Sulfate as a ligand in ruthenium(II) and (III) ammines

Abstract

The trans-[RuSO4(NH3)4(L)]Cl complexes, (L = nicotinamide (nia), L-histidine (L-hist), 4-picoline (4-pic), 4-chloropyridine (4-Clpy), isonicotinamide (isn), pyrazine (pyz), 4-aminopyridine (4-NH2py), 4-cyanopyridine (4-CNpy), pyridine (py), imidazole (Him), and water (H2O)), were characterized by elemental analysis cyclic voltammetry, UV-vis, IR, and electron paramagnetic resonance spectroscopies. From the four ν (SO42–) observed only ν3 and ν4 split in two bands each for the sulfate unidentate coordination. The values of Δ/ξ parameters, extracted from g values, allow us to write the following order of increasing π-donation ability: pyz < (py, 4-CNpy, 4-Clpy. 4-pic, isn, nia) < Him < L-hist < 4-NH2py. The intense absorption in the 317-347 nm (ε ~ 2.3-5.6 × 103 M-1 cm-1) region was tentatively assigned to sulfate-to-metal charge transfer (LMCT) and the absorption in the range of 230-270 nm (ε ~ 2 - 6 × 103 M-1 cm-1) assigned to an internal (IL) π-π* transition in the heterocyclic ligands. The rate for the sulfate aquation in trans-[RuSO4(NH3)4L]0 complexes was evaluated through chronopotentiometric measurements and are in the 2.6 s-1 (chloropyridine) to 20 s-1 (pyrazine) range. The SO42– is aquated in trans-[RuIIISO4(NH3)4(4-pic)]Cl at the specific rate constant of (1.4 ± 0.4) × 10-5 s-1, which is very much slower than in trans-[RuIISO4(NH3)4(4-pic)] (5.4 s-1). The X-ray crystal structure data show that the Ru-Cl (2.3444(9) Å) and Ru-NH3 (2.100(2) Å) mean distances in trans-[RuCl(NH3)4(4-pic)]Cl2·H2O are similar to the ones observed in other tetraammineruthenium(III) complexes.Key words: ruthenium, sulfate, ammines.