Four series of lanthanide coordination polymers based on the tetrabromobenzene-1,4-dicarboxylate ligand: structural diversity and multifunctional properties

Four series of lanthanide-based coordination polymers (LnCPs), namely [Ln(Br₄bdc)_1.5(MeOH)₃] (1Ln; Ln = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy), [Ln₂(Br₄bdc)₂(NO₃)₂(MeOH)₄] (2Ln; Ln = Ce, Pr, Nd, Sm), [Ln(Br₄bdc)(NO₃)(MeOH)] (3Ln; Ln = Gd, Tb, Dy), and [Ln₂(Br₄bdc)₃(H₂O)_2.3(MeOH)_2.7] (4Ln; Ln = Gd, Tb, Dy) have been synthesized by reacting hydrated lanthanide(III) salts with tetrabromobenzene-1,4-dicarboxylic acid (H₂Br₄bdc) in different solvents under solvothermal conditions. The structural diversity found in the system mainly resulted from the effects of anions, solvents, and the variation in the ionic radii of the lanthanide(III) ions. Compounds in series 1Ln feature a two-dimensional (2D) layered structure with sql topology based on {(Ln(COO)₂)₂(μ-COO)₂} secondary building units (SBUs). Compounds in series 2Ln and 3Ln comprise, respectively, infinite uniform and alternate chains of {Ln(COO)₂}_n SBUs that are assembled into a similar network topology to 1Ln. Meanwhile, compounds in series 4Ln feature 3D coordination networks of a pcu α-Po topological net consisting of binuclear {Ln₂(COO)₃} SBUs. The formation of polymeric networks in series 1Ln-4Ln is facilitated by the numerous coordination sites of the ligand Br₄bdc^2- and the fact that its bromine atoms can participate in the formation of various types of intermolecular interactions. The solid-state photoluminescence studies on Eu- (1Eu) and Tb- (1Tb, 3Tb, 4Tb) containing compounds indicate that the Br₄bdc^2- ligands can efficiently sensitize Eu³⁺ and Tb³⁺ emission. Notably, such compounds exhibit highly sensitive fluorescence sensing for acetone, water, and Fe³⁺ ions via the fluorescence quenching effect. As the representatives of the series, activated 1Eu, 2Pr, 3Tb, and 4Tb show the maximum CO₂ uptake capacities of 170.4, 273.7, 255.3, and 303.5 cm³ g^-1, respectively, at 50 bar and 298 K with good repeatability of the adsorption-desorption properties. Magnetic studies indicate that the Gd- and Dy-based compounds 1Gd, 1Dy, 3Gd, 3Dy, and 4Gd show simple paramagnetic behaviours, whereas compound 4Dy exhibits weak ferromagnetic interactions.

Self-Assembly of 1D Double-Chain and 3D Diamondoid Networks of Lanthanide Coordination Polymers through In Situ-Generated Ligands: High-Pressure CO2 Adsorption and Photoluminescence Properties

Two new lanthanide-based coordination polymers, [Sm2(bzz)(ben)6(H2O)3]·0.5H2O (1) and [Eu(bbz)(ben)3] (2), were synthesized and characterized. The described products were formed from in situ-generated benzoate (ben) and N'-benzoylbenzohydrazide (bbz) ligands, which were the products of transformation of originally added benzhydrazide (bzz) under hydrothermal conditions. Compound 1 exhibits a one-dimensional (1D) double-chain structure built up from the connection of the central Sm3+ ions with a mixture of bzz and ben ligands. On the other hand, 2 features a 3D network with a 4-connected (66) dia topology constructed from dinuclear [Eu2(ben)6] secondary building units and bbz linkers. High-pressure CO2 sorption studies of activated 1 show that maximum uptake increases to exceptionally high values of 376.7 cm3 g-1 (42.5 wt%) under a pressure of 50 bar at 298 K with good recyclability. Meanwhile, 2 shows a typical red emission in the solid state at room temperature with the decay lifetime of 1.2 ms.

The coordination chemistry of benzhydrazide with lanthanide(iii) ions: hydrothermal in situ ligand formation, structures, magnetic and photoluminescence sensing properties

