The synthesis of a (carboxyamido)pyridinepyrazolate (H(5)bppap) dinucleating lipid is described. Bimetallic iron and cobalt complexes of Hsbppap ([M(2)(II)H(2)bppap](+)) showed structural differences in both their primary and secondary coordination spheres. The binding of small molecules into the preorganized ligand cavity is verified by the hydration of [Fe(2)(II)H(2)bppap](+) and [Co(2)(II)H(2)bppap](+), leading to the formation of complexes [{Co-II(OH)}-Co(II)H(3)bppap](+) and [{Fe-II(OH)}Fe(II)H(3)bppap](+), in which one of the metal centers has a terminal hydroxo ligand.