The reaction of cyanide, carbon monoxide, and ferrous derivatives led to the isolation of three products, trans- and cis-[Fe(CN)(4)(CO)(2)](2-) and [Fe(CN)(5)(CO)](3-), the first two of which were characterized by single-crystal X-ray diffraction. The new compounds show self-consistent IR, C-13 NMR, and mass spectroscopic properties. The reaction of trans[Fe(CN)(4)(CO)(2)](2-) with Et4NCN gives [Fe(CN)(5)(CO)](3-) via a first-order (dissociative) pathway. The corresponding cyanation of cis-[Fe(CN)(4)(CO)(2)](2-), which is a minor product of the Fe(II)/CN-/CO reaction, does not proceed at measurable rates, Methylation of [Fe(CN)(5)(CO)](3-) gave exclusively cis-[Fe(CN)(4)(CNMe)(CO)](2-), demonstrating the enhanced nucleophilicity of CN- trans to CN- vs CN- trans to CO. Methylation has an electronic effect similar to that of protonation as determined electrochemically. We also characterized [M(CN)(3)(CO)(3)](n-) for Ru (n = 1) and Mn (n = 2) derivatives. The Ru complex, which is new, was prepared by cyanation of a [RuCl2(CO)(3)](2) solution.