A Porous 4-Fold-Interpenetrated Chiral Framework Exhibiting Vapochromism, Single-Crystal-to-Single-Crystal Solvent Exchange, Gas Sorption, and a Poisoning Effect

Abstract

The synthesis and characterization of a 4-fold-interpenetrated pseudodiamond metal-organic framework (MOF), Co(II)(pybz)2·2DMF [pybz = 4-(4-pyridyl)benzoate], are reported. N,N-Dimethylformamide (DMF) of the channels can be removed to give the porous framework, and it can also be exchanged for methanol, ethanol, benzene, and cyclohexane. It is a rare example of a stable MOF based on a single octahedral building unit. The single-crystal structures of Co(II)(pybz)2·2DMF, Co(II)(pybz)2, Co(II)(pybz)2·4MeOH, and Co(II)(pybz)2·2.5EtOH have been successfully determined. In all of them, the framework is marginally modified and contains a highly distorted and strained octahedral node of cobalt with two pyridine nitrogen atoms and two chelate carboxylate groups. In air, the crystals of Co(II)(pybz)2·2DMF readily change color from claret red to light pink. Thermogravimetric analysis and Raman spectroscopy indicate a change in coordination, where the carboxylate becomes monodentate and an additional two water molecules are coordinated to each cobalt atom. In a dry solvent, this transformation does not take place. Tests show that Co(II)(pybz)2 may be a more efficient drying agent than silica gel and anhydrous CuSO4. The desolvated Co(II)(pybz)2 can absorb several gases such as CO2, N2, H2, and CH4 and also vapors of methanol, ethanol, benzene, and cyclohexane. If Co(II)(pybz)2 is exposed to air and followed by reactivation, its sorption capacity is considerably reduced, which we associate with a poisoning effect. Because of the long distance between the cobalt atoms in the structure, the magnetic properties are those of a paramagnet.

Recent advances in metal–organic frameworks based on pyridylbenzoate ligands: properties and applications

“…Reprinted with permission from (ref29). The same phenomenon was also reported earlier on by Bourne and co-workers.…”

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

“…The explanation may be that the terminal ligandso nt he metal sites in the metal clusters could be apt to leave, enabling the clusters to serve as active sites to improve the H 2 affinities. [18] To quantitatively compare their affinities for H 2 molecules, as econd set of H 2 isothermsw as measured at 87 K, which show values of 80.7 cm 3 g À1 (0.68 wt %) and 91.1 cm 3 g À1 (0.81 wt %) for the uptake around 1bar for 1 and 2,r espectively.V irial analysis [19] of the H 2 adsorption isothermsr evealed that the isosteric heat of adsorption of 1 and 2 at zero surface coverage is 7.4 and 6.0 kJ mol À1 ,r espectively,a nd both slightly decrease as the H 2 uptake increases( see the inset of Figure S7 in the Supporting Information). These values of isosteric heat of adsorption are highert han that of MOF-5 (5.2kJmol À1 ).…”

Methanol mediated crystal transformations in a solvatochromic metal organic framework constructed from Co(ii) and 4-(4-pyridyl) benzoate

“…We note however that the unit cell dimensions of 2 correspond closely to those of the recently reported analogous compound {[Co(44pba) 2 ]•(MeOH) 4 } n . 30 Compound 3 crystallises in the monoclinic crystal system space group Pn. There are two cobalt centres Co(1) and Co(2) in the asymmetric unit with different coordination environments 18 and full crystallographic information can be obtained from the Cambridge Structural Database (CCDC 850072).…”