Synthesis, structure, water-induced reversible crystal-to-amorphous transformation, and luminescence properties of novel cationic spacer-filled 3D transition metal supramolecular frameworks from N,N′,N-tris(carboxymethyl)-1,3,5-benzenetricarboxamide

Four novel cationic spacer-filled 3D transition metal supramolecular frameworks from N,N',N' '-tris(carboxymethyl)-1,3,5- benzenetricarboxamide (L), {[ML(H2O)(3)](2)[M(H2O)(6)](H2O)(3)}(n) (M = Zn, 1; Mn, 2; Ni, 3; Co, 4), have been synthesized hydrothermally. X-ray single-crystal diffraction studies confirm that these complexes are isostructural and crystallize in the hexagonal crystal system, with the space group being P (3) over bar (1)c. Each metal ion coordinates to three ligands and each ligand L bridges three metal ions as well, resulting in an infinite 2D anionic (6, 3) layer with large honeycomblike cavities. Interestingly, two adjacent layers are staggered in such a way that non-interepenetrating double-layer structures are formed. Such double layers are separated by the layer of hexaqua-metal cations through O-H center dot center dot center dot O hydrogen bonds between the -CONH- groups and the coordinated aqua molecules. Four complexes could be considered as dynamic molecular solids and exhibit interesting water-induced reversible crystal-to-amorphous transformation properties that are confirmed by TGA and XRD studies. In addition, among them, complex 1 shows a strong blue-emitting fluorescence emission band at 457 nm at room temperature and may be a potential candidate for blue luminescence materials.