TY - JOUR AU - Hauser, Andreas AU - Enachescu, Cristian AU - Lawson Daku, Latévi Max AU - Vargas, Alfredo AU - Amstutz, Nahid TI - Low-temperature lifetimes of metastable high-spin states in spin-crossover and in low-spin iron(II) compounds: The rule and exceptions to the rule PY - 2006 JF - Coordination Chemistry Reviews JA - Coord. Chem. Rev. SN - 0010-8545 VL - 250 IS - 13-14 SP - 1642 EP - 1652 L1 - http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6TFW-4J2KRR2-1-2F&_cdi=5237&_user=779890&_orig=browse&_coverDate=07%2F31%2F2006&_sk=997499986&view=c&wchp=dGLbVzz-zSkWb&md5=48f4b2b232a8ae79678bf61019417566&ie=/sdarticle.pdf L2 - http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TFW-4J2KRR2-1&_user=779890&_handle=V-WA-A-W-AE-MsSWYWW-UUW-U-AACWZYVYVA-AACUWZCZVA-EWEDWVUED-AE-U&_fmt=full&_coverDate=07%2F31%2F2006&_rdoc=5&_orig=browse&_srch=%23toc%235237%232006%23997499986%23624607!&_cdi=5237&view=c&_acct=C000043220&_version=1&_urlVersion=0&_userid=779890&md5=86a47f1d0fcdc05a145b7bc76f10231c L3 - http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TFW-4J2KRR2-1&_user=779890&_handle=V-WA-A-W-AE-MsSWYWW-UUW-U-AACWZYVYVA-AACUWZCZVA-EWEDWVUED-AE-U&_fmt=summary&_coverDate=07%2F31%2F2006&_rdoc=5&_orig=browse&_srch=%23toc%235237%232006%23997499986%23624607!&_cdi=5237&view=c&_acct=C000043220&_version=1&_urlVersion=0&_userid=779890&md5=94268bd58127387192f3af810a46397c M3 - 10.1016/j.ccr.2005.12.006 UR - http://dx.doi.org/10.1016/j.ccr.2005.12.006 N2 - The high-spin → low-spin relaxation in spin-crossover compounds can be described as non-adiabatic multi-phonon process in the strong coupling limit, in which the low-temperature tunnelling rate increases exponentially with the zero-point energy difference between the two states. Based on the hypothesis that the experimental bond length difference between the high-spin and the low-spin state of ~0.2 Å is also valid for low-spin iron(II) complexes, extrapolation of the single configurational coordinate model allows an estimate of the zero-point energy difference for low-spin complexes from kinetic data. DFT calculations on low-spin [Fe(bpy)3]2+ support the structural assumption. However, for low-spin [Fe(terpy)2]2+ the relaxation rate constant shows an anomalous behaviour in so far as it is more in line with spin-crossover systems. This is attributed to very anisotropic bond length changes associated with the spin state change, and the subsequent breakdown of the single mode model. ID - 813 ER -