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On the Spin Behaviour of Iron(II)-Dipyridyl-Triazine Complexes and their Performance as Thermal and Photonic Spin Switches


S. K. Hain, F. W. Heinemann, K. Gieb, P. Müller, G. Hörner, and A. Grohmann

Eur. J. Inorg. Chem. (keine Band-Nr.) (2010) 221-232



The temp.-dependent and photodynamic spin behavior of three iron(II) complexes with different 2,6-dipyridyl-4-phenyltriazine ligands L1-L3 was investigated in the solid state and in soln. (DMSO). The ligands differ in the substituent R in the 4-position of the Ph ring (L1: R = H; L2: R = OCH3; L3: R = SAc), which allows the electronic properties of the ligands to be finetuned. The magnetic data for the complex [Fe(L3)2](BF4)2 in the solid state indicate an incomplete spin transition to the high-spin form upon warming from liq. helium temp., reaching about 30 % at 400 K. There is circumstantial evidence for paramagnetic contributions compatible with spin transitions, namely, temp.-dependent NMR spectroscopic line shifts and line broadening in soln. (DMSO). However, an efficient thermally induced spin crossover in soln. is hindered by the substitution lability of the complexes, as has been detected and analyzed in an extended temp.-dependent UV/Vis spectroscopic study. Essentially unaffected by thermally induced substitution lability, the transient dynamics of the iron(II) complexes after nanosecond laser radiation flash excitation of their metal-to-ligand charge-transfer bands provide good evidence for efficient photoinduced spin transitions in soln. in all cases. The range of measured lifetimes of the high-spin quintet states is in accord with previously published data. Importantly, in our series of iron(II) complexes, the lifetimes of the high-spin state reflect the electron-donating character of the ligands.