A zinc-organic coordination polymer of glycine-functionalized naphthalenediimide ligand

Preliminary chemical reduction for synthesizing a stable porous molecular conductor with neutral metal nodes

Preliminary chemical reduction of naphthalenediimide (NDI)-based organic ligands was applied to the synthesis of a porous molecular conductor (PMC) with neutral metal nodes (cobalt(ii) acetylacetonate). The obtained semiconductive PMC (PMC-2) was stable due to the neutral metal nodes, providing an advantage over electrochemical reduction.

Coordination Polymers Based on Highly Emissive Ligands: Synthesis and Functional Properties

Coordination polymers are constructed from metal ions and bridging ligands, linking them into solid-state structures extending in one (1D), two (2D) or three dimensions (3D). Two- and three-dimensional coordination polymers with potential voids are often referred to as metal-organic frameworks (MOFs) or porous coordination polymers. Luminescence is an important property of coordination polymers, often playing a key role in their applications. Photophysical properties of the coordination polymers can be associated with intraligand, metal-centered, guest-centered, metal-to-ligand and ligand-to-metal electron transitions. In recent years, a rapid growth of publications devoted to luminescent or fluorescent coordination polymers can be observed. In this review the use of fluorescent ligands, namely, 4,4'-stilbenedicarboxylic acid, 1,3,4-oxadiazole, thiazole, 2,1,3-benzothiadiazole, terpyridine and carbazole derivatives, naphthalene diimides, 4,4',4''-nitrilotribenzoic acid, ruthenium(II) and iridium(III) complexes, boron-dipyrromethene (BODIPY) derivatives, porphyrins, for the construction of coordination polymers are surveyed. Applications of such coordination polymers based on their photophysical properties will be discussed. The review covers the literature published before April 2020.

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.

Three zinc(II) and cadmium(II) complexes containing 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole and polynitrile ligands: synthesis, molecular and supramolecular structures, and photoluminescence properties

Three photoluminescent complexes containing either Zn^II or Cd^II have been synthesized and their structures determined. Bis[4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole-κ²N¹,N⁵]bis(dicyanamido-κN¹)zinc(II), [Zn(C₁₂H₁₀N₆)₂(C₂N₃)₂], (I), bis[4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole-κ²N¹,N⁵]bis(dicyanamido-κN¹)cadmium(II), [Cd(C₁₂H₁₀N₆)₂(C₂N₃)₂], (II), and bis[4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole-κ²N¹,N⁵]bis(tricyanomethanido-κN¹)cadmium(II), [Cd(C₁₂H₁₀N₆)₂(C₄N₃)₂], (III), all crystallize in the space group P-1, with the metal centres lying on centres of inversion, but neither analogues (I) and (II) nor Cd^II complexes (II) and (III) are isomorphous. A combination of N-H...N and C-H...N hydrogen bonds and π-π stacking interactions generates three-dimensional framework structures in (I) and (II), and a sheet structure in (III). The photoluminescence spectra of (I)-(III) indicate that the energies of the π-π* transitions in the coordinated triazole ligand are modified by minor changes of the ligand geometry associated with coordination to the metal centres.

Synthesis and characterization of a photochromic magnesium(II) coordination polymer based on a naphthalene diimide ligand

Naphthalene diimides, which are planar, chemically robust and redox-active, are an attractive class of electron-deficient dyes, which can undergo a single reversible one-electron reduction to form stable radical anions in the presence of electron donors upon irradiation. This makes them excellent candidates for organic linkers in the construction of photochromic coordination polymers. Such a photochromic one-dimensional linear coordination polymer has been prepared using N,N′-bis(3-carboxyphenyl)naphthalene-1,8:4,5-tetracarboximide (H2BBNDI). Crystallization of H2BBNDI with magnesium nitrate in an N,N′-dimethylformamide (DMF)/ethanol/H2O mixed-solvent system under solvothermal conditions afforded the one-dimensional coordination polymer catena-poly[[bis(dimethylformamide-κO)magnesium(II)]-bis[μ-N-(3-carboxylatophenyl)-N′-(3-carboxylphenyl)naphthalene-1,8:4,5-tetracarboximide-κ2 O:O′]], [Mg(C28H13N2O8)2(C3H7NO)2] n . The asymmetric unit contains half of a magnesium cation, one HBBNDI− ligand and one DMF molecule. Two partially deprotonated HBBNDI− ligands bridge two magnesium cations to form a one-dimensional chain. Strong inter-chain π–π interactions between the naphthalene rings of the HBBNDI− ligand and the imide rings of adjacent chains provide a two-dimensional structure. The supramolecular three-dimensional framework is stabilized by π–π interactions between naphthalene rings of neighbouring two-dimensional supramolecular networks. The complex exhibits a reversible photochromic behaviour, which may originate from the photoinduced electron-transfer generation of radicals in the HBBNDI− ligand.

