Fifty Shades of Phenanthroline: Synthesis Strategies to Functionalize 1,10-Phenanthroline in All Positions

1,10-Phenanthroline (phen) is one of the most popular ligands ever used in coordination chemistry due to its strong affinity for a wide range of metals with various oxidation states. Its polyaromatic structure provides robustness and rigidity, leading to intriguing features in numerous fields (luminescent coordination scaffolds, catalysis, supramolecular chemistry, sensors, theranostics, etc.). Importantly, phen offers eight distinct positions for functional groups to be attached, showcasing remarkable versatility for such a simple ligand. As a result, phen has become a landmark molecule for coordination chemists, serving as a must-use ligand and a versatile platform for designing polyfunctional arrays. The extensive use of substituted phenanthroline ligands with different metal ions has resulted in a diverse array of complexes tailored for numerous applications. For instance, these complexes have been utilized as sensitizers in dye-sensitized solar cells, as luminescent probes modified with antibodies for biomaterials, and in the creation of elegant supramolecular architectures like rotaxanes and catenanes, exemplified by Sauvage's Nobel Prize-winning work in 2016. In summary, phen has found applications in almost every facet of chemistry. An intriguing aspect of phen is the specific reactivity of each pair of carbon atoms ([2,9], [3,8], [4,7], and [5,6]), enabling the functionalization of each pair with different groups and leading to polyfunctional arrays. Furthermore, it is possible to differentiate each position in these pairs, resulting in non-symmetrical systems with tremendous versatility. In this Review, the authors aim to compile and categorize existing synthetic strategies for the stepwise polyfunctionalization of phen in various positions. This comprehensive toolbox will aid coordination chemists in designing virtually any polyfunctional ligand. The survey will encompass seminal work from the 1950s to the present day. The scope of the Review will be limited to 1,10-phenanthroline, excluding ligands with more intracyclic heteroatoms or fused aromatic cycles. Overall, the primary goal of this Review is to highlight both old and recent synthetic strategies that find applicability in the mentioned applications. By doing so, the authors hope to establish a first reference for phenanthroline synthesis, covering all possible positions on the backbone, and hope to inspire all concerned chemists to devise new strategies that have not yet been explored.

Dual reactivity based dynamic covalent chemistry: mechanisms and applications

Dynamic covalent chemistry (DCC) focuses on the reversible formation, breakage, and exchange of covalent bonds and assemblies, setting a bridge between irreversible organic synthesis and supramolecular chemistry and finding wide utility. In order to enhance structural and functional diversity and complexity, different types of dynamic covalent reactions (DCRs) are placed in one vessel, encompassing orthogonal DCC without crosstalk and communicating DCC with a shared reactive functional group. As a means of adding tautomers, widespread in chemistry, to interconnected DCRs and combining the features of orthogonal and communicating DCRs, a concept of dual reactivity based DCC and underlying structural and mechanistic insights are summarized. The manipulation of the distinct reactivity of structurally diverse ring-chain tautomers allows selective activation and switching of reaction pathways and corresponding DCRs (C-N, C-O, and C-S) and assemblies. The coupling with photoswitches further enables light-mediated formation and scission of multiple types of reversible covalent bonds. To showcase the capability of dual reactivity based DCC, the versatile applications in dynamic polymers and luminescent materials are presented, paving the way for future functionalization studies.

Shape-Dependent Complementary Ditopic Terpyridine Pair with Two Levels of Self-Recognition for Coordination-Driven Self-Assembly

Molecular recognition in biological systems plays a vital role in the precise construction of biomacromolecules and the corresponding biological activities. Such recognition mainly relies on the highly specific binding of complementary molecular pairs with complementary sizes, shapes, and intermolecular forces. It still remains challenging to develop artificial complementary motif pairs for coordination-driven self-assembly. Herein, a series of shape-dependent complementary motif pairs, based on ditopic 2,2':6',2″-terpyridine (TPY) backbone, are designed and synthesized. The fidelity degrees of self-assemblies from these motifs are carefully evaluated by multi-dimensional mass spectrometry, nuclear magnetic resonance spectroscopy, and molecular modeling. In addition, two levels of self-recognition in both homoleptic and heteroleptic assembly are discovered in the assembled system. Through finely tuning the shape and size of the ligands, a complementary pair is developed with error-free narcissistically self-sorting at two levels of self-recognition, and the intrinsic principle is carefully investigated.

