Synthesis, structure and luminescent properties of rare earth coordination polymers constructed from paddle-wheel building blocks

A series of three-dimensional (3D) novel coordination polymers M(bpdc)(1.5)(H2O)center dot 0.5DMF (M = Tb (1), Ho (2), Er (3), or Y (4)) have been synthesized by reaction of the rare earth ions (W) with 4,4'-biphenyldicarboxylic acid (H(2)bpdc) in a mixed solution of DMF and C2H5OH. They possess the same 3D architectures and crystallize in monoclinic space group G2/c. Two seven-coordinated metal centers and four dimonodentate bpdc groups construct a paddle-wheel building block. These building blocks connect with two carboxyl groups to lead to a one-dimensional inorganic chain, ---M-O-C-O-M---, along the [001] direction. The inorganic chains are linked with two biphenyl groups to form 25.15 angstrom x 17.09 angstrom rhombic channels along the c axis without interpenetration. These complexes exhibit strong fluorescence in the visible region, and complex 3 shows Er3+ characteristic emission in the range of 1450-1650 nm at room temperature. These complexes could be anticipated as potential fluorescent probes and an IR-emitter, respectively.