The Mulliken charges of the 12-metallacrown-3 complex [(C6H6)Ru(C5H3NO2)](3) were determined by a single point analysis at the HF level. For comparison, a Mulliken population analysis was carried out for the organic analogue 12-crown-3. The partial negative charges on the O-donor atoms of the metallamacrocycle were found to be larger than those on the O-donor atoms of 12-crown-3. The 12-metallacrown-3 complex [(cymene)Ru(C5H2ClNO2)](3) with chloro-substituents in position 5 of the pyridonate ligand was synthesized to determine the effect of electron withdrawing groups on the structure and the host-guest properties of the receptor. The chloro-substituents were found to have only a small influence on the structures, but they reduce the binding affinity for LiCl and NaCl by approximately 2 orders of magnitude.