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Stepwise Spin Transition in a Mononuclear Iron(II) Complex with Unusually Wide Plateau
Author(s) -
Weber Birgit,
Carbonera Chiara,
Desplances Cedric,
Létard JeanFrançois
Publication year - 2008
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200701216
Subject(s) - chemistry , spin transition , crystallography , spin states , spin crossover , magnetic susceptibility , molecule , octahedron , spin (aerodynamics) , mössbauer spectroscopy , ligand (biochemistry) , schiff base , crystal structure , inorganic chemistry , organic chemistry , biochemistry , receptor , engineering , aerospace engineering
The reaction of the Schiff‐base like ligand H 2 L [L 2– = ( E , E )‐({diethyl 2,2′‐[1,2‐phenylenebis(iminomethylidyne)]bis(3‐oxobutanato)})] with iron(II) acetate in methanol in the presence of 4‐cyanopyridine leads to the formation of an octahedral iron(II) complex with the formula FeL(CNpy) 2 · 0.25CNpy ( 1 ). The magnetic properties of this complex were investigated using temperature‐dependent susceptibility measurements (SQUID) and Mössbauer spectroscopy. Both measurements indicate that the complex performs a stepwise spin transition with a large plateau in the region from 225 K to 125 K and γ HS ≈ 0.25. The molecule structure of the compound was determined at room temperature, 240 K ( γ HS ≈ 0.5 according to susceptibility measurements) and 100 K. Two complex molecules were found in the asymmetric unit with strong π–π interactions between the phenylene rings of H 2 L. In agreement with outcomes from the magnetic measurements, both iron centres are in the high‐spin state at room temperature and in the low‐spin state at 100 K. At 240 K one of the two iron centres is high‐spin and the other one low‐spin. The reason for the wide step with one fourth of the iron centres in the high‐spin state is the additional distorted 4‐cyanopyridine in the crystal that influences the transition temperature of the surrounding iron centres. The spin transition was followed in solution by using 1 H NMR spectroscopy. A gradual spin transition with T 1/2 = 238 K is obtained. Temperature‐dependent diffuse reflectivity spectra show the occurrence of photoconversion at the surface of the sample but only about 6 % of the complex could be switched in bulk condition using a SQUID magnetometer and the stability of the photoinduced HS state with T LIESST = 40 K is very weak. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)