T. Buchen et P. Gutlich, THERMAL AND LIGHT-INDUCED SPIN-CROSSOVER IN IRON(II) COMPLEXES WITH MONODENTATE TETRAZOLE LIGANDS CARRYING LONG ALKYL CHAINS IN THE 1-POSITION, Chemical physics letters, 220(3-5), 1994, pp. 262-266
The complex compounds [Fe(otz)6](BF4)2 (I), [Fe(dotz)6](BF4)2 (II) and
[Fe(odetz)6](BF4)2 (III) (otz = 1-n-octyl-tetrazole, dotz = 1-n-dodec
yl-tetrazole, odetz = 1-n-octadecyl-tetrazole) with monodentate tetraz
ole ligands carrying long alkyl chains in the 1-position exhibit the t
hermal high-spin (HS, T-5(2)) half arrow right over half arrow left lo
w-spin (LS, 1A1) transitions below 250 K. All of them show a gradual t
ransition behaviour with transition temperatures T1/2(gamma(HS) = 0.5)
of 148 K for I, 120 K for II and 152 K for III. Compound II shows a r
esidual paramagnetism at low temperatures, while the transitions in I
and III are complete. The LIESST effect (light-induced excited spin st
ate trapping) can be performed with all complexes. The HS --> LS relax
ation after LIESST was followed by optical spectroscopy on compound I
which was pressed to a translucent tablet. The relaxation of the metas
table LIESST state deviates strongly from first-order kinetics due to
inhomogeneities in the material.