The magnetic properties of a series of organometallic complexes [LnCp3]− and Ln(CNT)2, where Cp = cyclopentadienyl and CNT = cyclononatetraenyl, of the lanthanide ions in the 2+ oxidation state, are theoretically studied in terms of the electronic structure obtained via multiconfigurational wave function-based methods. Calculations are performed for two groups of ion complexes selected based on their preferred electronic configuration 4fn+1 or 4fn5d1 (n is the number of f electrons in the 3+ ion). All the properties are discussed in terms of the electron density distribution of the ground state and ligand field effects. This analysis allows giving some molecular design strategies relevant to exploit the magnetic properties in applications like Single-Molecule Magnets (SMMs) for lanthanide ions in the 2+ oxidation state.