Zinc(II)-Based Ring-and-Rod Coordination Layer as an Excitation-Wavelength-dependent Dual-Emissive Chemosensor for Discriminating Fe3+, Cr3+, and Al3+ in Water

The reactions of Zn(NO3)2, 3,6-bis(pyridin-3-yl)-9H-carbazole (bpycz), and 2,5-dihydroxyterephthalic acid (H4dhbdc) or 2-bromoterephthalic acid (Br-1,4-H2bdc) under hydro(solvo)thermal conditions yielded corresponding coordination polymers (CPs) {[Zn(H2dhbdc)(bpycz)]•0.5H2O}n (1) and [Zn(Br-1,4-bdc)(bpycz)]•2DMAc•H2O (2), respectively, with high thermal stability approaching 350 °C. CP 1 adopts a ring-and-rod layer structure, which is topologically described as a 4-connected net with the point symbol of 2•65. Two layers are interpenetrated in parallel interlocking mode to form a double 2D → 2D polyrotaxane entanglement with extra-framework void space of 19.6%. CP 2 has a non-interpenetrating ring-and-rod layer structure of 4-connected 2•65 net topology, with extra-framework void space of 16.6%. Thermally activated 1 and 2 revealed CO2 uptakes of 101.1 and 98.6 cm3 g-1, respectively, at P/P0 = 1 and 195 K. X-ray powder diffraction (XRPD) patterns confirmed that 1 and 2 both possessed high chemical stability in H2O, CH3OH, acetone, and DMF, and framework stability during gas adsorption-desorption. The H2O suspension of 1 displayed excitation-dependent dual-emissive properties, appearing at 432 nm upon excitation at 300 nm and at 528 nm upon excitation at 365 nm. Of note, 1 was capable of detection of Fe3+, Cr3+, and Al3+ ions in H2O, showing good anti-interference ability, excellent selectivity, and high sensitivity. More interesting, the dual-emissive properties make 1 to be an excellent luminescence chemosensor to screen Fe3+, Cr3+, and Al3+ from a pool of metal ions in H2O upon excitation at 300 nm via luminescence quenching effect and then discriminate Fe3+, Cr3+, and Al3+ upon excitation at 365 nm via luminescence quenching, unaltered, and enhancement responses, respectively. On the other hand, the H2O suspension of 2 demonstrated an excitation-independent emission appearing at around 430 nm, which could be utilized to sensitively detect Fe3+ and Cr3+ ions with good anti-interference ability and excellent selectivity via luminescence quenching effect. Further, 1 and 2 were recyclability and possessed cycling stability. The plausible sensing mechanisms for 1 and 2 toward Fe3+, Cr3+, and Al3+ were also explored in detail.

Woven, Polycatenated, or Cage Structures: Effect of Modulation of Ligand Curvature in Heteroleptic Uranyl Ion Complexes

Combining the flexible zwitterionic dicarboxylate 4,4'-bis(2-carboxylatoethyl)-4,4'-bipyridinium (L) and the anionic dicarboxylate ligands isophthalate (ipht^2-) and 1,2-, 1,3-, or 1,4-phenylenediacetate (1,2-, 1,3-, and 1,4-pda^2-), of varying shape and curvature, has allowed isolation of five uranyl ion complexes by synthesis under solvo-hydrothermal conditions. [(UO₂)₂(L)(ipht)₂] (1) and [(UO₂)₂(L)(1,2-pda)₂]·2H₂O (2) have the same stoichiometry, and both crystallize as monoperiodic coordination polymers containing two uranyl-(anionic carboxylate) strands united by L linkers into a wide ribbon, all ligands being in the divergent conformation. Complex 3, [(UO₂)₂(L)(1,3-pda)₂]·0.5CH₃CN, with the same stoichiometry but ligands in a convergent conformation, is a discrete, binuclear species which is the first example of a heteroleptic uranyl carboxylate coordination cage. With all ligands in a divergent conformation, [(UO₂)₂(L)(1,4-pda)(1,4-pdaH)₂] (4) crystallizes as a sinuous and thread-like monoperiodic polymer; two families of chains run along different directions and are woven into diperiodic layers. Modification of the synthetic conditions leads to [(UO₂)₄(LH)₂(1,4-pda)₅]·H₂O·2CH₃CN (5), a monoperiodic polymer based on tetranuclear (UO₂)₄(1,4-pda)₄ rings; intrachain hydrogen bonding of the terminal LH⁺ ligands results in diperiodic network formation through parallel polycatenation involving the tetranuclear rings and the LH⁺ rods. Complexes 1-3 and 5 are emissive, with complex 2 having the highest photoluminescence quantum yield (19%), and their spectra show the maxima positions usual for tris-κ²O,O'-chelated uranyl cations.

