Blue fluorescence of three metal-organic zinc polymers containing tetrazinc units and asymmetric ligand of btc3−

Three new zinc coordination polymers [Zn2(btc)2(H2O)2]n·n[Zn(H2O)6] (1), [Zn3(btc)2(2,2′-bipy)2(H2O)3]n·2nH2O (2) and [Zn3(btc)2(H2O)6]n·nH2O (3) (H3btc=1,2,4-benzenetricarboxylic acid, 2,2′-bipy=2,2′-bipyridine) were obtained by the diffusion method and their crystal structures were determined by single-crystal X-ray diffraction. Compounds 1–3 have the similar tetrametallic unit [Zn4(btc)2] SBUs and these SBUs are further connected into stair-like structure, 2-D layer and 3-D framework for 1, 2 and 3, in which the btc3− ligands adopt μ3, μ4 and μ5 coordination modes, respectively. The title compounds show strong blue fluorescence, which may be assigned as π*→n transition of the ligand mixed with the ligand-to-metal change transfer (LMCT), indicating the fluorescence, indicates the title compounds may be good candidates for blue-light photoactive materials.