Chaojun Shen

Redox‐Responsive Photochromism and Fluorescence Modulation of Two 3D Metal–Organic Hybrids Derived from a Triamine‐Based Polycarboxylate Ligand

Photochromism is defined as the reversible transformation of a chemical species, induced by the absorption of electromagnetic radiation, to a form with a different vibronic absorption spectra. Photochromic materials have attracted considerable interest owing to prospective real or potential applications in many fields, including protection (in spectacles, photobarriers, anti-fake, and camouflage), decoration, information storage, displays, optical switches, photomechanics, and so forth. Although numerous photochromic families have been reported to date, those based on an electron-transfer (redox) chemical process, especially for metal–organic complexes (MOCs), are rare. One of the biggest challenges in photochromic MOCs without photochromic organic ligands is to design photoinduced bistable systems based on different electron-transfer mechanisms, such as metal-centered electron transition (MC), ligand-tometal charge transfer (LMCT), metal-to-metal charge transfer (MMCT), intra ACHTUNGTRENNUNGli ACHTUNGTRENNUNGgand charge transfer (ILCT), and ligand-to-ligand charge transfer (LLCT). Structurally well-defined hybrids will give us better insight into the structure–photochromism relationships; nevertheless, few hybrids based on transition metals have been explored with simultaneous characterization of their structure and photochromism. Chopoorian and Loeffler have discovered the electron-attractive ability of a porous glass matrix indicated by the blue radical-ion species after the irradiation with UV light, in which an aqueous solution of p-phenylenediaminetetraacetic acid (p-PTDA) is absorbed. Thus, in the presence of electron-accepting components, organic ligands containing N ACHTUNGTRENNUNG(CH2CO2H)2 groups in MOCs may undergo a similar electron-transfer process. However, no coordination polymer constructed from ligands containing N ACHTUNGTRENNUNG(CH2CO2H)2 groups shows photochromism so far. Guo and coworkers have reported the only metal-assisted LLCT photochromic MOC, [Cd2(ic)(mc)(4,4’-bipy)3]·4H2O (ic = itaconate, mc=mesaconate, bipy= bipyridine), which undergoes an interesting photochromic transformation from yellow to blue upon UV irradiation. Herein, we report two photochromic MOCs with adjustable fluorescent intensities, [Zn3ACHTUNGTRENNUNG(TTHA)(4,4’bipy)1.5 ACHTUNGTRENNUNG(H2O)2]·6H2O (1 a) and [Zn3ACHTUNGTRENNUNG(TTHA)(4,4’-bipy)1.5ACHTUNGTRENNUNG(H2O)2]·3H2O (2 a), derived from a novel triamine-based polycarboxylate ligand containing the N ACHTUNGTRENNUNG(CH2CO2H)2 group, 1,3,5-triazine-2,4,6-triamine hexaacetic acid (H6TTHA), as electron donor, although the ligand H6TTHA itself does not exhibit photochromism, and 4,4’-bipy as electron capturer. The photochromic mechanisms based on electron-transfer chemical processes have been verified with direct and powerful ESR and X-ray photoelectron spectroscopy (XPS) measurements. Yellow needlelike crystals of 1 a and prismatic crystals of 2 a were obtained by the hydrothermal reactions of ZnACHTUNGTRENNUNG(NO3)2, H6TTHA, and 4,4’-bipy in a molar ratio of 3:1:2 at 140 8C and 120 8C for 72 h, respectively. The single-crystal X-ray diffraction data reveal that complexes 1 a and 2 a are 3D networks. As shown in Figure 1 and S3 in the Supporting Information, the 3D frameworks can be described as 2D layers constructed of Zn ions and TTHA pillared by the coordinated 4,4’-bipy groups. The biggest difference between the structures of complexes 1 a and 2 a is the coordination modes of the ligands (Scheme 1). Due to the flexibility, six of the arms show sig[a] Q.-L. Zhu, Prof. T.-L. Sheng, Dr. R.-B. Fu, S.-M. Hu, Prof. L. Chen, C.-J. Shen, X. Ma, Prof. X.-T. Wu State Key Lab of Structural Chemistry Fujian Institute of Research on the Structure of Matter Chinese Academy of Science, Fuzhou Fujian 350002 (P.R. China) Fax: (+86) 591-8371-9238 E-mail : wxt@fjirsm.ac.cn [b] Q.-L. Zhu, C.-J. Shen, X. Ma Graduate School of the Chinese Academy of Sciences Beijing, 100049 (P.R. China) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201003274. Figure 1. 2D layer (left) and 3D framework along the c axis (right) in complex 1 a.

