Xiang-Jun Zheng

Second ligand-directed self-assembly of lanthanide(III) coordination polymers with 1,4-naphthalenedicarboxylate

Under hydrothermal conditions, 1,4-naphthalenedicarboxylic acid (H2NDC) reacts with lanthanide(III) chloride to form the coordination polymers [Ln2(NDC)3(H2O)2]·nH2O [n = 2, Ln = Eu (1); n = 1.5, Ln = Gd (2)]. If a second ligand, 4,4′-bipyridine (4,4′-bpy), is added to the reaction mixture, the coordination polymers [Ln2(NDC)3(4,4′-bpy)0.5(H2O)3]·(4,4′-bpy) [Ln = Eu (3); Ln = Yb (4)] are obtained. 1 and 2 are isostructural and they possess a porous 3D network with the lanthanide(III) ions bridged only by NDC anions. 3 and 4 are unprecedented lanthanide coordination polymers of polycarboxylate with 4,4′-bpy. They possess a 3D porous structure assembled by lanthanide ions with the linkers NDC and 4,4′-bpy, while lattice molecules of 4,4′-bpy are enclathrated in the cavities. The photophysical properties of 3 and the magnetic properties of 2 were investigated, and the thermogravimetric analyses of 1 and 3 were also carried out.

Hydrothermal synthesis and structural studies of novel 2-D lanthanide coordination polymers with phthalic acid

This paper presents four lanthanide coordination polymers, [Ln2(BDC)3(H2O)]n (Ln = La, 1; Ln = Eu, 2; Ln = Tb, 3; BDC = 1,2-benzenedicarboxylate) and [Yb4(BDC)6(H2O)2]n (4) prepared by the hydrothermal technique. They are all 2-D infinite structures with BDC anions connecting adjacent metal ions. In complex 1, La(III) ions are eight- and nine-coordinated, and all La(III) ions are coplanar in the 2-D structure. In complexes 2 and 3, Eu(III) and Tb(III) ions are also eight- and nine-coordinated, but they are distributed in a wave-like 2-D network. In complex 4, the Yb(III) ions have four different coordination numbers (6, 7, 8 and 9), which are rarely found in one lanthanide complex. Both the coordination numbers and the arrangement of Ln atoms in these coordination polymers show the lanthanide contraction. In the four complexes, all the oxygen atoms of BDC take part in coordination with Ln(III) ions, adopting tetra-, penta- and hexadentate coordination modes for the phthalate anions. The luminescent properties of complex 2 have been investigated and the results for the explanation of the chemical environment of the Eu(III) ion are consistent with the X-ray analysis.

Hydrothermal Syntheses, Structures, and Properties of First Examples of Lanthanide(III) 2,3-Pyrazinedicarboxylates with Three-Dimensional Framework

Lanthanide 2,3-pyrazinedicarboxylate complexes with three-dimensional frameworks, [Ln(2)(pzdc)(3)(H2O)]x.2xH(2)O [Ln = Pr (2), Nd (3), and Eu (4)], were obtained by hydrothermal reactions of 2,3-pyrazinedicarboxylic acid (H(2)pzdc) and the lanthanide(III) chlorides, while [La-2(pzdc)(3)(H2O)](x).2xH(2)O (1) was obtained by hydro(solvo)thermal reaction of LaCl3.7H(2)O and 2,3-pyrazinedicarboxylic acid. They are isomorphous and exhibit complicated 3-D structures based on [Ln(2)(pzdc)(3)(H2O)] building blocks. In the asymmetric unit, the two Ln(3+) ions are both nine-coordinate, but with different coordination environments. The ligand pzdc coordinates to the central Ln(3+) ions in a tetradentate, hexadentate, or heptadentate manner. Utilizing the characteristic of Eu3+ ion to act as a conformational probe, we determined the high-resolution spectra of 4, which show that there are two Eu3+ ion sites in the coordination polymer. This is also in agreement with the results of the X-ray single-crystal diffraction study. It was concluded that there are two La3+, two Pr3+ and two Nd3+ ion sites in polymers 1, 2, and 3, respectively. The thermogravimetric analyses of these complexes show that all coordinated and uncoordinated water molecules were lost at the first weight loss above 240 C

Structural diversity and properties of M(II) 4-carboxyl phenoxyacetate complexes with 0D-, 1D-, 2D- and 3D M-cpoa framework

