Electron-withdrawing/coordinating o-phenolacetyl-substituted viologen can act as a visual sensor for solvents, bases, and temperature in organic solvents. Due to chelating phenolacetyl groups, this viologen can coordinate to Fe(III), Cu(II), and ZnCl2 in aqueous and DMF solutions. Interestingly, this viologen can respond to temperature, grind, and NH3 vapor in its solid state. Stimuli response is visible, fast, and fully reversible in air at room temperature. The color change is attributed to the enolic and/or free radical structure. This is the most versatile chromic material that responds to chemical and physical stimuli in both solution and solid state.Topics: Sensors; Sensors; Solvation; Spectra; Thermal properties;

AbstractA polyethylene-glycol-functionalized perylene bisimide (PEPBI) was synthesized. Its concentration-, solvent- and temperature-dependent visible spectra were measured and its aggregation states were analyzed. PEPBI exists as an aggregate dimer in aqueous solution or predominantly as a monomer in organic solvents. The anionic surfactant sodium dodecylbenzenesulfonate (SDBS) can disperse PEPBI as a monomer in aqueous solution. The fluorescence of these solutions depends on the concentration of PEPBI and SDBS. The reduction of aggregated PEPBI with Na2S is slow and the monoanion radical as well as dianion species are the main forms of monomer. PEPBI exists predominantly as monomers in DMF and reacts with Na2S much faster. Interestingly, the anionic radical species exist in H-aggregate form at low PEPBI concentrations and J-aggregation occurs at high concentration. The dianion species is EPR-silent and its color highly depends on its concentration in DMF.

A colorful exchange: The concentration-, solvent- and temperature-dependent aggregation behaviors of poly(ethylene glycol)-functionalized perylene bisimide (PEPBI) were analyzed. PEPBI exists as an aggregate dimer in aqueous solution or as a monomer in organic solvents. The reduction of PEPBI with Na2S is slow and the monoanion radical and dianion species are the main forms of monomer. PEPBI exists predominantly as a monomer in DMF and reacts with Na2S very fast (symbolized by the airplane shown in the cover image). The dianion species is EPR-silent and its color highly depends on concentration in DMF. More information can be found in the Full Paper by Feifei Xing, Shourong Zhu et al. on page 1612 in Issue 11, 2017 (DOI: 10.1002/ajoc.201700334).

Three porous Cu(II) coordination polymers {[(CH3)2NH2]3[Cu7K(μ7-L1)2(μ7-L1)2(μ2-OH)2(H2O)6]·18H2O}3n (1), {[Cu5(μ8-L1)2(μ3-OH)2(H2O)5]·4.5DMF·18H2O}3n (2), {[Cu5(μ8-L2)2(μ3-OH)2(H2O)4]·DMF·10.5H2O}3n (3), where KH3L1 and H4L2 are semirigid 3-(3′,5′-dicarboxylphenoxy) phthalic acid and 4-(3′,5′-dicarboxylphenoxy) phthalic acid, respectively, were synthesized solvothermally. Their guest-accessible voids are 36%, 59%, and 39% in 1, 2, and 3, respectively. These three porous coordination polymers show high catalytic activities for the degradation of rhodamine B (RhB), methylene blue (MB), safranine T (ST), and orange II (OII) dyes in aqueous solution. The reaction kinetics follow v = k[H2O2][RhB], where k = 0.0260 ± 0.001 L·mol–1·min–1 in the presence of 3, while 1 and 2 follow v = [H2O2][RhB]/(1/kK + (1/k)[H2O2]), where K = 5.0 ± 0.5 M–1, k = 0.057 ± 0.007 min–1 for 1 and K = 4.5 ± 0.5 M–1, k = 0.083 ± 0.009 min–1 for 2 at pH 7.0. All three catalysts show good catalytic activity in pH 4.8–8 and are essentially constant in this pH range while further increases will decrease catalytic activity. Complexes 1 and 3 exhibited good structural stability in the catalytic process with no discernible catalytic activity decrease after three catalytic cycles. Complex 2 is unstable in the catalytic process. MS data show that the slow catalyst 3 degrades RhB into aromatic carboxylate. Faster 1 further degrades RhB into aromatic and aliphatic carboxylate, while fastest 2 not only degrades RhB, but also the catalyst itself. These catalysts not only degrade RhB but also methylene blue, saframine T, and orange II. Azo dye orange II was oxidized into red nitrosobenzene and then degraded nitrisobenzene into colorless species. Complex 1 has the advantage of good catalytic activity, stability, and availability. Along with ease of recovery, it will be useful in practical applications.

•Six Mn metal-organic frameworks have been assembled from V-shaped terphenyl tetracarboxylate ligand.•The coordination number of terphenyl tetracarboxylate ligand varies from 6 to 10, and each ligand links 4–8 Mn(II) ions.•The first coordination saturated phthalate is presented.•Compared to H2O solvent, DMF can increase coordination number of the ligand.Six Mn metal-organic frameworks have been synthesized under solvothermal conditions with V-shaped terphenyl tetracarboxylate ligands (H4ttac). Their structures were characterized by elemental analysis, infrared spectra, PXRD, thermogravimetric analysis, and single-crystal X-ray diffraction analysis. Crystal structures reveal that the coordination number of H4ttac ligand varies from 6 to 10, and each ligand links 4–8 Mn(II) ions. Coordination modes vary from η6μ4 to η10μ8. The existence of DMF solvent can increase coordination number of the ligand. The first coordination saturated phthalate is presented. The variable-temperature magnetic studies indicate that complexes exhibit dominant antiferromagnetic behaviors. Structural parameters and coordination modes were summarized. The porosity of these complexes is less than 15%, indicating that the V-shape ligand is not a good choice to construct porous coordination polymers.