Direct Detection of Hydrogen Bonds in Supramolecular Systems Using 1H-15N Heteronuclear Multiple Quantum Coherence Spectroscopy

Hydrogen-bonded supramolecular systems are usually characterized in solution through analysis of NMR data such as complexation-induced shifts and nuclear Overhauser effects (nOe). Routine direct detection of hydrogen bonding particularly in multicomponent mixtures, even with the aid of 2D NMR experiments for full assignment, is more challenging. We describe an elementary rapid ¹H-¹⁵N HMQC NMR experiment which addresses these challenges without the need for complex pulse sequences. Under readily accessible conditions (243/263 K, 50 mM solutions) and natural ¹⁵N abundance, unambiguous assignment of ¹⁵N resonances facilitates direct detection of intra- and intermolecular hydrogen bonds in mechanically interlocked structures and quadruply hydrogen-bonded dimers─of dialkylaminoureidopyrimidinones, ureidopyrimidinones, and diamidonaphthyridines─in single or multicomponent mixtures to establish tautomeric configuration, conformation, and, to resolve self-sorted speciation.

A Cavity-Tailored Metal-Organic Tetrahedral Nanocage and Gas Adsorption Property

Porous organometallic nanomaterials are a new class of materials based on a three-dimensional structure. They have excellent applications in different fields, but their applications in gas storage and separation have not been fully developed. CO₂ adsorption storage and hydrocarbon separation has been a challenging industrial problem. Several typical molecular adsorbents have been used to study the separation, but the problems of long-term stability, high selectivity and synthetic complexity of these adsorbents remain to be solved. Here, we have designed and synthesized tetrahedral metal supramolecular nanocage with custom cavities based on the unique rigid structure of triptycene derivatives. Using the unique discrete porous structure of tetrahedral metal nanocages, the gas adsorption and separation performance of the metal supramolecular nanocage was investigated. By analyzing the adsorption and desorption isotherms and the multi-component competitive adsorption curves, we noticed that the tetrahedral supramolecular nanocages had good CO₂ storage capacity and good separation capacity for C₂H₂/CO₂ and C₂H₂/N₂. All these indicate that porous organic metal nanomaterials are expected to be a new energy saving separation material.

Pre-arranged building block approach for the orthogonal synthesis of an unfolded tetrameric organic-inorganic phosphazane macrocycle

Inorganic macrocycles remain challenging synthetic targets due to the limited number of strategies reported for their syntheses. Among these species, large fully inorganic cyclodiphosphazane macrocycles have been experimentally and theoretically highlighted as promising candidates for supramolecular chemistry. In contrast, their hybrid organic-inorganic counterparts are lagging behind due to the lack of synthetic routes capable of controlling the size and topological arrangement (i.e., folded vs unfolded) of the target macrocycle, rendering the synthesis of differently sized macrocycles a tedious screening process. Herein, we report-as a proof-of-concept-the combination of pre-arranged building blocks and a two-step synthetic route to rationally enable access a large unfolded tetrameric macrocycle, which is not accessible via conventional synthetic strategies. The obtained macrocycle hybrid cyclodiphosphazane macrocycle, cis-[μ-P(μ-N^tBu)]₂(μ-p-OC₆H₄C(O)O)]₄[μ-P(μ-N^tBu)]₂ (4), displays an unfolded open-face cavity area of 110.1 Ų. Preliminary theoretical host-guest studies with the dication [MeNC₅H₄]₂²⁺ suggest compound 4 as a viable candidate for the synthesis of hybrid proto-rotaxanes species based on phosphazane building blocks.

Self-Sorting Governed by Chelate Cooperativity

Self-sorting phenomena are the basis of manifold relevant (bio)chemical processes where a set of molecules is able to interact with no interference from other sets and are ruled by a number of codes that are programmed in molecular structures. In this work, we study, the relevance of chelate cooperativity as a code for achieving high self-sorting fidelities. In particular, we establish qualitative and quantitative relationships between the cooperativity of a cyclic system and the self-sorting fidelity when combined with other molecules that share identical geometry and/or binding interactions. We demonstrate that only systems displaying sufficiently strong chelate cooperativity can achieve quantitative narcissistic self-sorting fidelities either by dictating the distribution of cyclic species in complex mixtures or by ruling the competition between the intra- and intermolecular versions of a noncovalent interaction.

