Cu2+-mediated dehydrogenative coupling and hydroxylation of an N-heterocyclic ligand: from generation of a new tetratopic ligand to the designed assembly of three-dimensional copper(I) coordination polymers

Syntheses and structures of two novel fluorescent metal-organic frameworks generated from a tridentate donor-acceptor motif ligand

The tridentate organic ligand 4,4',4''-(4,4,8,8,12,12-hexamethyl-8,12-dihydro-4H-benzo[9,1]quinolizino[3,4,5,6,7-defg]acridine-2,6,10-triyl)tribenzoic acid (H₃L) has been synthesized (as the methanol 1.25-solvate, C₄₈H₃₉NO₆·1.25CH₃OH). As a donor-acceptor motif molecule, H₃L possess strong intramolecular charge transfer (ICT) fluorescence. Through hydrogen bonds, H₃L molecules construct a two-dimensional (2D) network, which pack together into three-dimensional (3D) networks with an ABC stacking pattern in the crystalline state. Based on H₃L and M(NO₃)₂ salts (M = Cd and Zn) under solvothermal conditions, two metal-organic frameworks (MOFs), namely, catena-poly[[triaquacadmium(II)]-μ-10-(4-carboxyphenyl)-4,4'-(4,4,8,8,12,12-hexamethyl-8,12-dihydro-4H-benzo[9,1]quinolizino[3,4,5,6,7-defg]acridine-2,6-diyl)dibenzoato], [Cd(C₄₈H₃₇NO₆)(H₂O)₃]_n, I, and poly[[μ₃-4,4',4''-(4,4,8,8,12,12-hexamethyl-8,12-dihydro-4H-benzo[9,1]quinolizino[3,4,5,6,7-defg]acridine-2,6,10-triyl)tribenzoato](μ₃-hydroxido)zinc(II)], [Zn₂(C₄₈H₃₆NO₆)(OH)]_n, II, were synthesized. Single-crystal analysis revealed that both MOFs adopt a 3D structure. In I, partly deprotonated HL^2- behaves as a bidentate ligand to link a Cd^II ion to form a one-dimensional chain. In the solid state of I, the existence of weak interactions, such as O-H...O hydrogen bonds and π-π interactions, plays an essential role in aligning 2D nets and 3D networks with AB packing patterns for I. The deprotonated ligand L^3- in II is utilized as a tridentate building block to bind Zn^II ions to construct 3D networks, where unusual Zn₄O₁₄ clusters act as connection nodes. As a donor-acceptor molecule, H₃L exhibits fluorescence with a photoluminescence quantum yield (PLQY) of 70% in the solid state. In comparison, the PL of both MOFs is red-shifted with even higher PLQYs of 79 and 85% for I and II, respectively.

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.

Modular Synthesis of Highly Porous Zr-MOFs Assembled from Simple Building Blocks for Oxygen Storage

The last decade has witnessed significant advances in the scale-up synthesis of metal-organic frameworks (MOFs) using commercially available and affordable organic linkers. However, the synthesis of MOFs using elongated and/or multitopic linkers to access MOFs with large pore volume and/or various topologies can often be challenging due to multistep organic syntheses involved for linker preparation. In this report, a modular MOF synthesis strategy is developed by utilizing the coordination and covalent bonds formation in one-pot strategy where monoacid-based ligands reacted to form ditopic ligands, which then assembled into a three-dimensional MOF with Zr₆ clusters. Chemical stability of the resulting materials was significantly enhanced through converting the imine bond into robust linkage via cycloaddition with phenylacetylene. Oxygen storage capacities of the MOFs were measured, and enhanced volumetric O₂ uptake was observed for the stabilized MOF, NU-401-Q.

Constructing new metal-organic frameworks with complicated ligands from "One-Pot" in situ reactions

Metal-organic frameworks (MOFs) have emerged as one of the most fascinating libraries of porous materials. In spite of their myriad merits, practical application of most MOFs is restricted due to their high preparation cost because of the complicated organic ligands involved. To address this limitation, we propose to use simple and cheap organic precursors to synthesize MOFs with complicated ligands via "one-pot" in situ reactions of these precursors along with the formation of new MOFs. In this work, we have carefully screened several organic reactions, through which target ligands were generated in situ from easily available reactants during the MOF construction. With this "one-pot" approach, the fabrication of a series of novel MOFs by integrating the organic covalent bond and the coordinate bond has thus been realized through the judicious selection of organic reactions, which effectively simplifies the MOF synthesis process and thus reduces the cost.

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.

Syntheses and structures of two new coordination polymers generated from a 4-aminotriazole-bridged organic ligand and CoII salts

Organic ligands and counter-anions influence the coordination spheres of metal cations and hence the construction of coordination polymers (CPs). The specific bent geometries of five-membered heterocyclic triazole bridging organic ligands are capable of generating CPs with novel patterns not easily obtained using rigid linear ligands. A multidentate 4-aminotriazole-bridged organic ligand, namely 4-amino-3,5-bis(4,3'-bipyridyl-5'-yl)-4H-1,2,4-triazole (L) has been prepared and used to synthesize two Co^II coordination polymers, namely poly[[[μ₂-4-amino-3,5-bis(4,3'-bipyridyl-5'-yl)-4H-1,2,4-triazole-κ²N:N']bis(methanol-κO)cobalt(II)] bis(perchlorate)], {[Co(C₂₂H₁₆N₈)₂(CH₃OH)₂](ClO₄)₂}_n, (I), and poly[[μ₃-4-amino-3,5-bis(4,3'-bipyridyl-5'-yl)-4H-1,2,4-triazole-κ³N:N':N'']dichloridocobalt(II)], [CoCl₂(C₂₂H₁₆N₈)]_n, (II), using CoX₂ salts [X = ClO₄ for (I) and Cl for (II)] under solvothermal conditions. Single-crystal X-ray structure analysis revealed that they both feature two-dimensional networks. Cobalt is located on an inversion centre in (I) and in a general position in (II). In (I), L functions as a bidentate cis-conformation ligand linking Co^II ions, while it functions as a tridentate trans-conformation linker binding Co^II ions in (II). In addition, O-H...N and N-H...O hydrogen bonds and C-H...π interactions exist in (I), while N-H...Cl and π-π interactions exist in (II), and these weak interactions play an important role in aligning the two-dimensional nets of (I) and (II) in the solid state. As the compounds were synthesized under the same conditions, the significant structural variations between (I) and (II) are believed to be determined by the different sizes and coordination abilities of the counter-anions. IR spectroscopy and diffuse reflectance UV-Vis spectra were also used to investigate the title compounds.

