η<sup>2</sup>-Acetylene Sm<sup>II</sup> and Sm<sup>III</sup> complexes: mirage or reality?

The bis(carbazolide) complex of Sm<sup>II</sup>, Sm[3,6-Bu<sup>t</sup><sub>2</sub>-1,8-(Me<sub>3</sub>SiC≡C)<sub>2</sub>Carb]<sub>2</sub>, was synthesized by the transamination reaction of Sm[N(SiMe<sub>3</sub>)<sub>2</sub>]<sub>2</sub>(THF)<sub>2</sub> with two molar equivalents of carbazole 3,6-Bu<sup>t</sup><sub>2</sub>-1,8 (Me<sub>3</sub>SiC≡C)<sub>2</sub>CarbH. A similar reaction of the less sterically demanding carbazole 3,6-Bu<sup>t</sup><sub>2</sub>-1,8-(PhC≡C)<sub>2</sub>CarbH is accompanied by the oxidation of Sm<sup>II</sup> to Sm<sup>III</sup> and lead to the formation of bis(carbazolide) amido complex [3,6-Bu<sup>t</sup><sub>2</sub>-1,8-(PhC≡C)<sub>2</sub>Carb]<sub>2</sub>Sm[N(SiMe<sub>3</sub>)<sub>2</sub>]. For both Sm complexes, η<sup>2</sup>-interactions with C≡C bonds, which are unconventional for Ln<sup>II</sup> and Ln<sup>III</sup> metals, were experimentally confirmed by single-crystal X-ray diffraction, IR and Raman spectroscopy along with QTAIM analysis.