Rational syntheses, structure, and properties of the first bismuth(II) carboxylate

Bismuth(II) trifluoroacetate (1), the first inorganic salt of bismuth in oxidation state +2, has been obtained in its pure, unstabilized form. Several synthetic routes suggested for the isolation of the new compound include (i) mild oxidation of elemental bismuth with some metal trifluoroacetates, e.g., Ag(I) and Hg(II); (ii) mild reduction of bismuth(III) trifluoroacetate with metals, such as Zn; (iii) comproportionation reaction between Bi and Bi(O(2)CCF(3))(3). The last approach gives the title compound 1 in quantitative yield as a sole product. Bismuth(II) trifluoroacetate has been characterized by NMR, IR, and UV-vis spectroscopy as well as by single-crystal X-ray diffraction. Crystallographic study reveals the dinuclear paddle-wheel structure for diamagnetic molecules Bi(2)(O(2)CCF(3))(4). The Bi-Bi bond distances in dimetal units of 1 are averaged to 2.9462(3) A, and there are no axial intermolecular contacts between these units in the solid state. The compound is volatile and exists in vapor phase up to 220 degrees C when it disproportionates back to Bi(0) and Bi(III) species, i.e., by the reverse of the synthetic route iii. In contrast, the solution chemistry is quite limited: the bismuth(II) trifluoroacetate is decomposed by the majority of common solvents, but it can be stabilized by aromatic systems. The dibismuth unit has been shown to be preserved in the latter solvents and can be crystallized out in a form of pi-adducts with arenes. Two such adducts, Bi(2)(O(2)CCF(3))(4).(C(6)H(5)Me) (2) and Bi(2)(O(2)CCF(3))(4).(1,4-C(6)H(4)Me(2))(2) (3), have been isolated as single crystals and characterized by X-ray diffraction techniques. In the structures of both 2 and 3, the bismuth(II) centers exhibit weak eta(6)-coordination to aromatic rings.