Yong-Sheng Wei

Turning on the flexibility of isoreticular porous coordination frameworks for drastically tunable framework breathing and thermal expansion

To study the potential flexibility of the (3,9)-connected xmz frameworks, a series of isoreticular metal carboxylate frameworks [M3(μ3-OH)(L)3], namely MCF-18(L,M), were constructed by 3-connected, tripodal pyridyl-dicarboxylate ligands (H2L1 = pyridine-3,5-dicarboxylic acid; H2L2 = 4,4′-(pyridine-3,5-diyl)dibenzoic acid; H2L3 = 2,6-di-p-carboxyphenyl-4,4′-bipyridine) and 9-connected, tricapped trigonal-prismatic M3(μ3-OH)(O2CR)6(py)3 (M = Fe, Co, Ni; py = pyridyl group) clusters. Powder and single-crystal X-ray diffraction studies showed that, while other isoreticular analogs do not show framework flexibility, the newly designed material MCF-18(L3,Ni) can drastically swell 70–105% in volume and 75–121% in length upon inclusion of different guests, the latter of which is the highest reported value to date. Comparison study showed that the nearly uniaxial framework breathing is generated by the special regulation effect of the xmz topology, but can only be activated by a ligand with a suitable shape. Moreover, the thermal expansion profile of MCF-18(L3,Ni) can be drastically tuned by guest, showing extremely large thermal expansion coefficients up to 430 × 10−6 K−1. The guest-included crystals also show water-like thermal expansion behaviors depending on the cooling rate, which is unanticipated for intrinsic crystalline materials.

Coordination templated [2+2+2] cyclotrimerization in a porous coordination framework

Controlling chemical reactions by the supramolecular confinement effects of nanopores has attracted great attention. Here we show that open metal sites in porous coordination frameworks can constitute more powerful and strict templates for precision syntheses. A Fe(III) dicarboxylate framework functionalized with triangularly arranged metal sites is used to accomplish [2+2+2] cyclotrimerization reactions for organonitrile, alkyne and alkene monomers bearing a geometrically suitable pyridyl group. In situ single-crystal X-ray diffraction facilitates the direct observation of such a coordination templated reaction, before cylcotrimerization, the monomer coordinates at the Fe(III) centre by its pyridyl donor, which forces three unsaturated groups to gather around a position very similar with that of the desired covalent cyclic trimer. After the reaction, the trimers serve as tripodal ligands to perfectly fix the Fe(III) ions and the whole crystal to generate an exceptionally rigid and porous material with large surface area coupled with guest-proof zero thermal expansion.

New porous coordination polymers based on expanded pyridyl-dicarboxylate ligands and a paddle-wheel cluster

Solvothermal reactions of Cu(NO3)2 and 4,4′-([3,4′-bipyridine]-2′,6′-diyl)dibenzoic acid (H2L1), 3,3′-([4,4′-bipyridine]-2,6-diyl)dibenzoic acid (H2L2), or 4,4′-([4,4′-bipyridine]-2,6-diyl)dibenzoic acid (H2L3) yielded three new metal-carboxylate frameworks (MCF-28, MCF-29 and MCF-30) with a common formula [Cu2(L)2] (H2L = pyridyldicarboxylic acid). X-ray crystallography showed that MCF-28, MCF-29, and MCF-30 are three-dimensional (3,6)-connected rtl, eea and pyr networks, respectively, based on 3-connected tripodal ligands and 6-connected Cu2(RCOO)4(py)2 units (RCOO and py denote carboxylate and pyridyl groups, respectively). Thermogravimetry, powder X-ray diffraction, and gas adsorption measurements indicated that the three compounds became shrunk and amorphous structures after guest removal. Interestingly, single-crystal X-ray diffraction showed that MCF-28 exhibited drastic temperature-induced framework breathing.

Windmill Co4{Co4(μ4-O)} with 16 Divergent Branches Forming a Family of Metal–Organic Frameworks: Organic Metrics Control Topology, Gas Sorption, and Magnetism

A series of highly connected metal-organic frameworks (MOFs), [Co8 (O)(OH)4 (H2 O)4 (ina)8 ](NO3 )2 ⋅2 C2 H5 OH⋅4 H2 O (1), [Co8 (O)(OH)4 (H2 O)4 (pba)8 ](NO3 )2 ⋅8 C2 H5 OH⋅28 H2 O (2), and [Co8 (O)(OH)4 (H2 O)4 (pbba)8 ](NO3 )2 ⋅guest (3), in which ina=isonicotinate, pba=4-pyridylbenzoate, and pbba=4-(pyridine-4-yl)phenylbenzoate, is reported. These MOFs contain a new secondary building unit (SBU), with a square Co4 (μ4 -O) central unit having the rare μ4 -O(2-) motif, which is decorated by the other four peripheral cobalt atoms through μ3 -OH in a windmill-like shape. This SBU holds 16 divergent connecting organic ligands, pyridyl-carboxylates, to form three different frameworks. The high porosity of desolvated 2 is shown by the efficient gas absorption of N2 , CO2 , CH4 , and H2 . In addition, 1 and 2 exhibit unusual canted antiferromagnetic behavior with spin-glass-like relaxation, with blocking temperatures that are fairly high, 20 K (1) and 10 K (2), for cobalt materials. The relationship between the metal clusters and linkers has been studied, in which the size and rotational degrees of freedom of the ligands are found to control the topology, gas sorption, and magnetic properties.

