Keggin-Type Tridecanuclear Europium-Oxo Nanocluster Protected by Silsesquioxanes

The Keggin structure, known as an archetypical polyox-ometalate (POM) structural motif, has widened up our fundamentalunderstanding of the growth behavior of natural metal oxide minerals.However, devising a strategy for synthesis of such species consisting ofpure-metal ions remains a great challenge. Different from those six-coordinated early transition metal ions in Keggin POMs, lanthanide prefershigher coordination numbers, making the construction of lanthanide-Keggin structure more difficult. Here, we report the unprecedentedluminescent Keggin-type Eu13nanocluster constructed through a facilesolvothermal method using the high-symmetry macrocyclic tetrasilane(Ph4Si4O8)4-as the capping ligand. This protocol demonstrates animportant proof of concept for assembly of metallasilsesquioxanes. Thestructure shows a rare polyoxometalate-Eu-oxo-core@SiO2-shell@organic-shell (Eu13) consisting of a central EuO8cube, surrounded by 12 edge-sharing EuO7monocapped trigonal prisms. It is the highest-nuclearity lanthanide-silsesquioxane nanocluster. Electrospray ionization mass spectrometry reveals thatEu13is stable in solutionexcept for some labile terminal dimethylformamide on the ligand shell, which endowsEu13with a high catalytic activity for CO2cycloaddition reaction with small epoxides under ambient conditions.Eu13also exhibits intense red luminescence upon visible lightexcitation (466 and 535 nm). The photophysical and photoelectric properties of the drop-castingfilm ofEu13indicate its greatpotential in optoelectric device applications.

Automated summary

This study reports the synthesis of a novel Keggin-type Eu13 nanocluster through a solvothermal method and demonstrates the concept of assembling metallasilsesquioxanes. The Eu13 structure consists of a central EuO8 cube surrounded by 12 EuO7 monocapped trigonal prisms, making it the highest-nuclearity lanthanide-silsesquioxane nanocluster. The Eu13 nanocluster exhibits high stability and catalytic activity for CO2 cycloaddition reaction, as well as intense red luminescence upon visible light excitation, indicating its potential in optoelectric device applications.