Heterometallic Europium Disiloxanediolates: Synthesis, Structural Diversity, and Photoluminescence Properties

This
contribution presents a full account of a structurally diverse class
of heterometallic europium disiloxanediolates. The synthetic protocol
involves in situ metalation of (HO)­SiPh2OSiPh2(OH) (1) with either nBuLi or KN­(SiMe3)2 followed by treatment
with EuCl3 in suitable solvents such as 1,2-dimethoxyethane
(DME) or tetrahydrofuran (THF). Reaction of EuCl3 with
2 equiv of (LiO)­SiPh2OSiPh2(OLi) in DME afforded
the EuIII bis­(disiloxanediolate) “ate” complex
[{(Ph2SiO)2O}2{Li­(DME)}3]­EuCl2 (2), which upon attempted reduction
with Zn gave the tris­(disiloxanediolate) [{(Ph2SiO)2O}3{Li­(DME)}3]Eu (3). Treatment
of EuCl3 with (LiO)­SiPh2OSiPh2(OLi)
in a molar ratio of 1:2 yielded both the ate complex [{(Ph2SiO)2O}3Li­{Li­(THF)2}­{Li­(THF)}]­EuCl·Li­(THF)3 (4) and the LiCl-free europium­(III) complex
[{(Ph2SiO)2O}2{Li­(THF)2}2]­EuCl (5). Compound 5 was
found to exhibit a brilliant red triboluminescence. When (KO)­SiPh2OSiPh2(OK) was used as starting material in a 3:1
reaction with EuCl3, the EuIII tris­(disiloxanediolate)
[{(Ph2SiO)2O}3{K­(DME)}3]Eu (6) was isolated. Attempted ligand transfer between 5 and (DADDipp)2Ba­(DME) (DADDipp = N,N′-bis­(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene)
afforded the unique mixed-valent EuIII/EuII disiloxanediolate
cluster [(Ph2SiO)2O]6EuII4EuIII2Li4O2Cl2 (7). All new complexes were structurally
characterized by X-ray diffraction. Photoluminescence studies were
carried out for complex 5 showing an excellent color
quality, due to the strong 5D0→7F2 transition, but a weak antenna effect.