Lu-Lu Han

Three mixed-ligand coordination networks modulated by flexible N-donor ligands: syntheses, topological structures, and temperature-sensitive luminescence properties

Three new mixed-ligand metal–organic coordination networks based on tetrabromoterephthalic acid and different bis-imidazole or bis-triazole ligands, [Zn2(bmib)(tbtpa)2·2H2O]n (1), [Cd(ditb)(tbtpa)(H2O)2·2H2O]n (2), and [Zn(ditp)(tbtpa)]n (3) (bmib = 1,4-bis(2-methyl-1H-imidazol-1-yl)butane, ditb = 1,4-di(1H-1,2,4-triazol-1-yl)butane, ditp = 1,3-di(1H-1,2,4-triazol-1-yl)propane, H2tbtpa = tetrabromoterephthalic acid), have been synthesized under solvothermal conditions and structurally characterized by single-crystal X-ray diffraction analyses, infrared spectroscopy (IR), elemental analyses, powder X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). Single-crystal X-ray diffraction analysis reveals that 1 features a 4-fold class IIIa interpenetrated dia framework strengthened by Br⋯Br halogen bonds. Complex 2 possesses an infinite 2D layer structure with a 44-sql topology, and the 2D sheets were further packed into the 3D supramolecular framework in an –ABAB– fashion which is reinforced by hydrogen bonds and Br⋯Br halogen bonds. Complex 3 is a 2D 63-hcb network incorporating [Zn2(tbtpa)2] cyclic subunits, and the 2D layers were further extended to a 3D supramolecular framework incorporating π⋯π interactions and Br⋯Br and Br⋯O halogen bonds. In 1–3, all flexible N-donor ligands and dicarboxylates are 2-connected linkers, but networks with diverse topologies are formed, which indicates the coordination preferential geometries of the central metal ion and that the coordination conformations and modes of the ligands have important influences on the resultant structures. Furthermore, there is no solid-state photoluminescence observed for 1–3 at 298 K, and only 2 and 3 are emissive when cooled to liquid nitrogen temperature. The nanosecond range of lifetimes of 2 and 3 in the solid state at 77 K reveals that their emission is fluorescent in nature.

Simultaneous encapsulation of an infinite T4(0)A(0)6(0) water tape and discrete water hexamers in a hydrogen-bonded Ag(I) supramolecular framework

Self-assembly of Ag2O, 1,4-bis(pyrid-4-yl)benzene (dpb) and 1,3-benzenedicarboxylic acid (H2bdc) resulted in a one-dimensional mixed-ligand Ag(I) coordination polymer [Ag2(dpb)2(bdc)·9H2O]n (1), in which infinite 1D T4(0)A(0)6(0) water tapes and discrete water hexamers were simultaneously encapsulated. Chair-like water hexamers and D2h water tetramers with two dangling water molecules were alternately hydrogen-bonded into the unprecedented 1D T4(0)A(0)6(0) water tape. Additionally, results on the thermal stability, UV-Vis absorption and photoluminescence spectra of 1 were discussed.

Construction of a crystalline Ag(I) coordination polymer based on a new ligand generated from unusual in situ aza-Michael addition reaction

A two-dimensional (2D) Ag(I) coordination polymer [Ag(Htzsuc)]n (1, H2tzsuc = 2-(1H-1,2,4-triazol-1-yl)succinic acid) comprising a ligand not included in the original reaction mixture but instead generated through an unusual in situ aza-Michael addition reaction of 1H-1,2,4-triazole and fumaric acid during hydrothermal treatment was synthesised. Moreover, the thermal stability and luminescent properties of 1 were discussed.

Synthesis, structural versatility and magnetic properties of a series of copper(II) coordination polymers based on bipyrazole and various dicarboxylate ligands

Seven new copper(II) coordination networks combining flexible 3,3′,5,5′-tetramethyl-4,4′-bipyrazole (bpz) and diverse dicarboxylates, [Cu(bpz)0.5(adip)]n (1), [Cu2(bpz)4(sub)2]n (2), [Cu4(bpz)1.5(aze)·H2O]n (3), [Cu2(bpz)(pta)2(H2O)·H2O]n (4), [Cu2(bpz)(ipa)]n (5), [Cu2(bpz)(o-pda)2·H2O]n (6), and [Cu2(μ3-OH)(bpz)(p-pda)1.5·H2O]n (7) (H2adip = adipic acid, H2sub = suberic acid, H2aze = azelaic acid, H2pta = phthalic acid, H2ipa = isophthalic acid, H2o-pda = o-phenylenediacetic acid, H2p-pda = p-phenylenediacetic acid), have been obtained under solvothermal conditions and structurally verified by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, powder X-ray diffraction (PXRD), infrared spectroscopy (IR), UV-vis spectroscopy and thermogravimetric analyses (TGA). Single crystal X-ray diffraction analysis revealed that both 1 and 6 are 6-connected pcu networks (point symbol: {412·63}) based on paddle-wheel [Cu2(COO)4] secondary building units (SBU). Complexes 2 and 4 are 2D 44-sql networks based on a single metal ion node and a binuclear [Cu2(COO)4(H2O)] SBU, respectively, while complex 3 features an extremely rare 3D 5-connected hxg-d-5-C2/c (point symbol: {42·67·8}) network. Complex 5 shows a 1D tape structure built from bpz sealed 1D helical Cu2(ipa) chains along the b axis, and 7 is a 3D 8-connected hex (point symbol: {36·418·53·6}) network based on a centrosymmetric [Cu4(μ3-OH)2(COO)4] SBU. A thorough structural comparison of these coordination networks suggests that the coordination fashions, conformations of dicarboxylates along with the different inorganic Cu(II) SBUs simultaneously play a significant role in constructing the diverse networks. Variable-temperature magnetic susceptibility data denote that 4 and 7 display antiferromagnetic interactions in binuclear [Cu2(COO)4(H2O)] and [Cu4(μ3-OH)2(COO)4] SBUs. Moreover, the thermal stability and UV-vis spectra of 1–7 are discussed in detail.