Viologen cations are excellent electro- and photochromic materials. They generally have no response or very low sensitivity to bases. In this paper, three compounds, 1,1′-bis(2-oxo-2-phenylethyl)-4,4′-bipyridinium (viologen) with different substituents, including H (1), Cl (2), and OH (3), were synthesized. All three, especially 1 and 2, have very high sensitivity to base in both solution and solid state in air atmosphere. These viologens are responsive not only to bases but also to solvent polarity. NMR shows 1 became enolic and then a radical, whereas 3 is colored only in the radical form. These results are in agreement with EPR spectra. Crystal structures show that the C–C that links two pyridinium and N–C distances in coplanar pyridinium in the colored (radical) form is clearly longer than that of the pale-yellow form, indicating that the color is due to the viologen radical. Viologens containing an electron-withdrawing phenacetyl group are the most sensitive compounds for fast, naked eye detection of base and solvent polarity.Keywords: air-stable; electronic effect; solvatochromic; viologen; visual base sensor;

Two rht anionic metal–organic frameworks were synthesized. There are six [M(H2O)6]2+ ions held together by a super-strong H-bond and arranged in a regular octahedron in each medium cage. Dye adsorption studies revealed a rapid and selective adsorption of cationic dyes and the adsorbed dyes can be released in saturated NaCl aqueous solution.

A new neuromelanin-like ketocatechol-containing iminodiacetic acid ligand, (N-(3,4-dihydroxyl)phenacylimino)diacetic acid (H4L), which is also quite similar to compounds found in insect cuticle, has been synthesized and characterized. The X-ray crystal structure of H4L has been successfully determined. Proton binding and coordination with Fe(III), Cu(II), and Zn(II) have been studied by potentiometric titrations and UV-vis spectrophotometry in aqueous solution. UV spectra of H4L in the absence and presence of different metal ions indicate complexes formed with the catechol moiety of H4L in aqueous solution. Visible spectra and NMR reveal that H4L with Fe(III), Cu(II), and Zn(II) can all give stable mono-(ML) and dinuclear complexes [M(ML)]. Fe(III) can also form {Fe(FeL)2} and {Fe(FeL)3} species with sufficient base. The process is accompanied by a drastic color change from light blue to deep-blue to wine-red. The Fe(III)–Cu(II) heteronuclear complex also exists in aqueous solution whose spectra are similar to the homonuclear Fe(III) complex. However, the spectra of {Fe(CuL)} shifted to a longer wavelength and {Fe(CuL)2} and {Fe(CuL)3} shifted to a shorter wavelength. Keto–enol tautomerism was observed in weak basic aqueous solution as indicated by 1H NMR spectra. The reaction products of Cu(II) complex with H2O2 depend on the H2O2 concentration and pH value. Low concentrations of H2O2 oxidize H4L to a series of semiquinone and quinone compounds with absorption maxima at 314–400 nm, while a high concentration of H2O2 oxidizes H4L to colorless muconic acid derivatives. NaIO4 gives different oxidase products, but no 2,4,5-trihydroxyphenylalanine quinone (TPQ)-like hydroxyquinone can be found.

•Cationic pyridinium (or pyridione) is not well explored as a ligand to construct coordination polymer.•The ligand in 1–5 exist in 4(1H)-pyridinone form rather than commonly presented 4-oxypyridinium form.•π-π interaction between pyridinone rings exists in 1–4 and is stronger than that between two benzene rings.•The pyridinone oxygen is the strongest coordination atom, or it forms strongest H-bond.•Different from viologen (pyridinum) compound, all the complex do not change color upon heating or light irradiation.Five new coordination polymers, [Cd(η6-L)]n (1), [Cd(η4-L)(H2O)2]n (2), [Co(η4-L)(H2O)2]n (3), {[Cd(η4-L)(H2O)1.5]·H2O}n (4), and {[Cu2(η4-L)2(H2O)2]·2H2O}n (5) were synthesized by reactions of corresponding metal salts with 4-(4-oxypyridinium-1-yl)phthalic acid (H2L) hydrothermally. Ligands in complexes are deprotonated even in the absence of a base. Metal ions in these complexes are all in an octahedral environment. The coordination number of ligand varies from 4 to 6. Each ligand binds three or four metal ions. High temperature synthesis tends to give ligands with larger coordination numbers. 1–5 are all 2D double-layer coordination polymers. Complex 2 and 3 are isostructural. The ligands in 1–5 exist in 4(1H)-pyridinone form rather than commonly presented 4-oxypyridinium forms. Without water molecules, complex 1 is stacked through π–π interaction between 4(1H)-pyridinone moieties in adjacent layers. Compound 2 is connected by intrermolecular hydrogen bonds via coordinated water molecules to form a 3D structure. All capable protons in 2 and 3 form H-bonds. π–π interaction between pyridinone rings exists in 1–4 and is stronger than that between two benzene rings. 4 packed into 3D via H-bond and π–π interaction while 5 packs into 3D via H-bond only. The pyridinone oxygen either coordinates to metal ion or form very strong H-bond with water molecule at O⋯O distance of 2.58 Å. Of all these complexes, anhydrous 1 with non-redox Cd(II) can stable up to 410 °C and is the most thermally stable while redox active Cu(II) complex 5 is stable under 210 °C. All the Cd(II) complexes have ligand centered emission at 430 and 480 nm. According to bond lengths, ligand in complexes exists as pyridinone form rather than the commonly presented oxopyridinium form. Different from viologen (pyridinum) compound, the entire complex does not change color upon heating or light irradiation.

