The ditopic molecule 3-(1,3,5-trimethyl-4-1H-pyrazolyl)acetylacetone (HacacMePz) combines an acetylacetone group suitable for deprotonation and O,O′ coordination to a Pearson hard cation with a softer N-donor site. Both binding modes were employed individually: the pyrazolyl moiety was coordinated to ZnII, HgII, and AgI, and with trivalent iron the tris-chelating O,O′ complex [Fe(acacMePz)3] was isolated. The CuII derivative shows shorter O,O′ chelation and N coordination in the more distant Jahn–Teller sites and exists in two alternative crystal forms: namely, as a tetranuclear discrete complex and as a chain polymer. The different Pearson hardnesses of the coordination sites of acacMePz– allow for the design of well-ordered mixed-metal solids. Selective complexation to a hard and soft cations was achieved in coordination polymers combining hard FeIII and softer HgII or AgI. Even slight differences in Pearson hardness based on different oxidation states of the same cation imply sufficient selectivity, as shown by the successful synthesis of a mixed-valence CuII/CuI chain polymer. A synopsis of all structurally characterized compounds confirms that HacacMePz represents a bridging ligand with restricted conformational freedom. No full rotation about the single bond between the pyrazolyl and acetylacetone fragments occurs, and dihedral angles between these moieties are limited to values of 90 ± 17°.