The cyclopentadienylchromium carbonyl thiocarbonyls Cp 2 Cr 2 (CS) 2 (CO) n (n = 4, 3, 2, 1) have been studied by density functional theory using the B3LYP and BP86 functionals. The lowest energy Cp 2 Cr 2 (CS) 2 (CO) 4 structure can be derived from the experimentally characterized unbridged Cp 2 Cr 2 (CO) 6 structure by replacing the two terminal carbonyl groups furthest from the Cr–Cr bond with two terminal CS groups. The two lowest energy Cp 2 Cr 2 (CS) 2 (CO) 3 structures have a single four-electron donor η 2 -μ-CS group and a formal Cr–Cr single bond of length ∼3.1 Å. In contrast to the carbonyl analogue Cp 2 Cr 2 (CO) 5 these Cp 2 Cr 2 (CS) 2 (CO) 3 structures are viable with respect to disproportionation into Cp 2 Cr 2 (CS) 2 (CO) 4 and Cp 2 Cr 2 (CS) 2 (CO) 2 and thus are promising synthetic targets. The lowest energy Cp 2 Cr 2 (CS) 2 (CO) 2 structures have all two-electron donor CO and CS groups and short CrCr distances around ∼2.3 Å suggesting the formal triple bonds required to give the chromium atoms the favored 18-electron configurations. These Cp 2 Cr 2 (CS) 2 (CO) 2 structures are closely related to the known structure for Cp 2 Cr 2 (CO) 4 . In addition, several doubly bridged structures with four-electron donor η 2 -μ-CS bridges are found for Cp 2 Cr 2 (CS) 2 (CO) 2 at higher energies. The global minimum Cp 2 Cr 2 (CS) 2 (CO) structure is a triply bridged triplet with a CrCr triple bond (2.299 Å by BP86). A higher energy singlet Cp 2 Cr 2 (CS) 2 (CO) structure has a shorter Cr–Cr distance of 2.197 Å (BP86) suggesting the formal quadruple bond required to give each chromium atom the favored 18-electron configuration.