Carbide bromides are mixed anion compounds containing bromide and carbide anions. Many carbide bromides are cluster compounds, containing on, two or more carbon atoms in a core, surrounded by a layer of metal atoms, encased in a shell of bromide ions. These ions may be shared between clusters to form chains, double chains or layers.

The great majority of these carbide bromide compounds contain rare earth elements. Since these elements have similar properties, similar structures can be made by substituting the elements. R2CBr2 forms a structure with layers of R6C clusters that contain one carbon atom. Each layer has bromide coating the top and bottom. Very similar is R2CBr2 which has layers of R6C2 clusters containing pairs of carbon atoms. This dicarbon is an (C24−), and contains a double bond. Layers have bromide on both sides, and so they are only weakly held together by van der Waals forces. If these layers are aligned with each other a 1T- form results with a small c measurement on the unit cell. In some compounds the layers are not quite aligned, but repeat after three layers giving a 3R form, with a larger c unit cell height. Where the layers align, the crystal system is trigonal. But if the layers never quite align at any height, a monoclinic crystal results. The C2 unit sits at an angle to the layers, and thus reduces symmetry compared to compounds with single carbon atoms in the cluster.

In R2CBr there are layers of R6C that share bromide between layers.

List formulasystemspace groupunit cellvolumedensitycommentreferenceSc7CBr12trigonalR3a=13.628, c=9.2034.33Y2CBr2trigonalRma=3.7545, c=29.1254.90bronzeY2C2Br2monoclinicC12/m1a=6.953, b=3.764, c=9.938, β=99.983.85superconductor Tc=5.04KY2C0.7Br2trigonalPm1a=3.73 c=9.8644.83greyY10Br18(C2)2monoclinicP21/na=9.729 b=16.323 c=13.229 β =121.131° Z=241798.3blackNa0.23Y2C2Br2 monoclinicC2/ma=7.061, b=3.724, c=10.464, β=92.964.43copper redZr6CBr14orthorhombicCmcea=14.69 b=13.229 c=11.991NaZr6CBr14orthorhombicCmcaa=14.6876, b=13.2266, c=11.9864 K4Zr6Br18CtriclinicP1a=10.114, b=10.283, c=10.374, α=118.54, β=99.98, γ=104.08, Z=1RbZr6CBr14orthorhombicCmcaa=14.719, b=13.287, c=12.043 Cs2Zr6Br10CtrigonalRca=13.0862 c=35.823 Z=65312.8CsZr6Br9CtrigonalRca=13.1031 c=35.800 Z=65321.5Cs3Zr6Br15CtrigonalRca=13.116 c=35.980 Z=6Cs4Zr6Br15CtrigonalRca=13.098 c=35.756 Z=65312La2C2BrmonoclinicC12/c1a=15.313, b=4.193, c=6.842, β=100.53,905.87La3CBr5monoclinicC12/c1a=14.234, b=10.858, c=14.588, β =106.85.10yellowLa3C2Br3orthorhombicC2221 a=11.533, b=17.0698, c=17.0545.38bronzeLa4C2Br5orthorhombicImmma = 3.9950, b = 8.277, c = 18.1015.43blackLa5C2Br9orthorhombicPnmaa=11.309, b=9.9477, c=16.49115.15redLa5C6Br3monoclinicC12/m1a=22.809, b=3.9855, c=16.599, β=123.325.30bronzeLa6C2Br9monoclinicC2/ca=14,234 b=10.858 c=14.588 β=106.80 Z=42158.44.85yellow insulatorLa10(C2)6Br6monoclinicC2/ma = 22.809, b = 3.9855, c = 16.599, β = 123.32° Z=21260.95.301bronze; air sensitiveLa3Br2C2BPnmaf =15.323, b = 3.973, c =11.567blackCe2C2BrmonoclinicC2/ca = 15.120, b = 4.179, c = 6.743, β = 101.09 °Ce4CBr5monoclinicC2/ma = 18.306, b = 3.9735, c = 8.378, β=104.91°Ce4C1.5Br5monoclinicC2/ma = 18.996, b = 3.9310, c = 8.282, β = 106.74°Ce4C2Br5orthorhombicImmma = 3.9835, b = 8.186, c = 18.0175.54violetCe4Br3C4triclinicP 1a = 