Assembly and upconversion properties of lanthanide coordination polymers based on hexanuclear building blocks with (μ3-OH) bridges

Three novel hexanuclear core-based hydroxidolanthanide coordination polymers [Ln(3)(BDC)(3.5)(OH)(2)(H2O)(2)]center dot H2O [Ln = Y (1), Yb (2) and Er (3); BDC = 1,4-benzenedicarboxylate] were prepared by the hydrothermal method. The controlled hydrolysis of lanthanide ions led to an open hexanuclear cluster core. The hexanuclear core containing six (mu(3)-OH) bridged Ln(III) ions from two asymmetric units adopts a chair-like configuration. It behaves as a building block and is linked by the BDC ligands to form a 3D framework. The guest water molecules occupy the 1D channels in the structure. The upconversion spectra of the Y:Er-Yb codoped coordination polymers have been studied. The distinct upconversion emissions come from two-photon or three-photon excitation of Y:Er-Yb codoped coordination polymers and arise from Er-III transitions of the type F-4(5/2)-> I-4(15/2), H-2(11/2) I-4(15/2), S-4(3/2)-> I-4(15/2) and F-4(9/2) I-4(15/2). (c) Wiley-VCH Verlag GmbH & Co.