[RU6C(CO)17] - A CASE OF ORGANOMETALLIC CRYSTAL POLYMORPHISM

The molecular structure of the prototypical hexaruthenium carbidocarbonyl cluster [Ru6C(CO)17] has been redetermined on crystals obtained by two different routes. Form I is monoclinic, space group P2(1)/n, a = 9.19(1), b = 32.043(9), c = 9.598(4) angstrom, beta = 111.93(3)-degrees, Z = 4, R = 0.076, R' = 0.079, for 2764 [l(o) > 2-sigma(l(o))] out of 4755 absorption-corrected reflections; form II is also monoclinic, space group P2/a, a = 17.668(2), b = 9.335(1), c = 24.057(7) angstrom, beta = 97.96(2)-degrees, Z = 6, R = 0.023, R' = 0.028, for 7656 [l(o) > 2-sigma(l(o))] out of 10 288 absorption-corrected reflections. The structural analysis shows that the complex possesses three different molecular structures in the solid state (I, IIA and IIB), differing essentially in the rotameric conformation of the tricarbonyl units above and below the equatorial plane containing bridging and semibridging ligands. The conformation is staggered in form I, while II contains two nearly eclipsed conformers. The relationship between the structure of the three isomers and of their crystals has been investigated.