Impact of the Structural Modification of Diamondoid Cd(II) MOFs on the Nonlinear Optical Properties

A change in the degree of interpenetration (DOI) in metal-organic frameworks (MOFs) prompted by heat, pressure, or exchange of solvents is a fascinating phenomenon that can potentially impact the functional properties of MOFs. Structural transformation involving two noncentrosymmetric MOFs with different DOIs provides a rare opportunity to manipulate their optical properties. Herein, we report an unusual single-crystal-to-single-crystal (SCSC) transformation of a noncentrosymmetric 7-fold interpenetrated diamondoid (dia) Cd(II) MOF into another noncentrosymmetric but 8-fold interpenetrated dia MOF upon the removal of guest solvents. A hydrogen-bond network formed between the lattice solvents and linker trans-2-(4-pyridyl)-4-vinylbenzoate (pvb) in a 7-fold interpenetrated noncentrosymmetric MOF results in a significant increase in the two-photon absorption cross-section (11 times) as compared to that in the desolvated 8-fold interpenetrated MOF. Also, an increase in the DOI in the noncentrosymmetric crystals strengthened the π···π interaction between the individual diamondoid networks and enhanced the second-order nonlinear optical (NLO) coefficient (deff) by 4.5 times. These results provide a way to manipulate the optical properties of MOFs using a combined strategy of the formation of hydrogen bonds and interpenetration for access to tunable single-crystal NLO devices in an SCSC manner. By changing the experimental conditions, another dia Cd(II) MOF with 4-fold interpenetration can be isolated. In this centrosymmetric MOF, the olefin groups in the backbone of the ligand (pvb) undergo a [2 + 2] cycloaddition reaction quantitatively under UV light but in a non-SCSC fashion.

Construction of 2D Interdigitated Polyrotaxane Layers and their Transformation to a 3D Polyrotaxane by a Photocycloaddition Reaction between Wheels

Following the pioneering work of Sauvage and Stoddart on rotaxanes, construction of higher dimensional polyrotaxanes in metal-organic frameworks (MOFs) via a modified protocol is challenging. We present the formation of a two-dimensional (2D) polyrotaxane and its conversion to a three-dimensional (3D) polyrotaxane MOF via a photoreaction between interdigitated "olefin wheels". For this purpose, a 2-fold entangled 2D MOF [Pb₂(bpp)(sdc)₂] (1), showing a 2D + 2D → 2D polyrotaxane motif, has been synthesized from the solvothermal reaction of lead(II) nitrate, 3,3'-stilbenedicarboxylic acid (H₂sdc) containing an olefin group, and 1,4-bis(4-pyridyl)piperazine (bpp). The single-crystal X-ray diffraction analysis of 1 revealed that the adjacent entangled 2D layers are interdigitated, with the separation of 3.72 Å between C═C bond pairs in adjacent layers satisfying Schmidt's criteria for the occurrence of a [2 + 2] photocycloaddition reaction. Irradiation of the single crystals of 1 under UV light resulted in formation of a 3D polyrotaxane, [Pb₂(bpp)(rctt-tccb)]_n (2), due to a [2 + 2] photocycloaddition reaction between two wheels via a single-crystal to single-crystal transformation. The photocycloaddition and partial thermal cleavage reaction between 1 and 2 were confirmed by ¹H NMR and powder X-ray diffraction (PXRD) in solution and the solid state, respectively. The present approach could contribute to the understanding of the construction of higher dimensional polyrotaxanes which are not accessible by the traditional routes.

Metal–organic frameworks with different spatial dimensions for supercapacitors

Recent progress in MOF materials for SCs with different spatial dimensions, such as 2D MOFs, including conductive MOFs and nanosheets, and 3D MOFs, categorized as single metallic and multiple metallic MOFs, are reviewed.

