Mixed carbonyl-isocyanide and carbonyl-nitrile complexes derived from the reactions of the multiply bonded dirhenium(II) complexes Re2X4(dppm)2(CO) (X = chloro or bromo-; dppm = Ph2PCH2PPh2). The structural characterization of Cl2Re(.mu.-Cl)(.mu.-dppm)2ReCl(CO) and Cl2Re(.mu.-Cl)(.mu.-CO)(.mu.-dppm)