An aspartic acid-functionalized water-soluble perylene bisimide, N,N′-di(2-succinic acid)-perylene-3,4,9,10-tetracarboxylic bisimide (PASP) was synthesized and characterized. It has absorbance maximum A0–0 and A0–1 at 527 and 498 nm (ε ≈ 1.7 × 104 L cm–1 mol–1) respectively in pH 7.20 HEPES buffer. Two quasi-reversible redox processes with E1/2 at −0.17 and −0.71 V (vs Ag/AgCl) respectively in pH 7–12.5 aqueous solutions. PASP can react with Na2S in pure aqueous solution to form monoanion radical and dianion species consecutively. PASP–• has EPR signal with g = 1.998 in aqueous solution, whereas PASP2- is EPR silent. The monoanion radical formation is a first-order reaction with k = 8.9 × 10–2 s–1. Dianion species formation is a zero-order reaction and the rate constant is 4.3 × 10–8 mol L–1 s–1. The presence of H2O2 greatly increases the radical formation rate constant. PASP as a two-electron transfer reagent is expected to be used in the water photolysis.Keywords: anion radical; electron transfer; perylene bisimide;

Six new coordination polymers, namely, [Cd(SO4)(4-abpt)(H2O)]n·3nH2O (1), [Cu3(CN)3(4-abpt)2]n (2), [Cd(D-cam)(2-PyBIm)(H2O)]n (3), [Co(D-Hcam)(cptpy)]n (4), [Cd(D-cam)(btmb)]n (5), and [Cd2(D-cam)(L-cam)(btmbb)]n (6) (4-abpt = 4-amino-3,5-bis(4-pyridyl)-1,2,4-triazole, D-H2cam = d-camphoric acid, 2-PyBIm = 2-(2-pyridyl)benzimidazole, Hcptpy = 4′-(4-carboxyphenyl)-3,2′:6′,3″-terpyridine, btmb = 1,4-bis(1,2,4-triazol-1-ylmethyl)benzene, btmbb = 4,4′-bis(1,2,4-triazol-1-ylmethyl)-1,1′-biphenyl), have been synthesized under hydro(solvo)thermal conditions. Their structures were determined by single-crystal X-ray diffraction analysis and further characterized by elemental analysis, infrared spectra, powder X-ray diffraction, circular dichroism, and thermogravimetric analysis. Complex 1 features a 3D porous metal–organic framework, which is a rare example to obtain a homochiral compound from achiral components. Complex 2 exhibits a 2D polymeric network constructed from μ2-cyanide, μ2-4-abpt, and monodentate 4-abpt ligands. Complex 3 is a homochiral 1D helical chain polymer. Complex 4 displays a 1D ladder-like polymeric structure in which cptpy– is tetradentate and D-Hcam– acts as a side arm. Complex 5 displays a homochiral 2D network with (4,4) topology. Complex 6 shows a [Cd2(D-cam)(L-cam)]n (4,4)-connected network with a paddle-wheel Cd2(COO)4 as node, which is further pillared by a btmbb spacer into a 3D metal–organic framework. d-Camphoric acid underwent racemization under hydrothermal conditions. Cd(II) complexes 1, 3, and 5 crystallize in chiral space groups, and their circular dichroism spectra exhibit obvious positive or negative Cotton effects. Moreover, 1, 3, and 5 are SHG-active, and the SHG efficiency, respectively, is 0.15, 0.4, and 0.4 times as much as that of KH2PO4. All the complexes exhibit relatively high thermal stability. 1, 3, 5, and 6 emit violet luminescence originating from ligand-centered emission.

3,3′,5,5′-Azobenzenetetracarboxylic acid (H4abtc) was synthesized by reduction of 5-nitroisophthalic acid in basic aqueous/ethanol solution in the presence of Zn powder. Three novel coordination polymers {[Zn2(η6-ao2btc)(η2-2,2′-bpy)2(H2O)2]·2H2O}1n (1), {[Zn2(η8-aobtc)(η2-phen)(H2O)]·DMF}3n (2), and {(Hap)2[Zn3(η9-aobtc)2]·2H2O}3n (3) (2,2′-bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline, ap = 4-aminopyridine, ao2btc4− and aobtc4− are two oxidized forms of H4abtc ligand) were prepared under hydrothermal conditions. The structures of 1–3 were characterized by single-crystal X-ray diffraction. Complex 1 is a 1D chain polymer, while 2 and 3 are porous 3D metal–organic frameworks with a cavity size of 9 Å diameter and 7 × 15 Å rectangular cavities, respectively. In 1, ao2btc4− links four mononuclear ZnO6 chromophores. Ligand aobtc4− in 2 links four dinuclear Zn2(CO2)4(H2O)N2, while aobtc4− in 3 bridges four trinuclear Zn3(CO2)8. From a topology point of view, ao2btc4− or aobtc4− are all 4-connected linkers in 1–3, while the mononuclear ZnO6 in 1, dinuclear Zn2(CO2)4(H2O)N2 in 2 and trinuclear Zn3(CO2)8 in 3 are 2, 4 and 8 connected nodes, respectively. Zn(II) in complex 2 can be replaced by Cu(II), Ni(II) and Co(II) with simultaneous loss of crystallinity. The metal ion exchange rate decrease in the order Co(II) < Ni(II) < Cu(II). 2 can encapsulate iodine (I2) in cyclohexane solution to form 2⊃0.1I2. The encapsulated I2 can be released completely in ethanol. The Hap+ in 3 can be replaced by methylene blue in aqueous solution to form 3⊃0.1methylene blue. The insignificant replacement is an indication that the guest molecule in the cavity channel is immobile, which prevents further substitution. With a bis-oxo group in the azo moiety, the framework of 1 is so unstable that it will decompose at ∼150 °C with simultaneous release of NO. Complexes 2 and 3 are stable at 330 °C. IR and fluorescence spectra were also discussed.