Nonaqueous Emulsion Polycondensation Enabled by a Self‐Assembled Cage‐like Surfactant

Nonaqueous emulsions are crucial for a range of applications based on water‐sensitive systems such as controlled polymerizations requiring anhydrous reaction conditions and the stabilization of readily hydrolyzable reagents or pharmacologically active components. However, defined molecular surfactants to stabilize such nonaqueous emulsions are scarce. We introduce a self‐assembled coordination cage, decorated with cholesterol functionalities, to serve as a molecular surfactant for various oil‐in‐oil emulsions of immiscible organic solvents. While the positively charged cage forms the amphiphile's polar moiety, the non‐polar cholesterol appendices can bend in a common direction to stabilize the emulsion. Templated by the droplets, polycondensation reactions were carried out to produce microstructured polyurethane and polyurea materials of different particle sizes and morphologies. Further, the amphiphilic cage can encapsulate a guest molecule and the resulting host‐guest assembly was also examined as a surfactant. In addition, the aggregation behavior of the amphiphilic cage in an aqueous medium was examined.

Dynamic Covalent Chemistry Constrained Diphenylethenes: Control over Reactivity and Luminescence in both Solution and Solid State

Diarylethenes (DAEs) are an important class of building blocks in chemistry and materials science, and hence, their modulation and functionalization are of critical significance. Here we demonstrate a general strategy...

Ion Mobility Mass Spectrometry Uncovers Guest-Induced Distortions in a Supramolecular Organometallic Metallosquare

The encapsulation of the tetracationic palladium metallosquare with four pyrene-bis-imidazolylidene ligands [1]4+ with a series of organic molecules was studied by Electrospray ionization Travelling Wave Ion-Mobility Mass Spectrometry (ESI TWIM-MS). The method allowed to determine the Collision Cross Sections (CCSs), which were used to assess the size changes experienced by the host upon encapsulation of the guest molecules. When fullerenes were used as guests, the host is expanded ΔCCS 13 Å2 and 23 Å2 , for C60 or C70 , respectively. The metallorectangle [1]4+ was also used for the encapsulation of a series of polycyclic aromatic hydrocarbons (PAHs) and naphthalenetetracarboxylic diimide (NTCDI), to form complexes of formula [(NTCDI)2 (PAH)@1]4+ . For these host:guest adducts, the ESI IM-MS studies revealed that [1]4+ is expanded by 47-49 Å2 .. The energy-minimized structures of [1]4+ , [C60 @1]4+ , [C70 @1]4+ , [(NTCDI)2 (corannulene)@1]4+ in the gas phase were obtained by DFT calculations.Introduction.

Narcissistic self-sorting in anion-coordination-driven assemblies

Three tris-bis(urea) ligands with triphenylamine-based C₃-symmetric spacers were synthesized, which assembled with sulfate or phosphate to form anionic A₃L₂ pinwheel helices (A = anion and L = ligand) and A₄L₄ tetrahedra, respectively. Interestingly, narcissistic self-sorting was observed in both structures from the mixture of the ligands, wherein each assembly contains only one type of ligand with no detectable mixed-ligand product as confirmed by the NMR and MS studies.

Increasing structural and functional complexity in self-assembled coordination cages

Progress in metallo-supramolecular chemistry creates potential to synthesize functional nano systems and intelligent materials of increasing complexity. In the past four decades, metal-mediated self-assembly has produced a wide range of structural motifs such as helicates, grids, links, knots, spheres and cages, with particularly the latter ones catching growing attention, owing to their nano-scale cavities. Assemblies serving as hosts allow application as selective receptors, confined reaction environments and more. Recently, the field has made big steps forward by implementing dedicated functionality, e.g. catalytic centres or photoswitches to allow stimuli control. Besides incorporation in homoleptic systems, composed of one type of ligand, desire arose to include more than one function within the same assembly. Inspiration comes from natural enzymes that congregate, for example, a substrate recognition site, an allosteric regulator element and a reaction centre. Combining several functionalities without creating statistical mixtures, however, requires a toolbox of sophisticated assembly strategies. This review showcases the implementation of function into self-assembled cages and devises strategies to selectively form heteroleptic structures. We discuss first examples resulting from a combination of both principles, namely multicomponent multifunctional host-guest complexes, and their potential in application in areas such as sensing, catalysis, and photo-redox systems.

