X-RAY CRYSTALLOGRAPHIC STUDY OF THE RUTHENIUM BLUE COMPLEXES [RU2CL3(TACN)(2)](PF6)(2)CENTER-DOT-4H(2)O, [RU2BR3(TACN)(2)](PF6)(2)CENTER-DOT-2H(2)O, AND [RU2I3(TACN)(2)](PF6)(2) - STERIC INTERACTIONS AND THE RU-RU BOND-LENGTH

X-ray crystal structures are reported for the following complexes: [Ru 2Cl3(tacn)(2)](PF6)(2) . 4H(2)O (tacn = 1,4,7-triazacyclononane), mono clinic P2(1)/n, Z = 4, a = 14.418(8) Angstrom, b = 11.577(3) Angstrom, c = 18.471(1) Angstrom, beta = 91.08(5)degrees, V = 3082 Angstrom(3), R (R(w)) = 0.039 (0.043) using 4067 unique data with I > 2.5 sigma(I) at 293 K; [Ru2Br3(tacn)(2)](PF6)(2) . 2H(2)O, monoclinic P2(1)/a, Z = 4, a = 13.638(4) Angstrom, b = 12.283(4) Angstrom, c = 18.679(6) Angs trom, beta = 109.19(2)degrees, V = 3069.5 Angstrom(3), R (R(w)) = 0.05 2 (0.054) using 3668 unique data with I > 2.5 sigma(I) at 293 K; [Ru2I 3(tacn)(2)](PF6)(2), cubic P2(1)/3, Z = 3, a = 14.03(4) Angstrom, beta = 90.0 degrees, V = 2763.1(1) Angstrom(3), R (R(w)) = 0.022 (0.025) u sing 896 unique data with I > 2.5 sigma(I) at 293 K. All of the cation s have cofacial bioctahedral geometries, although [Ru2Cl3(tacn)(2)](PF 6)(2) . 4H(2)O, [Ru2Br3(tacn)(2)](PF6)(2) . 2H(2)O, and [Ru2I3(tacn)(2 )](PF6)(2) are not isomorphous. Average bond lengths and angles for th e cofacial bioctahedral cores, [N3Ru(mu-X)(3)RuN3](2+), are compared t o those for the analogous ammine complexes [Ru2Cl3(NH3)(6)](BPh(1))(2) and [Ru2Br3(NH3)(6)](ZnBr4). The Ru-Ru distances in the tacn complexe s are longer than those in the equivalent ammine complexes, probably a s a result of steric interactions.