Uncoordinated Carboxylate Oxygen Atoms Research Articles

Adenine-mediated amide-containing metal-organic framework toward one-step ethylene purification from a ternary mixture

Simultaneous removal of acetylene (C2H2) and ethane (C2H6) from a ternary gas mixture of acetylene/ethylene/ethane via a one-step process to achieve high purity of ethylene (C2H4) is challenging but highly desirable. Herein, an amide-containing adenine-mediated rod metal-organic framework (MOF) of 1 was solvothermally constructed by means of mixed-linker approach. Structural analysis illustrates that 1 displays 1D microporous channels and features open metal site-free concomitant with uncoordinated carboxylate oxygen atoms and amide functional groups decorated interior pore walls. Interestingly, both single-component gas adsorption and ideal adsorbed solution theory (IAST) prediction reveal that 1 is C2H2 and C2H6 selective, which were eventually confirmed by dynamic column breakthrough experiments through not only binary gas mixtures of C2H2/C2H4 and C2H6/C2H4, but also a ternary mixture of C2H2/C2H4/C2H6 to validate one-step ethylene purification.

Chemorobust 4p-5p {InPb}-organic framework for efficiently catalyzing cycloaddition of CO2 with epoxides and deacetalization-Knoevenagel condensation

Due to that the high charge density and small radius render In3+ cation a stronger Lewis acidity, multifunctional nanoporous In-MOFs have become one of the most promising catalysts for their high activity. Herein, the solvothermal self-assembly by employing 2,4,6-tri (2,4-dicarboxyphenyl)pyridine (H6TDP) as organic linker leads to a robust honeycomb skeleton of {[(CH3)2NH2][InIIIPbII(TDP) (H2O)]⋅3DMF⋅3H2O}n (NUC-52) with the merits of nanoscopic channels, high porosity (61.3%), large specific surface area, and thermal stability. To the best of our knowledge, this is the first 4p-5p heterometallic {InIIIPbII} cluster-based nano-porous host framework, whose activated state possesses the coexistence of Lewis acid-base sites including 7-coordinated Pb2+ ions, 4-coordinated In3+ ions, uncoordinated carboxyl oxygen atoms, and Npyridine atoms. Performed catalytic experiments exhibited that activated NUC-52 owned the high catalytic activity on the cycloaddition reactions of styrene oxide with CO2 under mild conditions with excellent turnover number (2475) and turnover frequency (619 h−1). Moreover, activated NUC-52 could greatly accelerate the deacetalization-Knoevenagel condensation reactions of benzaldehyde dimethyl acetal and malononitrile. Hence, this work lays down the groundwork for constructing heterometallic cluster-based nanoporous MOFs with excellent Lewis acidic catalysis and chemical stability, which should be ascribed to the reasonable coordination arrangement between organic ligands and distinct metal ions according to the hard–soft acid–base (HSAB) theory.

Nanochannel-based {BaZn}-organic framework for catalytic activity on the cycloaddition reaction of epoxides with CO2 and deacetalization-Knoevenagel condensation.

Herein, the rare combination of BaII (5s) and ZnII (3d) in the presence of the structure-oriented TDP6- ligand generated the nanochannel-based hybrid material {[(CH3)2NH2]2[BaZn(TDP)(H2O)]·DMF·5H2O}n (NUC-51, H6TDP = 2,4,6-tri(2,4-dicarboxyphenyl)pyridine), which possesses excellent physicochemical characteristics such as nanoscopic channels, high porosity, large specific surface area, and high heat/water-resistance. To the best of our knowledge, this is the first 3D [BaIIZnII(CO2)6(H2O)]-based nano-porous host framework, whose activated state possesses the coexistence of Lewis acid-base sites including 4-coordinated Zn2+ ions, 7-coordinated Ba2+ ions, uncoordinated carboxyl oxygen atoms, and Npyridine atoms. Catalytic experiments exhibited that activated NUC-51a possesses a high catalytic activity on the cycloaddition reactions of epoxides with CO2 at 55 °C, which can be ascribed to its structural advantages of nanoscale channels and rich bifunctional active sites. Moreover, NUC-51a could significantly accelerate the deacetalization-Knoevenagel condensation reaction in DMSO solvent at 70 °C.

