This paper reviews the results of electronic structure studies and investigations of the nature of chemical bonding and properties of binary d-metal carbides in the crystalline and molecular states. X-ray emission and X-ray photoelectron spectroscopy as well as quantum-chemical data are analyzed, and variations of the electronic properties and interatomic interactions are discussed for carbides of high-melting metals doped on the metal sublattice and a series of their reciprocal solid solutions: NbC–TaC, TiC–VC0.87, TiC–NbC, and NbC–MoC0.67 over a wide range of compositions. Prospects are discussed for application of quantum-chemical methods to structure and property modeling and forecasting for a new class of molecular clusters — binary metallocarbohedrenes M8−nMn′C12 and related metal–carbon nanoparticles of “mixed” composition.