The Effect of Sterically Active Ligand Substituents on Gas Adsorption within a Family of 3D Zn-Based Coordination Polymers

Abstract

An investigation of the adsorption properties of two structurally related, 3D coordination polymers of composition Zn(2-Mehba) and Zn(2,6-Me 2 hba) (2-Mehba = the dianion of 2-methyl-4-hydroxybenzoic acid and 2,6-Me 2 hba = the dianion of 2,6-dimethyl-4hydroxybenzoic acid) is presented. A common feature of these structures are parallel channels that are able to accommodate appropriately sized guest molecules. The structures differ with respect to the steric congestion within the channels arising from methyl groups appended to the bridging ligands of the network. The host network, Zn(2-Mehba), is able to take up appreciable quantities of H 2 (77 K) and CO 2 and CH 4 (298 K) in a reversible manner. In regard to the adsorption of N 2 by Zn(2-Mehba), there appears to be an unusual temperature dependence for the uptake of the gas such that when the temperature is increased from 77 to 298 K the uptake of N 2 increases. The relatively narrow channels of Zn(2,6-Me 2 hba) are too small to allow the uptake of N 2 and CH 4 , but H 2 molecules can be adsorbed. A pronounced step at elevated pressures in CO 2 and N 2 O isotherms for Zn(2,6-Me 2 hba) is noted. Calculations indicate that rotation of phenolate rings leads to a change in the available intraframework space during CO 2 dosing.

Multifunctional Coordination Polymer Exhibiting Reversible Mechanical Motion Allowing Selective Uptake of Guests and Leading to Enhanced Electrical Conductivity

“…The failure of Mn­(F 4 TCNQ)­(py) 2 to adsorb H 2 , N 2 , or CH 4 under conditions that include pressures approaching 3000 kPa reflects the relatively weak attraction of these molecules for the internal pore surfaces of the coordination polymer. The binding energies for H 2 , N 2 , or CH 4 with porous coordination polymers are generally low and commonly in the ranges of 5–10, 8–20, and 15–25 kJ mol –1 − respectively, indicating the relatively weak association between these species and typical host networks. The binding enthalpies for CO 2 are, in general, significantly higher (20–30 kJ mol –1 ), and thus a stronger van der Waals interaction may be anticipated between the F 4 TCNQ surfaces and CO 2 .…”

“…The binding energies for H 2 , N 2 , or CH 4 with porous coordination polymers are generally low and commonly in the ranges of 5–10, 8–20, and 15–25 kJ mol –1 − respectively, indicating the relatively weak association between these species and typical host networks. The binding enthalpies for CO 2 are, in general, significantly higher (20–30 kJ mol –1 ), and thus a stronger van der Waals interaction may be anticipated between the F 4 TCNQ surfaces and CO 2 . The sigmoidal isotherms suggest that the pore-opening process only begins when the pressure of CO 2 is great enough for CO 2 to force its way into the closed pores, thus separating the framework surfaces and initiating the concerted pore-opening process throughout the crystal.…”

Tylectomy Safety in Salvage of Eyes with Retinoblastoma

“…In low- and middle-income settings, such as China, it is not uncommon for children to abandon treatment for a variety of reasons, including unwillingness to enucleate, financial constraints, long distance from treatment center, and perception that the disease was cured [ 12 , 35 ]. A high proportion parents who refuse enucleation following failed eye salvage with chemotherapy, accept tylectomy as a last resort to save the child’s life and eye.…”

Hands-on X-ray Crystallography: A Research-Based Elective Program for Secondary School Students

“…We drew upon our own research interests to identify chemical systems that could be understood by high school students. Our research group has previously shown that Zn­(II) and Co­(II) ions can combine with the dianion of 4-hydroxybenzoic acid (H 2 hba; Figure ) to form porous coordination networks with particularly interesting gas adsorption properties. − Research on these systems has focused on applications directed toward the capture of environmentally harmful materials in addition to the storage and separation of gases.…”