Abstract
An unexpected substitution of the anionic chelating ligands at the MII centre by a neutral tripodal ligand has been observed in the reaction of MnII, CoII, NiII and CuII hexafluoroacetylacetonates (hfac) with tris(2-pyridyl)phosphine (Py3P) or its oxide (Py3P = O). The nature of the metal ion in M(hfac)2 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)2(H2O)2] in an equimolar ratio affords scorpionate [Cu(N,N',N''-Py3P = 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 Py3P in this reaction leads to [Cu(N,N',N''-Py3P)2](hfac)2, which contains a bis-scorpionate cation [Cu(Py3P)2]2+ and two noncoordinated hfac-anions. [Co(hfac)2(H2O)2] and [Ni(hfac)2(H2O)2], regardless of the M/L molar ratio, react with Py3P = O to give cationic scorpionates [M(N,N',N''-Py3P = O)(O,O'-hfac)(H2O)](hfac), in which one hfac-anion is noncoordinated. In contrast, [Mn(hfac)2(H2O)2], on interaction with Py3P, results in the cationic complex [Mn(N,N',N''-Py3P)2][Mn(hfac)3]2 bearing a bis-scorpionate cation [Mn(Py3P)2]2+ and two [Mn(hfac)3]2- counterions. The synthesized scorpionates have been characterized by X-ray diffractometry, cyclic voltammetry, SQUID magnetometry, FT-IR and UV-Vis techniques.
Highlights
During the past decades, pyridylphosphines and their chalcogenides have attracted increasing attention in coordination chemistry, catalysis and material science.[1,2,3] The combination of “soft” (P-atom) and “hard” (N-atoms) donor sites in pyridylphosphines makes them very important and versatile ligands for the design of unique catalysts,[4] luminescent materials[5] and prospective drugs.[6]
In the crystal of 8, there are two stereochemically different [Mn(hfac)3]− anions (Δ- and Λ-isomers), in which the MnII coordinates three hfac-anions to form a MnO6 twisted prism. These results suggest that the outcome of the reaction between M(hfac)[2] and Py3P or Py3P = O is strongly influenced by the nature of MII ions and, in the case of Cu(hfac)[2], by the M/L ratio specified
Complexes 3–8 have been characterized by X-ray diffraction analysis, SQUID magnetometry and ATR-IR spectroscopy, while their redox behaviour has been studied using cyclic voltammetry (CV)
Summary
Tris(2-pyridyl)phosphine, owing to its tripodal structure and heminal disposition of the N atoms towards the P atom, exhibits numerous coordination patterns, e.g. N-15 and P-monodentate,[14,16] P,N-bridging,[17] N,N′-chelating,[18,19] N,P,N′pincer,[20] N,N′/P-bridging[21] and N,N′,N′′-tripodal[9,22,23,24] ones. A while ago, N,N′,N′′-/P-coordination of substituted tris(2-pyridyl) phosphine was found in the dinuclear complex [(MeCN)3Cu. Tris(2-pyridyl)phosphine chalcogenides, Py3P = X (X = O, S or Se), are scarce, the latter are important ligands. In the course of this study, we have observed an unexpected replacement of the anionic chelating ligand at the metal center by the neutral tripodal ligand. The degree of such substitution ( partial vs complete) and, the structure of the resulting complexes (scorpionate vs bis-scorpionate) depend on the nature of the metal ion in M(hfac)[2] and, to a lesser extent, on a metal-to-ligand ratio
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