Enhanced Stability toward Humidity in a Family of Hybrid Ultramicroporous Materials Incorporating Cr₂O₇^2– Pillars

Dichromate (Cr₂O₇^2–) pillared <b>pcu</b> hybrid ultramicroporous materials, while previously shown to exhibit benchmark selectivity for small polarizable gases, sometimes suffer from poor stability when exposed to moisture, which could limit their potential application in gas separation systems. In attempting to improve their stability toward humidity, we have crystal engineered two new families of <b>DICRO-L-M-i</b> materials of formula [M­(L)₂(Cr₂O₇)]_<i>n</i> (M = Ni²⁺, Co²⁺; L = <b>5</b>: 1,4-bis­(4-pyridyl)­xylene; <b>6</b>: 1,4-bis­(4-pyridyl)­durene). Evaluating these materials in combination with a previously reported analogue, <b>DICRO-4-Ni-i</b>, in terms of their stability toward humidity has revealed a relationship between increasing the number of methyl groups on the dipyridyl organic linkers and a greater stability toward humidity

Highly Selective Separation of C₂H₂ from CO₂ by a New Dichromate-Based Hybrid Ultramicroporous Material

A new hybrid ultramicroporous material, [Ni­(1,4-di­(pyridine-2-yl)­benzene)₂(Cr₂O₇)]_<i>n</i> (DICRO-4-Ni-i), has been prepared and structurally characterized. Pure gas sorption isotherms and molecular modeling of sorbate–sorbent interactions imply strong selectivity for C₂H₂ over CO₂ (<i>S</i>_AC). Dynamic gas breakthrough coupled with temperature-programmed desorption experiments were conducted on DICRO-4-Ni-i and two other porous materials reported to exhibit high <i>S</i>_AC, TIFSIX-2-Cu-i and MIL-100­(Fe), using a C₂H₂/CO₂/He (10:5:85) gas mixture. Whereas CO₂/C₂H₂ coadsorption by MIL-100­(Fe) mitigated the purity of trapped C₂H₂, negligible coadsorption and high <i>S</i>_AC were observed for DICRO-4-Ni-i and TIFSIX-2-Cu-i