2013-06-20 13:58:36 173 R. Hinek, H. Spiering, P. Gütlich, A. Hauser Hinek, R. Spiering, H. Gütlich, P. Hauser, A. Chemistry - A European Journal Chem. - Eur. J. 0947-6539 1996 2 11 1435 1439 H hysteresis; iron complexes; LIESST; spin crossover; tetrazoles hysteresis iron complexes LIESST spin crossover tetrazoles http://www3.interscience.wiley.com/journal/112298255/abstract http://www3.interscience.wiley.com/cgi-bin/fulltext/112298255/PDFSTART In the [Fe(etz)₆](BF₄)₂ spincrossover system the iron(II) complexes occupy two nonequivalent lattice sites, sites A and B. Complexes on site A show a thermal high-spin (HS) → low-spin (LS) transition at 105 K, whereas complexes on site B remain in the HS state down to 10 K. Complexes on both sites exhibit light-induced spin state conversions (LIESST) at 20 K: LS → HS on site A with λ = 514.5 nm, and HS → LS on site B with λ = 820 nm. The relaxation processes subsequent to the HS → LS conversion on site B reveal a light-induced HS→LS bistability for the complexes on site B at 70 K. The bistability as well as the absence of a thermal spin transition on site B are attributed to a thermal hysteresis for the B-site complexes with a critical temperature T^↑_c K on heating. This hysteresis can be interpreted in terms of strong cooperative effects of elastic origin, which, in addition, cause characteristic deviations of the relaxation on site B from first-order kinetics (self-acceleration). In contrast, the HS → LS relaxation at 60 K on site A after irradiation with λ = 514.5 nm shows an unusual self-retardation.

]]> 10.1002/chem.19960021116 2977 172 R. Hinek, H. Spiering, D. Schollmeyer, P. Gütlich, A. Hauser Hinek, R. Spiering, H. Schollmeyer, D. Gütlich, P. Hauser, A. Chemistry - A European Journal Chem. - Eur. J. 0947-6539 1996 2 11 1427 1434 H iron complexes; LIESST; spin crossover; tetrazoles iron complexes LIESST spin crossover tetrazoles http://www3.interscience.wiley.com/journal/112298254/abstract http://www3.interscience.wiley.com/cgi-bin/fulltext/112298254/PDFSTART The [Fe(etz),](BF,), spin-cross-over system (etz = 1-ethyl-1 _H-tetrazole) crystallizes in space group P1, with the following lattice constants at 298 K: a10.419(3), b=15.709(1), c = 18.890(2) Ċ, α = 71.223(9), β =77.986(10), and γ = 84.62(1)° V = 2862.0(9) Ċ³ and Z = 3. Two nonequivalent lattice sites, one without (site A) and one with (site B) inversion symmetry, are observed. The population of the two sites n_A:n_B is 2:l. Iron(II) on site A undergoes a thermal low-spin (LS) → high-spin (HS) transition with T_1/2I, = 105 K. whereas that on site B remains in the high-spin state down to cryogenic temperatures. Application of external pressure of up to 1200 bar between 200 and 60 K does not cause formation of the low-spin state on site B. On site A the high-spin state can be populated as a metastable state at 20 K by irradiating the sample with λ = 514.5 nm; on site B a light-induced population of the low-spin state can be achieved with λ = 820 nm.

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