The reaction of LnX 3 (Ln=Ce, X=Br; Ln=Gd, Lu, X=Cl) with the “carbons adjacent” carborane monoanion, [2,3-(SiMe 3 ) 2 -2,3-C 2 B 4 H 5 ] − in 1:2 molar ratio in anhydrous tetrahydrofuran (THF) produced the dimeric half-sandwich halolanthanacarboranes, [closo-1-(X)-1,1-(THF) 2 -2,3-(SiMe 3 ) 2 -1-Ln(η 5 -C 2 B 4 H 4 )] 2 , in 72–92% yields along with one equivalent of the neutral nido-carborane precursor, 2,3-(SiMe 3 ) 2 -2,3-C 2 B 4 H 6 . This reliable synthetic route avoided complications such as solvent degradation and oxide ion incorporation that give rise to large multi-lanthanacarborane clusters. This method produced the first isolated halolanthanacarborane half-sandwich in the C 2 B 4 -cage systems.