Co(ii) coordination polymers constructed from a bent chiral linker: influencing framework topology using co-ligands

The reaction of a semi-rigid chiral ligand with Co(ii) and dipyridyl co-ligands of varying length yielded a series of 2D coordination frameworks, with the topology of the network mediated by the length of the co-ligands.

Two-fold interpenetrated Mn-based metal–organic frameworks (MOFs) as battery-type electrode materials for charge storage

Two novel interpenetrated 2-fold Mn-MOFs were successfully prepared and applied for the first time in a charge-storage field. As a result, the bulk electrodes behave as alkaline batteries and deliver high capacities of 1004 and 619 C g⁻¹ at 1 A g⁻¹.

Zr-MOF/Polyaniline Composite Films with Exceptional Seebeck Coefficient for Thermoelectric Material Applications

Controlling the polymerization of aniline in the presence of zirconium-based metal-organic frameworks (Zr-MOFs) using polystyrene sulfonic acid as a dopant resulted in the formation of a new type of free-standing thermoelectric composite film. Polyaniline chains interpenetrate into the Zr-MOFs to enhance the crystallinity of polyaniline, resulting in an improved degree of electrical conductivity. In addition, the inherent porosity of the Zr-MOFs functions to suppress the increase in thermal conductivity, thus dramatically promoting a negative Seebeck coefficient. When 20 wt % Zr-MOF was used, a power factor of up to 664 μW/(m K²) was obtained, which was accompanied by a surprisingly large, negative Seebeck coefficient. The new class of MOF-based composites offers a new direction for developing new types of efficient thermoelectric materials.

Crystal-engineering and luminescence studies of 1,3,5-tris(3-pyridylethynyl)benzene or 1,3,5-tris(4-pyridylethynyl)benzene with copper(i) iodides

The interlocking of 1-D frameworks into the 28-membered rings of the adjacent chains generates a novel 1-D (1-D → 1-D) polyrotaxane framework of 3.

Structural, thermal and topological characterization of coordination networks containing flexible aminocarboxylate ligands with a central biphenylene scaffold

Flexible aminocarboxylate ligands have been used to construct coordination networks containing Zr, Zn and Cd featured by different dimensionalities and topologies.

Elucidation of naphthalene diimide metallomacrocycles and catenanes by solvent dependent excimer and exciplex emission

The formation of metallocatenanes, and their disruption by aromatic solvents, is followed by excimer and exciplex emission.

An acetylenedicarboxylato-bridged Mn(ii)-based 1D coordination polymer: electrochemical CO2 reduction and magnetic properties

A Mn(ii)-based 1D coordination polymer, [Mn(adc)(4-phpy)₂(H₂O)₂]_n, (H₂adc = acetylenedicarboxylic acid and 4-phpy = 4-phenylpyridine) showed dual properties: electrochemical CO₂ reduction and anti-ferromagnetism.

A Cu(ii) metallocycle for the reversible self-assembly of coordination-driven polyrotaxane-like architectures

We report the design and synthesis of a Cu(ii) metallocycle (1) and use the possibility to expand the Cu(ii) coordination sphere to self-assemble mechanically interlocked species via interpenetration. Metallocycle 1 can be used as a platform to reversibly assemble a 1D + 1D → 1D coordination-driven polyrotaxane (3), where 1 acts as the hosting ring as well as the stopper, and 4,4'-bipyridine is the guest-axle. A coordinating solvent can substitute the 4,4'-bipyridine axle to disassemble the polyrotaxane (3 → 2) that is easily restored by further adding 4,4'-bipyridine (2 → 3). Other polyrotaxanes can be isolated by reacting 1 with pyridine (4) and phenylpyridine (5). Interconversion among the presented species is demonstrated and ensured by the open position of each copper center in platform 1.

