Rhodium trifluoride, structure

In contrast with the difluorides, the distribution of trifluorides extends to the third series of the transition metals, where iridium and gold trifluorides are fully characterized. In the second series, trifluorides are known for the elements from niobium to rhodium, with the exception of technetium, and in the first series, from titanium to cobalt. All the trifluorides have been characterized structurally, with earlier reports based on X-ray powder-diffraction data, since the compounds were not prepared in single-crystal form until more recently, when high-temperature, crystal-growth techniques became available. 

The rhombohedral unit cells for rhodium and iridium trifluorides (44) contain two formula units. The structure can be related to the first structure type by considering anion positions, which here correspond to a hexagonal, close-packed array. There are no vacant anion sites and the cations occupy one-third of the octahedral holes. This leads to M—F—M angles of 132°, characteristic for filling adjacent, octahedral holes in a hexagonal close-packed lattice. Alternatively, the structure can be described as a linking of octahedra through all corners, but the octahedra are now tilted with respect to each other. 

The reverse selectivity has been described with diborane/boron trifluoride, sodium borohydride/dibo-rane, 2 sodium borohydride/trichlorotrispyridine-rhodium, lithium 9,9-di-/i-butyl-9-borabicyclo-[3.3.1]nonanate (for structure, see Table 4), sodium cyanoborohydride/boron trifluoride, and... 

The chemistry of secondary phosphine oxides, R2P(H)0 and their phosphi-nous acid tautomers, R2POH, has continued to attract attention. The study of the phosphinous acid tautomers has been aided by the development of stereoselective procedures for direct conversion of secondary phosphine oxides to the phosphinous acid-boranes (83). Treatment of the secondary phosphine oxide with either a base-borane complex or boron trifluoride and sodium borohyd-ride provides the phosphinous acid-borane with predominant inversion of configuration at phosphorus. The phosphinous acid tautomers are usually trapped as ligands in metal complexes and further examples of this behaviour have been noted. Discrimination of enantiomeric forms of chiral phosphinous acids, Ph(R)OH, coordinated to a chiral rhodium complex, has been studied by NMR. °° Palladium complexes of di(t-butyl)phosphinous acid have found application as homogeneous catalysts.A lithium salt of the tellurophos-phinite Ph2PTeH has been prepared and structurally characterised. ... 

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