2013-05-20 23:24:30 1281 Pradip Chakraborty, Robert Bronisz, Céline Besnard, Laure Guénée, Phil Pattison and Andreas Hauser Chakraborty, Pradip Bronisz, Robert Besnard, Céline Guénée, Laure Pattison, Phil Hauser, Andreas Journal of the American Chemical Society J. Am. Chem. Soc. 0002-7863 2012 134 4049 4052 H http://pubs.acs.org/doi/abs/10.1021/ja211897t http://pubs.acs.org/doi/full/10.1021/ja211897t http://pubs.acs.org/doi/pdf/10.1021/ja211897t In the covalently linked 2D coordination network {[Fe(bbtr)₃](BF₄)₂}_∞, bbtr = 1,4-di(1,2,3-triazol-1-yl)butane, the iron(II) centers stay in the high-spin (HS) state down to 10 K. They can, however, be quantitatively converted to the low-spin (LS) state by irradiating into the near-IR spin allowed ⁵dd band and back again by irradiating into the visible ¹dd band. The compound shows true light-induced bistability below 100 K, thus, having the potential for persistent bidirectional optical switching at elevated temperatures.

]]> H332I564P788 10.1021/ja211897t 18789 http://www.unige.ch/sciences/chifi/publis/pics/double/ref01281.png http://www.unige.ch/sciences/chifi/publis/refs_pdf/ref01281.pdf 1227 Christian Chong, Ahmed Slimani, François Varret, Kamel Boukheddaden, Eric Collet, Jean-Claude Ameline, Robert Bronisz and Andreas Hauser Chong, Christian Slimani, Ahmed Varret, François Boukheddaden, Kamel Collet, Eric Ameline, Jean-Claude Bronisz, Robert Hauser, Andreas Chemical Physics Letters Chem. Phys. Lett. 0009-2614 2011 504 1-3 29 33 H Video1§§flv§mmc5.flv§§Crystals A, on cooling, 0.5 K/min.|Video2§§flv§mmc6.flv§§Crystals B, on cooling, 0.5 K/min.|Video3§§flv§mmc7.flv§§Crystals C at 98 K, after cooling from 120 K at 0.2 K/min.|Video4§§flv§mmc8.flv§§Crystals D at 98 K, after cooling from 120 K at 0.2 K/min.|Video5§§flv§mmc9.flv§§Crystal C, at 98 K, after second cooling from 120 K at 0.2 K/min. We investigated by optical microscopy the thermal spin transition in single crystals of [Fe(bbtr)₃](ClO₄)₂ (bbtr = 1,4-di(1,2,3-triazol-1-yl) butane). The growth of the low-spin phase was observed for different crystal orientations and sizes. The process always started from a corner of the crystal but its further development depended on the size, shape and thermal history of the crystal. In crystals of smaller size, under isothermal conditions, the low-spin phase developed in a continuous way, through the propagation of a rather well defined transformation front, with a higher propagation velocity inside the planes perpendicular to the c axis. In larger crystals the spontaneous occurrence of inhomogeneous stresses led to a stepwise propagation process.

]]> P901 10.1016/j.cplett.2011.01.041 16831 http://www.unige.ch/sciences/chifi/publis/refs_pdf/ref01227.pdf 1217 Itana Krivokapic, Pradip Chakraborty, Cristian Enachescu, Robert Bronisz, and Andreas Hauser Krivokapic, Itana Chakraborty, Pradip Enachescu, Cristian Bronisz, Robert Hauser, Andreas Inorganic Chemistry Inorg. Chem. 0020-1669 2011 50 5 1856 1861 H http://pubs.acs.org/doi/abs/10.1021/ic102269y http://pubs.acs.org/doi/full/10.1021/ic102269y http://pubs.acs.org/doi/pdf/10.1021/ic102269y Whereas the neat polymeric iron(II) compound [Fe(bbtr)₃](ClO₄)₂, bbtr = 1,4-di(1,2,3-triazol-1-yl)butane, shows a quantitative spin transition triggered by a crystallographic phase transition centered at 107 K with a 13 K wide hysteresis, the iron(II) complexes in the diluted mixed crystals [Fe_xZn_1−x(bbtr)₃](ClO₄)₂, x = 0.02 and 0.1, stay predominantly in the ⁵T₂ high-spin state down to cryogenic temperatures. However, the ¹A₁ low-spin state can be populated as metastable state via irradiation into the spin-allowed ⁵T₂→⁵E ligand-field transition of the high-spin species in the near-infrared. The quantum efficiency of the light-induced conversion is approximately 10% at low temperatures and decreases rapidly above 160 K. The lifetime of the light-induced low-spin state decreases from 15 days at 40 K to 30 ns at 220 K, that is, by 14 orders of magnitude. In the high-temperature regime the activation energy for the low-spin→high-spin relaxation is 1840(20) cm⁻¹.

