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Solvent Polarity Predictably Tunes Spin Crossover T1/2 in Isomeric Iron(II) Pyrimidine Triazoles
Inorganic Chemistry ( IF 4.6 ) Pub Date : 2018-05-16 00:00:00 , DOI: 10.1021/acs.inorgchem.8b00128
Santiago Rodríguez-Jiménez 1 , Alexis S. Barltrop 1 , Nicholas G. White 1 , Humphrey L. C. Feltham 1 , Sally Brooker 1
Affiliation  

Two isomeric pyrimidine-based Rdpt-type triazole ligands were made: 4-(4-methylphenyl)-3-(2-pyrimidyl)-5-phenyl-4H-1,2,4-triazole (L2pyrimidine) and 4-(4-methylphenyl)-3-(4-pyrimidyl)-5-phenyl-4H-1,2,4-triazole (L4pyrimidine). When reacted with [FeII(pyridine)4(NCE)2], where E = S, Se, or BH3, two families of mononuclear iron(II) complexes are obtained, including six solvatomorphs, giving a total of 12 compounds: [FeII(L2pyrimidine)2(NCS)2] (1), [FeII(L2pyrimidine)2(NCSe)2] (2), 2·1.5H2O, [FeII(L2pyrimidine)2(NCBH3)2]·2CHCl3 (3·2CHCl3), 3 and 3·2H2O, [FeII(L4pyrimidine)2(NCS)2] (4), 4·H2O, [FeII(L4pyrimidine)2(NCSe)2] (5), 5·2CH3OH, 5·1.5H2O, and [FeII(L4pyrimidine)2(NCBH3)2]·2.5H2O (6·2.5H2O). Single-crystal X-ray diffraction reveals that the N6-coordinated iron(II) centers in 1, 2, 3·2CHCl3, 4, 5, and 5·2CH3OH 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 3·2CHCl3, which is low spin (LS). Solid-state magnetic measurements show that only 3·2CHCl3 (T1/2 above 400 K) and 5·1.5H2O (T1/2 = 110 K) undergo spin crossover (SCO); the others remain HS at 300–50 K. When 3·2CHCl3 is heated at 400 K it desorbs CHCl3 becoming 3, which remains HS at 400–50 K. UV–Vis studies in CH2Cl2, CHCl3, (CH3)2CO, CH3CN, and CH3NO2 solutions for the BH3 analogues 3 and 6 led to a 6:1 ratio of Lnpyrimidine/Fe(II) being employed for the solution studies. These revealed SCO activity in all five solvents, with T1/2 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 T1/2 values in those solvents are observed for each complex, enabling predictable T1/2 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.

中文翻译:

溶剂极性可预测地调节异美铁(II)嘧啶三唑中的自旋交变T 1/2

制备了两个基于嘧啶的异构体Rdpt型三唑配体:4-(4-甲基苯基)-3-(2-嘧啶基)-5-苯基-4 H -1,2,4-三唑(L 2嘧啶)和4- (4-甲基苯基)-3-(4-嘧啶基)-5-苯基-4 H -1,2,4-三唑(L 4嘧啶)。当与[Fe II(吡啶)4(NCE)2 ],其中E = S,Se或BH 3反应时,会获得两个单核铁(II)配合物家族,其中包括六个溶剂型,总共提供了12种化合物: [Fe IIL 2嘧啶2(NCS)2 ](1),的[Fe II大号2pyrimidine2(NCSE)2 ](2),2 ·1.5H 2 O,的[Fe II大号2pyrimidine2(NCBH 32 ]·2CHCl 33 ·2CHCl 3),33 ·2H 2 O,[Fe IIL 4嘧啶2(NCS)2 ](4),4 ·H 2 O,[FeII大号4pyrimidine2(NCSE)2 ](5),5 ·2CH 3 OH,5 ·1.5H 2 O,和[铁II大号4pyrimidine2(NCBH 32 ]·2.5H 2 O(6 ·2.5H 2 O)。单晶X射线衍射显示,所述N个6中配位的铁(II)中心123 ·2CHCl 3455 ·2CH 3 OH具有两个赤道键合的二齿三唑配体和两个轴向NCE共配体反式配位。除3 ·2CHCl 3以外,所有结构均在100 K下具有高自旋(HS),这是低自旋(LS)。固态磁测量表明,只有3 ·2CHCl 3(高于400 K的T 1/2)和5 ·1.5H 2 O(T 1/2 = 110 K)经历自旋交叉(SCO)。其他的则保持在300–50 K的HS。当3 ·2CHCl 3加热到400 K时,它解吸的CHCl 3变成3,这仍然是在HS K. 400-50紫外可见在CH研究22,三氯甲烷3,(CH 32 CO,CH 3 CN,和CH 3 NO 2个的BH解决方案3的类似物36导致L n嘧啶/ Fe(II)的比例为6:1用于溶液研究。这表明所有五种溶剂中的SCO活性均为T 1/2无论使用哪种溶剂,2-嘧啶配合物(247-396 K)的值始终高于4-嘧啶配合物(216-367 K),这与2-嘧啶环提供的配体场强于2-嘧啶环4-嘧啶环。对于每种配合物,观察到溶剂极性指数与那些溶剂中的T 1/2值具有很强的相关性,从而可预测的T 1/2调节范围高达150K。尽管这种相关性令人着迷,但在这里也可能反映了溶剂依赖性形态-因此,此概念的未来测试应采用更稳定的复合物。突出显示了固态(配体场;晶体堆积;溶剂含量)和溶液(配体场;溶剂化;形态)对SCO的影响之间的差异。
更新日期:2018-05-16
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