Crystal growth and structural remarks on malonate-based lanthanide coordination polymers

The synthesis, structural and thermal studies of several malonate-containing lanthanide(iii) complexes plus a structural overview of twenty-three known homometallic Ln(iii)-malonate systems are provided herein.

Two samarium(iii) complexes with tunable fluorescence from in situ reactions of 2-ethoxy-6-((pyridin-2-ylmethylimino)methyl)phenol with Sm3+ ion

The solvothermal in situ C–C coupling reaction promoted by Sm³⁺ ion in Schiff base –CHN–CH₂– system is firstly reported, and two resulting temperature-dependent Sm(iii)-complexes 1 and 2 have different luminescent performance.

Synthesis and crystal structures of two coordination polymers and a binuclear cadmium(II) complex containing 3- and 4-aminobenzoate ligands

Due to their wide range of coordination modes and versatile conformations when binding to metal atoms, multicarboxylate ligands are of interest in the design of metal-organic frameworks (MOFs). Three Cd(II) complexes, namely catena-poly[diammonium [[chloridocadmium(II)]-di-μ-chlorido-[chloridocadmium(II)]-bis(μ-3-aminobenzoato)-κ(3)N:O,O';κ(3)O,O':N]], {(NH4)[CdCl2(C7H6NO2)]}n, (I), catena-poly[[[aquacadmium(II)]-bis(μ-4-aminobenzoato)-κ(3)N:O,O';κ(3)O,O':N] monohydrate], {[Cd(C7H6NO2)2(H2O)]·H2O}n, (II), and di-μ-acetato-κ(4)O:O'-bis[(4-aminobenzoato-κ(2)O,O')(2,2'-bipyridine-κ(2)N,N')cadmium(II)], [Cd2(CH3COO)2(C7H6NO2)2(C10H8N2)2], (III), with different stuctural forms are reported. Complex (I) has a one-dimensional ladder structure, with strong N-H···O and weak N-H···Cl hydrogen bonds linking the cations and anions in the three-dimensional supramolecular structure. Complex (II) has a one-dimensional chain structure. Extensive O-H···O and N-H···O hydrogen bonds between the anionic ligands and the solvent water molecules and π-π stacking interactions between the centroids of the benzene rings lead to the three-dimensional supramolecular structure. Complex (III) is a binuclear molecule which is extended into a three-dimensional supramolecular structure via strong N-H···O and weak C-H···O hydrogen bonds.

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.

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.

A three-dimensional manganese(II) metal-organic framework based on 5-methoxybenzene-1,3-dicarboxylic acid and exhibiting a pts net

The solvothermal reaction of MnCl2·H2O and 5-methoxybenzene-1,3-dicarboxylic acid (MeO-m-H2BDC) led to a three-dimensional Mn(II) metal-organic framework, namely poly[(dimethylformamide-κO)(μ4-5-methoxybenzene-1,3-dicarboxylato-κ(4)O(1):O(1'):O(3),O(3'):O(3))manganese(II)], [Mn(C9H6O5)(C3H7NO)]n or [Mn(MeO-m-BDC)(DMF)]n (DMF is dimethylformamide). The Mn(II) atom is six-coordinated and exhibits a distorted octahedral geometry formed by five carboxylate O atoms from four different MeO-m-BDC(2-) anionic ligands and by one DMF O atom. The three-dimensional framework of (I) formed by the bridging MeO-m-BDC(2-) ligands and the Mn(II) atoms exhibits a pts topological network when MeO-m-BDC(2-) and Mn(II) are viewed as four-connected nodes.

A twofold interwoven two-dimensional→two-dimensional (2-D→2-D) cluster-organic network based on the [Cu2I2] cluster and the 4,4'-(diazenediyl)dipyridine ligand: poly[[μ2-4,4'-(diazenediyl)dipyridine]-μ2-iodido-copper(I)]

In the polymeric title compound, [CuI(C(10)H(8)N(4))](n), the Cu(I) atom is in a four-coordinated tetrahedral geometry, formed by two I atoms and two pyridine N atoms from two different 4,4'-(diazenediyl)dipyridine (4,4'-azpy) ligands. Two μ(2)-I atoms link two Cu(I) atoms to form a planar rhomboid [Cu(2)I(2)] cluster located on an inversion centre, where the distance between two Cu(I) atoms is 2.7781 (15) Å and the Cu-I bond lengths are 2.6290 (13) and 2.7495 (15) Å. The bridging 4,4'-azpy ligands connect the [Cu(2)I(2)] clusters into a two-dimensional (2-D) double-layered grid-like network [parallel to the (10-2) plane], with a (4,4)-connected topology. Two 2-D grid-like networks interweave each other by long 4,4'-azpy bridging ligands to form a dense 2-D double-layered network. To the best of our knowledge, this interwoven 2-D→2-D network is observed for the first time in [Cu(2)I(2)]-organic compounds.