Syntheses and structures of three macrocyclic supramolecular complexes and one ZnII-containing coordination polymer generated from a semi-rigid multidentate N-containing ligand

Semirigid organic ligands can adopt different conformations to construct coordination polymers with more diverse structures when compared to those constructed from rigid ligands. A new asymmetric semirigid organic ligand, 4-{2-[(pyridin-3-yl)methyl]-2H-tetrazol-5-yl}pyridine (L), has been prepared and used to synthesize three bimetallic macrocyclic complexes and one coordination polymer, namely, bis(μ-4-{2-[(pyridin-3-yl)methyl]-2H-tetrazol-5-yl}pyridine)bis[dichloridozinc(II)] dichloromethane disolvate, [Zn₂Cl₄(C₁₂H₁₀N₆)₂]·2CH₂Cl₂, (I), the analogous chloroform monosolvate, [Zn₂Cl₄(C₁₂H₁₀N₆)₂]·CHCl₃, (II), bis(μ-4-{2-[(pyridin-3-yl)methyl]-2H-tetrazol-5-yl}pyridine)bis[diiodidozinc(II)] dichloromethane disolvate, [Zn₂I₄(C₁₂H₁₀N₆)₂]·2CH₂Cl₂, (III), and catena-poly[[[diiodidozinc(II)]-μ-4-{2-[(pyridin-3-yl)methyl]-2H-tetrazol-5-yl}pyridine] chloroform monosolvate], {[ZnI₂(C₁₂H₁₀N₆)]·CHCl₃}_n, (IV), by solution reaction with ZnX₂ (X = Cl and I) in a CH₂Cl₂/CH₃OH or CHCl₃/CH₃OH mixed solvent system at room temperature. Complex (I) is isomorphic with complex (III) and has a bimetallic ring possessing similar coordination environments for both of the Zn^II cations. Although complex (II) also contains a bimetallic ring, the two Zn^II cations have different coordination environments. Under the influence of the I^- anion and guest CHCl₃ molecule, complex (IV) displays a significantly different structure with respect to complexes (I)-(III). C-H...Cl and C-H...N hydrogen bonds, and π-π stacking or C-Cl...π interactions exist in complexes (I)-(IV), and these weak interactions play an important role in the three-dimensional structures of (I)-(IV) in the solid state. In addition, the fluorescence properties of L and complexes (I)-(IV) were investigated.

Is Gelation Behavior Predictable through a Crystal Engineering Approach? A Case Study in Four Similar Coordination Compounds

In this paper, a detailed study on the gelation properties of a series of terpyridine and dipyrazine-pyridine ligands in the presence of metal salts is reported. To reveal the driving forces for the self-assembly of the metallogelators, their crystal structure is scrutinized. Inspired by the gelation of CuCl₂[Terpy- nCN], where "Terpy- nCN" is 4'-( n-cyanophenyl)-2,2',6',2″-terpyridine, to look into the aggregation behavior of the related analogues, synthesis of CuCl₂[Dipyz-py- nCN] derivatives, where "Dipyz-py- nCN" is 4-( n-cyanophenyl)-2,6-di-pyrazin-2-yl-pyridine, with the same cyano groups is performed. We then find that the Dipyz-py counterpart forms crystals when the molecules are stacked in an alternating way, instead of the unidirectional one required for gel formation. A crystal engineering approach is applied to determine the interactions that are favorable for fabricating a fiber network that is likely to be present in both crystalline and gel states and to find the interaction that disturbs this delicate balance between gelation and crystallization in coordination compounds; then, we conclude that the subtle balance between the molecular shape and intermolecular interactions is the origin of the gelation and crystallization of the current molecular system. This enables us to find the mutual connection among the structure of molecules, assembly behavior, and intermolecular interactions. With our experiments, a deep understanding of the balance among solution, gelation, and crystallization with subtle molecular diversions is provided.

5-(1H-1,2,3-Triazol-5-yl)isophthalic Acid: A Versatile Ligand for the Synthesis of New Supramolecular Metallogels

The gelation ability of 5-(1H-1,2,3-triazol-5-yl)isophthalic acid (click-TIA) in the presence of different metal acetates has been studied in different solvents and ligand/metal ratios. This manuscript is focused on the metallogel obtained from the combination of click-TIA and copper(II) acetate, which has been used as a model system in terms of characterization and gelation studies. Sonication treatment of the initial mixture of compounds and the nature of the counter anion were found to be critical factors for the supramolecular assembly of the metal/click-TIA complexes and, hence, for the formation of stable and homogeneous metallogels. The gel materials have been characterized with a variety of techniques including infrared, rheology, UV-vis spectroscopy, powder X-ray diffraction, and scanning electron microscopy.

