Rare-Earth and Antimony-Oxo Clusters Simultaneously Connecting Antimonotungstates Comprising Divacant and Tetravacant Keggin Fragments.

Abstract

Four novel rare-earth (RE) and Sb-oxo clusters simultaneously bridging antimonotungstates (ATs) [H2N(CH3)2]8Na6H8{[RE4(H2O)6Sb6O4](SbW10O37)2(SbW8O31)2}·24H2O [RE = Dy3+ (1), Er3+ (2), Y3+ (3), Ho3+ (4)] were triumphantly isolated by using Na9[B-α-SbW9O33]·19.5H2O, dimethylamine hydrochloride, SbCl3, and RE(NO3)3·6H2O in acidic aqueous solution. Their tetrameric polyoxoanions are all established by two [SbW10O37]11- and two [B-α-SbW8O31]11- segments encapsulating a RE-Sb heterometal [RE4(H2O)6Sb6O4]22+ cluster. Under the O→W LMCT excitation at 268 nm of AT segments, RE ions in 1 and 2 can absorb the 3T1u→1A1g emission energy of AT segments, giving rise to the sensitization of AT segments to the emission of RE ions. Through the sensitization of AT segments, the emission intensities of RE ions in 1 and 2 are increased and lifetimes are prolonged. Photoluminescence and energy transfer measurements indicate that Dy3+ ions in 1 can obtain more energy from AT segments than to Er3+ ions in 2. Furthermore, the sensitization effects of AT segments to different f-f transitions of RE ions have been compared in 1 and 2. Under the sensitization of AT segments, the 4F9/2→6H15/2 transition obtains the most energy compared with the 4F9/2→6H13/2 and 4F9/2→6H11/2 transitions in 1, and the 2H11/2→4I15/2 transition obtains more energy than the 4S3/2→4I15/2 transition in 2. It seems that the better energy level match of 3T1u→1A1g transition of AT segments with f-f emission transitions of RE ions will lead to a stronger sensitization effect.