FeII Bi-Stable Materials Based on Dissymmetrical Ligands: N4 Schiff Bases Including 2-Pyridyl and 5-Methylimidazol-4-yl Rings Yield Various FeII Spin-Crossover Phenome

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• 作者：Nicolas Bré ; fuel ; Sergiu Shova ; Janusz Lipkowski ; Jean-Pierre Tuchagues
• 刊名：Chemistry of Materials
• 出版年：2006
• 出版时间：November 14, 2006
• 年：2006
• 卷：18
• 期：23
• 页码：5467 - 5479
• 全文大小：447K
• 年卷期：v.18,no.23(November 14, 2006)
• ISSN：1520-5002

文摘

The synthesis and characterization of six new spin-crossover (SCO) materials [FeL^Dx(NCX)₂] (1: X= S, x = 1; 2: X = Se, x = 1; 3: X = S, x = 2; 4: X = Se, x = 2; 5: X = S, x = 3; 6: X = S, x =4) are reported, where L^D1-L^D4 stand for the dissymmetrical tetradentate ligands obtained by 1:1:1 Schiffbase condensation of 1,3-diaminopropane (L^D1, L^D3) or 2,2-dimethyl-1,3-diaminopropane (L^D2, L^D4),2-acetylpyridine (L^D1, L^D2) or 6-bromo-2-acetylpyridine (L^D3, L^D4), and 5-methylimidazole-4-carboxaldehyde. Magnetic and Mössbauer studies and X-ray structures at 100, 200, and 300 K (low-spin (LS)state) and 350 and 400 K (high-spin (HS) state) for 3, and 180 K (HS state) for 6 revealed the occurrenceof unusual SCO behaviors: complex 3 undergoes a first-order SCO centered at 315 K with a 4 K widehysteresis associated with an order-disorder phenomenon for the propylene fragment of L^D2, whereas 1exhibits a two-step SCO occurring at ~202 (smooth) and 297.5 K (11 K wide hysteresis). A significantmass effect is induced upon changing the thiocyanate for selenocyanate ligands: the SCO of 4 (NCSe)occurs ~100 K higher than for 3. These new features are discussed comparatively to the results obtainedfor a related series of SCO materials. 5 and 6, which include a 6-bromopyridyl substituent, remain HSover the whole 80-300 K range.