Mixed‐Ligand Metal–Organic Frameworks with Large Pores: Gas Sorption Properties and Single‐Crystal‐to‐Single‐Crystal Transformation on Guest Exchange

Abstract Two isomorphous 3D metal–organic frameworks, {[Cu 2 (BPnDC) 2 (bpy)] ⋅ 8 DMF ⋅ 6 H 2 O} n ( 1 ) and {[Zn 2 (BPnDC) 2 (dabco)] ⋅ 13 DMF ⋅ 3 H 2 O} n ( 2 ), have been prepared by the solvothermal reactions of benzophenone 4,4′‐dicarboxylic acid (H 2 BPnDC) with Cu(NO 3 ) 2 ⋅ 2.5 H 2 O and 4,4′‐bipyridine (bpy), and with Zn(NO 3 ) 2 ⋅ 6 H 2 O and 4‐diazabicyclo[2.2.2]octane (dabco), respectively. Compounds 1 and 2 are composed of paddle‐wheel {M 2 (O 2 CR) 4 } cluster units, and they generate 2D channels with two different large pores (effective size of larger pore: 18.2 Å for 1 , 11.4 Å for 2 ). The framework structure of desolvated solid, [Cu 2 (BPnDC) 2 (bpy)] n ( SNU‐6 ; SNU=Seoul National University), is the same as that of 1 , as evidenced by powder X‐ray diffraction patterns. SNU‐6 exhibits high permanent porosity (1.05 cm 3 g −1 ) with high Langmuir surface area (2910 m 2 g −1 ). It shows high H 2 gas storage capacity (1.68 wt % at 77 K and 1 atm; 4.87 wt % (excess) and 10.0 wt % (total) at 77 K and 70 bar) with high isosteric heat (7.74 kJ mol −1 ) of H 2 adsorption as well as high CO 2 adsorption capability (113.8 wt % at 195 K and 1 atm). Compound 2 undergoes a single‐crystal‐to‐single‐crystal transformation on guest exchange with n ‐hexane to provide {[Zn 2 (BPnDC) 2 (dabco)] ⋅ 6 ( n ‐hexane) ⋅ 3 H 2 O} n ( 2 hexane ). The transformation involves dynamic motion of the molecular components in the crystal, mainly a bending motion of the square planes of the paddle‐wheel units resulting from rotational rearrangement of phenyl rings and carboxylate planes of BPnDC 2− .