Two new m-xylene/cyclohexane-linked bis-aspartic acid ligands, Lb and Lc, were synthesized via Michael addition in basic aqueous solution. Their structures were characterized by elemental analysis, NMR and MS spectrometry. Both ligands react with Cu(II) and Zn(II) to form dinuclear complexes, with M2L(OH)− the major species in neutral/weak basic aqueous solution. To quantify the relative interaction strength between a Lewis acid and base, a new parameter σ = log K/14 was proposed which compares the stability constant with the binding constant between H+ and OH−. The dinuclear copper complexes (Lb–2Cu and Lc–2Cu) react with H2O2 in aqueous solution. The reaction in 0.020 M phosphate buffer at pH 7.5 is first-order for [Lc–2Cu], but second-order for [Lb–2Cu]. The oxidation products are oxygenated and/or dehydrogenated species. Radical trapping tests indicate that both complexes slightly scavenge the OH˙ radical, but generate the H˙ radical. Lc–2Cu generates the H˙ radical much more effectively than that of Lb–2Cu when reacted with H2O2. Both complexes are excellent catalysts for the oxidation of nitrobenzene in the presence of H2O2 in weakly basic aqueous solution. The oxidation follows the rate-law v = k[complex][nitrobenzene][H2O2]. The k values in pH 8.0 phosphate buffer at 25 °C are 211.2 ± 0.3 and 607.9 ± 1.7 mol−2 L2 s−1 for Lb–2Cu and Lc–2Cu, respectively. The Arrhenius activation energies are 69.4 ± 2.2 and 70.0 ± 4.3 kJ mol−1 for Lb–2Cu and Lc–2Cu, respectively, while the Arrhenius pre-exponential factors are 2.62 × 1014 and 1.06 × 1015, respectively. The larger pre-exponential factor makes Lc–2Cu more catalytically active than Lb–2Cu. These complexes are some of the most effective oxidation catalysts known for the oxidation of nitrobenzene.

•Water soluble PDI was used in fluorescence sensor Cu2+ and ATP in pure aqueous solution.•The 0.3 μM fluorescence sensitivity is one of the highest.•Concentration- and pH-dependence spectra were investigated.Aspartic functionalized water-soluble perylene diimide, N,N′-di(2-succinic acid)-perylene-3,4,9,10-tetracarboxylic diimide (PASP) has two absorbance maximums at 527 and 498 nm (ε ≈ 1.7 × 104 L cm−1 mol−1) and two emission peaks at 547 and 587 nm respectively. Emission intensities decrease with the increase of PASP concentrations in 20–100 μM ranges. Spectral titrations demonstrate that each PASP can coordinate to two Cu2+ ions in the absence of HEPES buffer. Its stability constant is estimated to be about 1.0 × 1012 L2 mol−2 at pH 7.20 and its coordinate stoichiometry increased to 7.5 in the same pH in the presence of HEPES buffer. The emission of PASP will be completely quenched upon formation of Cu2+ complex. The lowest “turn-off” fluorescence detection limit was calculated to be 0.3 μM Cu2+. PASP–Cu solution was used as a “turn-on” fluorescence biosensor to detect ATP. The sensitivity towards ATP is 0.3 μM in 50 mM HEPES buffer at pH 7.20, which is one of the most sensitive fluorescence sensors.Water soluable aspartic acid functionalized perylene diimide (PDI) was used as turn-off fluorescence sensor for Cu(II) ion. The PDI–copper complex is very sensitive turn-on fluorescence sensor for ATP molecule.

Nine novel coordination polymers were prepared from flexible 1,2,3,4,5,6-cyclohexanehexacarboxylate (H6L) and corresponding metal ions at room temperature and/or hydrothermal conditions, namely from binary {[Zn3(η9-LI)(η2-H2O)1(η1-H2O)7]·(H2O)5}3n (1), {[Co3(η9-LI)(η2-H2O)1(η1-H2O)7]·(H2O)5}3n (2), {[Cu5(η8-HLI)2·10H2O]·(H2O)4}3n (3), {[Ni3(η12-LII)(η1-H2O)6]·1.5H2O}3n (4), to ternary {[Zn(η3-H4LI)(4,4′-bipy)(η1-H2O)]·(H2O)2}2n (5), {[Zn2(η4-H3LI)(1,10-phen)3·(η1-NO3)]·H2O}1n (6), {[Cd2(η4-H4LI)2(2,2′-bipy)2(η1-H2O)2]·(2,2′-bipy)·(H2O)3}1n (7), {[Co1.5(η3-H3LI)(η1-4,4′-bipy)3(η1-H2O)3]·6H2O}1n (8), [Mn(1,10-phen)2(H2O)2]·(H4LI)·(H2O)5 (9) (LI = all-cis (a,e,a,e,a,e) conformation L6−, LII = all-trans (e,e,e,e,e,e) conformation L6−, where a and e represent the carboxylate that is almost perpendicular/parallel to the least square of the cyclohexane moiety. 2,2′-bpy = 2,2′-bipyridine, 4,4′-bpy = 4,4′-bipyridine, 1,10-phen = 1,10-phenanthroline). Complexes 1, 2, 3 and 4 have 3D coordination frameworks, in which H6L are fully deprotonated or only mono-protonated, their coordination numbers are 8, 9 and 12. Complexes 1 and 2 are isomorphous with each other and exhibit 3,5-connected with {32;4}{3;63;86} network in the Schlafli notation. Complex 3 is a 3,6-connected {43}{45;67;83} network. Complex 4 is a 3,9-connected 9-noted with {42;6}3{46;621;89} network. 5–8 are ternary complexes with secondary building blocks where L binds 2 to 4 protons, respectively. The coordination number of L decreased to 3–4 in complexes 5–8. Complex 9 is a mononuclear complex where H4L2− acts as a counter ion to balance the charge of the metal ion. The ligand in hydrothermal synthesized 4 adopts the all-trans configuration LII, while in all the other room temperature complexes, L adopts an LI configuration. As a role, it is always the e-position carboxylate that prefers to coordinate to the metal ion. The solid state photoluminescence studied indicates that there are ligand-centered emissions in 1, 5, 6, and 7. Complex 2 is a breathable porous coordination polymer, X-ray powder diffraction patterns (PXRD) studies have shown that the dehydration/rehydration of 2 can be fully reversible under 100 °C.