Grafting alkylamine in UiO-66 by charge-assisted coordination bonds for carbon dioxide capture from high-humidity flue gas

Ethanolamine (Hea) was grafted onto the pore surface of a metal–organic framework [Zr6O4(OH)4(bdc)6] (UiO-66, H2bdc = benzene-1,4-dicarboxylic acid) by a two-step post-synthetic treatment, in which UiO-66 was first dehydrated to form [Zr6O6(bdc)6], and then reacted with Hea to form [Zr6O4(OH)2(ea)2(bdc)6] (UiO-66-EA). CO2 adsorption measurements showed that UiO-66-EA exhibits a CO2 adsorption enthalpy of 66 kJ mol−1, which is much higher than that of UiO-66 (30 kJ mol−1). Solid-state 13C NMR spectra demonstrated that carbamate species are formed by the reaction of CO2 with the amine groups in UiO-66-EA. Single-component gas adsorption measurements indicated a CO2/N2 selectivity of 365 for UiO-66-EA (15 : 75 CO2/N2 at 298 K), which is about 20 times higher than the value for UiO-66 (16). Breakthrough experiments under simulated flue gases conditions (10 : 90 CO2/N2 at 313 K) showed that the N2 purification capacity of UiO-66-EA is ca. 18 times that of UiO-66. More importantly, the breakthrough performance of UiO-66-EA can be completely maintained even at high relative humidity (82%).

Metal-ion controlled solid-state reactivity and photoluminescence in two isomorphous coordination polymers

Reactions of [M(NH3)2]OH (M = Ag and Cu) and 4-(1H-pyrazol-4-yl)pyridine (Hpypz), using p-xylene (C8H10) as the template, gave isomorphous two-dimensional porous metal azolate frameworks [Ag2(pypz)2]·0.5C8H10 (MAF-36(Ag), 1·g) and [Cu2(pypz)2]·0.5C8H10 (MAF-36(Cu), 2·g). Powder and single-crystal X-ray diffraction studies showed that, upon guest removal, 1·g transformed into a three-dimensional nonporous framework [Ag6(pypz)6] (1′), while 2·g can retain its porous two-dimensional structure. Depending on the metal ion, framework flexibility/rigidity, and/or porosity, 1·g and 2·g, as well as their guest-free derivatives, showed distinctly different photoluminescence and guest-responsive behaviors.

A flexible, porous, cluster-based Zn-pyrazolate-dicarboxylate framework showing selective adsorption properties

A flexible Zn-pyrazolate-carboxylate framework [Zn7O2(deppy)2(oba)4]·2.5DMF·2H2O (1) (Hdeppy = 3,5-diethyl-4-(4′-pyridyl)pyrazole, H2oba = 4,4′-oxobisbenzoic acid) was synthesized by solvothermal reaction. Single-crystal X-ray diffraction indicated that 1 possesses a 10-connected bct topological network based on a rare heptanuclear zinc(II) cluster. Comparison of crystal structures of 1 determined at 300 K and 150 K illustrated the conformational flexibility of deppy− ligands. Thermogravimetry analyses and powder X-ray diffraction measurements showed that 1 has high thermal stability and good water stability. Gas and liquid sorption experiments of 1 not only showed stronger adsorption of CO2 compared with N2, but also demonstrated highly efficient separation of n-propylbenzene from other C9H12 alkylbenzene isomers 1,2,4-trimethylbenzene and 1,3,5-trimethylbenzene.

Unique (3,9)-connected porous coordination polymers constructed by tripodal ligands with bent arms

Solvothermal reactions of Co(NO3)2 with tripodal ligands 3,3′-([3,4′-bipyridine]-2′,6′-diyl)dibenzoic acid (H2L4), 3,3′-([4,4′-bipyridine]-2,6-diyl)dibenzoic acid (H2L5), and 2,6-bis(4-(1H-tetrazol-5-yl)phenyl)-4,4′-bipyridine (H2L6) possessing one to three bent arms, yielded three new porous coordination polymers, namely [Co3(μ3-OH)(L4)3] (1), [Co3(μ3-OH)(L5)3] (2), and [Co3(μ3-OH)(L6)3] (3), respectively. Single-crystal X-ray crystallography showed that 1–3 are all three-dimensional (3,9)-connected coordination networks interconnected by the tripodal ligands and the classical tricapped trigonal-prismatic [Co3(μ3-OH)(RCOO)6(Py)3] (Py = pyridyl) or new tricapped trigonal-prismatic [Co3(μ3-OH)(Rtz)6(Py)3] (Rtz− = tetrazolate) clusters. However, instead of the classical xmz topology for such a kind of 3-connected ligands and 9-connected clusters, 1 and 2 show a new (3,9)-connected topology, wys, with a point symbol of {42·6}3{46·627·83}, while 3 has a (3,9)-connected eee topology. Thermogravimetry, powder X-ray diffraction, and gas adsorption measurements demonstrated that the desolvated forms of 1–3 are all porous, but different framework flexibilities were observed.