The reactions of the unsymmetrical, coordinatively unsaturated dirhenium(II) complexes [Re2Br3(mu-dppm)(2)(CO)(CNXyl)]Y (CNXyl)]Y (XylNC = 2,6-dimethylphenyl isocyanide; Y = O3SCF3 (3a), PF6 (3b)) with XylNC afford at least three isomeric forms of the complex cation [Re2Br3(mu-dppm)(2)(CO)(CNXyl)(2)](divided by). Two forms have very similar bis(mu-halo)-bridged edge-sharing bioctahedral structures of the type [(CO)BrRe(mu-Br)(2)(mu-dppm)(2)Re(CNXyl)(2)]Yx (Y = O3SCF3 (4a/4a’), PF6 (4b/4b’)), while the third is an open bioctahedron [(XyINC)(2)BrRe(mu-dppm)(2)ReBr2(CO)]Y (Y = O3SCF3 (5a), PF6 (5b)). While the analogous chloro complex cation [Re2Cl3(mu-dppm)(2)(CO)(CNXyl)(2)](+) was previously shown to exist in three isomeric forms, only one of these has been found to be structurally similar to the bromo complexes (i.e, the isomer analogous to 5a and 5b).