Nine new metal complexes with an asymmetric H2cpoa ligand, [Co(Hcpoa)2(bpe)2(H2O)2] (1), [Co(cpoa)(bpe)1.5(H2O)]·H2O (2), [Co(Hcpoa)2(4,4′-bpy)2] (3), [Co(4,4′-bpy)(H2O)4]·[Co(cpoa)2(H2O)2]·2H2O (4), [Ni(cpoa)(4,4′-bpy)(H2O)2] (5), [Ni(cpoa)(bpe)1.5(H2O)]·H2O (6), [Zn2(cpoa)2(bpe)(H2O)] (7), [Zn(cpoa)(bpe)0.5]·0.5(i-C3H7OH) (8) and [Zn(cpoa)(bpe)0.5]·0.5(n-C3H7OH) (9) (H2cpoa = 4-carboxyphenoxy acetic acid, bpe = 1,2-bis(4-pyridyl)ethane, 4,4′-bpy = 4,4′-bipyridine) were synthesized under hydro/solvothermal conditions. X-ray single-crystal structural analyses reveal that they have metal–organic frameworks ranging from 0D (1), 1D (3, 4), 2D (5, 7, 8) to 3D structure (2, 6, 9). The reaction of the CoCl2/H2cpoa/bpe (1 : 1 : 1) system results in the formation of complex 1 at the starting pH of ca. 8, and complex 2 at 12. The reaction of CoCl2/H2cpoa/4,4′-bpy (1 : 1 : 1) forms complex 3 with a 1D chain structure, while a molar ratio of 1 : 1 : 0.5 leads to the formation of complex 4 with two 1D metal–organic frameworks of rarely reported homometal complex ion pairs. By changing the added organic solvent, the 2D layer framework of complex 8 and the microporous 3D framework of complex 9 were obtained under the same reaction conditions. The guest n-C3H7OH molecules occupy 1D channels in 9. Thermogravimetric and powder X-ray diffraction analyses show that the microporous 3D framework of 9 is maintained after the removal of the guest molecule. And a reversible dealcoholization/realcoholization process can be observed. The magnetic measurements show antiferromagnetic interactions between the metal ions in 2, 4 and 5, and antiferromagnetic interaction in the range of 300–18 K and ferromagnetic interaction between Ni(II) ions below 18 K in 6.

Structural analyses and luminescent properties of a series of lead(II) metal–organic frameworks based on 2-sulfoterephthalate

Hydrothermal reaction of lead(II) salt with monosodium 2-sulfoterephthalate (2-NaH2stp) and three N-donor auxiliary ligands gives rise to a series of 1D–3D Pb(II) coordination polymers:[Pb(2-Hstp)(o-phen)] (1), [Pb(2-Hstp)(2,2′-bipy)(H2O)]·H2O (2), [Pb(2-Hstp) (4,4′-bipy)(H2O)] (3), [Pb(2-Hstp)(H2O)] (4), [Pb3(2-Hstp)(2-stp)(OH)(4,4′-bipy)] (5) and [Pb2(2-stp) (OH)] (6) (o-phen = 1,10-phenanthroline, 2,2′-bipy = 2,2′-bipyridine and 4,4′-bipy = 4,4′-bipyridine). X-ray diffraction structural analyses of these complexes reveal 1, 3, 4 and 6 crystallize in the monoclinic crystal system of the P21/c Space group, while 2 and 5 crystallize in the triclinic Pī space group. Complex 1 possesses 1D left- and right-handed helical double-stranded chains sharing a common axis and Pb nodes, and a great deal of H-bonds and π⋯π interactions between o-phen molecules. For 2, the square H-bond clusters link two left- and right-handed helical single-stranded chains to form 1D dual-chain supramolecular structures. Complex 3 features a 1D bimetallic chain structure containing four left-handed helical chains sharing one common axis: one main helix and three auxiliary helixes in ⋯ABC⋯ order twisting up the main helix. Structural analysis shows that complex 4 presents a 3D 5-connected architecture with the topology symbol as (44, 66). In 5, a 2D double-layer structure arises from the μ3-OH bridged [Pb3(OH)] triangle clusters with 2-stp3− anions. The 3D framework of 6 is constructed from a unique tetra-nuclear lead(II) [Pb4(OH)2] chair-like motif based on two μ3-OH groups and 2-stp3− anions, resulting in the (42, 66) topology. Solid-state fluorescence properties for these crystalline materials are also presented.

Water cluster supported architecture of lanthanide coordination polymers with pyrazinetricarboxylic acid

The first examples of lanthanide coordination polymers with pyrazinetricarboxylic acid, [Ln(PZTA)(H2O)4]·2H2O (Ln = Eu(1), Gd (2), PZTA = pyrazine-2,3,5-tricarboxylate) and [Ln(PZTA)(H2O)2]·H2O (Ln = Er(3), Yb(4)) were synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction. Structural analysis shows that complexes 1 and 2 are composed of 1-D lanthanide-pyrazinetricarboxylate (Ln-PZTA) framework and two types of water clusters while complexes 3 and 4 have 3-D Ln-PZTA framework with 1-D channel, at which a 1-D water cluster chain is located. This shows the effect of lanthanide contraction on the construction of the Ln-PZTA framework. The results of TG curves and PXRD display that the uncoordinated and coordinated water molecules are removed, the Ln-PZTA frameworks collapse, which shows that the water clusters play an important role in constructing Ln-PZTA frameworks in the title complexes.