Amide-Functionalized Chalcogen-Bridged Flexible Tetranuclear Rhenacycles: Synthesis, Characterization, Solvent Effect on the Structure, and Guest Binding

The synthesis of flexible rhenium(I)-based amide-functionalized chalcogen-bridged tetranuclear metallacycles of general formula [{(CO)₃Re(μ-ER)₂Re(CO)₃}₂(μ-L)₂] (1-8) was achieved by treating rhenium carbonyl with dialkyl/diaryl chalcogenide (RE-ER; E = S and Se) in the presence of ditopic flexible or semiflexible pyridyl ligand with amide functionality (L = N,N'-bis(4-pyridylcarboxamide)-1,2-ethane (bpce) and N,N'-bis(4-(4-pyridylcarboxamide)phenyl)methane (bpcpm)). Compounds 1-8 were formed by multicomponent self-assembly under one-pot reaction conditions via oxidative addition of dialkyl/diaryl chalcogenide to rhenium carbonyl with pyridyl ligands. The resultant metallacyclophanes were characterized using elemental analyses, infrared, ultraviolet-visible, and NMR spectroscopic techniques. Metallacyclophanes 1-3 and 7 were structurally characterized by single-crystal X-ray diffraction methods. The solvent-induced structural change of flexible tetranuclear metallacyclophane 2 was demonstrated by crystallizing 2 in dichloroethane and dimethylformamide. Molecular recognition capabilities of 2 and 7 were studied with few aromatic compounds containing ethereal linkages.

Gels with sense: supramolecular materials that respond to heat, light and sound

Advances in the field of supramolecular chemistry have made it possible, in many situations, to reliably engineer soft materials to address a specific technological problem. Particularly exciting are "smart" gels that undergo reversible physical changes on exposure to remote, non-invasive environmental stimuli. This review explores the development of gels which are transformed by heat, light and ultrasound, as well as other mechanical inputs, applied voltages and magnetic fields. Focusing on small-molecule gelators, but with reference to organic polymers and metal-organic systems, we examine how the structures of gelator assemblies influence the physical and chemical mechanisms leading to thermo-, photo- and mechano-switchable behaviour. In addition, we evaluate how the unique and versatile properties of smart materials may be exploited in a wide range of applications, including catalysis, crystal growth, ion sensing, drug delivery, data storage and biomaterial replacement.

Rapid self-healing and anion selectivity in metallosupramolecular gels assisted by fluorine–fluorine interactions

Metal complexes from perfluoroalkylamide terpyridine self-assemble into anion selective gels, which manifest self-healing and thermal rearrangement in aqueous dimethyl sulfoxide.

1D hacksaw chain bipyridine–sulfonate Schiff base-dicopper(ii) as a host for variable solvent guests

The current study related to five solvatomorphs containing the 1D hacksaw chain of bipyridine–sulfonate Schiff base-dicopper(ii) as a host provides the first example of a polymeric copper(ii) system with five interconvertible solvatomorphic forms.

Aminopyridine derivatives controlled the assembly and various properties of Cu–BTC metal–organic frameworks

Three Cu(ii) MOFs based on three aminopyridine derivatives and 1,3,5-benzenetricarboxylic acid have been synthesized and characterized. The electrocatalytic and photocatalytic properties of complexes 1–3 have been investigated in detail.

A new small molecule gelator and 3D framework ligator of lead(ii)

A new allene dicarboxylate ligand reacts with hydrated lead(ii) acetate in DMF to yield either a crystalline 3D framework or a metallogel dependent on the reaction temperature.

Supramolecular architectures with pyridine-amide based ligands: discrete molecular assemblies and their applications

This perspective offers an overview on the recent progress achieved in the design of discrete molecular assemblies utilizing assorted pyridine-amide based ligands.

On crystal versus fiber formation in dipeptide hydrogelator systems

Naphthalene dipeptides have been shown to be useful low-molecular-weight gelators. Here we have used a library to explore the relationship between the dipeptide sequence and the hydrogelation efficiency. A number of the naphthalene dipeptides are crystallizable from water, enabling us to investigate the comparison between the gel/fiber phase and the crystal phase. We succeeded in crystallizing one example directly from the gel phase. Using X-ray crystallography, molecular modeling, and X-ray fiber diffraction, we show that the molecular packing of this crystal structure differs from the structure of the gel/fiber phase. Although the crystal structures may provide important insights into stabilizing interactions, our analysis indicates a rearrangement of structural packing within the fibers. These observations are consistent with the fibrillar interactions and interatomic separations promoting 1D assembly whereas in the crystals the peptides are aligned along multiple axes, allowing 3D growth. This observation has an impact on the use of crystal structures to determine supramolecular synthons for gelators.