PENTAAMMINERUTHENIUM(III) PHENYLCYANAMIDE COMPLEXES - CRYSTAL-STRUCTURE DETERMINATION AND THE DEPENDENCE OF B1 STAR[-B1 LMCT OSCILLATOR STRENGTH ON THE NATURE OF THE PHENYLCYANAMIDE LIGAND

Seventeen pentaammineruthenium(III) complexes of phenylcyanamide anion ligands have been prepared and characterized by UV-vis spectroscopy and cyclic voltammetry. The complex [(NH3)5Ru(2,3-Cl2pcyd)] [SO4]·C2H5OH was characterized by X-ray diffraction. The anionic cyanamide group of the ligand (2,3-dichlorophenyl)cyanamide is shown to be nearly coplanar with the phenyl group due to strong π coupling and coordinated to ruthenium(III) via the nitrile nitrogen. A significant degree of π bonding between the cyanamide group and ruthenium(III) is indicated by the nearly linear bond angle (171.4 (10)°) and short bond length (1.980 (12) Å). Crystal data are space group P21/n with a = 6.267 (4) Å,b = 7.5227 (7) Å, c = 40.0978 (21) Å, β = 90.04 (1)°, V = 1968.74 (24) Å3, and Z = 4. The structure was refined by using 1763 Cu Kα reflections with I > 2.5σ(I) to an R factor of 0.068. A linear correlation was found between the b1* ← b1 ligand to metal charge-transfer energy and the difference between ligand, L(0/−), and metal Ru(III/II), reduction couples, indicating the complexes have similar properties with the only variable being the nature of the cyanamide-ruthenium interaction. The oscillator strength of the b1* ← b1 transition was found to decrease with increasing energy of the transition for the series of complexes studied. Using Mulliken's derivation of oscillator strength dependence on donor and acceptor overlap, we suggest that the trend in oscillator strength can be largely rationalized in terms of the π basicity of the phenylcyanamide ligand. © 1990, American Chemical Society. All rights reserved.