Antimony dicarbide was investigated employing coupled cluster and multiconfigurational methods. The relativistic effects were taken into account by using pseudopotentials for the Sb atom; additional corrections due to all-electron correlations and spin-orbit effects were also included. C2Sb is found to be quasilinear in the ground (2)A '' [X-2 Pi] state with a very small barrier to linearity (0.07 kJ mol(-1)); T-shaped cyclic C-2v(B-2(2)) geometry was found just about 2.9 kJ mol(-1) higher in energy. A molecular orbital analysis, spin-orbit constants, dissociation energies of C2Sb (X-2 Pi), and the low-lying excited valence-type electronic states are reported. (C) 2013 Elsevier B.V. All rights reserved.