η2-Acetylene SmII and SmIII complexes: mirage or reality?

The bis(carbazolide) complex of Sm^II, Sm[3,6-Bu^t₂-1,8-(Me₃SiC≡C)₂Carb]₂, was synthesized by the transamination reaction of Sm[N(SiMe₃)₂]₂(THF)₂ with two molar equivalents of carbazole 3,6-Bu^t₂-1,8 (Me₃SiC≡C)₂CarbH. A similar reaction of the less sterically demanding carbazole 3,6-Bu^t₂-1,8-(PhC≡C)₂CarbH is accompanied by the oxidation of Sm^II to Sm^III and lead to the formation of bis(carbazolide) amido complex [3,6-Bu^t₂-1,8-(PhC≡C)₂Carb]₂Sm[N(SiMe₃)₂]. For both Sm complexes, η²-interactions with C≡C bonds, which are unconventional for Ln^II and Ln^III metals, were experimentally confirmed by single-crystal X-ray diffraction, IR and Raman spectroscopy along with QTAIM analysis.