Three FeIII-MI heterometallic complexes with anions of cyclobutane-1,1-dicarboxylic acid (H2cbdc) dianions [MIFe(cbdc)2(H2O)2]n (MI = Na (1), Rb (2) or Cs (3)) were obtained, with the compounds being two-dimensional (2D)-coordination polymers built of bischelate moieties {Fe(cbdc)2(H2O)2}− bound with alkali metal ions. In 1, the two coordinated water molecules are in the cis-position, while in 2 and 3 they are in the trans-position. The DC magnetic data and ab initio calculations demonstrate that Fe3+ ions in 1 possess a negative D value, while those in 2 and 3 have a positive D value. The easy-axis anisotropy found for 1 is a rare example for Fe3+ ions. A topological analysis of the compounds synthesized and a series of known mononuclear octahedrally coordinated Fe3+ complexes (from Cambridge Structural Database) that are interconnected into a crystal structure by alkali metal cations in a way similar to complexes 1–3 was carried out.