Strong metal-to-ligand π-backbonding weakens the NN bond in 2-pyridinealdazine coordinated to tetraammine-ruthenium(II)

Abstract A new mononuclear Ru(II) complex of formula [Ru(NH 3 ) 4 (2-PCA)](PF 6 ) 2 , ( 1 ), with 2-PCA = 2-pyridinealdazine, has been synthesized and characterized by spectroscopic and electrochemical techniques. The complete structure of ( 1 ) was determined by X-ray diffraction. A strong π-backbonding effect d π (Ru) → π *(2-PCA) is disclosed in ( 1 ) by the high value of the Ru III /Ru II redox potential and the short Ru-N(imine) bond length, which leads to a weakened N N bond in coordinated 2-PCA compared to that of the free ligand and thus to an enhanced reactivity in acidic media. In effect, the product of the reaction of excess Ru with 2-PCA is not the dinuclear species bridged by 2-PCA, but the already known 2-iminopyridine complex of tetraammineruthenium(II). DFT and TD-DFT calculations of ( 1 ) were consistent with experimental results and allowed the complete assignment of its UV–Visible bands.