Feifei Xing

Coordination polymers of biphenyl-2,4,2′,4′-tetracarboxylic acid—synthesis, structures and adsorption properties

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.

Controlling interpenetration in metal-organic frameworks by tuning the conformations of flexible bis(triazole) ligands

Solvothermal syntheses afforded two new MOFs {[Zn2(L1)(btmbb)(H2O)4]·2H2O}n (1) and [Zn2(L1)(btmbb)2]n (2) [5,5′-(1,4-phenylenebis(methylene))bis(oxy)diisophthalic acid (H4L1), and 4,4′-bis((1H-1,2,4-triazol-1-yl)methyl)biphenyl (btmbb)]. Single crystal X-ray analyses reveal that compound 1 shows an example of a 2D non-interpenetrating network, while compound 2 is a 2D polythreading interpenetrating structure, in which two layered networks interpenetrate in a (2D/2D) parallel fashion. The different conformation of the flexible ligand might be the main factor resulting in these non-interpenetrated/interpenetrated structures. The powder X-ray diffraction, thermal stabilities, and the photoluminescence of 1–2 have also been investigated.

Synthesis, structure and adsorption of coordination polymers constructed from 3,3′,5,5′-azobenzenetetracarboxylic acid and Zn ions

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 A diameter and 7 × 15 A 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.

Novel complexes constructed by flexible 1,2,3,4,5,6- cyclohexanehexacarboxylate and transition metal ions – From 0D mononuclear to 3D porous coordination polymers

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.

Phenolacetyl Viologen as Multifunctional Chromic Material for Fast and Reversible Sensor of Solvents, Base, Temperature, Metal Ions, NH3 Vapor, and Grind in Solution and Solid State

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.

CCDC 1481631: Experimental Crystal Structure Determination

Related Article: Zhao-Xi Wang, Lin-Fei Wu, Xuan Zhang, Feifei Xing, Ming-Xing Li|2016|Dalton Trans.|45|19500|doi:10.1039/C6DT04010A