Hydrogen bonding of 18-crown-6 ether to ruthenium–ammine complexes at second sphere

The interaction with the second sphere of the complexes has been studied for a series of ruthenium–ammine complexes with 18-crown-6 (18C6) ether. Spectroscopic studies (UV, IR and NMR) gave the information about the nature of interaction and the interaction sites. Mononuclear ruthenium–ammine complexes form adducts through hydrogen bonding between the ammines coordinating to ruthenium and the ether oxygens of crown ethers. The position of the ammines interacting with the crown ether and the stoichiometry vary depending on the valence of central metal. The adduct formation perturbed the electronic state of the central metal ion and causes a modification of the properties of the complexes. The adduct formation through hydrogen bonding has been investigated focusing on the electrochemical properties of the complexes. Hydrogen bonding in the second sphere of the complex gave a prominent modification of electrochemical properties of the ruthenium–ammine complexes. Several factors were elucidated to influence on the modification of the electrochemical properties. The adduct formation with 18-crown-6 ether was also examined for a delocalized mixed-valence binuclear complex. The adduct formation stabilized the mixed-valence state of Ru(II)–Ru(III) and thereby the delocalized valence was trapped on each ruthenium atom. This was demonstrated by the isolation of the adducts.