4.227, b = 11.034, c = 11.268, α = 77.15°, β = 90.13° and γ = 84.42°Ce10(C2)6Br6monoclinicC2/ma = 22.483, b = 3.9253, c = 16.375, β = 123.15° Z=21209.95.558bronze; air sensitiveCe6Br3C3B2monoclinicP21/ma = 8.602, b = 3.829, c = 10.220, β = 112.53blackPr2CBrhexagonalP63/mmca=3.8071, c=14.77876.69blackPr2C2BrmonoclinicC12/c1a=15.054, b=4.139, c=6.713, β=101.086.24Pr3CBr3cubicI4131a=11.615.73Pr3CBr5triclinicPa=7.571, b=9.004, c=9.062, α=108.57, β=97.77, γ=106.285.09blackPr4C1.3Br5monoclinicC2/ma = 18.467, b = 3.911, c = 8.258, β = 105.25°Pr4C1.5Br5monoclinicC2/ma = 19.044, b = 3.9368, c = 8.254, β = 106.48°Pr5C2Br8triclinicPa=9.096, b=12.185, c=16.688, α=79.57, β=89.86, γ=84.385.02blackPr5C2Br9monoclinicP21/na = 10.069; b = 18.861; c = 10.459; β = 108.130° Z = 45.09dark redPr5C6Br3monoclinicC12/m1a=22.36, b=3.895, c=16.269, β=90,123.445,71Pr6C2Br10triclinicPa=7.571 b=9.004 c=9.062 α=108.57° β=97.77° γ=106.28° Z=1544.85.09blackPr7C3Br10a=9.054, b=11.1265, c=13.352, α=79.641, β=72.57, γ=64.675.22blackPr10C4Br15triclinicPa=9.098 b=10.127 c=10.965 α=70.38° β=66.31° γ=70.84° Z=1849.35.19silverPr10(C2)2Br16triclinicPa = 9.096, b = 12.185, c = 16.688, α = 79.57°, β = 89.86°, γ = 84.38°metallic blackPr10(C2)6Br6monoclinicC2/ma = 22.36, b = 3.895, c = 16.269, β = 123.44° Z=2bronze; air sensitivePr14C6Br20triclinicPa=9.098 b=10.935 c=13.352 α=86.27° β=75.57° γ=66.88° Z=11157.85.23blackPr6C2Cl5Br5monoclinicC2/ca = 13.689(1) Å, b = 10.383(1) Å, c = 14.089(1) Å, β = 106.49(1)°yellow to greenGd2CBrhexagonalP63/mmca=3.7858, c=14.2097.65dark greyGd2Br2CtrigonalPm1a=3.8209, c=9.824black3s-Gd2C2Br2monoclinicC2/ma = 7.066, b = 3.827, c = 9.967, β = 99.95°5.69black; contains C24−Gd2C2Br2monoclinicC2/ma=7.025, b=3.8361, c=9.868, β =94.476.24goldGd4C2Br3orthorhombicPnmaa = 10.844, b = 3.730, c = 20.3616.58bronzeGd10C4Br18monoclinicP21/na=9.7406 b=16.4817 c=11.8604 β =104.394° Z=24contains C24−Gd10(C2)6Br6monoclinicC2/ma = 21.507, b = 3.7193, c = 15.331, β = 123.34° Z=21024.56.254bronze; air sensitiveGd4Br3C2BmonoclinicP21/ma=9.547, b=3.693, c=12.44,5, β=106.68blackK2[Gd10(C2)2]Br19orthorhombicPbcna=12.751, b=23.17, c=14.423 5.01blackK2[Gd10(C2)2]Br20orthorhombicPbcaa=1.2751, b=2.317, c=1.44234.70blackRb2[Gd10(C2)2]Br19orthorhombicPbcna=1.2737, b=2.325, c=1.4412 5.15blackCs2[Gd10(C2)2]Br19orthorhombicTbCBrmonolinicC12/m1a=7.015, b=3.801, c=9.948, β=100.056.28Tb2CBrhexagonalP63/mmca=3.6915, c=14.0438.21Tb2CBrHhexagonalP63mca=3.7376, c=14.3157.88Tb4C2Br3orthorhombicPnmaa = 10.743, b = 3.706, c = 20.1947.31bronzeTb10Br18(C2)2monolinicP121/c1a=9.7562 b=16.4254 c=13.3043 β =120.675°1833.75.57dark redRb2[Tb10(C2)2]Br19orthorhombica=1.2664, b=2.3105, c=1.4303 blackDy10Br18(C2)2monolinicP21/ca = 9.740 b = 16.340 c = 13.247 β = 120.869° Z = 21809.6blackHo10Br18(C2)2monolinicP21/na=9.6838 b=16.2436 c=11.6374 β =104.427° Z=241772.8[Er10(C2)2]Br18monoclinicP21/na = 9.718, b = 16.234, c = 11.638, β = 104.00°; Z = 25.89blackLu2CBr2trigonalRma= 3.6663, c=28.7997.75goldLa0.9Lu0.1CBrmonoclinicC2/ma=7.434, b=4.0568, c=10.046, β=93.75.15W30C2(Cl,Br)68triclinicPa = 12.003, b = 14.862, c = 15.792, α = 88.75°, β = 68.85°, γ = 71.19° Z=12472.96.35blackTh6CBr15orthorhombicCmcea=15.764, b=14.16, c=13.1245.72greenY0.8Th0.2CBr monoclinicC2/ma=7.061, b=3.776, c=9.983, β=100.36 5.31

References