Catalytic transesterifications by a Zn-bissalen mof containing open pyridyl groups inside 1D channels

The new ligand N,N′,N″,N″′-tetrakis[3-tert-butyl-5- (4-pyridinyl)salicylidene]-1,2,4,5-benzenetetraamine (bisSalen) containing four pyridyl groups in its periphery was prepared and subsequently used as an organic linker for a Zn-bisSalen MOF. A 2D undulated sheet structure was determined from single-crystal X-ray diffraction studies. The bisSalen ligands bridge two Zn^II ions, and one of the pyridyl groups on each side of the bisSalen ligand further coordinates to a bisSalen-coordinated Zn^II ion to provide a 2D sheet structure. The undulated 2D sheets are stacked closely together to form a 3D-like structure containing well-defined 1D channels, the orientation of which is perpendicular to the 2D sheets. The geometry of the bisSalen in the MOF is not planar. The remaining uncoordinated pyridyl groups point toward the 1D channels. Because of these openly accessible pyridyl groups in the channels, the Zn-bisSalen MOF is a very active catalyst for transesterifications. A 3D-like 2D Zn-bisSalen MOF {bisSalen = N,N′,N″,N″′-tetrakis[3-tert-butyl-5-(4-pyridinyl) salicylidene]-1,2,4,5-benzenetetraamine} with a large void space and Lewis-basic openly accessible pyridyl groups inside 1D channels was prepared and structurally investigated. The solvent-free Zn-bisSalen MOF contains a solvent-accessible void volume of 41.1 %. The as-prepared Zn-bisSalen MOF effectively catalyzes transesterifications.