Symmetrically and unsymmetrically substituted methylsulfanyl derivatives of nickel(III) bis(dicarbollide) (BuN)[8,8'-(MeS)-3,3'-Ni(1,2-CBH)], (BuN)[4,4'-(MeS)-3,3'-Ni(1,2-CBH)], and (BuN)[4,7'-(MeS)-3,3'-Ni(1,2-CBH)] were synthesized, starting from [Ni(acac)] and the corresponding methylsulfanyl derivatives of -carborane (BuN)[10-MeS-7,8-CBH] and (BuN)[10-MeS-7,8-CBH]. Structures of the synthesized metallacarboranes were studied by single-crystal X-ray diffraction and quantum chemical calculations. The symmetrically substituted 8,8'-isomer adopts conformation stabilized by two pairs of intramolecular C-H···S hydrogen bonds between the dicarbollide ligands. The unsymmetrically substituted 4,7'-isomer adopts conformation, which is stabilized by two nonequivalent C-H···S hydrogen bonds and one short chalcogen B-H···S bond (2.53 Å, -1.4 kcal/mol). The conformation was found to be also preferred for the 4,7'-isomer.