In this work we report a Mo¨ssbauer study of iron‐copper clusters isolated in a rare gas solid. For the FeCu dimer we were able to determine the electronic ground state. The samples were prepared in a liquid‐helium cryostat evacuated to a pressure better than 10−7torr. The Cu and (90&percent; enriched)57Fe atomic beams were produced in alumina crucibles contained in resistance heated tantalum furnaces and codeposited with a stream of argon gas at 4.2K onto a Be disk. In this study very dilute samples were used (Ar/metal ?500) in order to identify correctly the FeCu dimer. From the Mo¨ssbauer parameters we were able to identify the molecule as2&pgr; with a spin at the iron atom of 1/2. A concentration dependence study of the iron‐copper multimer was carried out. It was observed that by increasing the number of copper nearest neighbors the isomer shift approaches the value obtained for iron in a copper matrix. For very high concentrations the Mo¨ssbauer parameters are similar to those of pure iron multimer. It seems that the presence of a large number of copper nearest neighbors produces a drastic change in the electronic structure of the iron atom.