Multitasking with Chemical Fuel: Dissipative Formation of a Pseudorotaxane Rotor from Five Distinct Components

A 3-fold completive self-sorted library of dynamic motifs was integrated into the design of the pseudorotaxane-based rotor [Zn(2·H⁺)(3)(4)]²⁺ operating at k₂₉₈ = 15.4 kHz. The rotational motion in the five-component device is based on association/dissociation of the pyridyl head of the pseudorotaxane rotator arm between two zinc(II) porphyrin stations. Addition of TFA or 2-cyano-2-phenylpropanoic acid as a chemical fuel to a zinc release system and the loose rotor components 2-4 enabled the liberated zinc(II) ions and protons to act in unison, setting up the rotor through the formation of a heteroleptic zinc complex and a pseudorotaxane linkage. With chemical fuel, the dissipative system was reproducibly pulsed three times without a problem. Due to the double role of the fuel acid, two kinetically distinct processes played a role in both the out-of-equilibrium assembly and disassembly of the rotor, highlighting the complex issues in multitasking of chemical fuels.

Multidentate, V-Shaped Pyridine Building Blocks as Tectons for Crystal Engineering

The formation of supramolecular structural units through self-assembly is a powerful method to design new architectures and materials endowed with specific properties. With the aim of adding a group of versatile tectons to the toolkit of crystal engineers, we have devised and synthesised four new V-shaped building blocks characterised by an aryl acetylene scaffold comprising three substituted pyridine rings connected by two triple bonds. The judicious choice of different substituents on the pyridine rings provides these tectons with distinctive steric, electrostatic and self-assembly properties, which influence their crystal structures and their ability to form co-crystals. Co-crystals of the tectons with tetraiododifluorobenzene were obtained both via traditional and mechanochemical crystallisation strategies, proving their potential use in crystal engineering. The energetic contributions of the supramolecular interactions at play in the crystal lattice have also been evaluated to better understand their nature and strength and to rationalise their role in designing molecular crystals.

Sequence-controlled supramolecular copolymer constructed by self-sorting assembly of multiple noncovalent interactions

A sequence-controlled supramolecular copolymer was constructed by self-sorting assembly of metal coordination and two types of host–guest interactions.

Unmasking Arene Ruthenium Building Blocks

We have, like many others, contributed to the development and to the popularity of arene ruthenium assemblies. From early on, our research was driven by applications, mainly biological (therapeutic, drug delivery, DNA interactions, photodynamic therapy, imaging). For nearly 15 years, we have focused on the use of arene ruthenium building block as a tool to construct added-value objects. In this account, we want to give the basic reasons behind our choice, and uncover our most successful examples, with an emphasis on the foreseen applications.

Using multiple self-sorting for switching functions in discrete multicomponent systems

Over years self-sorting has developed into a powerful tool in supramolecular chemistry, for instance, to promote the error-free formation of intricate multicomponent assemblies. However, in order to use the enormous potential of self-sorting for sophisticated information processing more recent developments have focused on the reversible reconfiguration of multicomponent systems driven by multiple self-sorting protocols. The present mini review will provide an overview over the latest advancements in this field with a focus on reversibly switchable functions in discrete supramolecular systems.

Construction of Macromolecular Pinwheels Using Predesigned Metalloligands

Developing a methodology to build target structures is one of the major themes of synthetic chemistry. However, it has proven to be immensely challenging to achieve multilevel elaborate molecular architectures in a predictable way. Herein, we describe the self-assembly of a series of pinwheel-shaped starlike supramolecules through three rationally preorganized metalloligands L1-L3. The key octa-uncomplexed terpyridine (tpy) metalloligand L3, synthesized with an 8-fold Suzuki coupling reaction to metal-containing complexes, has four different types of terpyridines connected with three ⟨tpy-Ru²⁺-tpy⟩ units, making this the most subunits known so far for a preorganized module. Based on the principle of geometric complementation and the high "density of coordination sites", these metalloligands were assembled with Zn²⁺ ions to form a pinwheel-shaped star trigon P1, pentagram P2, and hexagram P3 with precisely controlled shapes in nearly quantitative yields. With molecular weights ranging from 16756 to 56053 Da and diameters of 6.7-13.6 nm, the structural composition, shape, and rigidity of these pinwheel-shaped architectures have been fully characterized by 1D and 2D (NMR), electrospray ionization mass spectrometry, traveling-wave ion mobility mass spectrometry, and transmission electron microscopy.

