exo-nido- versus closo-Lanthanacarboranes. Synthesis and Structure of exo-nido-[(C₆H₅CH₂)₂C₂B₁₀H₁₀]Ln(DME)₃, [exo-nido-{(C₆H₅CH₂)₂C₂B₉H₉}Ln(THF)₃]₂ (Ln = Sm, Yb), and closo-exo-[(C₆H₅CH₂)₂C₂B₁₀H₁₀]₄Sm₂Na₃

Treatment of LnI 2 with 1 equiv of K 2 [(C 6 H 5 CH 2 ) 2 C 2 B 10 H 10 ] in THF at room temperature gave, after recrystallization from DME, the monomeric exo - nido -[(C 6 H 5 CH 2 ) 2 C 2 B 10 H 10 ]Ln(DME) 3 (Ln = Sm ( 1 ), Yb ( 2 )). They can react with another equivalent of Na 2 [(C 6 H 5 CH 2 ) 2 C 2 B 10 H 10 ] to afford closo - exo- [(C 6 H 5 CH 2 ) 2 C 2 B 10 H 10 ] 4 Ln 2 Na 4 (THF) 2 (Ln = Sm ( 4 ), Yb ( 5 )). Reaction of YbCl 3 with 2 equiv of K 2 [(C 6 H 5 CH 2 ) 2 C 2 B 10 H 10 ] in THF/DME yielded 2, while treatment of SmCl 3 with 2 equiv of K 2 [(C 6 H 5 CH 2 ) 2 C 2 B 10 H 10 ] in THF generated a novel cluster closo - exo- [(C 6 H 5 CH 2 ) 2 C 2 B 10 H 10 ] 4 Sm 2 Na 3 ( 3 ). LnI 2 reacted with 2 equiv of Na 2 [(C 6 H 5 CH 2 ) 2 C 2 B 9 H 9 ] in THF to produce the dimeric [ exo - nido -{(C 6 H 5 CH 2 ) 2 C 2 B 9 H 9 }Ln(THF) 3 ] 2 (Ln = Sm ( 6 ), Yb ( 7 )). These new compounds were fully characterized by spectroscopy and elemental analyses. The solid-state structures of 1 − 3, 6, and 7 have been further confirmed by single-crystal X-ray analyses. This study indicates that steric factors dominate the formation of exo - nido -lanthanacarboranes. In case the substituents are benzyl groups, closo - and exo - nido- lanthanacarboranes of C 2 B 10 systems are exchangeable by changing the ratio of metal to carborane.