The synthesis of an aqua trans-diphosphine complex of ruthenium: crystal structure of trans-[Ru(H₂O)(PEt₃) ₂(trpy)](ClO₄)₂· 3H₂O

The complexes cis- and _trans-[Ru(Cl)₂(PEt₃)- (trpy)], trans-[Ru(Cl)(PEt₃)₂(trpy)](Cl) and [Ru- (L)(PEt₃)₂(trpy)](ClO₄)x (trpy = 2,2′,2′'-terpyridine; L = NO₂, NO, OH₂; x = 1-3) were prepared. A novel synthetic strategy was employed to form the aqua trans-diphosphine complex because of the difficulty of forming it via a direct pathway. Characterization by electronic spectroscopy, electrochemistry and elemental analysis was conducted. The species [Ru(H₂O)(PEt₃)₂(trpy)](ClO₄)₂·3H₂O was further characterized by an X-ray structural analysis and is the first aqua trans-diphosphine complex of ruthenium to be synthesized. The complex [Ru- (H₂O)(PEt₃)₂(trpy)](ClO₄)₂·3H₂O crystallized in the centrosymmetric monoclinic space group P2₁/c with a = 9.886(5), b = 19.289(7), c = 20.255-(6) Å, β = 92.88(3)° and Z = 4. Diffraction data were collected on a Syntex P2₁ automated diffractometer and the structure refined to R_F= 8.8% for all 3407 reflections (R_F = 7.5% for those 2771 data with I> 3σ(I)). The structure contains a disordered PEt₃ ligand, highly librating ClO₄^- ions and (possibly) a less than unit occupancy for certain H₂O molecules of solvation. The [Ru(H₂O)(PEt₃)₂(trpy)]²⁺ cation has the trpy ligand in mer configuration and mutually trans PEt₃ ligands. Metal-ligand distances are RuN = 2.091(9), 1.952(9), 2.087(8) Å; Ru PEt₃ = 2.405(3), 2.411(4) Å; RuH₂O = 2.218(4) Å.