Tailoring Large Pores of Porphyrin Networks on Ag(111) by Metal–Organic Coordination

The engineering of nanoarchitectures to achieve tailored properties relevant for macroscopic devices is a key motivation of organometallic surface science. To this end, understanding the role of molecular functionalities in structure formation and adatom coordination is of great importance. In this study, the differences in formation of Cu‐mediated metal–organic coordination networks based on two pyridyl‐ and cyano‐bearing free‐base porphyrins on Ag(111) are elucidated by use of low‐temperature scanning tunneling microscopy (STM). Distinct coordination networks evolve via different pathways upon codeposition of Cu adatoms. The cyano‐terminated module directly forms 2D porous networks featuring fourfold‐coordinated Cu nodes. By contrast, the pyridyl species engage in twofold coordination with Cu and a fully reticulated 2D network featuring a pore size exceeding 3 nm² only evolves via an intermediate structure based on 1D coordination chains. The STM data and complementary Monte Carlo simulations reveal that these distinct network architectures originate from spatial constraints at the coordination centers. Cu adatoms are also shown to form two‐ and fourfold monoatomic coordination nodes with monotopic nitrogen‐terminated linkers on the very same metal substrate—a versatility that is not achieved by other 3d transition metal centers but consistent with 3D coordination chemistry. This study discloses how specific molecular functionalities can be applied to tailor coordination architectures and highlights the potential of Cu as coordination center in such low‐dimensional structures on surfaces.     

Porous Coordination Polymers of Diverse Topologies Based on a Twisted Tetrapyridylbiaryl: Application as Nucleophilic Catalysts for Acetylation of Phenols

Porous coordination polymers (CPs) with partially uncoordinated pyridyl rings based on rationally designed polypyridyl linkers are appealing from the point of view of their application as nucleophilic catalysts. A D_2d‐symmetric tetradentate organic linker L , that is, 2,2′,6,6′‐tetramethoxy‐3,3′,5,5′‐tetrakis(4‐pyridyl)biphenyl, was designed and synthesized for metal‐assisted self‐assembly aimed at porous CPs. Depending on the nature of the metal ion and the counter anion, the ligand L is found to function as a 3‐ or 4‐connecting building block leading to porous CPs of diverse topologies. The reaction of L with Zn(NO₃)₂ and Cd(NO₃)₂ yields porous 2 D CPs of “ fes ” topology, in which the tetrapyridyl linker L serves as a 3‐connecting unit with its free pyridyl rings well exposed into the pores. The functional utility of these porous CPs containing uncoordinated pyridyl rings is demonstrated by employing them as efficient heterogeneous nucleophilic catalysts for acetylation of a number of phenols with varying electronic properties and reactivities.     

Design,Synthesis, and X‐Ray Crystal Structure of a Fullerene‐Linked Metal–Organic Framework

Given the unique structural and electronic properties of C₆₀, metal–organic frameworks (MOFs) containing C₆₀ linkers are expected to exhibit interesting characteristics. A new hexakisfullerene derivative possessing two pairs of phenyl pyridine groups attached to two methano‐carbon atoms located at the trans‐1 positions was designed and synthesized. The four pyridyl nitrogen atoms define a perfectly planar rectangle. This new C₆₀ derivative was used to assemble the first fullerene‐linked two‐dimensional MOF by coordination with Cd²⁺.     

Framework Cationization by Preemptive Coordination of Open Metal Sites for Anion‐Exchange Encapsulation of Nucleotides and Coenzymes

Cationic frameworks can selectively trap anions through ion exchange, and have applications in ion chromatography and drug delivery. However, cationic frameworks are much rarer than anionic or neutral ones. Herein, we propose a concept, preemptive coordination (PC), for targeting positively charged metal–organic frameworks (P‐MOFs). PC refers to proactive blocking of metal coordination sites to preclude their occupation by neutralizing ligands such as OH^?. We use 20 MOFs to show that this PC concept is an effective approach for developing P‐MOFs whose high stability, porosity, and anion‐exchange capability allow immobilization of anionic nucleotides and coenzymes, in addition to charge‐ and size‐selective capture or separation of organic dyes. The CO₂ and C₂H₂ uptake capacity of 117.9 cm³ g^?1 and 148.5 cm³ g^?1, respectively, at 273 K and 1 atm, is exceptionally high among cationic framework materials.     

