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

Solution speciation of Rh(eta(5)-C5Me5), Ru(eta(6)-p-cymene) and Ru(eta(6)-toluene) complexes of 2,4-pyridinedicarboxylic acid (2,4-dipicH(2)) 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(eta(5)-C5Me5)(2,4-dipicH)Cl] 3H(2)O (1), 2[Ru(eta(6)-toluene)(2,4-dipicH)Cl] 3H(2)O (2) and [Ru(eta(6)-toluene)(2,4-dipic)](3) 7H(2)O (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(eta(6)-arene) than pic, with this difference being minor in the case of the Rh(eta(5)-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.

Automated summary

The solution speciation and reactivity of Rh(η5-C5Me5), Ru(η6-p-cymene), and Ru(η6-toluene) complexes with 2,4-pyridinedicarboxylic acid and 2-picolinic acid were studied and compared. X-ray diffraction analysis revealed structures of the complexes, showing different geometries and stability preferences. Complexes with 2,4-pyridinedicarboxylic acid were found to form more stable complexes compared to those with 2-picolinic acid, especially with Ru(η6-arene) complexes.