A mixed-valence copper coordination polymer generated by hydrothermal metal/ligand redox reactions

Mixed-valence metal-organic frameworks: concepts, opportunities, and prospects

Owing to increasing global demand for the development of multifunctional advanced materials with various practical applications, great attention has been paid to metal-organic frameworks due to their unique properties, such as structural, chemical, and functional diversity. Several strategies have been developed to promote the applicability of these materials in practical fields. The induction of mixed-valency is a promising strategy, contributing to exceptional features in these porous materials such as enhanced charge delocalization, conductivity, magnetism, etc. The current review provides a detailed study of mixed-valence MOFs, including their fundamental properties, synthesis challenges, and characterization methods. The outstanding applicability of these materials in diverse fields such as energy storage, catalysis, sensing, gas sorption, separation, etc. is also discussed, providing a roadmap for future design strategies to exploit mixed valency in advanced materials. Interestingly, mixed-valence MOFs have demonstrated fascinating features in practical fields compared to their homo-valence MOFs, resulting from an enhanced synergy between mixed-valence states within the framework.

In Situ Ligand Formation-Driven Synthesis of a Uranyl Organic Framework as a Turn-on Fluorescent pH Sensor

A uranium-based metal-organic framework, [(UO₂)(H₂DTATC)] (HNU-39, H₄DTATC = 5,5'-(9,10-dihydroxy-4a,9,9a,10-tetrahydroanthracene-9,10-diyl)diisophthalic acid) was successfully prepared by a hydrothermal method. The structure of HNU-39 comprises UO₈ hexagonal bipyramids linked by doubly protonated DTATC ligands, forming a ribbon arrangement. It is worth noting that the DTATC ligand was transformed in situ from 5,5'-(anthracene-9,10-diyl)diisophthalic acid (H₄DPATC) during the synthesis of HNU-39. Research on fluorescence properties has shown that HNU-39 exhibits fluorescence turn-on response under alkaline conditions and could be used as a potential pH sensor. Moreover, HNU-39 can also be successfully applied for pH sensing in real samples from a sewage treatment plant. The sensing mechanism can be interpreted as OH^- ions reacting with the protons in the organic ligand of HNU-39.

Tenacic Acids: A New Class of Tenacious Binders to Metal Oxide Surfaces

The backbone of 2-hydroxyisophthalic acid was identified as a potential metal oxide anchor because of the perfect alignment of all three of its donor groups for binding to inorganic surfaces. It can therefore be used in the design of organic linkers for metal oxide based hybrid materials. Optimized and scalable methods for the synthesis of 2-hydroxyisophthalic acid (1) and its 5-substituted derivatives: 5-bromo- (2), 5-sulfooxy- (3), 5-hydroxy- (4), and 5-PEG600 (5) are presented. Dynamic light scattering (DLS) demonstrated that compound 2 inhibits Fe(OH)3 precipitation when FeIII aqueous solutions are titrated with NaOH, while similar titrations in the presence of the structurally-related isophthalic and salicylic acids, both missing the third donor group, show turbidity at pHs as low as 2.3 and 3.5, respectively. The adduct synthesized from 4.5 nm γ-Fe2 O3 nanoparticles and 5 is water-, alcohol- and CH2 Cl2 -soluble, and forms stable aqueous colloids in the pH range of 4.4-8.7. Moreover, at a pH close to neutral these colloids survive at 100 °C, demonstrating the high practicality of 2-hydroxyisophthalic acid for nanoparticulate inorganic/organic hybrid material design.

A uniquely fabricated Cu(ii)-metallacycle as a reusable highly sensitive dual-channel and practically functional metalloreceptor for Fe3+ and Ca2+ ions: an inorganic site of cation detection

Dimeric Cu(ii)-complex developed from disulfane ligand, serves as dual-channel metalloreceptor for Fe³⁺/Ca²⁺ and detection of Fe³⁺ in real water samples.

Metal-Ion Induced In Situ Ligand Oxidation for Self-Assembled Clusters: from Bis(5-(2-pyridine-2-yl)-1,2,4-triazole-3-yl)methane to Alcohol or Ketone

Hydrothermal reactions of metal nitrates and ligand bis(5-(pyridine-2-yl)-1,2,4-triazol-3-yl)methane (H₂ L¹ ) gave three cluster compounds, {Cr₂ }, {Zn₁₂ } and {Fe₈ }. Notably, methylene group of H₂ L¹ was in situ oxidized either to hydroxymethylated (L² -O)^3- in the metallo-ring {Zn₁₂ } or to a rigid carbonylated (L³ =O)^2- in the screw-type {Fe₈ }. In light of comparative experimental results, NO₃^- was deduced to be of a catalytic role in the ligand oxidation. Metal ion could be regarded as an "induced" tool for clusters generation in self-assembly process.

New discrete iodometallates with in situ generated triimidazole derivatives as countercations (Mn+ = Ag+, Pb2+, Bi3+)

By employing solvothermal in situ N-alkylation of organic bases with alcohols, four new iodometallates were obtained, and their structures are reported.

