3D Coordination Polymers with Nitrilotriacetic and 4,4‘-Bipyridyl Mixed Ligands: Structural Variation Based on Dinuclear or Tetranuclear Subunits Assisted by Na−O and/or O−H···O Interactions

The solvent influenced coordination variation of flexible ligands to Y(iii) towards MOF structural diversity

Coordination variation by solvent environment change leading to various yttrium-based MOFs with flexible ligands.

Solvent-Effected Coordination Variation of Flexible Ligands to Cu(II) for the Formation of 1D and 2D Secondary Building Units for Metal-Organic Frameworks

Producing more than one structure from the same set of metal and ligand precursors will grant structural diversity in metal-organic framework (MOF) systems. One of the biggest obstacles of getting structural diversity for the late transition metals is that the coordination mode is pretty much fixed by nature. Herein, we show that two different coordination modes to Cu(II) are possible for flexible ligands containing hydrophilic terminal groups through solvent guidance. It is demonstrated that trans,trans-muconic acid (H₂muco) ligands coordinate to Cu(II) to form Cu(II) muconate MOFs having a 1D chain structure and a 2D plane structure in water-rich and DMF-rich water-DMF mixed solvent systems, respectively. It is suggested that the interaction between ligands and solvent is responsible for the selective coordination. A similar result was observed from the attempts using the fumaric acid ligand. Our results provide a new direction to obtain diverse secondary building units for the construction of diverse MOFs.

Micro-Blooming: Hierarchically Porous Nitrogen-Doped Carbon Flowers Derived from Metal-Organic Mesocrystals

Synthesis of 3D flower-like zinc-nitrilotriacetic acid (ZnNTA) mesocrystals and their conformal transformation to hierarchically porous N-doped carbon superstructures is reported. During the solvothermal reaction, 2D nanosheet primary building blocks undergo oriented attachment and mesoscale assembly forming stacked layers. The secondary nucleation and growth preferentially occurs at the edges and defects of the layers, leading to formation of 3D flower-like mesocrystals comprised of interconnected 2D micropetals. By simply varying the pyrolysis temperature (550-1000 °C) and the removal method of in the situ-generated Zn species, nonporous parent mesocrystals are transformed to hierarchically porous carbon flowers with controllable surface area (970-1605 m² g^-1 ), nitrogen content (3.4-14.1 at%), pore volume (0.95-2.19 cm³ g^-1 ), as well as pore diameter and structures. The carbon flowers prepared at 550 °C show high CO₂ /N₂ selectivity due to the high nitrogen content and the large fraction of (ultra)micropores, which can greatly increase the CO₂ affinity. The results show that the physicochemical properties of carbons are highly dependent on the thermal transformation and associated pore formation process, rather than directly inherited from parent precursors. The present strategy demonstrates metal-organic mesocrystals as a facile and versatile means toward 3D hierarchical carbon superstructures that are attractive for a number of potential applications.

An efficient approach to modulate the coordination number of yttrium ions for diverse network formation

Hidden role of water! It acts as a key to determine the coordination number of yttrium by controlling the active ligand concentration.

pH-Controlled Assembly of 3D and 2D Zinc-Based Metal-Organic Frameworks with Tetrazole Ligands

We report the synthesis and structural diversity of Zn(II) metal-organic framework (MOF) with in situ formation of tetrazole ligand 3-ptz [3-ptz = 5-(3-pyridyl)tetrazolate] as a function pH. By varying the initial reaction pH, we obtain high-quality crystals of the noncentrosymmetric three-dimensional MOF Zn(3-ptz)2 , mixed phases involving the zinc-aqua complex [Zn(H2O)4(3-ptz)2]·4H2O, and two-dimensional MOF crystals Zn(OH)(3-ptz) with a tunable microrod morphology, keeping reaction time, temperature, and metal-ligand molar ratio constant. Structures are characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and UV-vis spectroscopy. We discuss the observed structural diversity in terms of the relative abundance of hydroxo-zinc species in solution for different values of pH.

