The synthesis of a series of Ru^II complexes incorporating thiacrown ligands ([12]ane-S₄, [14]ane-S₄, [16]ane-S₄), as well as 2,2′-bipyridine (bpy) or pyridine, is reported. Structural studies on these complexes have been carried out using a variety of techniques. Detailed ¹H NMR spectroscopic studies on the previously reported [Ru([12]ane-S₄)(bpy)]²⁺ (1) reveal that—contrary to earlier reports—the observed fluxional ¹H NMR behavior is not due to chemical exchange involving cleavage of the bpy RuN bond but is, in fact, due to lone-pair inversion of coordinated macrocyclic sulfur donor atoms. This phenomenon is also observed for the [14]ane-S₄ and [16]ane-S₄ analogues of 1. For the first time, using a combination of X-ray crystallography, more detailed ¹H NMR experiments, and computational methods, an in-depth study on the energetics and dynamics of invertomer formation and conversion for macrocyclic coordination complexes has been carried out. These studies reveal that the steric constraints of assembling each sulfur macrocycle and bpy ligand around the octahedral Ru^II center lead to close intramolecular contacts. These contacts are largely dependent on the orientation of the electron lone pairs of equatorial sulfur donor atoms and correlate with the comparative stability of the different invertomeric forms. Thus, the conformational preferences of the three macrocyles in [Ru([n]ane-S₄)(bpy)]²⁺ complexes are determined by steric rather than electronic effects.

Mittlerweile steht fest, dass NO trotz seiner hohen Toxizität in Säugetieren als Botenstoff fungiert. Da NO⁺ und CO isoelektronisch sind, sollte es nicht überraschen, dass CO eine gleichartige Funktion zukommt. Der Mensch produziert selbst etwa 3–6 cm³ CO pro Tag, wobei bestimmte Entzündungszustände sowie pathologische Bedingungen, die mit der Hämolyse der roten Blutkörperchen verbunden sind, die produzierte Menge merklich erhöhen. In den letzten zehn Jahren ist das Interesse an den biologischen Wirkungen von CO stark gestiegen und inzwischen gilt es in der medizinischen Literatur als gesichert, dass CO in Säugetieren eine wesentliche Rolle als Signalmolekül spielt. Dabei ist der Hauptwirkungsbereich das Herz-Kreislauf-System, z. B. bei der Unterdrückung von Abstoßungsreaktionen bei Organtransplantationen und beim Schutz des Gewebes vor ischämischer Schädigung und Apoptose. Vor kurzem wurde gezeigt, dass Carbonylmetallkomplexe im Organismus CO freisetzen und ähnliche biologische Wirkungen wie CO selbst zeigen können. Dies eröffnet die Möglichkeit, pharmazeutisch wichtige Carbonylmetallkomplexe zu entwickeln.

It is now established that NO is a messenger molecule in mammals despite its high toxicity. As NO⁺ and CO are isoelectronic, it should not be unexpected that CO could also have a role as a messenger. CO is produced naturally in humans at a rate of between 3 and 6 cm³ per day, and this rate is increased markedly by certain inflammatory states and pathological conditions associated with red blood cell hemolysis. Over the last 10 years, the interest in the biological effects of CO has greatly increased, and it is now established in the medical literature that CO does have a major role as a signaling molecule in mammals. It is particularly active within the cardiovascular system, for example, in suppressing organ graft rejection and protecting tissues from ischemic injury and apoptosis. Recently it has been shown that metal carbonyls can also function as CO-releasing molecules and provide similar biological activities. This opens the possibility to develop pharmaceutically important metal carbonyls.