Interpenetrated Cage Structures

This Review covers design strategies, synthetic challenges, host–guest chemistry, and functional properties of interlocked supramolecular cages. Some dynamic covalent organic structures are discussed, as are selected examples of interpenetration in metal–organic frameworks, but the main focus is on discrete coordination architectures, that is, metal‐mediated dimers. Factors leading to interpenetration, such as geometry, flexibility and chemical makeup of the ligands, coordination environment, solvent effects, and selection of suitable counter anions and guest molecules, are discussed. In particular, banana‐shaped bis‐pyridyl ligands together with square‐planar metal cations have proven to be suitable building blocks for the construction of interpenetrated double‐cages obeying the formula [M₄L₈]. The peculiar topology of these double‐cages results in a linear arrangement of three mechanically coupled pockets. This allows for the implementation of interesting guest encapsulation effects such as allosteric binding and template‐controlled selectivity. In stimuli‐responsive systems, anionic triggers can toggle the binding of neutral guests or even induce complete structural conversions. The increasing structural and functional complexity in this class of self‐assembled hosts promises the construction of intelligent receptors, novel catalytic systems, and functional materials.     

Design,Synthesis, and X‐Ray Crystal Structure of a Fullerene‐Linked Metal–Organic Framework

Given the unique structural and electronic properties of C₆₀, metal–organic frameworks (MOFs) containing C₆₀ linkers are expected to exhibit interesting characteristics. A new hexakisfullerene derivative possessing two pairs of phenyl pyridine groups attached to two methano‐carbon atoms located at the trans‐1 positions was designed and synthesized. The four pyridyl nitrogen atoms define a perfectly planar rectangle. This new C₆₀ derivative was used to assemble the first fullerene‐linked two‐dimensional MOF by coordination with Cd²⁺.     

Interconversion of Highly Entangled Polyhedra into Concave Polyhedra by Nitrate-Induced Ternary Coordination

Entangled (M₃L₂)_n polyhedral complexes represent a unique class of supramolecular architectures that are stabilized by relatively weak metal–acetylene interactions in cooperation with conventional metal–pyridyl coordination. Counter-anion exchange of these complexes with a nitrate (NO₃⁻) ion triggered formal metal insertion between the metal centers, and a heteroleptic ternary coordination mode with acetylenic, pyridyl, and nitrate donors was generated on the metal centers. As a result, the main frameworks of the polyhedral complexes M₁₈L₁₂ and M₁₂L₈ were formally extended into a new series of concave polyhedra having the compositions M₂₁L₁₂ and M₁₃L₈, respectively. This transformation also resulted in the local disconnection of the highly entangled trifurcate topology of the framework, providing clues toward the skeletal editing of extended and complex three-dimensional (3D) architectures.     

An Interwoven Metal‐Organic Framework Combining Mechanically Interlocked Linkers and Interpenetrated Networks

New dibenzo[24]crown‐8 ether derivatives were prepared that contain appendages with thioether donors that can coordinate to a metal ion. These macrocycles were then combined with 1,2‐bis(pyridinium) ethane axles to create two types of [2]rotaxane ligands; those with the four thioether donors on the crown ether and those with six donor groups, four from the crown ether and two more attached to the stoppering groups of the dumbbell. The crown ethers and both types of [2]rotaxane ligands were allowed to react with Ag^I ions to form metal‐organic rotaxane framework (MORF) style coordination polymers. The interlocked hexadentate ligand forms the first example of a new type of lattice containing interwoven frameworks resulting from both interpenetration of frameworks due to the presence of an interlocked ligand and more classical interpenetration of independent frameworks.     

Conformational Adaptation of β-Peptide Foldamers for the Formation of Metal–Peptide Frameworks

Metal-coordinated frameworks derived from small peptidic ligands have received much attention thanks to peptides’ vast structural and functional diversity. Various peptides with partial conformational preferences have been used to build metal–peptide frameworks, however, the use of conformationally constrained β-peptide foldamers has not been explored yet. Herein we report the first metal-coordination-mediated assembly of β-peptide foldamers with 12-helical folding propensity. The coordination of Ag⁺ to the terminal pyridyl moieties afforded a set of metal–peptide frameworks with unique entangled topologies. Interestingly, formation of the network structures was accompanied by notable conformational distortions of the foldamer ligands. As the first demonstration of new metal–peptide frameworks built from modular β-peptide foldamers, we anticipate that this work will be an important benchmark for further structural evolution and mechanistic investigation.     