Dynamics of Hydrogen Bonding in Three-Component Nanorotors

The dynamics of hydrogen bonding do not only play an important role in many biochemical processes but also in Nature's multicomponent machines. Here, a three-component nanorotor is presented where both the self-assembly and rotational dynamics are guided by hydrogen bonding. In the rate-limiting step of the rotational exchange, two phenolic O-H-N,N(phenanthroline) hydrogen bonds are cleaved, a process that was followed by variable-temperature 1 H NMR spectroscopy. Activation data (ΔG≠ 298 =46.7 kJ mol-1 at 298 K, ΔH≠ =55.3 kJ mol-1 , and ΔS≠ =28.8 J mol-1  K-1 ) were determined, furnishing a rotational exchange frequency of k298 =40.0 kHz. Fully reversible disassembly/assembly of the nanorotor was achieved by addition of 5.0 equivalents of trifluoroacetic acid (TFA)/1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) over three cycles.

Triple Self-Sorting in Constitutional Dynamic Networks: Parallel Generation of Imine-Based CuI , FeII , and ZnII Complexes

Three imine-based metal complexes, having no overlap in terms of their compositions, have been simultaneously generated from the self-sorting of a constitutional dynamic library (CDL) containing three amines, three aldehydes, and three metal salts. The hierarchical ordering of the stability of the three metal complexes assembled and the leveraging of the antagonistic and agonistic relationships existing between the constituents within the constitutional dynamic network corresponding to the CDL were pivotal in achieving the sorting. Examination of the process by NMR spectroscopy showed that the self-sorting of the FeII and ZnII complexes depended on an interplay between the thermodynamic driving forces and a kinetic trap involved in their assembly. These results also exemplify the concept of "simplexity"-the fact that the output of a self-assembling system may be simplified by increasing its initial compositional complexity-as the two complexes could self-sort only in the presence of the third pair of organic components, those of the CuI complex.

Towards a Generalized Synthetic Strategy for Variable Sized Enantiopure M4L4 Helicates

The reliable and predictable synthesis of enantiopure coordination cages is an important step towards the realization of discrete cages capable of enantioselective discrimination. We have built upon our initial report of a lantern-type helical cage in attempts to expand the synthesis into a general approach. The use of a longer, flexible diacid ligand results in the anticipated cage [Cu4(L1)4(solvent)4] with a similar helical pitch to that previously observed and a cavity approximately 30% larger. Using a shorter, more rigid ligand gave rise to a strained, conjoined cage-type complex when using DABCO as an internal bridging ligand, [{Co4(L2)4(DABCO)(OH2)x}2 (DABCO)]. The expected paddlewheel motif only forms for one of the Co2 units within each cage, with the other end adopting a “partial paddlewheel” with aqua ligands completing the coordination sphere of the externally facing metal ion. The generic approach of using chiral diacids to construct lantern-type cages is partially borne out, with it being apparent that flexibility in the core group is an essential structural feature.

Efficient self-assembly of heterometallic triangular necklace with strong antibacterial activity

Sophisticated mechanically interlocked molecules (MIMs) with interesting structures, properties and applications have attracted great interest in the field of supramolecular chemistry. We herein report a highly efficient self-assembly of heterometallic triangular necklace 1 containing Cu and Pt metals with strong antibacterial activity. Single-crystal X-ray analysis shows that the finely arranged triangular necklace 1 has two racemic enantiomers in its solid state with intriguing packing motif. The superior antibacterial activity of necklace 1 against both standard and clinically drug-resistant pathogens implies that the presence of Cu(I) center and platinum(II) significantly enhance the bacterium-binding/damaging activity, which is mainly attributed to the highly positively charged nature, the possible synergistic effect of heterometals in the necklace, and the improved stability in culture media. This work clearly discloses the structure-property relationships that the existence of two different metal centers not only facilitates successful construction of heterometallic triangular necklace but also endows it with superior nuclease properties and antibacterial activities.

Precise assembly of heterometallic complexes is a challenge. Here, the authors design a heterometallic triangular necklace through a highly efficient threading-and-ring-closing approach driven by metal-ligand coordination, which shows strong bacterium-binding and cell wall/plasma membrane-disrupting capacity for killing bacterial cells.

Adaptive Covalent Networks Enabled by Dual Reactivity: The Evolution of Reversible Covalent Bonds, Their Molecular Assemblies, and Guest Recognition

Adaptive chemistry allows transformation and selection within molecular networks, and adaptive systems composed of different types of dynamic covalent reactions (DCRs) are challenging. Herein, we demonstrate dual reactivity-based covalent networks encompassing the regulation of and switching between C-N- and C-S-based reversible covalent assemblies. The creation and exchange of C-N- or C-S-derived assemblies exhibiting diverse architectures, including linear structures, macrocycles, and cages, were achieved. The shift of reactivity then permitted the interconversion between C-N- and C-S-containing assemblies. Moreover, the adaption of intramolecular and intermolecular scaffolds was feasible via linker design. The latent hemiaminal chirality center offered a pathway for the induction of chirality within assemblies. Finally, switchable structural change and controlled extraction of ions were realized with Hg²⁺ as a guest for macrocycles. The remarkable complexity of networks described herein could open the door for the utility in sophisticated functional systems.