Eight coordination polymers {[Co3(L)2(H2O)6Cl6]·4H2O}n (1), {[Co(L)2Cl2]·13H2O}n (2), {[Cu3(L)2(H2O)6Cl6]·4H2O}n (3), {[Cu(L)2Cl2]·12H2O}n (4), {[Zn(L)2(H2O)2](NO3)2·4H2O}n (5), {[Zn(L)2(H2O)2](PF6)2·6H2O}n (6), {[ZnL(mal)]·3H2O}n (7), and {[Zn3(L)2(fum)3(H2O)6]·2H2O}n (8) were synthesized by reactions of the flexible tripodal ligand 1,3,5-tris(triazol-1-ylmethyl)-2,4,6-trimethylbenzene (L) and/or fumaric acid (H2fum)/malonic acid (H2mal), with corresponding metal salts, respectively. The structures of these polymers were established by elemental analysis, IR, powder and single-crystal X-ray diffraction analysis. Complexes 1 and 3 had an infinite two-dimensional (2D) honeycomb network. L as a cis-tridentate ligand coordinated to metal ions up and down alternatively. Complexes 2 and 4 possessed a one-dimensional (1D) chain hinged structure. L was a cis-bidentate ligand. Complexes 5 and 6 had a 2D network structure with (4,4) topology. L was a trans-bidentate ligand in 5, while in 6, L adopted a cis-configuration coordinated to metal ion bidentately. Complex 7 had a wavy 2D structure. L adopted a trans-configuration coordinated ion in the c-direction, while the malonate anion coordinated to metal ions in the b-direction in left- and right-helix alternatively. Complex 8 had an unusual 2D to three-dimensional (3D) interpenetration network structure. L was in trans-configuration coordinated to metal ions tridentately in the bc plane to form a ladder structure, and fumarate anion bridged the ladder in the a-axis to form a porous 2D coordination polymer. Adjacent 2D coordination polymers penetrated each other in the c-direction to form a 3D coordination with void dimensions consisting of 11 Å rhombic channels. The structures of 1 and 2 (or 3 and 4) indicate ligand/metal ratios had a significant influence on the structures of coordination polymers. The distinct structures of all these complexes demonstrated that the counteranions played an important role in the construction of coordination polymers. The isostructure between complexes 1 and 3, 2 and 4, and 5 indicate that the metal centers did not affect the structure of the complexes. Complex 8 with the characteristic of hydrophilic carboxylate groups and hydrophobic L was capable of absorbing water reversibly under 50 °C and encapsulating guest molecules, such as curcumin, diphenylcarbonohydrazide, and phenylfluorone, to form {(guest molecule)x ⊂ 8}n. (where x = 0.2–0.4). The encapsulation behavior of 8 had been studied by elemental analysis, IR, thermogravimetric analysis (TG), and X-ray powder diffraction patterns (PXRD). Complex 8 could heterogeneously catalyze the oxidation of diphenylcarbonohydrazide in the presence of H2O2 in ethanol effectively. The oxidation process was facile, efficient, and environmental friendly.

Three novel 3D complexes {H2[Zn6(μ4-O)(TATB)4]}n (1), [Cd3(TATB)2]n (2), and [Mn3(TATB)2]n (3) were synthesized from 4,4′,4″-s-triazine-2,4,6-triyltribenzoic acid (H3TATB) and corresponding metal salts under hydrothermal conditions. These complexes were characterized by elemental analyses, IR spectra, luminescent spectra, thermogravimetric analysis (TGA), and single crystal structure. Complex 1 adopted a straight Zn4(μ4-O) linked by TATB3− subunit to form an adamantane structure with a fully empty tetrahedral cavity. Two naked protons floated in the complex. This structure supports the existence of naked protons in nature. In complexes 2–3, the six deprotonated carboxylic oxygen of TATB3− coordinated to eight metal ions to form a 3D close-packed structure. Its density of 1.837 mg m− 3 made complex 2 one of the most closely packed structure based on H3TATB ever determined. Coordination polyhedral linked each other to form a diamondoid metal–oxygen framework in 2 and 3. All the coordination polymers were thermally stable up to 470 °C. These were the most thermally stable coordination polymers. A high-resolution transmission electron microscope indicated that the metal oxide is porous with pore diameters of ~ 2 nm.Three new coordination polymers were assembled from 4,4′,4″-s-triazine-2,4,6-triyltribenzoic acid and corresponding metal salts under hydrothermal conditions. All three have adamantine M–O framework with very higher thermal stability. {H2[Zn6(μ4-O)(TATB)4]}n (1) has nano-size tetrahedron cavity and naked protons.Research highlights► {H2[Zn6(μ4-O)(TATB)4]}n, [Cd3(TATB)2]n and [Mn3(TATB)2]n were synthesized. ► {H2[Zn6(μ4-O)(TATB)4]}n has empty tetrahedron cavity with a dimension of ~ 18 Å. ► Two naked protons exist in {H2[Zn6(μ4-O)(TATB)4]}n. ► [Cd3(TATB)2]n and [Mn3(TATB)2]n are both packed tightly with very high thermal stability. ► After removal of the organic ligand, [Mn3(TATB)2]n becomes a porous metal oxide.