Coordination‐Driven Folding and Assembly of a Short Peptide into a Protein‐like Two‐Nanometer‐Sized Channel

Short peptide helices have attracted attention as suitable building blocks for soft functional materials, but they are rarely seen in crystalline materials. A new artificial nanoassembly of short peptide helices in the crystalline state is presented in which peptide helices are arranged three‐dimensionally by metal coordination. The folding and assembly processes of a short peptide ligand containing the Gly‐Pro‐Pro sequence were induced by silver(I) coordination in aqueous alcohol, and gave rise to a single crystal composed of polyproline II helices. Crystallographic studies revealed that this material possesses two types of unique helical nanochannel; the larger channel measures more than 2 nm in diameter. Guest uptake properties were investigated by soaking the crystals in polar solutions of guest molecules; anions, organic chiral molecules, and bio‐oligomers are effectively encapsulated by this peptide‐folded porous crystal, with moderate to high chiral recognition for chiral molecules.     

Pyridyl‐Dicarboxylate Tuned Cadmium(II) Complexes and Their Fluorescence Emission Properties

To investigate the effect of organic anions on coordination frameworks, the complexes [Cd(2, 6‐pydc)(bibix)₂(H₂O)₂]_n ( 1 ) and {[Cd₄(2, 5‐pydc)₄(bibix)₄(H₂O)₄](H₂O)₈}_n ( 2 ) were isolated by the reactions of 1‐{4‐[(1H‐benzoimidazol‐1‐yl)methyl]benzyl}‐1H‐benzoimidazole (bibix) and two distinct pyridyl‐dicarboxylates as organic anions with d¹⁰ metal salts. In the resulting structures, bibix adopts different coordination modes affected by the aromatic anions, which have distinct geometric structure and bonding modes. Thus, complex 1 has a 1D chain structure, whereas complex 2 has a 2D architecture. Both complexes 1 and 2 have a strong fluorescence emission, which may be tentatively assigned to metal‐perturbed intraligand interactions.     

Synergistically Directed Assembly of Aromatic Stacks Based Metal‐Organic Frameworks by Donor‐Acceptor and Coordination Interactions

A synergistically directed assembly approach to distinctive metal‐organic frameworks utilizing both donor‐acceptor (D‐A) interaction from aromatic systems and coordination interactions is presented. Based on such an approach, the coronene‐tpt (tpt = 2,4,6‐tri(4‐pyridyl)‐1,3,5‐triazine) stacks based coronene‐MOF‐1 — 4 have been successfully fabricated. Their structural discrepancies with coronene‐ absent control products, 1′ — 4′ , illustrate clearly the significance of coronene‐tpt based D‐A interactions in these architectures. All these coronene‐MOFs contain varied coronene‐tpt stacks as organic secondary building blocks (SBUs), which are closely interrelated with the coordination based framework structures. Moreover, porous coronene‐MOF‐1 and ‐2 exhibit high physicochemical stability and significant light hydrocarbons storage and separation performances.     

Dimethyl 2,2′‐bipyridine‐6,6′‐dicarboxylate and bis(dimethyl 2,2′‐bipyridine‐6,6′‐dicarboxylato‐κ2N,N′)copper(I) tetrafluoroborate

The single‐crystal X‐ray structures of dimethyl 2,2′‐bipyridine‐6,6′‐dicarboxylate, C₁₄H₁₂N₂O₄, and the copper(I) coordination complex bis(dimethyl 2,2′‐bipyridine‐6,6′‐dicarboxylato‐κ²N,N′)copper(I) tetrafluoroborate, [Cu(C₁₄H₁₂N₂O₄)₂]BF₄, are reported. The uncoordinated ligand crystallizes across an inversion centre and adopts the anticipated anti pyridyl arrangement with coplanar pyridyl rings. In contrast, upon coordination of copper(I), the ligand adopts an arrangement of pyridyl donors facilitating chelating metal coordination and an increased inter‐pyridyl twisting within each ligand. The distortion of each ligand contrasts with comparable copper(I) complexes of unfunctionalized 2,2′‐bipyridine.     

New metallomesogenic polymers built by self-assembly of non-mesomorphic stilbazole dimers and CF3SO3Ag through coordination bonds

Supramolecular liquid-crystalline main-chain polymers have been obtained by self-assembly of non-mesomorphic bifunctional ligands and a transition metal ion. Stibazole dimers, bis[2-(2-{4-[2-(4-pyridyl)vinyl]phenoxy}ethoxy)ethyl] ether (1) and 1,2-bis[2-(2-{4-[2-(4-pyridyl)vinyl]phenoxy}ethoxy)ethoxy]benzene (2) have been synthesized and complexed with silver trifluoromethanesulfonate (CF₃SO₃Ag). The metallomesogenic polymeric complexes formed by coordination bonds between the pyridyl groups of the stilbazole dimers and the silver ion exhibit smectic phases.     