Synthesis of Metallopolymers and Direct Visualization of the Single Polymer Chain

During the past few decades, the study of the single polymer chain has attracted considerable attention with the goal of exploring the structure-property relationship of polymers. It still, however, remains challenging due to the variability and low atomic resolution of the amorphous single polymer chain. Here, we demonstrated a new strategy to visualize the single metallopolymer chain with a hexameric or trimeric supramolecule as a repeat unit, in which Ru(II) with strong coordination and Fe(II) with weak coordination were combined together in a stepwise manner. With the help of ultrahigh-vacuum, low-temperature scanning tunneling microscopy (UHV-LT-STM) and scanning tunneling spectroscopy (STS), we were able to directly visualize both Ru(II) and Fe(II), which act as staining reagents on the repeat units, thus providing detailed structural information for the single polymer chain. As such, the direct visualization of the single random polymer chain is realized to enhance the characterization of polymers at the single-molecule level.

Dimensional Matching versus Induced-Fit Distortions: Binding Affinities of Planar and Curved Polyaromatic Hydrocarbons with a Tetragold Metallorectangle

A tetragold(I) rectangle-like metallocage containing two pyrene-bis-imidazolylidene ligands and two carbazolyl-bis-alkynyl linkers is used for the encapsulation of a series of polycyclic aromatic hydrocarbons (PAHs), including corannulene. The binding affinities obtained for the encapsulation of the planar PAHs guests in CD₂ Cl₂ are found to exponentially increase with the number of π-electrons of the guest (1.3 > logK >6.6). For the bowl-shaped molecule of corannulene, the association constant is much lower than the expected one according to its number of electrons. The molecular structure of the host-guest complex formed with corannulene shows that the molecule of the guest is compressed, while the host is expanded, thus showing an interesting case of artificial mutual induced-fit arrangement.

Heterocomponent ternary supramolecular complexes of porphyrins: A review

Porphyrins are prominent host molecules which are widely used due to their structural characteristics and directional interaction sites. This review summarizes non-covalently bound ternary complexes of porphyrins, constructed from at least three non-identical species. Progress in supramolecular chemistry allows the creation of complex molecular machinery tools, such as rotors, motors and switches from relatively simple structures in a single self-assembly step. In the current review, we highlight the collection of sophisticated molecular ensembles including sandwich-type complexes, cages, capsules, tweezers, rotaxanes, and supramolecular architectures mediating oxygen-binding and oxidation reactions. These diverse structures have high potential to be applied in sensing, production of new smart materials as well as in medical science.

Architecture transition of supramolecular polymers through hierarchical self-assembly: from supramolecular polymers to fluorescent materials

A new supramolecular crosslinked polymer and a gel with excellent self-repairing capability were prepared by double host–guest interactions.

A pH-Switchable Triple Hydrogen-Bonding Motif

A stimuli responsive linear hydrogen bonding motif, capable of in situ protonation and deprotonation, has been investigated. The interactions of the responsive hydrogen bonding motif with complementary partners were examined through a series of 1H NMR experiments, revealing that the recognition preference of the responsive hydrogen bonding motif in a mixture can be switched between two states.

A pH-responsive graftable supramolecular polymer with tailorable surface functionality by orthogonal halogen bonding and hydrogen bonding

Orthogonal halogen (X)-bonding and hydrogen (H)-bonding have been employed for constructing a surface functionalizable supramolecular polymer in water featuring tunable morphology and dual stimuli (pH and temperature) responsive properties.

