Effect of the Additional Carboxyl Group in Half‐Sandwich Organometallic 2,4‐Dipicolinate Complexes on Solution Speciation and Structure

Solution speciation of Rh(η5-C5Me5), Ru(η6-p-cymene) and Ru(η6-toluene) complexes of 2,4-pyridinedicarboxylic acid (2,4-dipicH2) was studied and compared to that of 2-picolinic acid (picH) in addition to their reactivity towards chloride and bromide ions, 1-methylimidazole and guanosine. Structures of [Rh(η5-C5Me5)(2,4-dipicH)Cl] ⋅ 3H2O (1), 2[Ru(η6-toluene)(2,4-dipicH)Cl] ⋅ 3H2O (2) and [Ru(η6-toluene)(2,4-dipic)]3 ⋅ 7H2O (3) were analyzed by X-ray diffraction. 1 and 2 show typical piano stool geometry, while 3 is a triangular complex stabilized via the monodentate coordination of the second carboxylate group to the neighboring Ru(II) center. High stability [M(arene)L(H2O/Cl)] species predominate at pH 7.4. 2,4-Dipic forms more stable complexes with Ru(η6-arene) than pic, with this difference being minor in the case of the Rh(η5-C5Me5) complexes. A lower affinity of 2,4-dipic complexes to halide ions was found compared to the corresponding pic complexes due to the additional COO− moiety.