Assembly and Upconversion Properties of Lanthanide Coordination Polymers Based on Hexanuclear Building Blocks with (μ 3 ‐OH) Bridges

Three novel hexanuclear core‐based hydroxidolanthanide coordination polymers [Ln 3 (BDC) 3.5 (OH) 2 (H 2 O) 2 ] · H 2 O [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 (μ 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‐photonexcitation of Y:Er‐Yb codoped coordination polymers andarise from Er III transitions of the type 4 F 5/2 → 4 I 15/2 , 2 H 11/2 → 4 I 15/2 , 4 S 3/2 → 4 I 15/2 and 4 F 9/2 → 4 I 15/2 . (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)