Self-sorting of two imine-based metal complexes: balancing kinetics and thermodynamics in constitutional dynamic networks

A major hurdle in the development of complex constitutional dynamic networks (CDNs) is the lack of strategies to simultaneously control the output of two (or more) interconnected dynamic processes over several species, namely reversible covalent imine bond formation and dynamic metal–ligand coordination. We have studied in detail the self-sorting process of 11 constitutional dynamic libraries containing two different amines, aldehydes and metal salts into two imine-based metal complexes, having no overlap in terms of their compositions. This study allowed us to determine the factors influencing the fidelity of this process (concentration, electronic and steric parameters of the organic components, and nature of the metal cations). In all 11 systems, the outcome of the process was primarily determined by the ability of the octahedral metal ion to select its pair of components from the initial pool of components, with the composition of the weaker tetrahedral complex being imposed by the components rejected by the octahedral metal ions. Different octahedral metal ions required different levels of precision in the “assembling instructions” provided by the organic components of the CDN to guide it towards a sorted output. The concentration of the reaction mixture, and the electronic and steric properties of the initial components of the library were all found to influence the lifetime of unwanted metastable intermediates formed during the assembling of the two complexes.

Constitutional dynamic networks have been developed to simultaneously control the output of two interconnected dynamic processes over several species of the same reaction mixture.

Dynamic Covalent Switches and Communicating Networks for Tunable Multicolor Luminescent Systems and Vapor-Responsive Materials

Molecular switches are an intensive area of research, and in particular, the control of multistate switching is challenging. Herein we introduce a general and versatile strategy of dynamic covalent switches and communicating networks, wherein distinct states of reversible covalent systems can induce addressable fluorescence switching. The regulation of intramolecular ring/chain equilibrium, intermolecular dynamic covalent reactions (DCRs) with amines, and both permitted the activation of optical switches. The variation in electron-withdrawing competition between the fluorophore and 2-formylbenzenesulfonyl unit afforded diverse signaling patterns. The combination of switches in situ further enabled the creation of communicating networks for multistate color switching, including white emission, through the delicate control of DCRs in complex mixtures. Finally, reversible and recyclable multiresponsive luminescent materials were achieved with molecular networks on the solid support, allowing visualization of different types of vapors and quantification of primary amine vapors with high sensitivity and wide detection range. The results reported herein should be appealing for future studies of dynamic assemblies, molecular sensing, intelligent materials, and biological labeling.

Metallosupramolecular Architectures of Ambivergent Bis(Amino Acid) Biphenyldiimides

The metallosupramolecular chemistry of two enantiopure dicarboxylate ligands has been explored for their potential to form discrete or polymeric interlocked motifs. Consequently, both discrete and polymeric supramolecular complexes have been synthesised, yielding M₂ L₂ metallomacrocycles (1 and 2), a heteroleptic M₂ L₃ metallomacrobicycle (3), a non-interpenetrated coordination polymer (4), and highly unusual chiral M₈ L₈ squares (5 and 6). There appears to be a preference for the ligands to form M₂ L₂ -type metallomacrocyclic structural units (which feature in 1-4), although these do not engage in any mechanical interlocking, which is perhaps a combined function of the ligand flexibility and relatively small pi-surface contrasted to previous analogues. Using copper paddlewheel SBUs, chiral double-walled squares (5 and 6) are formed with large internal cavities yet poor stabilities, unexpectedly featuring the paddlewheel motifs at the vertices of the polygonal complex.

Structural and magnetic characterization of Ni(ii), Co(ii), and Fe(ii) binuclear complexes on a bis(pyridyl-triazolyl)alkane basis

Reactions of bis[5-(2-pyridyl)-1,2,4-triazol-3-yl]alkanes (alkane spacers = -CH2- in L2, -C3H6- in L3, -C4H8- in L4) with M(ii)A2 salts (M = Ni, Co, Fe) resulted in the preparation of five series of mononuclear ([M(L2)(H2O)2]2+, 1a-c) or binuclear ([M2(L3)2(H2O)4]4+, 2a-c; ([M2(L4)2(H2O)4]4+, 3a-c, [M2(L3)2(μ-ox)]2+, 4a-c; [M2(L4)2(μ-ox)]2+, 5a-c) complexes. The crystal structures of ten complexes were determined by single-crystal X-ray crystallography. Magnetic properties of the compounds were characterized by SQUID magnetometry and were analyzed by fitting on a spin Hamiltonian model. It was revealed that Fe(ii) and Co(ii) compounds exhibit non-negligible anisotropy and in the case of 2a-c and 3a-c complexes weak ferromagnetic interactions between the metal centers were observed. In the case of complexes containing an {M2(μ-ox)}2+ core strong antiferromagnetic interactions were observed within the dimer. Remarkably, solid state luminescence of Co(ii) and Fe(ii) complexes (1b, 2b, 3b and 1c, 2c, 3c) was observed.