A new CdII coordination polymer with a self-penetrating architecture induced by the molecular conformation of a rigid bithiophene ligand

The design and synthesis of coordination polymers with a self-penetrating architecture has attracted much interest not only due to their interesting structures but also due to their potential applications. 5,5'-Bis(pyridin-4-yl)-2,2'-bithiophene (bpbp), as a conjugated bithiophene ligand, can exhibit trans and cis conformations and this can lead to the construction of a self-penetrating architecture. In addition, the semi-rigid ancillary ligand 4,4'-oxybis(benzoic acid) (H₂oba) can adopt different coordination modes, resulting in coordination polymers with high-dimensional skeletons. A new Cd^II coordination polymer based on mixed ligands, namely poly[diaquapentakis[μ-5,5'-bis(pyridin-4-yl)-2,2'-bithiophene-κ²N:N']bis(nitrato-κ²O,O')tetrakis(μ₃-4,4'-oxydibenzoato)-κ¹⁰O:O,O':O'',O''';κ⁶O:O':O''-pentacadmium(II)], [Cd₅(C₁₄H₁₄O₅)₄(NO₃)₂(C₁₈H₁₂N₂S₂)₅(H₂O)₂]_n, (I), has been synthesized under solvothermal conditions and characterized by single-crystal X-ray diffraction, IR spectroscopy and elemental analysis. Single-crystal X-ray diffraction indicates that there are three crystallographically independent Cd^II cations, three bpbp ligands, two deprotonated oba^2- ligands, one nitrate ligand and one coordinated water molecule in the asymmetric unit. One Cd^II centre is seven-coordinated, exhibiting a distorted {CdN₂O₅} pentagonal bipyramidal geometry, while the other two Cd centres are both six-coordinated, showing slightly distorted {CdN₂O₄} octahedral geometries. The most interesting feature is the co-existence of trans and cis conformations in a single net, allowing structural interpenetration via self-threading and yet the expected self-penetrating structure was obtained. Topological analysis shows that the whole three-dimensional framework can be classified as a 3-nodal (4,6,6)-c net with Schläfli symbol {6¹³.8²}₂{6⁶}, which is a new topology. Furthermore, the luminescence properties of (I) were examined in the solid state at room temperature.

Assembly of a series of coordination polymers built from rigid a tetracarboxylate ligand and flexible bis(imidazole) linker: syntheses, structural diversities, luminescence sensing, and photocatalytic properties

Hydrothermal reactions of aromatic terphenyl-4,2'',5'',4'-tetracarboxylic acid (H₄tta) and transitional metal cations in the presence of two flexible N-donor ancillary ligands afforded four novel coordination polymers, namely, {[Zn(tta)_0.5(m-bimb)]·H₂O}_n (1), [Ni₂(tta)(m-bimb)₂(H₂O)]_n (2), [Ni(H₂tta)(o-bimb)·H₂O]_n (3), and [Cd(tta)_0.5(o-bimb)]_n (4), from solvothermal reactions in the presence of bis(imidazole) bridging linkers (m-bimb = 1,3-bis(imidazol-1-ylmethyl)benzene, and o-bimb = 1,2-bis(imidazol-1-ylmethyl)benzene). Their structures were determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses (EA), powder X-ray diffraction (PXRD), and thermogravimetric (TG) analyses. Compound 1 displayed a 2-fold 3D → 3D parallel entangled (4,4)-connected bbf net with the point symbol of (6⁴·8²)(6⁶)₂. Compound 2 featured a predocumented 3D (4,8)-connected (3²·5³·6)(3⁴·4⁴·5⁹·6¹¹) net. Compound 3 exhibited a 2D 4-connected sql sheet with the point symbol of (4⁴·6²), and compound 4 showed a 2D 4-connected (3²·6²·7²) kgm sheet. To our delight, fluorescence measurements showed that compound 1 could selectively and sensitively detect Cr³⁺ cations and nitrobenzene derivatives (nitrobenzene (NB), p-nitrotoluene (PNT), and p-nitroaniline (PNA)), which suggested that CPs of 1 was a promising bifunctional luminescence sensor material that could sense metal ions and small organic molecules. Moreover, 1 showed excellent photocatalytic activity.

Acid- and base-stable porous mechanically interlocked 2D metal–organic polyrotaxane forin situorganochlorine insecticide encapsulation, sensing and removal

The encapsulation and removal of extremely toxic dieldrin by compound1.

Assembly of ZnII-coordination polymers constructed from benzothiadiazole functionalized bipyridines and V-shaped dicarboxylic acids: topology variety, photochemical and visible-light-driven photocatalytic properties

Photocatalytic properties of four benzothiadiazole functionalized coordination polymers have been reported.

