Bulk spin-crossover in the complex [FeL(NCS)<sub>2</sub>] of a tris(pyridyl)ethane-derived N<sub>4</sub>-ligand—a temperature-dependent crystallographic study
作者:Dennis Wiedemann、Andreas Grohmann
DOI:10.1039/c3dt53070a
日期:——
We have recently shown that the vacuum-deposited complex [FeIIL(NCS)2] (L: 1-6-[1,1-di(pyridin-2-yl)ethyl]-pyridin-2-yl}-N,N-dimethylmethanamine) is capable of a thermally induced spin crossover (SCO) in direct contact with a graphite surface. The SCO significantly differs from the transition behaviour in the bulk phase (powder). In the present work, the assumption of virtually no intermolecular interaction in the powder is confirmed by comparison with the spin transition in acetone solution (T1/2 = 234[3] K, ÎT80 = 58[4] K), as monitored by temperature-dependent UV/Vis spectroscopy. The complex crystallises from chlorocarbons in the form of a number of pseudopolymorphs. Amongst these, the sufficiently stable solvate [FeIIL(NCS)2]·CHCl3 is investigated by variable-temperature single-crystal X-ray diffractometry. Its SCO behaviour (T1/2 = 240[3] K, ÎT80 = 35[4] K) correlates with features of molecular structure that are unambiguously identified by analysis of the tensor of thermal expansion. Following comprehensive comparison of spin-transition properties in different states of aggregation (also in relation to the newly synthesised high-spin iron(II) and iron(III) complexes [FeIICl2L] and [FeIIICl2L]PF6), a mode of adsorption on graphite surfaces is proposed, that complies with all previous findings.
我们最近发现,真空沉积的复合物 [FeIIL(NCS)2](L:1-6-[1,1-二(吡啶-2-基)乙基]-吡啶-2-基}-N,N-二甲基甲胺)能够在与石墨表面直接接触时发生热诱导自旋交叉(SCO)。SCO 与体相(粉末)中的过渡行为有很大不同。在本研究中,通过与丙酮溶液中的自旋转变(T1/2 = 234[3] K,δT80 = 58[4] K)进行比较,证实了粉末中几乎不存在分子间相互作用的假设。该复合物以多种假多晶型的形式从碳酰氯中结晶出来。其中,足够稳定的溶质 [FeIIL(NCS)2]Â-CHCl3 通过变温单晶 X 射线衍射仪进行了研究。它的 SCO 行为(T1/2 = 240[3] K,δT80 = 35[4] K)与分子结构的特征相关,这些特征通过对热膨胀张量的分析得以明确确定。在对不同聚集状态下的自旋转变特性(也与新合成的高自旋铁(II)和铁(III)络合物 [FeIICl2L] 和 [FeIIICl2L]PF6 有关)进行全面比较后,提出了一种在石墨表面的吸附模式,该模式与之前的所有发现一致。