Effect of Functionalized Groups on Gas‐Adsorption Properties: Syntheses of Functionalized Microporous Metal–Organic Frameworks and Their High Gas‐Storage Capacity

The microporous metal-organic framework (MMOF) Zn4O(L1)2⋅9 DMF⋅9 H2O (1-H) and its functionalized derivatives Zn4O(L1-CH3)2⋅9 DMF⋅9 H2O (2-CH3) and Zn4O(L1-Cl)2⋅9 DMF⋅9 H2O (3-Cl) have been synthesized and characterized (H3L1=4-[N,N-bis(4-methylbenzoic acid)amino]benzoic acid, H3L1-CH3=4-[N,N-bis(4-methylbenzoic acid)amino]-2-methylbenzoic acid, H3L1-Cl=4-[N,N-bis(4-methylbenzoic acid)amino]-2-chlorobenzoic acid). Single-crystal X-ray diffraction analyses confirmed that the two functionalized MMOFs are isostructural to their parent MMOF, and are twofold interpenetrated three-dimensional (3D) microporous frameworks. All of the samples possess enduring porosity with Langmuir surface areas over 1950 cm(2) g(-1). Their pore volumes and surface areas decrease in the order 1-H>2-CH3 >3-Cl. Gas-adsorption studies show that the H2 uptakes of these samples are among the highest of the MMOFs (2.37 wt% for 3-Cl at 77 K and 1 bar), although their structures are interpenetrating. Furthermore, this work reveals that the adsorbate-adsorbent interaction plays a more important role in the gas-adsorption properties of these samples at low pressure, whereas the effects of the pore volumes and surface areas dominate the gas-adsorption properties at high pressure.

Syntheses, structural aspects, luminescence and magnetism of four coordination polymers based on a new flexible polycarboxylate

Four novel coordination polymers, {Na2[Co3(H2TTHA)2(H2O)12](H2O)2}·4(H2O) (1), {Na[Cu4(H2TTHA)(HTTHA)(H2O)8](H2O)3}·5(H2O) (2), [Cd3(TTHA)(H2O)4] (3) and [Ca5(HTTHA)2(H2O)8] (4), (H6TTHA = 1,3,5-triazine-2,4,6-triamine hexaacetic acid) have been synthesized by self-assembly of the flexible hexapodal acid H6TTHA and corresponding metal salts. The four complexes exhibit novel frameworks with different topologies due to diverse coordination modes and different conformations of the flexible H6TTHA. Complex 1 shows a 3D network with (4,4,6)-connected topology constructed from parallel one-dimensional hybrid ribbons with nearly planar 24-membered rings, in which all Co(II) atoms are located in one plane. Complex 2 features a 3D (3,4,4,4,7)-connected network bridged by sodium ions from 2D layer structures which are formed through the interconnection of the tetranucleate units and the flexible ligands. Complex 3 possesses hybrid layers constructed from zigzag Cd–O chains. These layers are further linked by the TTHA6− ligands with two configurations, leading to another 3D (3,3,8)-connected framework. The metal ions in complex 4 are connected into wall-like infinite metal chains which are bridged by the carboxylate groups of ligands into a 3D (3,3)-connected hybrid framework. The framework is further furnished with the ligands forming hydrophobic channels with approximate sizes 3.5 A × 9 A based on the distances of the opposite atoms. The enantiometric pairs of ligands are formed in spite of no asymmetric carbon atom in complexes 1–3. Variable temperature magnetic studies down to 2 K reveal antiferromagnetic interactions in complexes 1 and 2. Complexes 3 and 4 are both highly emissive at room temperature. And the luminescent intensities are largely enhanced once they are frozen to 10 K.

A series of goblet-like heterometallic pentanuclear [LnIIICuII4] clusters featuring ferromagnetic coupling and single-molecule magnet behavior

A series of fascinating goblet-like clusters based on [Ln(III)Cu(II)(4)] cores have been assembled from a flexible carboxylate ligand, which exhibit a dominant ferromagnetic exchange coupling and single-molecule magnet behavior.

Synthesis and crystal structure of two new heterometallic thioantimonates(III) [Ni(pda)2]CuI4SbIII2S6 and [Ni(dien)2]CuISbIII3S6,

Two different dimensional inorganic–organic hybrid heterometallic sulfide, [Ni(pda)2]Cu4Sb2S6 (1) and [Ni(dien)2]CuSb3S6 (2) were obtained by using 1,2-propanediamine (pda) and diethylenetriamine (dien) as the ligand, respectively.