]]> H250I500P1658 10.1021/ic102269y 14980 http://www.unige.ch/sciences/chifi/publis/pics/double/ref01217.png http://www.unige.ch/sciences/chifi/publis/refs_pdf/ref01217.pdf 1198 Itana Krivokapic, Pradip Chakraborty, Robert Bronisz, Cristian Enachescu and Andreas Hauser Krivokapic, Itana Chakraborty, Pradip Bronisz, Robert Enachescu, Cristian Hauser, Andreas Angewandte Chemie Angew. Chem. 0044-8249 2010 49 45 8509 8512 H In the dilute mixed-crystal system [Zn_1−xFe_x(bbtr)₃](ClO₄)₂, x=2 % (bbtr=1,4-di(1,2,3-triazol-1-yl)butane), the iron(II) centers are predominantly in the high-spin state. The low-spin state can be populated as a metastable state by irradiation with near-IR light; the rate constant of the low-spin→high-spin relaxation spans 14 orders of magnitude between 40 and 220 K

]]> P361 10.1002/anie.201004500 14713 http://www.unige.ch/sciences/chifi/publis/refs_pdf/ref01198.pdf 932 Itana Krivokapic, Cristian Enachescu, Robert Bronisz and Andreas Hauser Krivokapic, Itana Enachescu, Cristian Bronisz, Robert Hauser, Andreas Inorganica Chimica Acta Inorg. Chim. Acta 0020-1693 2008 361 12-13 3616 3622 H The thermal and the light-induced spin transition in [Fe(bbtr)₃](ClO₄)₂ (bbtr = 1,4-di(1,2,3-triazol-1-yl)) as well as the high-spin → low-spin relaxation following the light-induced population of the high-spin state below the thermal transition temperature are discussed in relation to the accompanying crystallographic phase transition. The experimental data have exclusively been obtained using optical single crystal absorption spectroscopy.

]]> H234I468P1726 10.1016/j.ica.2008.03.064 3576 http://www.unige.ch/sciences/chifi/publis/pics/double/ref00932.png http://www.unige.ch/sciences/chifi/publis/refs_pdf/ref00932.pdf 931 Itana Krivokapic, Cristian Enachescu, Robert Bronisz and Andreas Hauser Krivokapic, Itana Enachescu, Cristian Bronisz, Robert Hauser, Andreas Chemical Physics Letters Chem. Phys. Lett. 0009-2614 2008 455 4-6 192 196 H The spin-crossover compound [Fe(bbtr)₃](ClO₄)₂ (bbtr = 1,4-di(1,2,3-triazol-1-yl)butane) forms a polymeric hexagonal sheet structure. It shows an abrupt thermal spin transition with 13 K wide hysteresis around 105 K, as evidenced by single crystal optical spectroscopy. The transition temperature for the thermal high-spin→low-spin transition on cooling as well as the relaxation kinetics just below T_c^↓ depend upon the history of the sample. This is typical for a nucleation and growth mechanism and domain formation. In contrast, the high-spin→low-spin relaxation following the light-induced population of the high-spin state at low temperatures is governed by the intersystem crossing process.

]]> P362 10.1016/j.cplett.2008.02.088 74 http://www.unige.ch/sciences/chifi/publis/refs_pdf/ref00931.pdf