The synthesis and structures of a mononuclear copper(l) carbonyl complex [CU(OClO3)(CO)(H(2)CPz'(2))J (3) and a dinuclear copper(l) carbonyl complex [{Cu(CO)(H(2)CPz'(2))}(2)(mu-pyrazine)](ClO4)(2) (4), where H2CP4 bis(3,5-dimethylpyrazo-1-yl) methane, are described. These two compounds were generated by the carbonylation of the corresponding copper(I)-acetonitrile complexes, [Cu(H(2)CPz'(2))(MeCN)](ClO4) (1) and [{Cu(H(2)CPz'(2))(2) (MeCN)}(2)(mu-pyrazine)](ClO4)(2) (2). Alternatively, treatment of mononuclear 1 and 3, respectively, with pyrazine in a molar ratio of 2:1 produces the pyrazine-bridged dinuclear Cu-i complexes 2 and 4. Each of the complexes 1-4 can react with PPh3 to generate a common three-coordinated copper(l) complex [Cu(PPh3)(H(2)CPZ(2)')](ClO4) (5). The structures of complexes 1-5 were all confirmed by X-ray crystallography. Comparison of the Cu-I-C(CO) bond distances and the CO stretching frequencies of 3 and 4 indicates the back-donating properties of d pi(Cu)-pi(star)(pyrazine) bonds in 4, and accordingly, stabilizes the mixed-valence species generated from 2. Complex 3, stabilized by the strong interaction between copper(I) ion and perchlorate counteranion (Cu-I-O(ClO4) = 2.240(3) angstrom), is a potential precursor for polynuclear copper(I) carbonyl complexes.