On the nature of the plateau in two-step dinuclear spin-crossover complexes |
| |
Authors: | Ksenofontov Vadim Gaspar Ana B Niel Virginie Reiman Sergey Real José A Gütlich Philipp |
| |
Affiliation: | Institut für Anorganische und Analystiche Chemie, Johannes Gutenberg Universit?t, Staudinger Weg 9, 55099 Mainz, Germany. |
| |
Abstract: | A remarkable feature of the spin-crossover process in several dinuclear iron(II) compounds is a plateau in the two-step transition curve. Up to now, it has not been possible to analyse the spin state of dinuclear pairs that constitute such a plateau, due to the relative high temperatures at which the transition takes place in complexes investigated so far. We solved this problem by experimentally studying a novel dinuclear spin-crossover compound [[Fe(phdia)(NCS)(2)](2)(phdia)] (phdia: 4,7-phenanthroline-5,6-diamine). We report here on the synthesis and characterisation of this system, which exhibits a two-step spin transition at T(c1)=108 K and T(c2)=80 K, displaying 2 K and 7 K wide thermal hysteresis loops in the upper and the lower steps, respectively. A plateau of approximately 20 K width centred at about 90 K, which corresponds to the 50 % of the spin conversion, separates the two transitions. The composition of the plateau was identified in metastable state after quenching to 4.2 K by means of M?ssbauer spectroscopy in an external magnetic field. Such experiments revealed that the plateau consists mainly of [HS-LS] pairs (HS=high spin, LS=low spin) and confirmed the hypothesis that the spin conversion in dinuclear entities proceeds through [LS-LS]<-->[HS-LS]<-->[HS-HS] pairs. The results are discussed in terms of a thermodynamic model based on the regular solution theory adapted for dinuclear spin-crossover compounds. |
| |
Keywords: | iron LIESST effect Mössbauer spectroscopy N ligands spin crossover |
本文献已被 PubMed 等数据库收录! |
|