenes to complete the Pt-coordination environment enhanced the quantum yield of phosphorescence as high as 39% (λmax = 512 nm) with a lifetime of 21.2 μs. [ABSTRACT FROM AUTHOR]

The quantum yields of organic fluorophores used as donors in coordination-driven self-assembly often suffer from the heavy atom effect of nearby metal sites. Here, the role of intersystem crossing from a deactivating process to one that delivers emissive triplet states was reversed. A phosphorescent trans bis- N-heterocyclic carbene platinum(II) compound, Pt(dhim)2(C≡C-4-py)2 ( D1; dhim=1,3-dihexyl-2-H-imidazol-2-ylidene), was used along with other linear donors 4,4′-bipyridine ( D2) and 1,4-bis(4-pyridyl ethynyl)benzene ( D3) in self-assembly reactions with Pt(dtbpy)X2 acceptors (dtbpy=4,4′-di-tert-butyl-2,2′-bipyridine) to afford three metallacycles. Photophysical investigations revealed that, although the building blocks used to construct M1 have relatively low quantum yields ( Φ=1.2 and <1 % for D1 and 2, respectively), the metallacycle has a quantum yield of 14 %. This increase reflects a change in radiative rate constant from 3.6×104 s−1 for D1 to 2.1×105 s−1 for M1. [ABSTRACT FROM AUTHOR]

A theranostic agent combines diagnostic reporter with therapeutic activity in a single entity, an approach that seeks to increase the efficacy of cancer treatment. Herein, we describe the synthesis of a highly emissive tetraphenylethene-based metallacage using multicomponent coordination-driven self-assembly that exhibits a coordination-triggered aggregation-induced emission (AIE) enhancement. The formation of metallacage-loaded nanoparticles (MNPs) occurs when the assembly is treated with two variants of a 1,2-distearoyl-phosphatidylethanolamine (DSPE)/polyethylene glycol (PEG) conjugate, mPEG-DSPE, and biotin-PEG-DSPE. This combination endows the resultant MNPs with excellent stability and targeting ability, specifically enabling selective delivery of the metallacages to cancer cells that overexpress biotin receptors via receptor- mediated endocytosis. Although the mechanism of activity is based on existing Pt(II) anticancer drugs such as oxaliplatin, carboplatin, and cisplatin, in vitro and in vivo studies indicate that the MNPs are more active and show low systemic activity while also possessing emissive properties that allow for fluorescence-based imaging. This pioneering example of a metallacage that combines biologically active components with AIE imaging establishes supramolecular coordination complexes imbedded within nanoparticles as a promising potential theranostic platform for cancer treatment. [ABSTRACT FROM AUTHOR]

[Display omitted] • A pioneering example of incorporating [CB 11 H 12 ]- into Platinum triplet emitters. • Anionic [CB 11 H 12 ]- enforced the charge neutrality of cationic Platinum emitter. • Anionic [CB 11 H 12 ]- optimized the Platinum emitter PLQY from 54% to 97%. • OLEDs exhibited green electroluminescence with CIE coordinates of (0.28, 0.55). • OLEDs exhibited the maximum external quantum efficiency (EQE max) of 18.51%. The use of organometallic triplet emitters in OLED applications may be complicated when the luminescent complex bears a formal charge. By designing ligands containing pendant closo -monocarborane clusters [CB 11 H 11 ]−, it is possible to neutralize the otherwise cationic cores of cyclometalated Pt(II) complexes bearing bis -carbenes, resulting in significantly enhanced photophysical properties. Herein, we report four Pt(II) complexes decorated with a monoanionic closo -monocarborane by coupling the cluster to the classic cyclometallating moiety, phenylpyridine (ppy). All four complexes were fully characterized by NMR, HR-MS, UV–Vis, and cyclic voltammetry. Complexes 1b , 1c and 2a were characterized by single-crystal X-ray diffraction. Moreover, all four complexes show interesting photophysical behaviors, with complex 1a exhibiting a photoluminescent quantum yield of 97% in a 2 wt% PMMA film. This high efficiency prompted the incorporation of 1a and 1c into an OLED device using solution processing, resulting in green emission with CIE coordinates of (0.28, 0.55) for 1a and yellow emission with CIE coordinates of (0.44, 0.50) for 1c. The measured maximum external quantum efficiency (EQE max) was 18.51% for 1a , an EQE max that is among the highest for solution-processed OLED devices containing Pt(II) complexes with simple cyclometalated ppy ligands. [ABSTRACT FROM AUTHOR]