Two new isomeric zinc(II) metal–organic frameworks based on 1,5-bis(2-methyl-1H-imidazol-1-yl)pentane and 5-methylisophthalate ligands

Many factors, such as temperature, solvent, the central metal atom and the type of coligands, may affect the nature of metal–organic frameworks (MOFs) and the framework formation in the self-assembly process, which results in the complexity of these compounds and the uncertainty of their structures. Two new isomeric ZnIImetal–organic frameworks (MOFs) based on mixed ligands, namely, poly[[μ-1,5-bis(2-methyl-1H-imidazol-1-yl)pentane-κ2N3:N3′](μ-5-methylisophthalato-κ2O1:O3)zinc(II)], [Zn(C9H6O4)(C13H20N4)]n, (I), and poly[[μ-1,5-bis(2-methyl-1H-imidazol-1-yl)pentane-κ2N3:N3′](μ3-5-methylisophthalato-κ3O1:O1′:O3)(μ3-5-methylisophthalato-κ4O1:O1′:O3,O3′)dizinc(II)], [Zn2(C9H6O4)2(C13H20N4)]n, (II), have been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction, IR spectroscopy, elemental analysis and thermogravimetric analysis. Complex (I) displays a two-dimensional layer net, while complex (II) exhibits a twofold interpenetrating three-dimensional framework. Both complexes show high stability and good fluorescence in the solid state at room temperature.

Synthesis, structure, thermostability and luminescence properties of Zn(II) and Cd(II) coordination polymers based on dimethysuccinate and flexible 1,4-bis(imidazol-1-ylmethyl)benzene ligands

The design and synthesis of functional coordination polymers is motivated not only by their structural beauty but also by their potential applications. Zn(II) and Cd(II) coordination polymers are promising candidates for producing photoactive materials because these d(10) metal ions not only possess a variety of coordination numbers and geometries, but also exhibit luminescence properties when bound to functional ligands. It is difficult to predict the final structure of such polymers because the assembly process is influenced by many subtle factors. Bis(imidazol-1-yl)-substituted alkane/benzene molecules are good bridging ligands because their flexibility allows them to bend and rotate when they coordinate to metal centres. Two new Zn(II) and Cd(II) coordination polymers based on mixed ligands, namely, poly[[μ2-1,4-bis(imidazol-1-ylmethyl)benzene-κ(2)N(3):N(3')]bis(μ3-2,2-dimethylbutanoato-κ(3)O(1):O(4):O(4'))dizinc(II)], [Zn2(C6H8O4)2(C14H14N4)]n, and poly[[μ2-1,4-bis(imidazol-1-ylmethyl)benzene-κ(2)N(3):N(3')]bis(μ3-2,2-dimethylbutanoato-κ(5)O(1),O(1'):O(4),O(4'):O(4))dicadmium(II)], [Cd2(C6H8O4)2(C14H14N4)]n, have been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction, elemental analysis, IR spectroscopy and thermogravimetric analysis. Both complexes crystallize in the monoclinic space group C2/c with similar unit-cell parameters and feature two-dimensional structures formed by the interconnection of S-shaped Zn(Cd)-2,2-dimethylsuccinate chains with 1,4-bis(imidazol-1-ylmethyl)benzene bridges. However, the Cd(II) and Zn(II) centres have different coordination numbers and the 2,2-dimethylsuccinate ligands display different coordination modes. Both complexes exhibit a blue photoluminescence in the solid state at room temperature.

Photochromic metal-organic frameworks for inkless and erasable printing

Inkless and erasable printing is the key solution towards a more sustainable paper industry, in terms of reducing paper wastages and the associated environmental hazards from waste paper processing. However, only a few cases have been reported in the literature where inkless printing has been tested in some practical systems. In an attempt to address this solution, we used photochromic metal-organic frameworks (MOFs) and tested their capability as inkless and erasable printing media. The printing was performed using sunlight as the light source on MOF-coated papers. The resulting printing had good resolution and stability, and was capable of being read both by the human eye and smart electronic devices; furthermore, the paper could be reused for several cycles without any significant loss in intensity. Interestingly, different coloured printing with a similar efficiency was achieved by varying the structure of the MOF.

Engineering entanglement: controlling the formation of polycatenanes and polyrotaxanes using π interactions

A reproducible metallocyclic motif containing amino-acid functionalised aromatic diimides has been employed to demonstrate remarkable control over entanglement topologies.