An Acetylacetonate or a Pyrazole? Both! 3-(3,5-Dimethyl-pyrazol-4-yl)pentane-2,4-dione as a Ditopic Ligand

The alternative coordination sites of 3-(3,5-dimethyl-pyrazol-4-yl)pentane-2,4-dione (H(2)acacPz) differ with respect to Pearson hardness. The softer, heterocyclic moiety was used as N donor toward Zn(II) and Ag(I); it yielded a tetrahedral, neutral Zn complex in the former and a monocationic, linear bis(ligand) Ag complex in the latter case. After deprotonation with silver benzoate, the pyrazolyl ring may act as a monoanionic N,N'-bridge between neighboring cations in a hexanuclear Ag aggregate; in addition to ligand-supported Ag center dot center dot center dot Ag distances of ca. 3.2 angstrom, these aggregates feature ligand-unsupported argentophilic interactions of ca. 2.9 angstrom. With stronger bases and in the presence of oxophilic Mg cations, the harder hydroxyketone part of the H(2)acacPz ligand may be deprotonated to a chelating acetylacetonate. The resulting bis(ligand) Mg complex has been used as starting compound for a bimetallic derivative: the ditopic ligand allows coordinating cadmium acetate to its dangling N donor site, thus, bridging divalent Mg and Cd in a bimetallic three-dimensional coordination network of pts topology.