CRYSTAL-STRUCTURES AND REVERSIBLE THERMAL-ISOMERIZATION OF 3 GEOMETRICAL-ISOMERS OF OBIS(2-ETHYL-8-QUINOLINOLATO)NITROSYLRUTHENIUM(II)

Crystal structures of the three geometrical isomers (1,2 and 3) of [Ru Cl(2eqn)(2)NO] (H2eqn = 2-ethyl-8-quinolinol) have been determined by X-ray diffraction. The Cl atom is cis to the NO group in 1 and 2, and is trans to the NO group in 3. The N and O atoms of the two quinolinol ato ligands for 1, 2 and 3 are in trans(N,N) and cis(O,O), in cis(N,N) and cis(O,O), and in trans(N,N) and trans(O,O) configurations, respec tively. Crystallographic data for 1: triclinic, a = 10.140(4), b = 13. 498(5), c = 7.902(3) Angstrom, alpha = 94.08(3), beta = 104.19(2), gam ma = 73.35(3)degrees, V = 1006.8(6) Angstrom(3), Z = 2, space group <P (1)over bar>; for 2: monoclinic, a = 14.730(2), b = 10.028(2), c = 13. 761(4) Angstrom, beta = 92.65(2)degrees, V = 2030.5(7) Angstrom(3), Z = 4, space group P2,/a; for 3: monoclinic, a = 14.830(4), b = 8.700(2) , c = 16.711(4) Angstrom, beta = 110.40(3)degrees, V = 2021,0(9) Angst rom(3), Z = 4, space group Cc. The structures were solved by the heavy -atom method and were refined by full-matrix (1 and 2) and block-diago nal (3) least-squares procedures to R = 0.0378 (1), 0.0320 (2) and 0.0 397 (3) for 5207 (1), 4032 (2) and 1675 (3) reflections with I greater than or equal to 3 sigma(I). The variable-temperature H-1 NMR spectra in dimethyl sulfoxide-d(6) revealed the steric hindrance due to the e thyl group of the quinolinolato ligands, reflecting the results of the crystal structure analysis. At high temperature (373-413 K), the reve rsible thermal isomerization reaction among the three isomers was obse rved in degassed dimethyl sulfoxide (DMSO). The mole ratio of 1, 2 and 3 was 19:4:1 at 413 K and did not depend on the starting species. Kin etic analysis revealed that the reaction was reversible between any tw o isomers and the isomerization between 1 and 3 proceeded by a mechani sm distinct from the others.