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

The trans-[RuS[O.sub.4][(N[H.sub.3]).sub.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-N[H.sub.2]py), 4-cyanopyridine (4-CNpy), pyridine (py), imidazole (Him), and water ([H.sub.2]O)), were characterized by elemental analysis cyclic voltammetry, UV-vis, IR, and electron paramagnetic resonance spectroscopies. From the four v (S[O.sup.2-.sub. 4]) observed only [v.sub.3] and [v.sub.4] split in two bands each for the sulfate unidentate coordination. The values of [DELTA]/[xi] parameters, extracted from g values, allow us to write the following order of increasing [pi]-donation ability: pyz < (py, 4-CNpy, 4-Clpy. 4-pic, isn, nia) < Him < L-hist < 4-N[H.sub.2]py. The intense absorption in the 317-347 nm ([epsilon] ~ 2.3-5.6 x [10.sup.3] [M.sup.-1] [cm.sup.-1]) region was tentatively assigned to sulfate-to-metal charge transfer (LMCT) and the absorption in the range of 230-270 nm ([epsilon] ~ 2 - 6 x [10.sup.3] [M.sup.-1] [cm.sup.-]) assigned to an internal (IL) [pi]-[[pi].sup.*] transition in the heterocyclic ligands. The rate for the sulfate aquation in trans-[[RuS[O.sub.4][(N[H.sub.3]).sub.4]L].sup.0] complexes was evaluated through chronopotentiometric measurements and are in the 2.6 [s.sup.-1] (chloropyridine) to 20 [s.sup.-1] (pyrazine) range. The S[O.sup.2-.sub.4] is aquated in trans-[[Ru.sup.III]S[O.sub.4][(N [H.sub.3]).sub.4](4-pic)]Cl at the specific rate constant of (1.4 [+ or -] 0.4) x [10.sup.-5] [s.sup.-1], which is very much slower than in trans-[[Ru.sup.II]S[O.sub.4][(N[H.sub.3]).sub.4](4-pic)] (5.4 [s.sup.-1]). The X-ray crystal structure data show that the Ru--Cl (2.3444(9) [Angstrom]) and Ru--N[H.sub.3] (2.100(2) [Angstrom]) mean distances in trans-[RuCl[(N[H.sub.3]).sub.4](4-pic)][Cl.sub.2]* [H.sub.2]O are similar to the ones observed in other tetraammineruthenium(III) complexes. Key words: ruthenium, sulfate, ammines.