Department of Chemistry and MacDiarmid Institute for Advanced Materials and Nanotechnology , University of Otago , PO Box 56, Dunedin 9054 , New Zealand.
Inorg Chem. 2018 Jun 4;57(11):6266-6282. doi: 10.1021/acs.inorgchem.8b00128. Epub 2018 May 16.
Two isomeric pyrimidine-based Rdpt-type triazole ligands were made: 4-(4-methylphenyl)-3-(2-pyrimidyl)-5-phenyl-4 H-1,2,4-triazole (L) and 4-(4-methylphenyl)-3-(4-pyrimidyl)-5-phenyl-4 H-1,2,4-triazole (L). When reacted with [Fe(pyridine)(NCE)], where E = S, Se, or BH, two families of mononuclear iron(II) complexes are obtained, including six solvatomorphs, giving a total of 12 compounds: [Fe(L)(NCS)] (1), [Fe(L)(NCSe)] (2), 2·1.5HO, [Fe(L)(NCBH)]·2CHCl (3·2CHCl), 3 and 3·2HO, [Fe(L)(NCS)] (4), 4·HO, [Fe(L)(NCSe)] (5), 5·2CHOH, 5·1.5HO, and [Fe(L)(NCBH)]·2.5HO (6·2.5HO). Single-crystal X-ray diffraction reveals that the N-coordinated iron(II) centers in 1, 2, 3·2CHCl, 4, 5, and 5·2CHOH have two bidentate triazole ligands equatorially bound and two axial NCE co-ligands trans-coordinated. All structures are high spin (HS) at 100 K, except 3·2CHCl, which is low spin (LS). Solid-state magnetic measurements show that only 3·2CHCl ( T above 400 K) and 5·1.5HO ( T = 110 K) undergo spin crossover (SCO); the others remain HS at 300-50 K. When 3·2CHCl is heated at 400 K it desorbs CHCl becoming 3, which remains HS at 400-50 K. UV-Vis studies in CHCl, CHCl, (CH)CO, CHCN, and CHNO solutions for the BH analogues 3 and 6 led to a 6:1 ratio of L /Fe(II) being employed for the solution studies. These revealed SCO activity in all five solvents, with T values for the 2-pyrimidine complex (247-396 K) that were consistently higher than for the 4-pyrimidine complex (216-367 K), regardless of solvent choice, consistent with the 2-pyrimidine ring providing a stronger ligand field than the 4-pyrimidine ring. Strong correlations of solvent polarity index with the T values in those solvents are observed for each complex, enabling predictable T tuning by up to 150 K. While this correlation is tantalizing, here it may also be reflecting solvent-dependent speciation-so future tests of this concept should employ more stable complexes. Differences between solid-state (ligand field; crystal packing; solvent content) and solution (ligand field; solvation; speciation) effects on SCO are highlighted.
两种异构嘧啶基 Rdpt 型三唑配体被合成：4-(4-甲基苯基)-3-(2-嘧啶基)-5-苯基-4H-1,2,4-三唑（L）和 4-(4-甲基苯基)-3-(4-嘧啶基)-5-苯基-4H-1,2,4-三唑（L）。当与[Fe(pyridine)(NCE)]反应时，其中 E = S、Se 或 BH，得到两种单核铁(II)配合物家族，包括六种溶剂化物变体，共得到 12 种化合物：[Fe(L)(NCS)]（1）、[Fe(L)(NCSe)]（2）、2·1.5HO、[Fe(L)(NCBH)]·2CHCl（3·2CHCl）、3 和 3·2HO、[Fe(L)(NCS)]（4）、4·HO、[Fe(L)(NCSe)]（5）、5·2CHOH、5·1.5HO 和[Fe(L)(NCBH)]·2.5HO（6·2.5HO）。单晶 X 射线衍射表明，1、2、3·2CHCl、4、5 和 5·2CHOH 中配位的铁(II)中心具有两个轴向 NCE 配位基团的赤道配位的双齿三唑配体。在 100 K 下，所有结构均为高自旋（HS），除 3·2CHCl 外，其为低自旋（LS）。固态磁性测量表明，只有 3·2CHCl（高于 400 K 的 T）和 5·1.5HO（T = 110 K）经历自旋交叉（SCO）；其他在 300-50 K 下保持 HS。当 3·2CHCl 在 400 K 下加热时，它会解吸 CHCl 成为 3，其在 400-50 K 下保持 HS。在 CHCl、CHCl、(CH)CO、CHCN 和 CHNO 溶液中对 BH 类似物 3 和 6 的 UV-Vis 研究导致溶液研究中 L/Fe(II)的比例为 6:1。这表明在所有五种溶剂中都具有 SCO 活性，2-嘧啶配合物（247-396 K）的 T 值始终高于 4-嘧啶配合物（216-367 K），无论溶剂选择如何，这与 2-嘧啶环提供比 4-嘧啶环更强的配体场一致。观察到每个配合物在这些溶剂中的溶剂极性指数与 T 值之间存在很强的相关性，这使得 T 值可以通过高达 150 K 的预测进行调整。虽然这种相关性很有吸引力，但这里也可能反映了溶剂依赖性的特异性，因此未来对这一概念的测试应该使用更稳定的配合物。突出了固态（配体场；晶体堆积；溶剂含量）和溶液（配体场；溶剂化；特异性）对 SCO 的影响之间的差异。
