Interlayer Interaction of Two-Dimensional Layered Spin Crossover Complexes [FeIIH3LMe][FeIILMe]X (X-= ClO4-, BF4-, PF6-, AsF6-, and SbF6-; H3LMe= Tris[2-(((2-methylimidazol-4-yl)methylidene)amino)ethyl]amine)
- 8 November 2003
- journal article
- research article
- Published by American Chemical Society (ACS) in Inorganic Chemistry
- Vol. 42 (25) , 8406-8416
- https://doi.org/10.1021/ic034439e
Abstract
A series of two-dimensional (2D) spin crossover complexes, [FeIIH3LMe][FeIILMe]X (X- = ClO4-, BF4-, PF6-, AsF6-, SbF6-) 1−5, have been synthesized, where H3LMe denotes an hexadentate N6 tripodlike ligand containing three imidazole groups, tris[2-(((2-methylimidazol-4-yl)methylidene)amino)ethyl]amine. Compounds 1−5 exhibit a two-step (HS-[FeIIH3LMe]2+ + HS-[FeIILMe]-) ↔ (HS-[FeIIH3LMe]2+ + LS-[FeIILMe]-) ↔ (LS-[FeIIH3LMe]2+ + LS-[FeIILMe]-) spin-transition. The crystal structure of [FeIIH3LMe][FeIILMe]PF6 (3) was determined at 295, 200, and 100 K. The structure consists of homochiral extended 2D puckered sheets, in which the complementary [FeIIH3LMe]2+ and [FeIILMe]- capped tripodlike components, linked together by imidazole−imidazolate hydrogen bonds, are alternately arrayed in an up-and-down mode. The Fe−N bond distances and angles revealed that the FeII sites of both constituting units are in the high-spin (HS) state at 295 K; at 200 K, the FeII sites of [FeIIH3LMe]2+ and [FeIILMe]- are in the HS and low-spin (LS) states, respectively. The FeII sites of both constituting units are in the LS state at 100 K. The size of the counteranion affects significantly the intra- and interlayer interactions leading to modifications of the spin crossover behavior. The onset of the second spin-transition of the ClO4- (1) and BF4- (2) salts adjoins the first spin-transition, while a mixed (HS-[FeIIH3LMe]2+ + LS-[FeIILMe]-) spin-state spans a temperature range as wide as 70 K for salts 3−5 with larger counteranions, PF6-, AsF6-, and SbF6-, respectively. Compounds 1 and 2 showed remarkable LIESST (light induced excited spin state trapping) and reverse-LIESST effects, whereas 3−5 showed no remarkable LIESST effect. The interlayer interaction due to the size of the counteranion is an important factor governing the spin crossover behavior and LIESST effect.Keywords
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