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Heterometallic Europium Disiloxanediolates: Synthesis, Structural Diversity, and Photoluminescence Properties
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contribution presents a full account of a structurally diverse class
of heterometallic europium disiloxanediolates. The synthetic protocol
involves <i>in situ</i> metalation of (HO)SiPh<sub>2</sub>OSiPh<sub>2</sub>(OH) (<b>1</b>) with either <sup><i>n</i></sup>BuLi or KN(SiMe<sub>3</sub>)<sub>2</sub> followed by treatment
with EuCl<sub>3</sub> in suitable solvents such as 1,2-dimethoxyethane
(DME) or tetrahydrofuran (THF). Reaction of EuCl<sub>3</sub> with
2 equiv of (LiO)SiPh<sub>2</sub>OSiPh<sub>2</sub>(OLi) in DME afforded
the Eu<sup>III</sup> bis(disiloxanediolate) “ate” complex
[{(Ph<sub>2</sub>SiO)<sub>2</sub>O}<sub>2</sub>{Li(DME)}<sub>3</sub>]EuCl<sub>2</sub> (<b>2</b>), which upon attempted reduction
with Zn gave the tris(disiloxanediolate) [{(Ph<sub>2</sub>SiO)<sub>2</sub>O}<sub>3</sub>{Li(DME)}<sub>3</sub>]Eu (<b>3</b>). Treatment
of EuCl<sub>3</sub> with (LiO)SiPh<sub>2</sub>OSiPh<sub>2</sub>(OLi)
in a molar ratio of 1:2 yielded both the ate complex [{(Ph<sub>2</sub>SiO)<sub>2</sub>O}<sub>3</sub>Li{Li(THF)<sub>2</sub>}{Li(THF)}]EuCl·Li(THF)<sub>3</sub> (<b>4</b>) and the LiCl-free europium(III) complex
[{(Ph<sub>2</sub>SiO)<sub>2</sub>O}<sub>2</sub>{Li(THF)<sub>2</sub>}<sub>2</sub>]EuCl (<b>5</b>). Compound <b>5</b> was
found to exhibit a brilliant red triboluminescence. When (KO)SiPh<sub>2</sub>OSiPh<sub>2</sub>(OK) was used as starting material in a 3:1
reaction with EuCl<sub>3</sub>, the Eu<sup>III</sup> tris(disiloxanediolate)
[{(Ph<sub>2</sub>SiO)<sub>2</sub>O}<sub>3</sub>{K(DME)}<sub>3</sub>]Eu (<b>6</b>) was isolated. Attempted ligand transfer between <b>5</b> and (DAD<sup>Dipp</sup>)<sub>2</sub>Ba(DME) (DAD<sup>Dipp</sup> = <i>N</i>,<i>N</i>′-bis(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene)
afforded the unique mixed-valent Eu<sup>III</sup>/Eu<sup>II</sup> disiloxanediolate
cluster [(Ph<sub>2</sub>SiO)<sub>2</sub>O]<sub>6</sub>Eu<sup>II</sup><sub>4</sub>Eu<sup>III</sup><sub>2</sub>Li<sub>4</sub>O<sub>2</sub>Cl<sub>2</sub> (<b>7</b>). All new complexes were structurally
characterized by X-ray diffraction. Photoluminescence studies were
carried out for complex <b>5</b> showing an excellent color
quality, due to the strong <sup>5</sup>D<sub>0</sub>→<sup>7</sup>F<sub>2</sub> transition, but a weak antenna effect
