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

Dichromate (Cr₂O₇^2-) pillared pcu 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 DICRO-L-M-i materials of formula [M(L)₂(Cr₂O₇)]_n (M = Ni²⁺, Co²⁺ L = 5: 1,4-bis(4-pyridyl)xylene; 6: 1,4-bis(4-pyridyl)durene). Evaluating these materials in combination with a previously reported analogue, DICRO-4-Ni-i, 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.