Lanthanide coordination polymers assembled from triazine-based flexible polycarboxylate ligands and their luminescent properties

Two flexible triazine-based polycarboxylate ligands, 1,3,5-triazine-2-iminodiacetic acid-4,6-bis(L-alanine) (H4L1) and 1,3,5-triazine-2-iminodiacetic acid-4,6-biglycine (H4L2), have been designed and used to construct a series of luminescent lanthanide coordination polymers {[Ln(HL1)](H2O)5}n (Ln = 1, Tb; 2, Eu; 3, Gd) and {[Ln(HL2)(H2O)](H2O)2}n (Ln = 4, Tb; 5, Eu; 6, Gd). The complexes were structurally authenticated by single-crystal X-ray diffraction, revealing that isostructural complexes 1–3, derived from H4L1, possess a 2-D framework with the monoclinic space group C2/c, whereas isostructural complexes 4–6, based on H4L2, exhibit a 2-D layer structure with the monoclinic space group P2(1)/c. Solid-state photoluminescence properties of the complexes were investigated. Complexes 1 and 2 exhibit remarkable green and red luminescence emissions with high quantum yields up to 67% and 68%, respectively, and millisecond-level lifetimes. Nevertheless, complexes 4 and 5 feature weak quantum yields (9.9% for 4; and 30% for 5).

Four new cobalt(II) coordination complexes: thermochromic switchable behavior in the process of dehydration and rehydration

Four cobalt(II) coordination complexes, {[Co11(L1)6(HL1)2(H2O)28]·12H2O}n (1), [Co4(H2L1)4(HL1)2(H2O)8]·2H3L1·2H2O (2), {[Co(H2L3)(H2O)3]·2H2O}n (3) and [Co(HL1)(4,4′-bpy)(H2O)2]n (4), (H3L1 = 2,4,6-tri(3-carboxyphenylthio)-1,3,5-triazine, H4L3 = 2,4-bis(3-carboxyphenylthio)-6-(4-carboxyphenylamino -1,3,5-triazine, 4,4′-bpy = 4,4′-bipyridine), was synthesized hydrothermally and characterized by single-crystal X-ray diffraction, powder X-ray diffraction, IR, thermal analysis, UV-vis spectroscopy and magnetic measurements. Complex 1 shows a 2D layer structure composed of three types of secondary building units (SBUs), [M1], [M3] and [M4] bridged by [HL1]2− and [L1]3− linkers. While complex 2 is a tetranuclear compound and further forms a 3D supramolecular network structure based on eight types of hydrogen-bonding interactions between the molecules. The 2D framework of complex 3 can be described as 1D infinite chains interconnected by [H2L3]2− ligands. Furthermore, the hydrogen-bonding interactions between the adjacent layers along the ac plane makes the 2D layer structure extend to a 3D network. The structure of complex 4 can be illustrated as a 1D zigzag infinite chain with 4,4′-bipyridine as the secondary ligand. Additionally, the π⋯π stacking interactions can be observed between the adjacent chains. An aquo-accessible thermochromic change in complexes 1–4 was induced by means of the reversible dehydration and rehydration of the crystals. Magnetic measurements showed antiferromagnetic coupling between the Co2+ ions in all of the four complexes.

A three-dimensional coordination polymer based on linear trinuclear copper(II) clusters featuring a ferromagnetic exchange interaction

A new triazine-based dicarboxylic acid, 2,4-bis(4-aminobenzoic acid)-6-(dimethylamino)-1,3,5-triazine (H2L), has been designed and prepared, which has been used for the support of a new coordination polymer constructed from trinuclear copper(II) clusters. The compound was structurally authenticated by single-crystal X-ray diffraction revealing that the compound possesses a three-dimensional (4,8)-connected alb network constructed from trinuclear copper(II) clusters with the general formula [Cu3(L)2(μ2-OH)2] (1). Additionally, compound 1 contains left- and right-handed helical chains along the b axis, which are interlinked by the trinuclear copper(II) clusters. In the basic trinuclear copper(II) cluster, the central copper ion is located on an inversion center with strictly planar four-coordinate coordination geometry, while the coordination spheres of the terminal copper ions are square pyramidal. The three copper atoms are in an exactly linear arrangement, and adjacent coppers are connected by a hydroxo bridge and a bidentate syn–syn carboxylate group. Variable-temperature magnetic susceptibility measurements reveal a ferromagnetic coupling between adjacent copper(II) ions with J = 42.39 cm−1, which is confirmed by the EPR spectrum.