Using ab initio multireference methods and large correlation consistent basis sets, we have investigated the ground electronic structure of the carbides BC and AIC, the ground and the first two excited states of the corresponding anions, BC-and AlC-. and the ground (linear) structures of the hydrides H-BC and H-AlC. By employing a series of increasing size basis sets for the BC molecule, i.e., cc-pVnZ, aug-cc-pVnC, cc pCVnZ, and aug-cc-pCVnZ, n = 2, 3, 4, and 5, we have examined the convergence of its properties as a function of n. For both the neutral diatomic species and their anions we have obtained full potential energy curves, bond distances (r(e)), dissociation energies (D-e), and the usual spectroscopic constants. For the BC molecule, our best r(e) and D-e values are r(e) = 1.4911 Angstrom and D-e, = 102.2 kcal/mol in excellent agreement with experimental results. In the AlC case the calculated D-e = 77.13 kcal/mol is at least 12 kcal/mol higher than the experimental number. No experimental or theoretical data exist in the literature for the anion BC-. For this system we obtain r(e) = 1.4445 Angstrom and D-e = 118.67 kcal/mol; the corresponding values of the AlC- species are r(e)= 1.8945 Angstrom and D-e = 77.16 kcal/mol.