The reaction of 4,4′-bis(1,2,4-triazol-1-ylmethyl)biphenyl (L) with Zn(NO3)2·6H2O or Co(NO3)2·6H2O in the presence of NH4PF6 in water−methanol or water−acetone produced both {[ZnL3](PF6)2(H2O)2}n (1) or {[CoL3](PF6)2(H2O)2}n (2). The metal ions in both complexes coordinate with six identical N atoms from six different ligands in an ideal octahedral environment where each ligand binds to two metal ions. Both complexes are one-dimensional triple-helical chains each containing an empty lotus-root-structured polymetallocage. The metallocage in 1 is fully empty, while the cage in 2 contains two water molecules. However, metallocages in 1 have a void volume of ∼200 Å3, which is much smaller than the 1020 Å3 void in 2. The void in 2 is comparable to the size of fluorescein. Both complexes are capable of encapsulating fluorescein anion in pH 9 aqueous solution to form {C20H10O5 ⊂ [ML3]}n, where C20H10O52− is fluorescein dianion, and M is Zn or Co. The encapsulation occurs via anion exchange. The cages in 1 are increased drastically to fit the size of fluorescein due to the flexibility of ligand, while in 2 the cages have no discernible change after fluorescein encapsulation due to a perfect match between the cavity size in 2 and the fluorescein. Fluorescein encapsulated 1 and 2 have identical powder X-ray diffraction patterns, indicating that they have similar structures after fluorescein encapsulation. Both complexes show fluorescence after fluorescein encapsulation.

Coordination polymers, especially porous coordination polymers have attracted much attention due to novel structures and potential applications. Biphenyl-3,5,3′,5′-tetracarboxylate (3, 5-H4bptc) and biphenyl-3,4,3′,4′-tetracarboxylate (3, 4-H4bptc) have been used in construction of porous coordination polymers. In this paper, a series of metal–organic framework polymers constructed from biphenyl-2,4,2′,4′-tetracarboxylate (2,4-H4bptc), [Zn(2,4-H2bptc)(4,4′-bipy)·H2O]n (1), {[Zn3(2,4-Hbptc)2(2,2′-bpy)2]·2H2O}n (2), {[Zn2(2,4-bptc)(2,2′-bpy)]·(2,2′-bpy)0.5·(H2O)}n (3), {[Zn2(2,4-bptc)(2,2′-bpy)2](H2O)}n (4), {[Cd2·(2,4-bptc)·(2,2-bpy)2·H2O]·H2O}n (5), {[Zn2·(2,4-bptc)·(phen)·H2O]n (6), {[Co5(2,4-bptc)2(μ3-OH)2(μ2-H2O)2(μ1-H2O)2]·2H2O}n (7) and {[Co5(2,4-bptc)2(μ3-OH)(μ2-H2O)2(μ1-H2O)2]·6H2O}n (8). Complexes 1 and 2 are 1D chains linked through partially deprotonated H4bptc carboxylate oxygen. 2,4-H2bptc2− in 1 acts as a bidentate ligand while 2,4-Hbptc3− in 2 acts as hexadentate ligand. In complexes 3–8, bptc4− is fully deprotonated to form 3D coordination polymers. The 2,4-bptc4− can form 6–9 coordination bond with metal ions. There are free 2,2′-bpy fill in the porous channel in complex 3. Complexes 7 and 8 were obtained under the same condition except reaction temperature. Using a higher temperature tends to form 7 with a lower water content. In complexes 7 and 8, the Co ions form Co2O2 diamond-core ribbon. In all the complexes, the two benzene rings in the 2,4-bptc4− ligand have torsion angle varies from 7.83 to 81.4°. When the torsion angle ranges from 61–73°, the two 2-carboxylate coordination to a metal ion to form 9-membered coordination rings. The coordination rings have stereoisomers. This phenomena did not exist in 3,5-H4bptc and 3,4-H4bptc complexes. The water molecules in all complexes can be removed by heating. The water molecules in 7 and 8 continually lost without discernable difference between coordination water and crystalline water molecules. The dehydrated sample of 7 and 8 still keep crystallinity. Dehydrated 7 can adsorbs 10% methanol corresponding to all water molecules replaced by methanol. Fully dehydrated 8 can adsorbs 20% ethanol molecules. All the complexes, except 7 and 8, have similar fluorescence to that of 2,4-H4bptc, therefore, all the fluorescence can be attributed intra-ligand emission.

4,4′-Bipyridine-2,6,2′,6′-tetracarboxylic acid H4L·3H2O, (1) and its copper(II) and cobalt (II) coordination polymers [Cu2L(H2O)4]2n (2) and {[Co(H2O)6]·[Co3L2(H2O)2]·10H2O}3n (3) have been hydrothermally synthesized. Compound 1 packs into a crystal viaH-bonds. Complex 2 is a 2D coordination grid, in which Cu is in an elongated octahedral constructed by a mer-geometry pyridyl-2,6-dicarboxylate, one bridging carboxylate oxygen and two water molecules. The L4− is central symmetrical. Each pyridyl-2,6-dicarboxylate chelete to Cu(II) and one carboxylate bridge Cu(II) ions in a 1,1-fashion. The 2D coordination polymer links to adjacent layers viaH-bonds. Complex 3 is a metal–organic framework with 11.6 × 10.5 Å rectangular channels. All Co(II) ions are located in an octahedral coordination environment. The rectangular channels are composed of Co2+-L4− walls and the walls are linked through carboxylate oxygen atoms and Co(II) ions. Co(H2O)62+ as counter ions fill in porous channel. The removal of water molecules from 3 at 210 °C or higher affords the porous material [Co4L2]n, which can adsorb 16 (36%) methanol or 9 (32%) ethanol in the vapour phase. The porosity of 3 is higher than reported 4,4′-bipyridine-2,6,2′,6′- tetracarboxylate complexes. The framework of 3 remains but the crystallinity is lost upon removal of the H2O molecules. The dehydrated framework of 3 partially recovery crystallinity after it adsorbs H2O, CH3OH and C2H5OH. The methanol in the framework can be replaced by H2O reversibly.

