Synthetic and Characterization Studies of the Complexes [Ru(NH₃)₃(2-Pyridyl; X = N, COH, CH, P), and the X-Ray Crystal Structure of [Ru(NH₃)₃(Py₃COH)]Br₂.H₂O

Abstract

Reaction of molar ratios of the ligands tri(2-pyridyl)amine (Py₃N), or tri(2-pyridyl)-methanol (Py₃COH) with [ Ru (NH₃)₃(OH₂)₃]²⁺ in aqueous solution produces the respective [ Ru (NH₃)₃(tripod)]²⁺ complexes. The analogous reaction with tri(2-pyridyl)methane (Py₃CH) yields [ Ru (NH₃)₂(OH₂)(Py₃CH)]²⁺, while the reaction with the tri(2-pyridyl ) phosphine ligand produces several (unidentified) species. The N- and CH-bridged ligands appear coordinated in a tripodal manner through the three pyridine-N atoms of the ligand , whereas tri(2- pyridyl )-methanol is coordinated in an N,N′,O mode through two pyridine-N atoms and the hydroxy group of the bridge. The X-ray crystal structure of [ Ru (NH₃)₃(Py₃COH)]Br₂.H₂O confirms this assignment: the complex of formula C₁₆H₂₄Br₂N₆O₂Ru is monoclinic, space group P2₁/c, with cell dimensions a 13.916(6), b 10.300(2), c 15.910(7)Ǻ, β 111.90(3)°, and Z 4. Full-matrix least-squares refinement on 2062 reflections with 1 ≥ 2.5σ(I) converged to final R 0.030 and Rw 0.035. The coordinated OH group in the complex has a pKa of 6.5(±0.1) at 25°C (aqueous 0.1 mol dm^-3 KNO₃).