Unsaturation in binuclear cyclopentadienylchromium carbonyl thiocarbonyls: Viability of (η5-C5H5)2Cr2(CS)2(CO)3 in contrast to (η5-C5H5)2Cr2(CO)5

► Cp2Cr2(CS)2(CO)4 has a structure analogous to the known Cp2Cr2(CO)6. ► Cp2Cr2(CS)2(CO)3 with a four-electron donor bridging CS group is predicted to be viable. ► A Cp2Cr2(CS)2(CO)2 structure with a formal CrCr triple bond is found.