Properties and emerging applications of mechanically interlocked ligands

Mechanically interlocked molecules have a long and rich history as ligands thanks to the key role coordination chemistry has played in the development of high yielding passive template syntheses of rotaxanes and catenanes. In this Feature Article, we highlight the effect of the mechanical bond on the properties of metal ions bound within the sterically hindered environment of the macrocycle cavity, and discuss the emerging applications of interlocked ligands in catalysis, sensing and supramolecular materials.

Rotaxane synthesis exploiting the M(i)/M(iii) redox couple

In the context of advancing the use of metal-based building blocks for the construction of mechanically interlocked molecules, we herein describe the preparation of late transition metal containing [2]rotaxanes (1). Capture and subsequent retention of the interlocked assemblies are achieved by the formation of robust and bulky complexes of rhodium(iii) and iridium(iii) through hydrogenation of readily accessible rhodium(i) and iridium(i) complexes [M(COD)(PPh₃)₂][BAr^F₄] (M = Rh, 2a; Ir, 2b) and reaction with a bipyridyl terminated [2]pseudorotaxane (3·db24c8). This work was underpinned by detailed mechanistic studies examining the hydrogenation of 1 : 1 mixtures of 2 and bipy in CH₂Cl₂, which proceeds with disparate rates to afford [M(bipy)H₂(PPh₃)₂][BAr^F₄] (M = Rh, 4a[BAr^F₄], t = 18 h @ 50 °C; Ir, 4b[BAr^F₄], t < 5 min @ RT) in CH₂Cl₂ (1 atm H₂). These rates are reconciled by (a) the inherently slower reaction of 2a with H₂ compared to that of the third row congener 2b, and (b) the competing and irreversible reaction of 2a with bipy, leading to a very slow hydrogenation pathway, involving rate-limiting substitution of COD by PPh₃. On the basis of this information, operationally convenient and mild conditions (CH₂Cl₂, RT, 1 atm H₂, t ≤ 2 h) were developed for the preparation of 1, involving in the case of rhodium-based 1a pre-hydrogenation of 2a to form [Rh(PPh₃)₂]₂[BAr^F₄]₂ (8) before reaction with 3·db24c8. In addition to comprehensive spectroscopic characterisation of 1, the structure of iridium-based 1b was elucidated in the solid-state using X-ray diffraction.

Solid-State Gas Adsorption Studies with Discrete Palladium(II) [Pd2 (L)4 ]4+ Cages

The need for effective CO₂ capture systems remains high, and due to their tunability, metallosupramolecular architectures are an attractive option for gas sorption. While the use of extended metal organic frameworks for gas adsorption has been extensively explored, the exploitation of discrete metallocage architectures to bind gases remains in its infancy. Herein the solid state gas adsorption properties of a series of [Pd₂ (L)₄ ]⁴⁺ lantern shaped coordination cages (L = variants of 2,6-bis(pyridin-3-ylethynyl)pyridine), which had solvent accessible internal cavities suitable for gas binding, have been investigated. The cages showed little interaction with dinitrogen gas but were able to take up CO₂ . The best performing cage reversibly sorbed 1.4 mol CO₂ per mol cage at 298 K, and 2.3 mol CO₂ per mol cage at 258 K (1 bar). The enthalpy of binding was calculated to be 25-35 kJ mol^-1 , across the number of equivalents bound, while DFT calculations on the CO₂ binding in the cage gave ΔE for the cage-CO₂ interaction of 23-28 kJ mol^-1 , across the same range. DFT modelling suggested that the binding mode is a hydrogen bond between the carbonyl oxygen of CO₂ and the internally directed hydrogen atoms of the cage.

Six new coordination compounds based on rigid 5-(3-carboxy-phenyl)-pyridine-2-carboxylic acid: synthesis, structural variations and properties

Compounds 1–6 have rich structural chemistry ranging from mononuclear (1 and 2), one-dimensional (3 and 4), two-dimensional (5) to three-dimensional (6) structures.

Polycatenation tuned microporosity of two metal–tris(4′-carboxybiphenyl)amine frameworks with multilayer structures

By employing a nanosized tris(4′-carboxybiphenyl)amine ligand to assemble with Zn²⁺ ions, a novel trilayer network (FIR-37) and an unprecedented 2D → 3D microporous polycatenation framework (FIR-38) based on unusual tetralayers have been synthesized and structurally characterized.