Mass-selected heteronuclear iron-copper carbonyl cluster anions CuFe(CO)(n)(-) (n = 4-7) are studied by infrared photodissociation spectroscopy in the carbonyl stretching frequency region in the gas phase. The cluster anions are produced via a laser vaporization supersonic cluster ion source. Their geometric structures are determined by comparison of the experimental spectra with those calculated by density functional theory. The experimentally observed CuFe(CO)(n)(-) (n = 4-7) cluster anions are characterized to have (OC)(4)Fe-Cu(CO)(n-4) structures, each involving a C-3v symmetry Fe(CO)(4)(-) building block. Bonding analysis indicates that the Fe- Cu bond in the CuFe(CO)(n)(-) (n = 4-7) cluster anions is a s type single bond with the iron center possessing the most favored 18-electron configuration. The results provide important new insight into the structure and bonding of hetronuclear transition metal carbonyl cluster anions.