One of the two isomeric forms of the complex Re2Br4(mu-dppm)(2)(CO) (1b), both of which are formed by the reaction of the triply bonded complex Re2Br4(mu-dppm)(2) with CO, is shown to have the same A-frame-like structure as that characterized previously for Re2Cl4(mu-dppm)(2)(CO) (1a) by X-ray crystallography. Crystal data for Re2Br4(mu-dppm)(2)(CO) . CH2Cl2 (1b) at 293 K : monoclinic space group Cc (No. 9) with a 19.584(5) Angstrom, b = 17.109(2) Angstrom, c = 17.649(6) Angstrom, beta = 105.92(2)degrees, V = 5686(5) Angstrom(3), Z = 4. The structure was refined to R = 0.055 (R(W) = 0.073) for 4891 data with I > 3.0 sigma(I). The CO ligand is terminally bound, and the Re-Re distance of 2.336(1) Angstrom accords with the retention of a Re=Re bond. The second isomeric form of Re(2)X(4)(mu-dppm)(2)(CO) has been identified as having an open unsymmetrical structure X(3)Re(mu-dppm)(2)ReX(CO). The reaction of 1b with xylyl and tert-butyl isocyanides produces bioctahedral complexes of the type (RNC)Br2Re(mu-dppm)(2)ReBr2(CO) (R = xylyl (3a), t-Bu (3b)), in which two Re-Br bonds are collinear with the Re=Re bond, and the terminally bound RNC and CO ligands are anti to one another on separate Re centers. This structure has been established by a single-crystal X-ray structure determination of 3b. Crystal data for Re2Br4(mu-dppm)(2)(CO)(CN-t-Bu). CH2Cl2 . 2.5C(6)H(6) (3b) at 203 K : monoclinic space group P2(1)/n (No. 14) with a = 12.892(2) Angstrom, b = 19.478(4) Angstrom, c = 27.231(4) Angstrom, beta = 93.623(13)degrees, V = 6824(4) Angstrom(3), Z = 4. The structure was refined to R = 0.066 (R(W) = 0.084) for 5165 data with I > 3.0 sigma(I). The Re-Re distance is 2.381(1) Angstrom. The mixed carbonyl-isocyanide complexes 3a and 3b react with TlO3SCF3 in dichloromethane to give the triply-bonded compounds [Re2Br3(mu-dppm)(2)(Co)(CNR)]O(3)sCF(3) (R = xylyl (49), t-Bu (4b)),which have an unsymmetrical structure with the two metal centers possessing different coordination numbers and the CO and RNC ligands trans to one another. This conclusion is based upon a single-crystal X-ray structure determination of 4a. Crystal data for [Re2Br3(mu-dppm)(2)(CO)(CNxyl)]O3SCF3 (4a) at 293 K : monoclinic space group P2(1)/c (No. 14) with a = 14.182(3) A, b = 15.749(4) Angstrom, c = 31.580(5) Angstrom, beta = 98.58(2)degrees, V = 6974(5) Angstrom(3), Z = 4. The structure was refined to R = 0.066 (R(W) = 0.088) for 5333 data with I > 3.0 sigma(I). A comparison is made between these results and those obtained previously for the related dirhenium chloro complexes which contain CO and RNC ligands.