Can Serendipity Still Hold Any Surprises in the Coordination Chemistry of Mixed-Donor Macrocyclic ligands? The Case Study of Pyridine-Containing 12-Membered Macrocycles and Platinum Group Metal ions PdII, PtII, and RhIII

This study investigates the coordination chemistry of the tetradentate pyridine-containing 12-membered macrocycles L-1-L-3 towards Platinum Group metal ions Pd-II, Pt-II, and Rh-III. The reactions between the chloride salts of these metal ions and the three ligands in MeCN/H2O or MeOH/H2O (1:1 v/v) are shown, and the isolated solid compounds are characterized, where possible, by mass spectroscopy and H-1- and C-13-NMR spectroscopic measurements. Structural characterization of the 1:1 metal-to-ligand complexes [Pd(L-1)Cl](2)[Pd2Cl6], [Pt(L-1)Cl](BF4), [Rh(L-1)Cl-2](PF6), and [Rh(L-3)Cl-2](BF4)center dot MeCN shows the coordinated macrocyclic ligands adopting a folded conformation, and occupying four coordination sites of a distorted square-based pyramidal and octahedral coordination environment for the Pd-II/Pt-II, and Rh-III complexes, respectively. The remaining coordination site(s) are occupied by chlorido ligands. The reaction of L-3 with PtCl2 in MeCN/H2O gave by serendipity the complex [Pt(L-3)(mu-1,3-MeCONH)PtCl(MeCN)](BF4)(2)center dot H2O, in which two metal centers are bridged by an amidate ligand at a Pt1-Pt2 distance of 2.5798(3) angstrom and feature one square-planar and one octahedral coordination environment. Density Functional Theory (DFT) calculations, which utilize the broken symmetry approach (DFT-BS), indicate a singlet d(8)-d(8) Pt-II-Pt-II ground-state nature for this compound, rather than the alleged d(9)-d(7) Pt-I-Pt-III mixed-valence character reported for related dinuclear Pt-complexes.

Automated summary

This study investigates the coordination chemistry of tetradentate pyridine-containing macrocycles towards Platinum Group metal ions Pd-II, Pt-II, and Rh-III, showing the structural characterization of the resulting complexes and the unique coordination environments of the ligands in different metal complexes. The study also utilizes Density Functional Theory calculations to determine the ground-state nature of a specific dinuclear Pt-II compound, providing insights into its electronic structure.