Octanuclear Ni(II) cubes based on halogen-substituted pyrazolates: synthesis, structure, electrochemistry and magnetism

The employment of halogen-substituted pyrazole ligands in nickel(II) clusters afforded three anionic Ni(II) cubes, (HNEt3)2[Ni8(Xpz)12(OH)6] (X = Cl, 1·2CH3CN; X = Br, 2·2CH3CN; X = I, 3·12CH3CN; pz = pyrazolate). Clusters 1–3 are isolated as dianionic compounds which have similar cube geometry with each vertex occupied by a Ni(II) atom and eight μ4-OH− capped on eight square faces. The Xpz ligands adopt a bidentate mode to bind paired Ni(II) atoms on the edge of the cube. Interestingly, the three Ni8 cubes have similar symmetry, size and shape but pack together to form different lattice symmetry, which should be dictated by the halogen-related supramolecular interactions (C–X⋯H, C–X⋯π and X⋯X halogen bonding) in different crystals. The electrochemistry of 1–3 showed a Ni(II)/Ni(I) redox couple with E1/2 at ca. 900 mV and the oxidization potential order is 1 > 3 > 2 depending on the halogen substituents. 1–3 exhibit excellent electrocatalytic performances toward the oxidation of nitrite. The different packing of Ni8 cubes in 1–3 also has an important influence on their magnetic behaviors. Complex 2 showed antiferromagnetic couplings between the Ni(II) ions within the cubes, whereas 1 and 3 exclusively exhibited mixed ferromagnetic and antiferromagnetic properties, leading to frustration and typical spin glass behavior.

Synthesis, crystal structure, thermal stability, and photoluminescence of a 3-D silver(I) network with twofold interpenetrated dia-f topology

A silver(I) coordination polymer with mixed 3,3′,5,5′-tetramethyl-4,4′-bipyrazole (bpz) and maleic acid, [Ag2(bpz)3(fum)]n (1, H2fum = fumaric acid), was synthesized under hydrothermal condition by in situ isomerization of maleic acid to fumaric acid and characterized by elemental analysis, IR spectroscopy, powder X-ray diffraction, TGA, and single-crystal X-ray diffraction. The maleic acid in situ isomerizes to fumaric acid and participates in the formation of 1. Topologically, the structure of 1 features a rare 3-connected twofold interpenetrated dia-f net with a point symbol of {4.142}. Compound 1 exhibits photoluminescence in the solid state with an emission maximum at 470 nm upon excitation at 365 nm at room temperature, which is attributed to intraligand or/and interligand π → π* transition. With bpz and in situ generated fumaric acid ligands, a new polymer of [Ag2(bpz)3(fum)]n was synthesized under hydrothermal conditions. It presents a unique twofold interpenetrated 3-D network with a rare dia-f topology. If the Ag(I)⋯Ag(I) interaction is included in the simplification of the net, each Ag(I) is a 4-connected node, thus, a non-interpenetrated 4-connected upd net with a point symbol of {4.63.82} is obtained.

Mixed Linker Strategy for the Construction of a Fluorescent 2D Network Based on [Ag2(COO)2] as Secondary Building Unit

The ultrasound-assisted reaction of AgNO3, 2-amino-4,6-dimethylpyrimidine (dmapym) and 2,6-naphthalenedicarboxylic acid (H2npd) gave rise to a new 2D network of the formula [Ag2(dmapym)2(npd)]n (1). The atoms Ag1 and Ag2 in the complex show seesaw and distorted tetrahedral coordination geometries, respectively. The dmapym ligand acts as a bidentate bridge to bind paired Ag(I) ions into a chain. The chains are further connected by npd linkers to form the resultant 2D network reinforced by N-H···O hydrogen bonds between dmapym and npd. Weak C-H···p interactions are also found in the crystal structure. Complex 1 exhibits photoluminescence in the solid state at room temperature with an emission maximum at 418 nm upon excitation at 330 nm. Graphical Abstract Mixed Linker Strategy for the Construction of a Fluorescent 2D Network Based on [Ag2(COO)2] as Secondary Building Unit