Highly Robust 3s-3d {CaZn}-Organic Framework for Excellent Catalytic Performance on Chemical Fixation of CO2 and Knoevenagel Condensation Reaction.

In terms of ligand-directed synthetic strategy, multifunctional metal-organic frameworks (MOFs) could be assembled by employing organic ligands with nitrogen-containing heterocycles, which could serve as Lewis base sites in crystallized porous frameworks. Here, the acidic one-pot hydrothermal reaction of CaCl2, Zn(NO3)2, and 2,4,6-tri(2,4-dicarboxyphenyl)pyridine (H6TDP) generates one robust honeycomb-shaped double-walled material of {[(CH3)2NH2]2[CaZn(TDP)(H2O)]·3DMF·3H2O}n (NUC-21), which has the excellent physicochemical characteristics of nanoscopic channels, high porosity (58.3%), large specific surface area, and high heat/water-resisting property. To the best of our knowledge, this is the first 3s-3d dinuclear [CaZn(CO2)6(OH2)]-based nanoporous host framework, whose activated state possesses the coexistence of Lewis acid-base sites including four-coordinated Zn2+ ions, four-coordinated Ca2+ ions, uncoordinated carboxyl oxygen atoms, and Npyridine atoms. As expected, because of the coexistence of Lewis acid-base nature, desolvated NUC-21 displays satisfactory catalytic activity on the chemical cycloaddition of various epoxides with CO2 into the corresponding alkyl carbonates under comparatively mild conditions. Furthermore, the efficient conversion of benzaldehydes and malononitrile confirms that NUC-21 is simultaneously a bifunctional heterogeneous catalyst for Knoevenagel condensation reactions. Hence, the achievements broaden the way for assembling nanoporous multifunctional MOFs by employing ligand-directed synthetic strategy, which can accelerate the transformation from simple structural research to socially demanding applications.

A Zinc Metal-Organic Framework for Concurrent Adsorption and Detection of Uranium.

Uranium is one of the principal raw materials in the nuclear industry, but if released into the natural environment, it also poses latent health risks to mankind. Therefore, there is an urgent need to develop a strategy that can concurrently detect and adsorb uranium to realize the sustainable development of nuclear power and protect the environment. In this work, a fluorescent zinc-based metal-organic framework (HNU-50) was designed and synthesized for the effective detection and extraction of U(VI). The amide groups on N-pyridin-4-ylpyridine-4-carboxamide ligands and two uncoordinated carboxyl oxygen atoms on pyromellitic acid ligands in HNU-50 provide potential uranium-binding sites. Consequently, HNU-50 is competent of selectively and efficiently catching uranyl ions, achieving an optimum adsorption capacity of 632 mg/g. Additionally, the adsorption of U(VI) results in fluorescence quenching of HNU-50, thus allowing sensitive and selective detection of U(VI) by fluorescence change. Note that HNU-50 exhibits a considerably low detection limit of 1.2 × 10-8 M for U(VI) in aqueous solution, which is below the World Health Organization maximum pollution standards for potable water (6.3 × 10-8 M).

A first new porous d-p HMOF material with multiple active sites for excellent CO2 capture and catalysis.

