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⁺ (<b>1</b>), Er³⁺ (<b>2</b>), Y³⁺ (<b>3</b>), Ho³⁺ (<b>4</b>)] 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 <b>1</b> and <b>2</b> can absorb the ³T_1u→¹A_1g 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 <b>1</b> and <b>2</b> are increased and lifetimes are prolonged. Photoluminescence and energy transfer measurements indicate that Dy³⁺ ions in <b>1</b> can obtain more energy from AT segments than to Er³⁺ ions in <b>2</b>. Furthermore, the sensitization effects of AT segments to different <i>f</i>-<i>f</i> transitions of RE ions have been compared in <b>1</b> and <b>2</b>. Under the sensitization of AT segments, the ⁴F_9/2→⁶H_15/2 transition obtains the most energy compared with the ⁴F_9/2→⁶H_13/2 and ⁴F_9/2→⁶H_11/2 transitions in <b>1</b>, and the ²H_11/2→⁴I_15/2 transition obtains more energy than the ⁴S_3/2→⁴I_15/2 transition in <b>2</b>. It seems that the better energy level match of ³T_1u→¹A_1g transition of AT segments with <i>f</i>-<i>f</i> emission transitions of RE ions will lead to a stronger sensitization effect.