Temperature-Induced Solid-State Valence Tautomeric Interconversion in Two Cobalt−Schiff Base Diquinone Complexes
2003; American Chemical Society; Volume: 42; Issue: 20 Linguagem: Inglês
10.1021/ic034210z
ISSN1520-510X
AutoresOlivier Cador, F. Chabre, Andrea Dei, Claudio Sangregorio, Joris van Slageren, Maria G. F. Vaz,
Tópico(s)Lanthanide and Transition Metal Complexes
ResumoThe mixed-ligand complexes [Co(III)(tpy)(Cat-N-SQ)]Y and [Ni(II)(tpy)(Cat-N-BQ)]PF(6) (tpy = 2,2':6',2' '-terpyridine; Cat-N-BQ, Cat-N-SQ = mononegative and radical dinegative Schiff base diquinone ligand; Y = PF(6), BPh(4)) were prepared. Structural and spectroscopic data support the different charge distribution of the two compounds. The temperature-dependent electronic and spectral properties of solutions containing the [Co(III)(tpy)(Cat-N-SQ)](+) suggest that this compound undergoes a thermally driven valence tautomeric interconversion to [Co(II)(tpy)(Cat-N-BQ)](+) complex, the metal ion being in high-spin configuration. The comparison of the electrochemical properties of the cobalt and nickel derivatives supports the observed behavior. The same interconversion process was found to occur also in the solid state with a significant higher T(c) value than in solution. It was found that the previously reported [Co(III)(Cat-N-BQ)(Cat-N-SQ)] shows a similar behavior. The large difference between the interconversion T(c) in the solid state and in solution is suggested to come from the entropy changes associated with the modifications of vibronic interactions.
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