In this work, a new monometallic metal-organic framework (MOF), namely {[Pb2(L)2(H2O)]·H2O}n (1), was prepared via a N,O-mixed 2-(imidazol-1-yl)terephthalic acid (H2L) ligand and Pb(ii) ions. Then, a first new porous d-p heterometallic MOF (HMOF), namely {[PbZn(L)2]·DMA·H2O}n (2), was yielded via Zn(ii) ions and MOF 1 as the precursor because of the different coordination affinity of oxygen and nitrogen atoms with various metal ions. MOF 1 is a condensed packing motif, whereas HMOF 2 is a porous three-dimensional (3D) framework with unsaturated Pb(ii) and Zn(ii) active sites, uncoordinated carboxylate oxygen atoms and two kinds of porous channels due to the introduction of Zn(ii) ions into the framework of MOF 1, which thus endowed HMOF 2 with excellent sorption and selectivity for CO2 over CH4. Moreover, HMOF 2 was explored to be an efficient heterogeneous catalyst for the fixation of CO2 with various epoxides because of the existence of the abundant unsaturated bimetallic sites as the Lewis acid. It is hoped that this work may supply an effective strategy to build plenty of d-p HMOF materials with excellent gas adsorption and catalytic properties.

Series of Water-Stable Lanthanide Metal-Organic Frameworks Based on Carboxylic Acid Imidazolium Chloride: Tunable Luminescent Emission and Sensing.

A series of isomorphic lanthanide metal-organic frameworks (Ln-MOFs), {[Ln(L)(H2O)2]·5H2O}n (1-Ln, where Ln = Eu, Tb, Gd, and EuxTb1-x), have been synthesized by a rigid 1,3-bis(3,5-dicarboxyphenyl)imidazolium chloride (H4L+Cl-) ligand and Ln3+ ions via a solvothermal method. Single-crystal X-ray diffraction indicated that 1-Ln exhibited similar three-dimensional porous frameworks with one-dimensional channels decorated by the uncoordinated carboxylate oxygen atoms. The luminescent sensing studies indicated that 1-Eu is an outstanding reusable luminescent probe suitable for the simultaneous detection of Cr2O72-, CrO42-, and MnO4- ions in an aqueous solution. Remarkably, the different proportions of Eu3+ and Tb3+ can be combined into the same Ln-MOF to yield a new series of differently doped 1-EuxTb1-x MOFs. At the same excitation wavelength, they generated dual-emission peaks of Eu3+ and Tb3+ to show a gradual change in luminous color between yellow-green, yellow, orange, orange-red, and red. On the basis of the excellent optical properties of 1-Ln complexes, they can be employed as promising luminescent probe and multicolor tunable photoluminescence materials.

A Zinc MOF with Carboxylate Oxygen‐Functionalized Pore Channels for Uranium(VI) Sorption

A three‐dimensional zinc MOF, JXNU‐4, constructed from adeninate and 4,4′‐biphenyldicarboxylate (BPDC2–) ligands was utilized for capture of uranium(VI). JXNU‐4 features one‐dimensional channels decorated by uncoordinated carboxylate oxygen atoms, which are the potential binding sites for uranium(VI) ions. The sorption of uranium(VI) onto the water‐stable JXNU‐4 was systematically investigated. The batch experimental results indicate that JXNU‐4 captures uranium(VI) from aqueous solutions efficiently and quickly. The uranium(VI) sorption behavior of JXNU‐4 follows the Langmuir sorption model and is assigned to chemisorption, which is due to the presence of the periodic arrangement of uncoordinated carboxylate oxygen atoms exposed on the channels. This work presents an elegant example for the efficient separation of uranium(VI) from aqueous solution by using carboxylate oxygen‐functionalized pore channels.

Simultaneous Trapping of C2 H2 and C2 H6 from a Ternary Mixture of C2 H2 /C2 H4 /C2 H6 in a Robust Metal-Organic Framework for the Purification of C2 H4.

