@Article{CoordChemRev_190-192_471, author = {A. Hauser and J. Jeftic and H. Romstedt and R. Hinek and H. Spiering}, title = {{Cooperative phenomena and light-induced bistability in iron(II) spin-crossover compounds}}, journal= {Coord. Chem. Rev.}, ISSN = {0010-8545}, volume= {190-192}, pages = {471-491}, url = {http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TFW-3Y6XDC8-Y&_user=779890&_handle=W-WA-A-A-ZE-MsSAYVA-UUW-AUCYCVDAUD-AVYBAYUWE-ZE-U&_fmt=summary&_coverDate=09%2F30%2F1999&_rdoc=27&_orig=browse&_srch=%23toc%235237%231999%23998079999%23150249!&_cdi=5237&view=c&_acct=C000043220&_version=1&_urlVersion=0&_userid=779890&md5=bec203d62ab6a3897f68ce8b35157aef}, eprint= {http://www.unige.ch/sciences/chifi/publis/refs_pdf/ref00303.pdf}, doi= {10.1016/S0010-8545(99)00111-3}, keywords= {iron(II) coordination compounds;spin-crossover;cooperative effects;high-spinlow-spin relaxation;bistability}, abstract = {{In iron(II) spin-crossover compounds, the transition from the $^1$A$_1$ low-spin state at low temperatures to the $^5$T$_2$ high-spin state at elevated temperatures is accompanied by a large increase in metal-ligand bond lengths. The resulting elastic interactions may be pictured as an internal pressure which is proportional to the concentration of the low-spin species. Because pressure stabilises the low-spin state relative to the high-spin state this results in a positive feedback. Thermal transition curves in neat iron(II) spin-crossover compounds are thus invariable much steeper than in diluted mixed crystals, and the high-spin→low-spin relaxation following the light-induced population of the high-spin state at low temperatures is self-accelerating. Strong interactions give rise to a thermal hysteresis, and light-induced bistabilities may be observed for compounds with initially a high-spin ground state and the potential for a light-induced population of the low-spin state. For such compounds, the increasing internal pressure may stabilise the low-spin state sufficiently so that it becomes the molecular ground state above some critical light-induced low-spin fraction. Secondary effects of the elastic interactions include crystallographic phase transitions, inhomogeneous distributions of sites, and anomalies such as steps in the transition curve.}}, year = {1999} }