Architecture of europium complexes with sulfobenzenedicarboxylates

Four new Eu(III) coordination polymers with sulfobenzenedicarboxylates, [Eu(4-sp)(H2O)2]n (1), [Eu(4-sp)(phen)(H2O)]n (2), {[Eu(2-stp)(phen)(H2O)]·H2O}n (3) and [Eu(5-sip)(phen)(H2O)]n (4) (4-sp = 4-sulfophthalate anion, 2-stp = 2-sulfoterephthalate anion, 5-sip = 5-sulfoisophthalate anion, phen = 1,10-phenanthroline) were synthesized under hydrothermal conditions and characterized by single-crystal diffraction. The results of structural analysis show that in each Eu(III) coordination polymer there is only one crystallographically independent Eu(III) ion and one sulfobenzenedicarboxylate anion, and the number of sulfobenzenedicarboxylate ligands (A) that surround one Eu(III) ion is the same as the number of Eu(III) ions (B) coordinated by one sulfobenzenedicarboxylate anion. The connection modes (A, B) of 1–4 are (5, 5), (4, 4), (3, 3) and (4, 4) for 1, 2, 3 and 4, respectively. The Schlafli symbols of the title complexes are (48, 62) for 1, (4, 65) for 2, (103) for 3 and (42, 63, 8) for 4. Their red emissions are also discussed.

Structure and photophysical properties of europium complexes of succinamic acid and 1,10-phenanthroline

Abstract Two binuclear europium complexes [Eu2(SA)6(phen)2]·6H2O (1) and [Eu2(SA)4(phen)2(H2O)4](ClO4)3 (phenH)·H2O (2) (where SA=succinamate, phen=1,10-phenanthroline) have been synthesized and characterized by X-ray single crystal diffraction. For 1, the unit cell contains two crystallographically independent Eu(SA)3(phen) species in which the Eu3+ ions have two different coordination environments. Two types of binuclear molecule are arranged in different orientations in the crystal. The 7F0→5D0 excitation peaks at 580.16 and 580.46 nm at 77 K and the Stark components of 5D0→7FJ transitions, especially 5D0→7F1 and 5D0→7F2 emission lines, show that complex 1 has two Eu(III) ion sites, which is in good agreement with the results of the structure determination. In complex 2, four water molecules take the place of two bidentate chelating SA anions in the inner coordination sphere of 1. Outside the coordination sphere, the protonated phen molecule forms a hydrogen bond with a tridentate-coordinated carboxyl group and has a π–π stacking interaction with the coordinated phen molecule.

Hydrothermal synthesis and crystal structure of two new lanthanide coordination polymers with 1,2-phenylenediacetate

Two new compounds {[Ln2(1,2-pda)3(H2O)2]· 2H2O} n (1,2-H2pda = 1,2-phenylenediacetic acid, Ln = Tb, 1; Ho, 2) were prepared by hydrothermal reaction and characterized by X-ray crystallography. The Ln3+ is nine-coordinate by eight oxygen atoms of six 1,2-pda ligands and one oxygen of water. Ln3+ ions are bridged by 1,2-pda ligands via bridging/chelating-bridging pentadentate and chelating-bridging/chelating-bridging hexadentate coordination to form 3-D framework structures. Complex 1 emits strong green fluorescence corresponding to 5D4 ⟹ 7Fj (j = 6–3) transitions of the Tb3+.

Crystal Structure and Luminescence of a Europium Nitrate Complex with Furancarboxylic Acid and 2,2′-Bipyridine

Abstract A quaternary mixed ligand europium complex, [Eu(FA)2NO3bipy]2, has been synthesized, where FA = α-furancarboxylic acid anion and bipy=2,2′-bipyridine. The europium complex crystallizes in the triclinic system, space group P1. Its structure was determined by X-ray diffraction methods. The two europium ions in the dimer are held together by four carboxylate groups of furancarboxylic acid and each europium ion is further bonded to one chelated bidentate nitrate and one 2,2′-bipyridine molecule. The coordination modes of the four carboxylate groups are divided into two types, bidentate bridging and tridentate bridging, making a coordination number of 9. Excitation and luminescence spectra observed at 77 K show that the europium ion site in the crystal has low symmetry and emission 5D 1→7 FJ of the Eu3+ ion disappears after 20 μs.