New in situ generated acylhydrazidate-coordinated complexes and acylhydrazide molecules: Synthesis, structural characterization and photoluminescence property

By utilizing the hydrothermal in situ acylation of organic acids with N2H4, three acylhydrazidate-coordinated compounds [Mn(L1)2(H2O)2] (L1=2,3-quinolinedicarboxylhydrazidate; HL1=2,3-dihydropyridazino[4,5-b] quinoline-1,4-dione) 1, [Mn2(ox)(L2)2(H2O)6]·2H2O (L2=benzimidazolate-5,6-dicarboxylhydrazide; HL2=6,7-dihydro-1H-imidazo[4,5-g]phthalazine-5,8-dione; ox=oxalate) 2, and [Cd(HL3)(bpy)] (L3=4,5-di(3'-carboxylphenyl)phthalhydrazidate; H3L3=6,7-dihydro-1H-imidazo[4,5-g]phthalazine-5,8-dione; bpy=2,2'-bipyridine) 3, as well as two acylhydrazide molecules L4 (L4=oxepino[2,3,4-de:7,6,5-d'e']diphthalazine-4,10(5H,9H)-dione) 4 and L5 (L5=4,5-dibromophthalhydrazide; L5=6,7-dibromo-2,3-dihydrophthalazine-1,4-dione) 5 were obtained. X-ray single-crystal diffraction analysis reveals that (i) 1 only possesses a mononuclear structure, but it self-assembles into a 2-D supramolecular network via the NhydrazineH⋯Nhydrazine and OwH⋯Ohydroxylimino interactions; (ii) 2 exhibits a dinuclear structure. Ox acts as the linker, while L2 just serves as a terminal ligand; (iii) In 3, L3 acts as a 3-connected node to propagate the 7-coordinated Cd(2+) centers into a 1-D double-chain structure; (iv) 4 is a special acylhydrazide molecule. Two OH groups for the intermediates 3,3'-biphthalhydrazide further lose one water molecule to form 4; (v) 5 is a common monoacylhydrazide molecule. Via the NhydrazineH⋯Ohydrazine, OhydroxyliminoH⋯Oacylamino and the π⋯π interactions, it self-assembles into a 2-D supramolecular network. The photoluminescence analysis reveals that 4 emits light with the maxima at 510nm.

A 3D mixed-valence Cu(I)/Cu(II) coordination polymer constructed by 2-(2-fluorophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline and 1,3-benzenedicarboxylate

A mixed-valence Cu(I)/Cu(II) coordination polymer, namely, [Cu2(L)(1,3-BDC)] n (1), has been synthesized under hydrothermal conditions (HL = 2-(2-fluorophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline and 1,3-H2BDC = 1,3-benzenedicarboxylic acid). Its structure has been determined by single crystal X-ray diffraction analysis and powder X-ray diffraction. The crystals are the monoclinic space group P21/c with a = 10.686(4), b = 17.376(8), c = 11.759(4) Å, β = 92.072(14)°, C27H14Cu2FN4O4, M r = 604.50, V = 2182.1(15) Å3, Z = 4, D calcd. = 1.84 g cm–3, R = 0.0588 and wR = 0.1202 (all data). In complex 1, the mixed-valence Cu(I)/Cu(II) atoms are linked by L and 1,3-BDC to give a rare 3D (3,3,4)-connected (4.7.9)(7.8.9)(4.7.8.93) framework. The temperature-dependent magnetic susceptibility of 1 was investigated in the temperature range of 2–300 K.

Hydrothermal synthesis, X-ray structure and DFT and magnetic studies of a (H2SiW12O40)2− based one-dimensional linear coordination polymer

In this paper, we report the synthesis and characterization of a novel POM-based inorganic–organic hybrid with an in situ transformation of pyridine-2,3-dicarboxylic acid into nicotinic acid and 2-hydroxynicotinic acid under hydrothermal conditions.

Controlled in situ reaction for the assembly of Cu(ii) mixed-ligand coordination polymers: synthesis, structure, mechanistic insights, magnetism and catalysis

Controlled in situ nucleophilic addition reaction results in two Cu(ii) mixed-ligand coordination polymers, and the one-step nucleophilic addition for in situ reaction is proposed.

Exceptional sensitivity to the synthetic approach and halogen substituent for Zn(ii) coordination assemblies with 5-halonicotinic acids

The significant influence of the synthetic approach and halogen substituent on Zn(ii) coordination assemblies with 5-halonicotinic acids has been demonstrated.

Guanine-copper coordination polymers: crystal analysis and application as thin film precursors

Three copper-N9-modified guanine complexes are reported with structures ranging from a discrete trinuclear motif to a mixed-valence coordination polymer. These complexes were used as precursors for the deposition and growth of copper oxide thin films on Si(100), at two different annealing temperatures, by using a CVD technique. Subsequent resistivity measurements suggest the formation of conductive thin films, raising the possibility of using nucleobase-metal complexes as versatile thin film precursors.

DNA binding, cytotoxicity and apoptosis induction activity of a mixed-ligand copper(II) complex with taurine Schiff base and imidazole

A novel binuclear copper(II) complex (complex 1) with taurine Schiff base and imidazole has been synthesized and structurally characterized by single crystal X-ray diffraction, elemental analysis, ESI-MS spectrometry, UV-vis and IR spectroscopy. Single-crystal analysis revealed that 1 displays the sulfonate-bridged dinuclear copper(II) centers. Both copper atoms are five-coordinated and exhibit slightly distorted square pyramidal geometries. Each of copper atom is surrounded by three oxygen atoms and one nitrogen atom from different taurine Schiff base ligands, and one nitrogen atom from one imidazole ligand. The interaction between 1 and calf thymus DNA (CT-DNA) was investigated by UV-vis, fluorescence, circular dichroism (CD) spectra and agarose gel electrophoresis. The experimental results indicated that 1 could bind to CT-DNA via an intercalative mode and show efficient cleavage activity. In addition, 1 showed an antitumor effect on cell cycle and apoptosis. Flow cytometric analysis revealed that MGC-803 cells were arrested in the S phase after treatment with 1. Fluorescence microscopic observation indicated that 1 could induce apoptosis of MGC-803 cells.

Observation of allylic rearrangement in water-rich reaction

Allylic rearrangement was first observed in a hydrothermal reaction of cyclic dicarboxylic anhydride with different metal centres, which can be rationalised as an S_E1 mechanism via the isolation of two resonated intermediates and DFT calculations.