The syntheses and infrared spectra of a series of mono(tetracarbonylcobalt)tin(IV) derivatives of the general formula RnX3-x-SnCo(CO)4 [R = C6H5; X = Cl, Br, I; n = 0, 1, 2] are reported. Several triphenylphosphine complexes are also described. Assignments are suggested for the carbonyl stretching bands. Cobalt carbonyl reacts with tin(II) fluoride to form FSn-[Co(CO)4]3 and with tin(II) acetate to yield (CH3CO2)2Sn[Co(CO)4]2 and (CH3CO2)Sn[Co(CO)4]3. The preparation of Sn-[Co(CO)4]4 is also reported. © 1968, American Chemical Society. All rights reserved.