Five new metal-organic frameworks based on 2,4,6-tris(4-pyridyl)-1,3,5-triazine (tpt) ligand have been hydrothermally synthesized. Reaction of tpt and AgNO3 in an acidic solution at 180 °C yields {[Ag(Htpt)(NO3)]NO3·4H2O}n (1). Ag(I) is trigonally coordinated by two pyridyl nitrogen and one nitrato oxygen to form a 1D zigzag chain. Reaction of tpt with CuSO4 affords {[Cu2(tpt)2(SO4)2(H2O)2]·4H2O}n (2). Copper(II) is bonded to two pyridyl nitrogen, two sulfato oxygen, and two water oxygen atoms to form an elongated octahedral geometry. Each H2O ligand bridges two copper(II), whereas sulfate bridges copper(II) via µ-1,3 and µ-1,1 fashions. The copper(II)−sulfate−H2O 2D layers are linked by bidentate tpt to form a 3D polymeric structure. Reaction of Cu(SO4)2, tpt, and 1,2,4,5-benzenetetracarboxylic acid (H4btec) in the presence of piperidine gives [Cu(tpt)(H2btec)1/2]n (3). Copper(I) is located in a trigonal-pyramidal coordination environment and coordinated by three pyridyl nitrogen of tpt in a plane, whereas a carboxylate oxygen is coordinated to the copper(I) axially. The tpt−Cu forms a layer, and the layers are linked through H2btec2− to form a 2D double-layered coordination polymer. Replacing CuSO4 with ZnI2 in the synthesis gives {[Zn(tpt)(btec)1/2]·H2O}n (4). Zinc(II) is in a distorted tetrahedral geometry and linked through bidentate tpt and exotetradentate btec4− to form a 2D coordination grid. Reaction of tpt with CuCN leads to the assembly of a 3D metal-organic framework [Cu3(CN)3(tpt)]n (5). Copper(I) is trigonally coordinated by one pyridyl nitrogen and two cyanides to form an intriguing honeycomb architecture. Luminescence study shows that 1, 3, 4, and 5 have blue fluorescence, which can be assigned to be ligand-centered emissions. Thermal analysis shows that all of these complexes are quite stable, and especially for 4, the framework is stable up to 430 °C.

A novel cyclic dimer of a trinuclear zinc complex, {[Zn3(bmtac)(H2O)8] · 6H2O}2, with very long Zn–Zn distances, was synthesized in aqueous solution by adopting a new type of flexible multicarboxylate ligand, H6bmtac (H6bmtac = 1,3,5-benzenemethyltriiminodiacetic acid). The X-ray crystal structure of {[Zn3(bmtac)(H2O)8] · 6H2O}2 reveals that all Zn(II) ions are six-coordinated with octahedral geometry. The dimer as basic building units assembled into a three-dimensional supramolecular framework through the multiple intermolecular O–H⋯O hydrogen bonds interactions. The complex shows a blue fluorescent emission band at 428 nm as the result of the intraligand (π–π∗) fluorescent emission.The titled cyclic dimer of a trinuclear zinc complex, {[Zn3(bmtac)(H2O)8] · 6H2O}2, based on the flexible 1,3,5-benzenemethyltriiminodiacetic acid (H6bmtac) ligand not only is the first reported crystal structure of complex of H6bmtac, but also is possibly one of the largest hexanuclear zinc(II) complex.

Under similar hydrothermal synthetic conditions, the reactions of Fe(NO3)3/FeCl2, CuCl2, NiCl2, and CdCl2 with phenanthroline (phen) and 3,3′,4,4′-biphenyltetracarboxylic acid (H4BPTC) afforded complexes [Fe(phen)3](H3BPTC)2 (1), [Cu(phen)(BPTC)0.5 · H2O] · H2O (2), [Ni3(phen)3(BPTC)1.5(H2O)5] · 4H2O (3) and [Cd(phen)(BPTC)0.5] · H2O (4). The short Fe–N distance in the monomeric Fe(phen)3(H3 BPTC)2 (1) shows that the Fe(II) is in a low-spin state. H3 BPTC4− acts as a counter-ion in this complex. In [Cu(phen)(BPTC)0.5 · H2O] · H2O (2), the central Cu(II) is five-coordinated in a square-pyramidal geometry. The ligand BPTC4− is centrosymmetric and the four deprotonated carboxylic groups of BPTC4− are coordinated to four different copper ions to form a 1D ladder complex indicating a comparatively strong coordination. In [Ni3(phen)3(BPTC)1.5(H2O)5] · 4H2O (3), all nickel(II) atoms are in an octahedral coordination environment. There are two different BPTC4− ligands; one is centrosymmetric and the other is asymmetric. Metal ions are linked through fully deprotonated BPTC4− ligands to form a 2D metal-organic sheet. [Cd(phen)(BPTC)0.5] · H2O (4) has a 3D metal-organic framework. TG, IR, and fluorescence data for the complexes are presented.