A lithium‐organic framework as a fluorescent sensor for detecting aluminum (III) ion

Due to the low coordination number and the relatively weak coordination ability, it is a great challenge to introduce Li⁺ into the construction of metal–organic frameworks (MOFs). Here, one Li‐based metal–organic framework (Li‐MOF), [Li₄L(DMF)₂]_n ( HNU‐31 ), is constructed by the assembly of LiNO₃ and 5‐(bis(4‐carboxybenzyl)amino)isophthalic acid (H₄L) ligand, which possesses a 3D framework, and can be serve as a luminescent sensor for detecting Al³⁺ ion with the detection limit of 4 × 10^?6 M.     

Sponge‐Like Behaviour in Isoreticular Cu(Gly‐His‐X) Peptide‐Based Porous Materials

We report two isoreticular 3D peptide‐based porous frameworks formed by coordination of the tripeptides Gly‐L ‐His‐Gly and Gly‐L ‐His‐L ‐Lys to Cu^II which display sponge‐like behaviour. These porous materials undergo structural collapse upon evacuation that can be reversed by exposure to water vapour, which permits recovery of the original open channel structure. This is further confirmed by sorption studies that reveal that both solids exhibit selective sorption of H₂O while CO₂ adsorption does not result in recovery of the original structures. We also show how the pendant aliphatic amine chains, present in the framework from the introduction of the lysine amino acid in the peptidic backbone, can be post‐synthetically modified to produce urea‐functionalised networks by following methodologies typically used for metal–organic frameworks built from more rigid “classical” linkers.     

Nanocomposite Made of an Oligo(p‐phenylenevinylene)‐Based Trihybrid Thixotropic Metallo(organo)gel Comprising Nanoscale Metal–Organic Particles,Carbon Nanohorns,and Silver Nanoparticles

A silver ion (Ag⁺)‐triggered thixotropic metallo(organo)gel of p‐pyridyl‐appended oligo(p‐phenylenevinylene) derivatives (OPVs) is reported for the first time. Solubilization of single‐walled carbon nanohorns (SWCNHs) in solutions of the pure OPVs as well as in the metallogels mediated by π–π interactions has also been achieved. In situ fabrication of silver nanoparticles (AgNPs) in the SWCNH‐doped dihybrid gel leads to the formation of a trihybrid metallogel. The mechanical strength of the metallogels could be increased stepwise in the order: freshly prepared gel<dihybrid gel<trihybrid gel. Microscopic studies of the trihybrid gel indicate the formation of three distinct morphologies, that is, nanoscale metal–organic particles (NMOPs), flowerlike aggregates of SWCNHs and AgNPs, and also their integration with each other. Detailed studies suggest lamellar organizations of the linear metal–ligand complexes in the NMOPs, which upon association create a three‐dimensional network that eventually immobilizes the solvent molecules.     

AgI and CuI binuclear macrocyclic complexes with 1‐(3‐pyridyl)­ethano­ne oxime

Bis­[μ‐1‐(3‐pyridyl)­ethanone oxime‐κ²N:N′]­bis­[nitrato­sil­ver(I)], [Ag₂(NO₃)₂(C₇H₈N₂O)₂], crystallizes as a centrosymmetric binuclear macrocylic complex containing silver(I) ions bridged by the organic 1‐(3‐pyridyl)­ethanone oxime ligand. The ligand coordinates via the pyridine and the oxime N atoms. A similar metal–ligand arrangement was found in the copper(I) complex catena‐poly­[[bis­[μ‐1‐(3‐pyridyl)­ethano­ne oxime‐κ²N:N′]­dicopper(I)]‐di‐μ‐iodo], [Cu₂I₂(C₇H₈N₂O)₂]_n, but here the centrosymmetric macrocycles are connected by double anion bridges, resulting in the formation of a one‐dimensional coordination polymer.     

[5‐Benzyl‐3‐phenyl‐2‐(2‐pyridyl‐κN)thiazolidin‐4‐one‐κS]dichloropalladium(II)

The palladium(II) centre in the title compound, [PdCl₂(C₂₁H₁₈N₂OS)], is coordinated to the pyridyl N atom and to the thia­zolidinone S atom of the 5‐benzyl‐3‐phenyl‐2‐(2‐pyridyl)­thia­zolidin‐4‐one ligand, resulting in a five‐membered chelate ring. Two cis‐chloro ligands complete the square‐planar coordination environment of the metal. Although the geometry at the Pd centre is essentially planar, the N—Pd—S bite angle of 85.20 (8)° causes deviations in the cis angles from the ideal value of 90°. Opposite enantiomers form one‐dimensional chains in the cell via a short S?O intermolecular interaction.