A Fluorescent Chemosensor for Zn2+ Based on a C3-Symmetrical and Pre-Organized 2,2′,2″-Nitrilotribenzoic Acid Material

A C3-symmetrical 4,4″,4⁗-nitrilotris(2′-methyl-[1,1′-biphenyl]-3-carboxylic acid) (4) derived from nitrilotriacetic acid (NTA) was found to selectively bind Zinc(ii) ions both in DMSO or MeOH. A synergistic effect of the anionic counter ion SO42− on the sensing behaviour of 4 to metal ions was clearly observed in DMSO. Interestingly, 4 showed a rapid hypochromatic shift in emission ascribed to the deprotonation and the concomitant formation of a 4–metal complex upon the addition of Zn2+ ions, instead of the bathochromic shift and emission enhancement attributed to the SO42−-involved hydrogen-bonding interaction for Ni2+, Li+, Mg2+, and Na+ ions at ratios below 1:1 in DMSO. The observed sensing process of sulfate salts associated with the SO42−-involved hydrogen-bonding interaction, deprotonation, and the concomitant complexation can also be clearly monitored by titration methods utilising UV-vis, fluorescence, and NMR spectroscopy in solution. In comparison with 4, compound 1 showed an obvious difference in the binding interaction with zinc sulfate in MeOH, probably owing to the decreased acidity. Anion-induced hydrogen-bonding interactions and deprotonation of the COOH protons in the excited state also endowed 4 versatile spectroscopic properties. The addition of F− and SO42− anions resulted in a remarkable enhancement probably related with a rigidifying effect. 2,2′,2″-Nitrilotribenzoic acid can be utilised as a potential scaffold to build a series of conjugated fluorescent sensors by its chelation effect owing to the rigid cavity pre-organised by the triphenylamine moiety and the carboxylic groups and the conjugation extension in the 4,4′,4″ positions.

Self-assembly of triangular metallomacrocycles using unsymmetrical bisterpyridine ligands: isomer differentiation via TWIM mass spectrometry

Three unsymmetrical, 60°-bended bisterpyridine ligands with varying phenylene spacer lengths have been synthesized via the Suzuki-Miyaura coupling reactions. Their self-assembly processes were found to be strongly dependent on the ligand geometry. Upon complexation with Zn(II) ions, only 2,4''-di(4'-terpyridinyl)-1,1':4',1''-terphenyl underwent self-selection to give a trinuclear metallomacrocycle with perfect heteroleptic connectivity and the other two afforded a mixture of constitutional isomers. The metallosupramolecular assemblies were characterized by NMR spectroscopy, electrospray mass spectrometry (ESI MS), and single-crystal X-ray diffraction. In particular, the identification of isomeric architecture was accomplished using tandem mass spectrometry (MS(2)) coupled with traveling wave ion mobility mass spectrometry (TWIM MS).

Solvent-dependent assemblies, structure diversities and magnetic properties of two homochiral Co(ii)/Na(i) coordination polymers

Two novel homochiral Co(ii)/Na(i) coordination polymers based on chiral tridentate S-H₃L ligand have been successfully synthesized and structurally characterized.

Functionalities and architectures of coordination polymers with multi-dimensionalities via transition metal–dicarboxylate ligands

Five coordination polymers based on the flexible H₂dpd ligand and different metal salts have been synthesised. The configuration of the ligand and the reaction temperature have important effects on the final structures.

Synthesis, structures and magnetic properties in 3d-electron-rich isostructural complexes based on chains with sole syn–anti carboxylate bridges

A series of isostructures based on 2,2′,4,4′-biphenyltetracarboxylic acid have been synthesized via solvothermal reaction, whereas magnetic studies reveal the polymers with sole syn–anti carboxylate bridges show different magnetic behaviors of uniform chains.

Synthesis of a series of coordination polymers based on mixed ligands to tune the structural dimension

Schematic illustrating the 2D network of complex 1. Color code: yellow, Mn; cob²⁻ ligand, red.