HEXAKIS(PYRIDINE)RUTHENIUM(II) TETRAFLUOROBORATE - MOLECULAR-STRUCTURE AND SPECTROSCOPIC PROPERTIES

Hexakis(pyridine)ruthenium (ll) tetrafluoroborate has been prepared by extended reflux of a methanol solution of [RuHS3(PPh33)2] [BF4] (S = CH3OH or H2O) and pyridine. Spectroscopic and electrochemical characterizations of this complex are reported. The observed 1H and 13C chemical shift values are discussed in terms of previous reports concerning NMR properties of complexed pyridine. A comparison of ruthenium-nitrogen force constants for pyridine and ammine ligands is based upon far-infrared vibrational data. Rationalization of the larger force constant evident in the case of pyridine is presented in terms of both σ and π interactions in the case of this unsaturated heterocyclic ligand. Assignment of a metal-to-ligand charge transfer band at 341 nm, in conjunction with electrochemical reduction potentials, provides data for a general qualitative molecular orbital scheme for a series of [Ru(py)„(NH3)6.„]2+ complexes (n = 6, 2, 1, 0). The electrochemistry of [Ru(py)6]2+ is virtually indistinguishable from that of the [Ru(bpy)3]2+ ion. Crystals of [Ru(py)e] [BF4]2 were found to be orthorhombic, space group Pna21, with a unit cell of dimensions a = 16.933 (27), b= 10.431 (7), and c = 18.197 (14) Å. The observed density is 1.54(2) g cm-3 while a density of 1.536 g cm-3 is calculated for Z = 4. The structure was refined to R -0.063 and Rw = 0.075 using 2142 reflections with I < 3σ(I).The Ru(py)62+ cation exhibits Ru-N bond lengths in the range from 2.10 (1) to 2.14 (1) Å with an average length of 2.12 Å for the six metal-ligand bonds. The rotational orientation of the six planar ligands is such that the isolated cation belongs to the C1 point group, i.e., there is clearly no symmetry operation present other than the identityitself. © 1979, American Chemical Society. All rights reserved.