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 Pd(II), Pt(II), and Rh(III)

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/H(2)O or MeOH/H(2)O (1:1 v/v) are shown, and the isolated solid compounds are characterized, where possible, by mass spectroscopy and (1)H- and (13)C-NMR spectroscopic measurements. Structural characterization of the 1:1 metal-to-ligand complexes [Pd(L(1))Cl](2)[Pd(2)Cl(6)], [Pt(L(1))Cl](BF(4)), [Rh(L(1))Cl(2)](PF(6)), and [Rh(L(3))Cl(2)](BF(4))·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 PtCl(2) in MeCN/H(2)O gave by serendipity the complex [Pt(L(3))(μ-1,3-MeCONH)PtCl(MeCN)](BF(4))(2)·H(2)O, in which two metal centers are bridged by an amidate ligand at a Pt1-Pt2 distance of 2.5798(3) Å 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.