Two rht anionic metal–organic frameworks were synthesized. There are six [M(H2O)6]2+ ions held together by a super-strong H-bond and arranged in a regular octahedron in each medium cage. Dye adsorption studies revealed a rapid and selective adsorption of cationic dyes and the adsorbed dyes can be released in saturated NaCl aqueous solution.

4,4′-Bipyridine-2,6,2′,6′-tetracarboxylic acid H4L·3H2O, (1) and its copper(II) and cobalt (II) coordination polymers [Cu2L(H2O)4]2n (2) and {[Co(H2O)6]·[Co3L2(H2O)2]·10H2O}3n (3) have been hydrothermally synthesized. Compound 1 packs into a crystal viaH-bonds. Complex 2 is a 2D coordination grid, in which Cu is in an elongated octahedral constructed by a mer-geometry pyridyl-2,6-dicarboxylate, one bridging carboxylate oxygen and two water molecules. The L4− is central symmetrical. Each pyridyl-2,6-dicarboxylate chelete to Cu(II) and one carboxylate bridge Cu(II) ions in a 1,1-fashion. The 2D coordination polymer links to adjacent layers viaH-bonds. Complex 3 is a metal–organic framework with 11.6 × 10.5 Å rectangular channels. All Co(II) ions are located in an octahedral coordination environment. The rectangular channels are composed of Co2+-L4− walls and the walls are linked through carboxylate oxygen atoms and Co(II) ions. Co(H2O)62+ as counter ions fill in porous channel. The removal of water molecules from 3 at 210 °C or higher affords the porous material [Co4L2]n, which can adsorb 16 (36%) methanol or 9 (32%) ethanol in the vapour phase. The porosity of 3 is higher than reported 4,4′-bipyridine-2,6,2′,6′- tetracarboxylate complexes. The framework of 3 remains but the crystallinity is lost upon removal of the H2O molecules. The dehydrated framework of 3 partially recovery crystallinity after it adsorbs H2O, CH3OH and C2H5OH. The methanol in the framework can be replaced by H2O reversibly.

Two new m-xylene/cyclohexane-linked bis-aspartic acid ligands, Lb and Lc, were synthesized via Michael addition in basic aqueous solution. Their structures were characterized by elemental analysis, NMR and MS spectrometry. Both ligands react with Cu(II) and Zn(II) to form dinuclear complexes, with M2L(OH)− the major species in neutral/weak basic aqueous solution. To quantify the relative interaction strength between a Lewis acid and base, a new parameter σ = log K/14 was proposed which compares the stability constant with the binding constant between H+ and OH−. The dinuclear copper complexes (Lb–2Cu and Lc–2Cu) react with H2O2 in aqueous solution. The reaction in 0.020 M phosphate buffer at pH 7.5 is first-order for [Lc–2Cu], but second-order for [Lb–2Cu]. The oxidation products are oxygenated and/or dehydrogenated species. Radical trapping tests indicate that both complexes slightly scavenge the OH˙ radical, but generate the H˙ radical. Lc–2Cu generates the H˙ radical much more effectively than that of Lb–2Cu when reacted with H2O2. Both complexes are excellent catalysts for the oxidation of nitrobenzene in the presence of H2O2 in weakly basic aqueous solution. The oxidation follows the rate-law v = k[complex][nitrobenzene][H2O2]. The k values in pH 8.0 phosphate buffer at 25 °C are 211.2 ± 0.3 and 607.9 ± 1.7 mol−2 L2 s−1 for Lb–2Cu and Lc–2Cu, respectively. The Arrhenius activation energies are 69.4 ± 2.2 and 70.0 ± 4.3 kJ mol−1 for Lb–2Cu and Lc–2Cu, respectively, while the Arrhenius pre-exponential factors are 2.62 × 1014 and 1.06 × 1015, respectively. The larger pre-exponential factor makes Lc–2Cu more catalytically active than Lb–2Cu. These complexes are some of the most effective oxidation catalysts known for the oxidation of nitrobenzene.

A new neuromelanin-like ketocatechol-containing iminodiacetic acid ligand, (N-(3,4-dihydroxyl)phenacylimino)diacetic acid (H4L), which is also quite similar to compounds found in insect cuticle, has been synthesized and characterized. The X-ray crystal structure of H4L has been successfully determined. Proton binding and coordination with Fe(III), Cu(II), and Zn(II) have been studied by potentiometric titrations and UV-vis spectrophotometry in aqueous solution. UV spectra of H4L in the absence and presence of different metal ions indicate complexes formed with the catechol moiety of H4L in aqueous solution. Visible spectra and NMR reveal that H4L with Fe(III), Cu(II), and Zn(II) can all give stable mono-(ML) and dinuclear complexes [M(ML)]. Fe(III) can also form {Fe(FeL)2} and {Fe(FeL)3} species with sufficient base. The process is accompanied by a drastic color change from light blue to deep-blue to wine-red. The Fe(III)–Cu(II) heteronuclear complex also exists in aqueous solution whose spectra are similar to the homonuclear Fe(III) complex. However, the spectra of {Fe(CuL)} shifted to a longer wavelength and {Fe(CuL)2} and {Fe(CuL)3} shifted to a shorter wavelength. Keto–enol tautomerism was observed in weak basic aqueous solution as indicated by 1H NMR spectra. The reaction products of Cu(II) complex with H2O2 depend on the H2O2 concentration and pH value. Low concentrations of H2O2 oxidize H4L to a series of semiquinone and quinone compounds with absorption maxima at 314–400 nm, while a high concentration of H2O2 oxidizes H4L to colorless muconic acid derivatives. NaIO4 gives different oxidase products, but no 2,4,5-trihydroxyphenylalanine quinone (TPQ)-like hydroxyquinone can be found.