Synthesis, structural, spectroscopic and electrochemical characterization of new ruthenium(II) tetramer complexes containing 1,4-bis(diphenylphosphine)butane and alterdentate ligands

In this work a series of {[RuCl2(dppb)](mu-4,4'-N-N)}(4) complexes were synthesized and characterized by elemental analysis, cyclic voltammetry and differential pulse voltammetry and UV-Vis and P-31{H-1} NMR spectroscopies; [(mu-4,4'-N-N = pyrazine (pz), 4,4'-bipyridine = (4,4'-bipy), 1,2-bis-trans-(4-pyridyl)ethane = (pyeta) and 1,2-bis-trans-(4-pyridyl)ethylene = (pyetil) as bridging alterdentate ligands (alterdentate ligands are molecules (or ions), with two equivalent ligating atoms or ligating sites that do not simultaneously bind to a metallic center [Zelewsky von A. in Stereochemistry of Coordination Compounds, Inorganic Chemistry, A Textbook Series; John Wiley & Sons, Inc.: New York, 1995: p. 451 [1]) and 1,4-bis(diphenylphosphino)butane = dppb]. Electrochemical experiments (cyclic voltammetry and differential pulse voltammetry) suggest that for longer ligands the interaction between two ruthenium atoms is weak and for short ligands like pyrazine the corresponding interaction is strong. The analysis of the X-ray structure of the {[RuCl2(dppb)](mu-4,4'-bipy)}(4) complex showed that the molecular squares obtained are stacked on top of each other along the alpha axis forming infinite columns and that the formation of central tunnels is prevented by the bulky character of the phenyl groups of the diphenylphosphine ligands.