Preparation and structure of ruthenium tetrafluoride and a structural comparison with ruthenium trifluoride and ruthenium pentafluoride

A new synthetic approach has provided RuF4 as a deep pink polycrystalline solid from the interaction of AsF5 with RuF62- in anhydrous hydrogen fluoride solution. The structure has been determined from a combination of X-ray synchrotron and neutron powder diffraction data. The unit cell, refined from the neutron data, is monoclinic with a = 5.6068 (6) angstrom, b = 4.9456 (5) angstrom, c = 5.413 (2) angstrom, beta = 121.27 (2)-degrees, V = 128.3 angstrom3, Z = 2, and space group P2(1)/n. Each Ru atom has six near-neighbor F ligands on an octahedral framework, four in the same plane, each shared with another Ru atom, to form a puckered-sheet array. The fluorine-bridge bonding is very similar to that which occurs in RuF3 and in the tetrameric molecule (RuF5)4. The structure of RuF3 has been confirmed from X-ray powder data on samples prepared by pyrohydrolysis of SF3RuF6. The structure of RuF5 has been redetermined for this comparison and found to have a monoclinic unit cell with a = 5.4969 (6) angstrom, b = 9.946 (1) angstrom, c = 12.531 (2) angstrom, beta = 99.98 (1)-degrees, V = 674.7 (2) angstrom3, and Z = 8. The bridging interatomic distances in the three fluorides are as follows: RuF3, 1.982 (6) angstrom; RuF4, 2.00 (1) and 2.00 (3) angstrom; RuF5, 1.995 (1), 1.999 (1), 2.003 (1), and 2.007 (1) angstrom. The Ru-F-Ru angles are as follows: RuF3, 136 (1)-degrees; RuF4, 133 (1)-degrees; RuF5, 136.8 (1) and 140.8 (1)-degrees. The nonbridging F ligands in RuF4 are trans to one another, above and below the Ru in the sheet array. The puckered sheets are packed with the nonbridging F ligands nestling in holes, in the array of such ligands of the adjacent sheet. The RuF4 restrained nonbridging interatomic distance, Ru-F = 1.82 (2) angstrom, matches those in (RuF5)4 perpendicular to the eight-membered ring, where the interatomic distances are 1.817, 1.821, 1.823, and 1.824 angstrom (all occurring twice, with sigma = 0.001 angstrom). The equatorial nonbridging Ru-F distances are significantly shorter, with two each at 1.793, 1.795, 1.796, and 1.798 angstrom (all sigma = 0.001 angstrom).