Single crystals of the title compounds were prepared by solid state reactions from barium carbonate and ruthenium metal using a BaBr 2 flux and investigated by X-ray diffraction method using Mo(Ka) radiation and a Charge Coupled Device (CCD) detector. A structural model for the term n ¼ 2, Ba 5 Ru 2 Br 2 O 9 (1) was established in the hexagonal symmetry, space group P6 3 /mmc, a ¼ 5.8344(2) A ˚, c ¼ 25.637(2) A ˚, Z ¼ 2. Combined refinement and maximum-entropy method (MEM) unambiguously show the presence of CO 3 2À ions in the three other compounds (2, 3, 4). Their crystal structures were solved and refined in the trigonal symmetry, space group P3ml, a ¼ 5.8381(1) A ˚, c ¼ 15.3083(6) A ˚for the term n ¼ 3, Ba 6 Ru 3 Br 1.54 (CO 3 ) 0.23 O 12 (2), and space group R3m, a ¼ 5.7992(1) A ˚, c ¼ 52.866(2) A ˚and a ¼ 5.7900(1) A ˚, c ¼ 59.819(2) A ˚for the terms n ¼ 4, Ba 7 Ru 4 Br 1.46 (CO 3 ) 0.27 O 15 (3), and n ¼ 5, Ba 8 Ru 5 Br 1.64 (CO 3 ) 0.18 O 18 (4), respectively. The structures are formed by the periodic stacking along [0 0 1] of (n+1) hexagonal closepacked [BaO 3 ] layers separated by a double layer of composition [Ba 2 Br 2À2x (CO 3 ) x ]. The ruthenium atoms occupy the n octahedral interstices created in the hexagonal perovskite slabs and constitute isolated dimers Ru 2 O 9 of face-shared octahedra (FSO) in 1 and isolated trimers Ru 3 O 12 of FSO in 2. In 3 and 4, the Ru 2 O 9 units are connected by corners either directly (3) or through a slab of isolated RuO 6 octahedra (4) to form a bidimensional arrangement of RuO 6 octahedra. These four oxybromocarbonates belong to the family of compounds formulated [Ba 2 Br 2À2x (CO 3 ) x ][Ba n+1 Ru n O 3n+3 ] where n represents the thickness of the octahedral string in hexagonal perovskite slabs. These compounds are compared to the oxychloride series.