Synthetic routes to the octahalogenoditechnetates [Tc2 X 8]2?,3? (X = Cl, Br), and normal coordinate analyses on the metal-metal multiple bond systems [Re2 X 8]2? (X = F, Cl, Br, I), [Tc2 X 8]2?,3? (X = Cl, Br)(D4h ), and [Os2 X 8]2? (X = Cl, Br, I)(D4d )

Abstract

Quick, facile, and high-yield syntheses of di- and trinegative octachloro- and octabromoditechnetates by reduction of tetrahalogenooxotechnetates(V) or hexahalogenotechnetates(IV) with tetrahydridoborate in organic solvents are described. The compounds are easily convertible by ligand exchange reactions. Under exclusion of air the octahaloditechnetates(lII, III) are stable in organic solvents and unstable in conc. hydrohalic acids, in contrast to the octahaloditechnetates(II, III) being stable in conc. hydrohalic acids and unstable in organic solvents. Based on a general valence force field, normal coordinate analyses on the metal-metal multiple bond systems [Re2X8]2− (X = F, Cl, Br, I), [Tc2X8]2−,3− (X = Cl, Br)(D4h), including35Cl and37Cl labeled species, and [Os2X8]2− (X = Cl, Br, I)(D4d) have been performed. With sets of seven or ten force constants very good agreement between observed and calculated frequencies has been achieved. The metal-metal valence force constants range from 2.7 to 4.9 mdyne/A, the strength of the bonds depending on the bond order and the masses of the ligands. The bromo compounds in particular exhibit a strong vibrational coupling of the metal-metal stretching mode with the symmetric breathing vibration of the ligand sphere.