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 [Cu(2)(L)(2)(SO(4))(Br)(2)]·xH(2)O (1). The framework structure of 1 flexes reversibly upon removal or addition of water to form semihydrated ([Cu(2)(L)(2)(SO(4))(Br)(2)]·4H(2)O) and dehydrated ([Cu(2)(L)(2)(SO(4))(Br)(2)]·0H(2)O) 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.