Pyridine ligands 264 Subject

Nomenclature is always a vexing subject the ligand (Fig. 1) has been known variously as 2,2, 2"-tripyridyl, 2,2, 2"-tripyridine, 2,6 -bis(2-pyridyl)-pyridine, and 2,2 6, 2"-terpyridine. The latter is the systematic name (262) and will be used throughout this article. All other compounds will be named systematically, according to lUPAC recommendation A-54. In this article, the abbreviations terpy, quaterpy, quinquepy, bipy, and phen will be used for the ligands in Figs. 1-5, respectively. Substituted derivatives will not be similarly described thus 4,4"-diethyl-4 -phenyl-2,2 6, 2"-terpyridine (Fig. 6) will be denoted 4,4"-Et2-4 -Phterpy. 

Previously reported work demonstrated that substituents can be used to tune the energies of excited states responsible for the emission spectra of certain group VIII metal complexes (1) and to modify significantly the absorption spectra of complexes displaying metal-to-ligand charge transfer (MLCT) bands (2). In this presentation, we summarize some recent attempts to use ligand substituents in our studies of transition metal complex photochemical reaction mechanisms. The particular subjects of interest are the metal ammine complexes M(NH3)5L where M is Rh(III) or Ru(II) and L is a meta- or para-substituted pyridine. 

---