Variable coordination of tris(2-pyridyl)phosphine and its oxide toward M(hfac): a metal-specifiable switching between the formation of mono- and bis-scorpionate complexes.

An unexpected substitution of the anionic chelating ligands at the M centre by a neutral tripodal ligand has been observed in the reaction of Mn, Co, Ni and Cu hexafluoroacetylacetonates (hfac) with tris(2-pyridyl)phosphine (PyP) or its oxide (PyP = O). The nature of the metal ion in M(hfac) and the M/L ratio determine the degree of substitution of hfac-anions (partial vs. total) and therefore, the structure of the complex formed (scorpionate vs. bis-scorpionate ones, respectively). Hence, the reaction of the ligands with [Cu(hfac)(HO)] in an equimolar ratio affords scorpionate [Cu(N,N',N''-PyP = X)(O,O'-hfac)(O-hfac)], wherein one hfac-ligand chelates metal, while the other hfac acts as an O-monodentate one. Using the two equivalents of PyP in this reaction leads to [Cu(N,N',N''-PyP)](hfac), which contains a bis-scorpionate cation [Cu(PyP)] and two noncoordinated hfac-anions. [Co(hfac)(HO)] and [Ni(hfac)(HO)], regardless of the M/L molar ratio, react with PyP = O to give cationic scorpionates [M(N,N',N''-PyP = O)(O,O'-hfac)(HO)](hfac), in which one hfac-anion is noncoordinated. In contrast, [Mn(hfac)(HO)], on interaction with PyP, results in the cationic complex [Mn(N,N',N''-PyP)][Mn(hfac)] bearing a bis-scorpionate cation [Mn(PyP)] and two [Mn(hfac)] counterions. The synthesized scorpionates have been characterized by X-ray diffractometry, cyclic voltammetry, SQUID magnetometry, FT-IR and UV-Vis techniques.