Effects of Solvation on the Framework of a Breathing Copper MOF Employing a Semirigid Linker

A semirigid di-1,2,4-triazole ligand leads to formation of the MOF [Cu2(L)2(SO4)­(Br)2]·xH2O (1). The framework structure of 1 flexes reversibly upon removal or addition of water to form semihydrated ([Cu2(L)2(SO4)­(Br)2]·4H2O) and dehydrated ([Cu2(L)2(SO4)­(Br)2]·0H2O) MOFs, 1′ and 1″, respectively. Single-crystal X-ray analysis demonstrated that the 2-butene subunit of the ligand rotates between two positions for 1 and 1′, causing a change in the solvent-accessible volume in the framework. This double hinge within the semirigid ligand is a built-in breathing mechanism and suggests a novel approach for general synthesis of breathing MOFs.