The removal of C2 H2 and C2 H6 from C2 H4 streams is of great significance for feedstock purification to produce polyethylene and other commodity chemicals but the simultaneous adsorption of C2 H6 and C2 H2 over C2 H4 from a ternary mixture has never been realized. Herein, a robust metal-organic framework, TJT-100, was designed and synthesized, which demonstrates remarkably selective adsorption of C2 H2 and C2 H6 over C2 H4 . Breakthrough experiments show that TJT-100 can be used as an adsorbent for high-performance purification of C2 H4 from a ternary mixture of C2 H2 /C2 H4 /C2 H6 (0.5:99:0.5) to afford a C2 H4 purity greater than 99.997 %, beyond that required for ethylene polymerization. Computational studies reveal that the uncoordinated carboxylate oxygen atoms and coordinated water molecules pointing towards the pore can trap C2 H2 and C2 H6 through the formation of multiple C-H⋅⋅⋅O electrostatic interactions, while the corresponding C2 H4 -framework interaction is unfavorable.

Simultaneous Trapping of C2H2 and C2H6 from a Ternary Mixture of C2H2/C2H4/C2H6 in a Robust Metal–Organic Framework for the Purification of C2H4

AbstractThe removal of C2H2 and C2H6 from C2H4 streams is of great significance for feedstock purification to produce polyethylene and other commodity chemicals but the simultaneous adsorption of C2H6 and C2H2 over C2H4 from a ternary mixture has never been realized. Herein, a robust metal–organic framework, TJT‐100, was designed and synthesized, which demonstrates remarkably selective adsorption of C2H2 and C2H6 over C2H4. Breakthrough experiments show that TJT‐100 can be used as an adsorbent for high‐performance purification of C2H4 from a ternary mixture of C2H2/C2H4/C2H6 (0.5:99:0.5) to afford a C2H4 purity greater than 99.997 %, beyond that required for ethylene polymerization. Computational studies reveal that the uncoordinated carboxylate oxygen atoms and coordinated water molecules pointing towards the pore can trap C2H2 and C2H6 through the formation of multiple C−H⋅⋅⋅O electrostatic interactions, while the corresponding C2H4–framework interaction is unfavorable.

Efficient and Selective Removal of Copper(II) from Aqueous Solution by a Highly Stable Hydrogen-Bonded Metal–Organic Framework

Copper(II) is an indispensable element in nature, while exposure to excessive Cu2+ will potentially cause health issues. It is imperative to develop new strategies for efficient Cu2+ uptake from aqueous solution. Herein, a hydrogen-bonded metal–organic framework (MOF) [(Zn3L3(H2O)6][(Na)(NO3)] (1) with high stability was elaborately constructed. The uncoordinated carboxylate oxygen atoms in the channels of MOF were designed as active sites to recognize Cu2+ and further coordinate with it. Without pretreatment, MOF 1 demonstrated a relatively high adsorption capacity (379.13 mg g–1), exceeding most Cu2+ adsorbents. Even with the existence of different metal ions and a high concentration of interfering ions, highly selective adsorption of Cu2+ can be achieved. Moreover, the excellent water stability together with the high removal efficiency in the presence of coexisting ions offers MOF 1 the possibility in practical application. The mechanism for Cu2+ selective adsorption was systematically investigated by ...

Eu3+-functionalized metal-organic framework composite as ratiometric fluorescent sensor for highly selective detecting urinary 1-hydroxypyrene

An anionic three-dimensional metal-organic framework of JXNU-4 with one-dimensional channels occupied by the extraframework dimethylammonium cations was chosen as a parent compound to host Eu3+ cations by uncoordinated carboxylate oxygen atoms in its pores through a cation exchange experiment. The Eu3+-incorporated sample Eu3+@JXNU-4 is structurally characterized and displays excellent Eu3+ luminescence and good fluorescence stability in aqueous solution, which is resulted from the sensitization and protection provided by the parented framework. The Eu3+@JXNU-4 was developed as a fluorescent probe for urine 1-hydroxypyrene (1-HP), which is a biomarker of polycyclic aromatic hydrocarbons (PAHs) carcinogens and represents the internal dose of PAHs exposure in the human body. In the presence of 1-HP, the 1-HP emission emerges and Eu3+@JXNU-4 exhibits 1-HP- and Eu3+-based dual emission. The intensity of the 1-HP emission increases with the concentration of 1-HP increasing, while the Eu3+ emission recedes in the meantime. The ratio value of 1-HP emission at 502 nm (I502) and Eu3+ emission at 616 nm (I616) versus the concentration of 1-HP reveals a good linear relationship, which indicates the Eu3+@JXNU-4 is an excellent candidate for ratiometric fluorescence sensing for 1-HP. Finally, the fluorescence mechanism was discussed.

