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The electronic spectra of the hexafluoroosmate(V) and hexafluoroiridate(V) anions have been studied by diffuse reflectance between 4 and 50 kK. For OsFe-the relatively weak bands at 8. 00, 10.3, 10.8, 16.3, and 18.2 kK are ascribed to formally spin-forbidden transitions within the tsg3 manifold, while a much stronger band at 37.5 kK, with a shoulder at 41.7 kK, is thought to involve both 4Aig -4Tzg and 4A8g -* 4Tig, tzg3 -* t2g2eg excitations, as well as a Laporte-allowed charge-transfer transition. For IrFe-the absorption at about 4 kK and the well-marked peak at 6.5 kK are assigned to transitions within the spin-orbit split 3Tig(t2g4) ground state, and the weaker bands at 12.9 and 19.8 kK to spin-forbidden transitions within the t2g4 subshell. The weak band at 24.1 kK is attributed to the 3Tig(t2g4) -5Eg(t2g3eg) transition, and the fairly strong shoulder at about 33 kK to spin-allowed t2g4 -* Í2gseg excitations. It seems likely that the strong band with a maximum at 41.8 kK contains both charge-transfer and further t2g4 -»t2gseg transitions, The bands were fitted using the complete strongfield electrostatic and spin-orbit matrices for d3 and d4 systems, assuming C/B = 4.75 and 4.90 for Os(V) and Ir(V), respectively, yielding for OsFe-the parameters Dq = 3500 cm-1, B = 410 cm-1, and -3200 cm-1 and for IrF6the values Dq = 2850 cm-1, B -360 cm-1, and { = 3400 cm-1. The degree of covalency indicated is high for fluoride complexes and comparable with that found for quadrivalent MFe2-species of the 3d series.

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