Synthesis and crystal structures of the racemic and meso forms of [1-{1'-4'-cyclopentadienyl-4'-cobalta-1',12'-dicarba-closo-dodecaboranyl(10)}-4-cyclopentadienyl-4-cobalta-1,12-dicarba-closo-dodecaborane(10)], the former as its tetrahydrofuran disolvate.

Both rac-[1-(1'-4'-Cp-4',1',12'-closo-CoC2B10H11)-4-Cp-4,1,12-closo-CoC2B10H11]·2THF (Cp is cyclopentadienyl and THF is tetrahydrofuran) or [Co2(C5H5)2(C4H22B20)]·2C4H8O, (1), and meso-[1-(1'-4'-Cp-4',1',12'-closo-CoC2B10H11)-4-Cp-4,1,12-closo-CoC2B10H11] or [Co2(C5H5)2(C4H22B20)], (2), were prepared by thermolysis of a rac/meso mixture of the precursor species [1-(1'-4'-Cp-4',1',6'-closo-CoC2B10H11)-4-Cp-4,1,6-closo-CoC2B10H11] and were separated, spectroscopically characterized and studied crystallographically. Cage C-atom identification was accomplished by both the vertex-to-centroid distance and boron-hydrogen distance methods, and, in both cases, the structure established crystallographically is fully consistent with the spectroscopic data. Both the rac-(1) and meso-(2) forms share the same overall conformation (Co-C-C'-Co' ca 136°) and show clear evidence of intramolecular steric crowding resulting in tilted cyclopentadienyl ligands.