Encapsulation of one-dimensional cation chains into pseudo-channels by varying monomers with opposite charge

Two compounds with cation chains and monomers, [Co1/2(bpbenz)1/2]+·[Co1/2(oba)]− (1) and [Ni(DPT)(H2O)4]2+ [tpdc]2− (2) have been synthesized under hydrothermal condition (bpbenz = 1,4-bis(4-pyridyl)benzene, H2oba = 4,4′-oxybis- (benzoate), DPT = 2,5-dipyridinethiophene, H2tpdc = biphenyldicarboxylic acid). In compound 1, the monomer [Co1/2(oba)]− anions stack in three orientations to generate a 1D pseudo channels encapsulation of cationic chains [Co1/2(bpbenz)1/2]+. When considering the H-bonding interaction between coordinated water O atoms of the [Co1/2(bpbenz) 1/2]+ cationic chain and uncoordinated carboxylate oxygen atoms of the [Co1/2(oba)]− anion, a binodal 3,6-coordinated 3D architecture is generated. Like 1, the one-dimensional cation chains [Ni(DPT)(H2O)4]2+ locate in pseudo-channels by [tpdc]2− monomers anions in compound 2. A 3D net is also generated considering the H-bonding interaction.

Unusual 1D Tape of Pentameric and Tetrameric Water Clusters Trapped in a 2D Cobalt(II) Coordination Polymer: Synthesis, Characterization, and Catalytic Properties

1D tape of pentameric and tetrameric water clusters have been observed in a complex of [Co(oba)(H2O)3]·(H2O)2·(dmbpy)]n (1), (H2oba = 4,4′-oxybis(benzoic acid), dmbpy = 2,2′-dimethyl-4,4′-bipyridine), which has been synthesized and characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis (TGA), powder X-ray diffraction and single-crystal X-ray diffraction. In 1, a cyclic pentamer formed by four water molecules and one carboxylate oxygen, as well as a chain-like tetrameric water-(carboxyl oxygen) cluster are observed. The uncoordinated carboxylate oxygen atoms of oba anions, water molecules and free dmbpy ligands interact via hydrogen bonds forms a tape in which the dmbpy ligands point alternately up and down, and extend 2D 1 into a 3D supramolecular structure. Moreover, 1 has a remarkable activity for degradation of methyl orange in a photo-assisted Fenton-like process.

Unusual self-assembled 1D tape of tetramers and water–nitrate clusters trapped in a zinc(II) complex: Synthesis, characterization, luminescence and catalytic properties

Unusual tetramers and water–nitrate clusters have been observed in a mononuclear zinc(II) complex of [Zn(4-cpa)(phen)2(H2O)]·(H2O)·(NO3)] (1), (4-Hcpa=4-chlorophenoxyacetic acid, phen=1,10-phenanthroline), which was synthesized under hydrothermal conditions and characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis (TGA), powder X-ray diffraction, UV–vis absorption spectra and single-crystal X-ray diffraction. The crystal structure analysis of 1, reveals that the nitrate anions, water molecules and carboxylate oxygen atoms (O3) pack to form a one-dimensional infinite tape parallel to the c-axis. The uncoordinated carboxylate oxygen atoms (O3) of 4-cpa ligands, water molecules and nitrate anions interact via hydrogen bonds and extend 1 into a water–anion-cation tape, which are finally connected into a 3D supramolecular structure via π⋯π stacking interactions. Excitation (λex=310nm) and luminescence data observed at room temperature show that 1 emits bright blue fluorescence. Moreover, 1 has a remarkable activity for degradation of methyl orange in a photo-assisted Fenton-like process.