Palladium(II)-Based Self-Assembled Heteroleptic Coordination Architectures: A Growing Family

Metal-driven self-assembly is one of the most effective approaches to lucidly design a large range of discrete 2D and 3D coordination architectures/complexes. Palladium(II)-based self-assembled coordination architectures are usually prepared by using suitable metal components, in either a partially protected form (PdL') or typical form (Pd; charges are not shown), and designed ligand components. The self-assembled molecules prepared by using a metal component and only one type of bi- or polydentate ligand (L) can be classified in the homoleptic series of complexes. On the other hand, the less explored heteroleptic series of complexes are obtained by using a metal component and at least two different types of non-chelating bi- or polydentate ligands (such as L^a and L^b ). Methods that allow the controlled generation of single, discrete heteroleptic complexes are less understood. A survey of palladium(II)-based self-assembled coordination cages that are heteroleptic has been made. This review article illustrates a systematic collection of such architectures and credible justification of their formation, along with reported functional aspects of the complexes. The collected heteroleptic assemblies are classified here into three sections: 1) [(PdL')_m (L^a )_x (L^b )_y ]-type complexes, in which the denticity of L^a and L^b is equal; 2) [(PdL')_m (L^a )_x (L^b )_y ]-type complexes, in which the denticity of L^a and L^b is different; and 3) [Pd_m (L^a )_x (L^b )_y ]-type complexes, in which the denticity of L^a and L^b is equal. Representative examples of some important homoleptic architectures are also provided, wherever possible, to set a background for a better understanding of the related heteroleptic versions. The purpose of this review is to pave the way for the construction of several unique heteroleptic coordination assemblies that might exhibit emergent supramolecular functions.

Interplay between n→π* Interactions and Dynamic Covalent Bonds: Quantification and Modulation by Solvent Effects

Orbital donor-acceptor interactions play critical roles throughout chemistry, and hence, their regulation and functionalization are of great significance. Herein we demonstrate for the first time the investigation of n→π* interactions through the strategy of dynamic covalent chemistry (DCC), and we further showcase its use in the stabilization of imine. The n→π* interaction between donor X and acceptor aldehyde/imine within 2-X-2'-formylbiphenyl derivatives was found to significantly influence the thermodynamics of imine exchange. The orbital interaction was then quantified through imine exchange, the equilibrium of which was successfully correlated with the difference in natural bond orbital stabilization energy of n→π* interactions of aldehyde and its imine. Moreover, the examination of solvent effects provided insights into the distinct feature of the modulation of n→π* interaction with aprotic and protic solvents. The n→π* interaction involving imine was enhanced in protic solvents due to hydrogen bonding with the solvent. This finding further enabled the stabilization of imine in purely aqueous solution. The strategies and results reported should find application in many fields, including molecular recognition, biological labeling, and asymmetric catalysis.

Self-Assembled Amphiphilic Janus Double Metallacycle

A double metallacycle was prepared via the size-selective integrative self-sorting of four different building blocks driven by a reversible metal-ligand coordination interaction. A hydrophobic dendron was placed on a metallacycle and a hydrophilic dendron was attached to the other metallacycle, producing a two-faced Janus-type supramolecule with two distinct functionalities. In aqueous media, hierarchical self-assembly of the supramolecular system was induced by the combination of coordination interactions and hydrophobic-hydrophilic interactions resulting in the formation of micrometer-sized fiber-like structures, a morphology distinct from metallacycles bearing only one type of functionality. This study provides a versatile approach for the construction of Janus-type molecules and demonstrates that integrative self-sorting of a supramolecular coordination system can be utilized for the preparation of complex supramolecular systems with predesigned functionalities and morphologies.

Molecular Lemniscates from Organic-Metal Terpyridine-Based Self-Assembly and Host-Guest Recognition

The intricate discrete supramolecular architectures via two or more noncovalent interactions are very attractive for chemists. In this paper, a series of homomeric metallo-supramolecular lemniscates were prepared in nearly quantitative yields by assembling either dialkylammonium salt- or benzo-21-crown-7 (B21C7)-containing terpyridyl metallo-organic ligands with Zn²⁺. Furthermore, the heteromeric analogue could be obtained through two ways: (1) the cooperative interaction of coordination-driven self-assembly and host-guest recognition and (2) the transformation from homodimers to heterodimers driven by host-guest interaction. These supramolecules were characterized by nuclear magnetic resonance (NMR), diffusion-ordered NMR spectroscopy, electrospray ionization mass spectrometry, and two-dimensional (2D) ion-mobility mass spectrometry.