DIMERIC (PENTAMETHYLCYCLOPENTADIENYL)RHODIUM AND IRIDIUM COMPLEXES .4. CRYSTAL AND MOLECULAR-STRUCTURE OF [ETA-5-C5ME5)RHBR]2(MU-BR)2 AND OF PARTIALLY HALIDE-EXCHANGED SPECIES [(ETA5-C5ME5)RHX]2(MU-X')2 OBTAINED BY RECRYSTALLIZATION OF BROMO COMPLEX FROM 1,2-DICHLOROETHANE