Three new solvent-directed 3D lead(ii)–MOFs displaying the unique properties of luminescence and selective CO2 sorption

Three new solvent-directed three-dimensional (3D) lead(II) coordination polymers, [Pb2(L)2]n (1), [Pb3(L)3]n (2) and [Pb(L)]·H2O (3) [H3L = 2-(pyridine-2-yl)-1H-imidazole-4,5-dicarboxylic acid], have been synthesized solvothermally. As influenced by different solvent systems, compounds 1 and 3 exhibit varying architectures from a multi-nodal 3,3,4,4-connected to a uninodal 3-connected net, while 2 with helices represents a binodal 3,4-connected topological net. Moreover, 3 possesses a micropore which is decorated with pyridyl systems and uncoordinated carboxylate oxygen atoms. In addition, the small-sized and highly polar pores enable 3 to attract CO2 strongly, leading to a high sorption heat for CO2 and significant selectivity for CO2 over H2 and N2 at 293 K. The luminescent behaviors and emissive lifetimes of 1-3 are also discussed.

Structural diversity of the encapsulated water clusters in the 3D supramolecular assemblies: a cyclic quasi-planar hexamer of water constructed through strong hydrogen bonding interactions

In the three-dimensional (3D) supramolecular assemblies having the general formula [Mn2(dicarboxylate)2(tpa)2]·xH2O (where tpa = N,N,N-tris(2-pyridylmethyl)-amine; dicarboxylate = acetylene dicarboxylate (adc) and x = 6 (1); fumarate and x = 8 (2) and succinate and x = 6 (3)), the dimanganese subunits differing in the dicarboxylate with a variation in the aliphatic chain structure (triple bond to double bond to single bond, respectively) provide the structural diversity of the encapsulated water clusters. These neutral supramolecular assemblies are held together by strong hydrogen bonding and π–π interactions, where the two dimensional (2D) water clusters are formed through strong hydrogen bonding (O–H⋯O). In each case, these water clusters connect the dimanganese subunits through hydrogen bonding with the uncoordinated carboxylate oxygen atoms of the dicarboxylates that bridge the Mn(II) centers of the subunit. The strength of the hydrogen bonding observed in these clusters (the range of O⋯O distances is 2.724 Å to 2.845 Å) is very similar to that found in water and ice. These are synthesized in high yields from a one-pot self-assembly reaction using Mn(OAc)2·4H2O, tpa and the corresponding acid in methanol at ambient conditions. Each of these is characterized by elemental analysis, single crystal and powder X-ray diffraction, IR and Raman spectroscopy and thermogravimetric analysis (TGA). Based on the X-ray crystal structures and TGA, the unusual stability of 2 compared to 1 and 3 is the result of different motifs including a cyclic quasi-planar hexamer formed through hydrogen bonding interactions. In 1 and 2, the Mn(II) centers are hexa-coordinated in a distorted octahedral geometry (N4O2), bonded to four nitrogen atoms of the ligand and two oxygen atoms from two monodentate carboxylate groups, while in 3 each Mn(II) center is heptacoordinated in a pentagonal bipyramidal geometry (N4O3), where in addition to the tpa ligand each succinate binds in chelated as well as monodentate mode, from opposite ends.

