Idiosyncrasies of Co2(dhtp): In situ-annealing by methanol

• Uptake in big crystals of MOF Co2(dhtp) was studied using IR microscopy.
• The MOF structure is extremely sensitive towards humid surrounding air.
• 30 s exposure to air caused a surface blockage preventing any guest uptake.
• After annealing in methanol atmosphere, Co2(dhtp) adsorbs reversibly hydrocarbons.
• Air contact of 4 h changes the bulk material which is reversed by exposure to methanol.

Structural instability in humid surroundings is one of the major drawbacks of many metal organic frameworks (MOFs) compared to zeolites. In this study we investigate the pronounced sensitivity of MOF Co2(dhtp) (Co-MOF-74 or CPO-27-Co) towards humid air. Guest uptake in big Co2(dhtp) crystals has been studied by IR microscopy. We found that already a short exposure of 30 s to moist air causes a surface blockage, completely preventing the adsorption of even small guest molecules. It could be confirmed in complementary PXRD measurements that the interior of the crystals remains intact during such short exposure times. Indications for a loss of crystallinity were evidenced only for notably longer exposure times (4 h). Most remarkably, the defects could at least be partially annealed in methanol atmosphere. Reversible adsorption of hydrocarbons in initially blocked crystals was found after exposing the crystals to methanol vapor for about 0.5 h.

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