From 1D to 2D Cd(II) and Zn(II) Coordination Networks by Replacing Monocarboxylate with Dicarboxylates in Partnership with Azine Ligands: Synthesis, Crystal Structures, Inclusion, and Emission Properties

Eight mixed-ligand coordination networks, [Cd(2-aba)(NO₃)(4-bphz)_3/2]_n·n(dmf) (1), [Cd(2-aba)₂(4-bphz)]_n·0.75n(dmf) (2), [Cd(seb)(4-bphz)]_n·n(H₂O) (3), [Cd(seb)(4-bpmhz)]_n·n(H₂O) (4), [Cd(hpa)(3-bphz)]_n (5), [Zn(1,3-bdc)(3-bpmhz)]_n·n(MeOH) (6), [Cd(1,3-bdc)(3-bpmhz)]_n ·0.5n(H₂O)·0.5n(EtOH) (7), and [Cd(NO₃)₂(3-bphz)(bpe)]_n·n(3-bphz) (8) were obtained by interplay of cadmium nitrate tetrahydrate or zinc nitrate hexahydrate with 2-aminobenzenecarboxylic acid (H(2-aba)), three dicarboxylic acids, sebacic (decanedioic acid, H₂seb), homophthalic (2-(carboxymethyl)benzoic acid, H₂hpa), isophthalic (1,3-benzenedicarboxylic acid, H₂(1,3-bdc)) acids, bis(4-pyridyl)ethane (bpe) and with four azine ligands, 1,2-bis(pyridin-4-ylmethylene)hydrazine (4-bphz), 1,2-bis(1-(pyridin-4-yl)ethylidene) hydrazine (4-bpmhz), 1,2-bis(pyridin-3-ylmethylene)hydrazine (3-bphz), and 1,2-bis(1-(pyridin-3-yl) ethylidene)hydrazine (3-bpmhz). Compounds 1 and 2 are 1D coordination polymers, while compounds 3–8 are 2D coordination polymers. All compounds were characterized by spectroscopic and X-ray diffraction methods of analysis. The solvent uptakes and stabilities to the guest evacuation were studied and compared for 1D and 2D coordination networks. The de-solvated forms revealed a significant increase of emission in comparison with the as-synthesized crystals.

Assembly of Three Lanthanide Coordination Polymers from 2-(4-Carboxybenzyloxy) Benzoic Acid Ligand: Synthesis, Structure, and Fluorescent Properties

Three new coordination polymers, {[Ln(cbb)(Hcbb)(DMF)·H2O]n, Ln=Sm (1), Eu (2), Tb(3), H2cbb=2-(4-carboxybenzyloxy) benzoic acid, DMF=N,N-dimethylformamide}, have been synthesised by a solvothermal reaction and structurally characterised by infrared spectroscopy, elemental analysis, thermogravimetry analysis, and X-ray single-crystal diffraction. The results of single-crystal X-ray diffraction indicate that the coordination polymers 1–3 are isostructural, belong to a triclinic system, space group P-1, and show 1D chain structures through the H2cbb ligands connecting adjacent lanthanide ions. In addition, the fluorescence properties of polymers 1–3 were also investigated.

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.

A two-dimensional cadmium(II) coordination polymer based on 5-(pyridin-4-yl)isophthalic acid: poly[[tetraaquabis[μ3-5-(pyridin-4-yl)isophthalato]dicadmium(II)] pentahydrate]

The title CdIIcompound, {[Cd2(C13H7NO4)2(H2O)4]·5H2O}n, was synthesized by the hydrothermal reaction of Cd(NO3)2·4H2O and 5-(pyridin-4-yl)isophthalic acid (H2L). The asymmetric unit contains two crystallographically independent CdIIcations, two deprotonatedL2−ligands, four coordinated water molecules and five isolated water molecules. One of the CdIIcations adopts a six-coordinate octahedral coordination geometry involving three O atoms from one bidentate chelating and one monodentate carboxylate group of two differentL2−ligands, one N atom of anotherL2−ligand and two coordinated water molecules. The second CdIIcation adopts a seven-coordinate pentagonal–bipyramidal coordination geometry involving four O atoms from two bidentate chelating carboxylate groups of two differentL2−ligands, one N atom of anotherL2−ligand and two coordinated water molecules. EachL2−ligand bridges three CdIIcations and, likewise, each CdIIcation connects to threeL2−ligands, giving rise to a two-dimensional graphite-like 63layer structure. These two-dimensional layers are further linked by O—H...O hydrogen-bonding interactions to form a three-dimensional supramolecular architecture. The photoluminescence properties of the title compound were also investigated.

A one-dimensional cobalt(II) coordination polymer based on 2,4'-oxydibenzoic acid: poly[[[diaquabis[2-(4-carboxyphenoxy)benzoato-κO(1)]cobalt(II)]-μ-4,4'-bipyridine-κ(2)N:N'] dihydrate]

The reaction of CoSO4 with 2,4-oxydibenzoic acid (H2oba) and 4,4'-bipyridine (bipy) under hydrothermal condition yielded a new one-dimensional cobalt(II) coordination polymer, {[Co(C14H9O5)2(C10H8N2)(H2O)2]·2H2O}n, which was characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, magnetic properties and single-crystal X-ray diffraction. The Co(II) ions are connected by bipy ligands into infinite one-dimensional chains. The Hoba(-) ligands extend out from the two sides of the one-dimensional chain. O-H···O hydrogen bonding extends these chains into a two-dimensional supramolecular architecture.

catena-Poly[zinc(II)-bis-[μ(2)-3-(3-pyrid-yl)-benzoato]-κO:N;κN:O]

In the title compound, [Zn(C(12)H(8)NO(2))(2)](n), the Zn(2+) cation is coordinated by a pair of carboxyl-ate O atoms as well as two pyridyl N atoms to afford a distorted tetra-hedral environment. Adjacent Zn(2+) cations, with a separation of 8.807 (2) Å, are linked by two 3-(3-pyrid-yl)benzoate ligand bridges, generating an infinite ribbon extending parallel to [001].

Porous metal-organic frameworks as platforms for functional applications

Metal-organic frameworks (MOFs), also known as coordination polymers, have emerged as a new class of crystalline porous materials, which are constructed from metal ions or metal ion clusters and bridging organic linkers. MOFs have tunable pores and functionalities, and usually exhibit very high surface areas. The potential applications of porous MOFs cover a broad range of fields and most of their applications are related to pore sizes, shapes and structures/environments. In this feature article, we provide an overview of the recent developments of porous MOFs as platforms in the functional applications of sorption and separation, heterogeneous catalysis, as supports/host matrices for metal nanoparticles, and as templates/nanoreactors for new material preparation.