Synthesis, characterization and crystal structures of two polymorphs of the iodo-bridged ruthenium salt, μ-iodido-bis{η5-cyclopentadienyl-dicarbonyl-ruthenium(II)} tetrafluoroborate

The reaction of RpI (Rp = (η5-C5H5)Ru(CO)2) and AgBF4 in two different solvents, tetrahydrofuran and dichloromethane afforded two polymorphs of the iodo-bridged cationic complex [Rp2I]BF4. Polymorph I precipitates out of solution as yellow broad-shaped blocks while polymorph II crystallises out as thin-shaped blocks. While I crystallizes in the monoclinic P2/c space group with a = 12.0982(5) Å, b = 9.7923(4) Å, c = 15.5321(6) Å, β = 102.9880(10)°, polymorph (II) crystallizes in the monoclinic P21/c with a = 7.00560(10) Å, b = 14.1446(3) Å, c = 18.2226(3) Å, β = 96.2390(10)°. The IR spectra of the compound showed the presence of terminal carbonyl groups but the absence of bridging carbonyl groups. Thermal studies of the two polymorphs reveal very close melting points, 432.2 and 435.2 K for I and II respectively. The enthalpies associated with their melting points are +15.1 kJ mol−1 and +21.9 kJ mol−1 for polymorphs I and II, respectively. ESI-mass spectroscopy showed the presence of a number of statistically possible combinations of the cationic species. The two polymorphs have also been characterized using DSC, IR and NMR.