• Biphasic Behaviour in the High-Spin -> Low-Spin Relaxation of [Fe(btpa)](PF6)2 in solution (btpa = N,N,N',N'-Tetrakis(2-pyridylmethyl)-6,6'-bis(aminomethyl)-2,2'-bipyridine)
    S. Schenker, P.C. Stein, J.A. Wolny, C. Brady, J.J. McGarvey, H. Toftlund and A. Hauser
    Inorganic Chemistry, 40 (1) (2001), p134-139
    DOI:10.1021/ic000656t | unige:3336 | Abstract | Article HTML | Article PDF
The light-induced high-spin → low-spin relaxation for the Fe(II) spin-crossover compounds [Fe(btpa)](PF6)2 and [Fe(b(bdpa))](PF6)2 in solution, where btpa is the potentially octadentate ligand N,N,N‘,N‘-tetrakis(2-pyridylmethyl)-6,6‘-bis(aminomethyl)-2,2‘-bipyridine and b(bdpa) is the analogous hexadentate ligand N,N‘-bis(benzyl)-N,N‘-bis(2-pyridylmethyl)-6,6‘-bis(aminomethyl)-2,2‘-bipyridine, respectively, has been studied by temperature-dependent laser flash photolysis. [Fe(b(bdpa))](PF6)2 shows single-exponential 5T2 → 1A1 relaxation kinetics, whereas [Fe(btpa)](PF6)2 exhibits solvent-independent biphasic relaxation kinetics. The fast process of [Fe(btpa)](PF6)2 with a rate constant, kHL, of 2.5 × 107 s-1 at 295 K and an activation energy, Ea, of 1294(26) cm-1 in methanol can be assigned to the 5T2 → 1A1relaxation as well. The slow process with a kHL(295 K) of 3.7 × 105 s-1 and a Ea of 2297(32) cm-1 in methanol - which is the slowest light-induced relaxation process observed so far for an Fe(II) spin-crossover complex in solution - is assigned to a coupling of the 5T2 → 1A1relaxation process to a geometrical rearrangement within the pendent pyridyl arms.



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