The influence of synthetic conditions on the solid-state structural formation of lanthanide(iii) complexes based on a hydrazide ligand have been investigated and reported. Depending on the solvents and reaction temperatures, the reactions of hydrated Ln(NO₃)₃ with a benzohydrazide (bzz) ligand afforded three classes of lanthanide(iii) coordination complexes viz. [Ln(bzz)(NO₃)](NO₃)₂ (1Ln; Ln = Sm (1), Eu (2), Gd (3), Tb (4), Dy (5)), [Ln(bzz)(ben)₃(H₂O)]·H₂O (2Ln; Ln = Pr (6), Nd (7), Sm (8), Eu (9), Gd (10), Tb (11), Dy (12), Er (13)), and [Ln₃(ben)₃] (3Ln; Ln = Eu (14), Gd (15), Tb (16), Dy (17), Er (18), Tm (19), Yb (20), Lu (21)). Complexes 1-5 in series 1Ln were isolated by slow evaporation of their isopropanol solutions at ambient temperature, and the complexes display similar discrete structures bearing distinct intermolecular N-H⋯O hydrogen bonds to generate a three-dimensional (3D) supramolecular architecture. Complexes 6-13 in series 2Ln were obtained under hydrothermal conditions at 110 °C where the in situ generated benzoate (ben) ligands participated in the formation of one-dimensional (1D) coordination polymers (CPs) with the bzz ligands. At a temperature of 145 °C the hydrothermal conditions result in the formation of the thermodynamically more stable products of 14-21 in series 3Ln, in which the bzz ligand underwent complete in situ hydrolysis to create the ben ligand. These coordination assemblies feature 1D zigzag chains that are formed by unusual low coordination numbers of the six- and seven-fold coordinated Ln³⁺ centers bridged by the ben ligands in μ ₂- and μ ₃-coordination modes. Notably, the chain structures of 2Ln can be transformed into the zigzag tape-like structures of 3Ln upon heating the crystalline samples to 400 °C in air. In the solid state at room temperature, the Eu- (2, 9, 14) and Tb- (4, 11, 16) containing complexes emit red and green light, respectively. The luminescence investigations show that the Eu- (9, 14) and Tb-(11, 16) based CPs could be used as fluorescent probes for acetone and Co²⁺ ions via an energy competition mechanism. Meanwhile, the Gd- (10, 15) and Dy- (12, 17) based CPs show typical antiferromagnetic interactions.

Coordination-driven self-assembly of a series of dinuclear M2L2 mesocates with a bis-bidentate pyridylimine ligand

Four isostructural dinuclear M2L2 mesocates of the general formula [M2(NCS)4(L)2]·4.5MeOH (1M; M = Mn, Fe, Co, Zn) were constructed by using the coordination-driven self-assembly of the [M(NCS)2] precursor and the flexible bis-bidentate pyridylimine Schiff base ligand L (L = 4,4'-(1,4-phenylenebis(oxy))bis(N-(pyridin-2-ylmethylene)aniline). The centrosymmetric M2L2 mesocate forms through the side-by-side coordination of two L ligands to a pair of M(ii) ions. The mesocates exhibit a reversible temperature induced desolvation-solvation behavior without losing their structural integrity. The activated 1Co, as the representative M2L2 mesocate, shows an exceptionally high MeOH vapour uptake capacity of 481.9 cm3 g-1 (68.8 wt%) at STP with good recyclability. Notably, it also exhibits CO2 adsorption with an uptake capacity of 20.2 cm3 g-1 (3.6 wt%) at room temperature and 1 bar.

Two-dimensional halogen-bonded organic frameworks based on the tetrabromobenzene-1,4-dicarboxylic acid building molecule

2D halogen-bonded organic frameworks were readily engineered by strong and directional effects of the primary Br⋯O and the secondary Br⋯π halogen bonding interactions from the tetrabromobenzene-1,4-dicarboxylic acid building molecule involving 100% supramolecular yields.

Self-assembly of three-dimensional oxalate-bridged alkali(i)–lanthanide(iii) heterometal–organic frameworks

Three isostructural 3D oxalate bridged alkali(i)–lanthanide(iii) MOFs with a pcu net based on cubane-like [Ln₄O₄] clusters and their magnetic, CO₂ adsorption, and photoluminescence sensing properties are presented.

A new luminescent anionic metal-organic framework based on heterometallic zinc(II)-barium(II) for selective detection of Fe3+ and Cu2+ ions in aqueous solution

Over the past two decades, the development of novel inorganic-organic hybrid porous crystalline materials or metal-organic frameworks (MOFs) using crystal engineering has provoked significant interest due to their potential applications as functional materials. In this context, luminescent MOFs as fluorescence sensors have recently received significant attention for the sensing of ionic species and small molecules. In this work, a new luminescent heterometallic zinc(II)-barium(II)-based anionic metal-organic framework, namely poly[imidazolium [triaqua(μ₆-benzene-1,3,5-tricarboxylato)bariumtrizinc] tetrahydrate], {(C₃H₄N₂)[BaZn₃(C₉H₃O₆)₃(H₂O)₃]·4H₂O}_n (1), was synthesized under hydrothermal conditions and characterized. Compound 1 presents a three-dimensional framework with an unprecedented (3,5)-connected topology of the point symbol (3.9²).(3³.4².5.9³.10), and exhibits `turn-off' luminescence responses for the Cu²⁺ and Fe³⁺ ions in aqueous solution based on significantly different quenching mechanisms.

Temperature-dependent 3D structures of lanthanide coordination polymers based on dicarboxylate mixed ligands

Four families of fourteen three-dimensional (3D) lanthanide coordination polymers (CPs) with dicarboxylate mixed ligands have been synthesized hydrothermally at different temperatures.