Observation of a water–anion tape constructed from unusual trimeric and tetrameric water clusters embedded in a copper(II) complex

Unusual trimeric and tetrameric water clusters have been observed in a complex of [Cu(DBA)(phen)2·(H2O)4·(NO3)] (1), (HDBA=benzilic acid, phen=1,10-phenanthroline), which was prepared under solvothermal conditions and characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis (TGA), UV–Vis spectroscopy, powder X-ray diffraction and single-crystal X-ray diffraction. In 1, a butterfly-like water–nitrate trimer formed by two water molecules and one nitrate anion, as well as a cyclic tetrameric water cluster are observed. The uncoordinated carboxylate oxygen atoms of DBA ligands, water molecules and nitrate anions interact via hydrogen bonds and extend 1 into a water–anion–cation tape, which in turn join to form a double water–anion–cation tape viaπ···π stacking interactions involving neighboring pyridyl and phenyl groups of DBA ligands.

Two enantiomorphic 3D Zn(ii)–carboxylate MOFs with double helical structures serving as a chiral source induced by hydrogen bonding

Two enantiomorphic 3D Zn(II)–carboxylate metal–organic frameworks [Zn(bpydc)(H2O)2] (1M and 1P) (H2bpydc = 2,2′-bipyridyl-5,5′-dicarboxylic acid) have been synthesized. They both contain an elegant double helix, self-organized through hydrogen bonds between the coordinated water molecules and uncoordinated carboxylate oxygen atoms. This double helical structure serves as a chiral source which transmits chiral information over the whole 3D framework.

Lanthanide(III)/Pyrimidine-4,6-dicarboxylate/Oxalate Extended Frameworks: A Detailed Study Based on the Lanthanide Contraction and Temperature Effects

Detailed structural, magnetic, and luminescence studies of six different crystalline phases obtained in the lanthanide/pyrimidine-4,6-dicarboxylate/oxalate system have been afforded: {[Ln(μ-pmdc)(μ-ox)(0.5)(H(2)O)(2)]·3H(2)O}(n) (1-Ln), {[Ln(μ-pmdc)(μ-ox)(0.5)(H(2)O)(3)]·2H(2)O}(n) (2-Ln), {[Ln(μ(3)-pmdc)(μ-ox)(0.5)(H(2)O)(2)]·~2.33H(2)O}(n) (3-Ln), {[Ln(2)(μ(3)-pmdc)(μ(4)-pmdc)(μ-ox)(H(2)O)(3)]·5H(2)O}(n) (4-Ln), {[Ln(μ(3)-pmdc)(μ-ox)(0.5)(H(2)O)(2)]·H(2)O}(n) (5-Ln), and [Ln(pmdc)(1.5)(H(2)O)(2.5)] (6-Ln). The slow generation of the oxalate (ox) anion, obtained from the in situ partial hydrothermal decomposition of the pyrimidine-4,6-dicarboxylate (pmdc) ligand, allows us to obtain good shaped single crystals, while direct addition of potassium oxalate provides the same compounds but as polycrystalline samples. The crystal structures of all compounds are based on the double chelation established by the pmdc and ox ligands to provide distorted 2D honeycomb layers that, in some cases, are fused together, leading to 3D systems, by replacing some of the coordinated water molecules that complete the coordination sphere of the lanthanide by uncoordinated carboxylate oxygen atoms of the pmdc. The presence of channels occupied by crystallization water molecules is also a common feature with the exception of compounds 5-Ln. It is worth noting that compounds 3-Ln present a commensurate crystal structure related to the partial occupancy of the crystallization water molecules placed within the channels. Topological analyses have been carried out, showing a previously nonregistered topology for compounds 4-Ln, named as jcr1. The crystal structures are strongly dependent on the lanthanide ion size and the temperature employed during the hydrothermal synthesis. The lanthanide contraction favors crystal structures involving sterically less hindranced coordination environments for the final members of the lanthanide series. Additionally, reinforcement of the entropic effects at high temperatures directs the crystallization process toward less hydrated crystal structures. The magnetic data of these compounds indicate that the exchange coupling between the lanthanide atoms is almost negligible, so the magnetic behavior is dominated by the spin-orbit coupling and the ligand field perturbation. The luminescence properties that exhibit the compounds containing Nd(III), Eu(III), and Tb(III) have been also characterized.