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Iron(II) complexes of 2,6-bis(imidazo[1,2-a]pyridin-2-yl)pyridine and related ligands with annelated distal heterocyclic donors
Dalton Transactions ( IF 3.5 ) Pub Date : 2023-10-02 , DOI: 10.1039/d3dt02747c
Rafal Kulmaczewski 1 , Malcolm A Halcrow 1
Affiliation  

Following a published synthesis of 2,6-bis(imidazo[1,2-a]pyridin-2-yl)pyridine (L1), treatment of α,α′-dibromo-2,6-diacetylpyridine with 2 equiv. 2-aminopyrimidine or 2-aminoquinoline in refluxing acetonitrile respectively gives 2,6-bis(imidazo[1,2-a]pyrimidin-2-yl)pyridine (L2) and 2,6-bis(imidazo[1,2-a]quinolin-2-yl)pyridine (L3). Solvated crystals of [Fe(L1)2][BF4]2 (1[BF4]2) and [Fe(L2)2][BF4]2 (2[BF4]2) are mostly high-spin, although one solvate of 1[BF4]2 undergoes thermal spin-crossover on cooling. The iron coordination geometry is consistently distorted in crystals of 2[BF4]2 which may reflect the influence of intramolecular, inter-ligand N⋯π interactions on the molecular conformation. Only 1 : 1 Fe : L3 complexes were observed in solution, or isolated in the solid state; a crystal structure of [FeBr(py)2L3]Br·0.5H2O (py = pyridine) is presented. A solvate crystal structure of high-spin [Fe(L4)2][BF4]2 (L4 = 2,6-di{quinolin-2-yl}pyridine; 4[BF4]2) is also described, which exhibits a highly distorted six-coordinate geometry with a helical ligand conformation. The iron(II) complexes are high-spin in solution at room temperature, but 1[BF4]2 and 2[BF4]2 undergo thermal spin-crossover equilibria on cooling. All the compounds exhibit a ligand-based emission in solution at room temperature. Gas phase DFT calculations mostly reproduce the spin state properties of the complexes, but show small anomalies attributed to intramolecular, inter-ligand dispersion interactions in the sterically crowded molecules.

中文翻译:

2,6-双(咪唑并[1,2-a]吡啶-2-基)吡啶和相关配体与稠合远端杂环供体的铁(II)配合物

在公开合成 2,6-双(咪唑并[1,2- a ]吡啶-2-基)吡啶 (L 1 ) 后,用 2 当量处理 α,α'-二溴-2,6-二乙酰吡啶。2-氨基嘧啶或2-氨基喹啉在回流乙腈中分别得到2,6-双(咪唑并[1,2- a ]嘧啶-2-基)吡啶(L 2 )和2,6-双(咪唑[1,2-] a ]喹啉-2-基)吡啶(L 3 )。[Fe(L 1 ) 2 ][BF 4 ] 2 ( 1[BF 4 ] 2 ) 和 [Fe(L 2 ) 2 ][BF 4 ] 2 ( 2[BF 4 ] 2 ) 的溶剂化晶体大多是高-自旋,尽管1[BF 4 ] 2的一种溶剂化物在冷却时会经历热自旋交叉。2[BF 4 ] 2晶体中铁的配位几何结构始终是扭曲的,这可能反映了分子内、配体间的N⋯π相互作用对分子构象的影响。仅在溶液中观察到 1 : 1 Fe : L 3配合物,或在固态中分离;给出了[FeBr(py) 2 L 3 ]Br·0.5H 2 O(py=吡啶)的晶体结构。还描述了高自旋[Fe(L 4 ) 2 ][BF 4 ] 2 (L 4 = 2,6-di{quinolin-2-yl}pyridine; 4[BF 4 ] 2 )的溶剂化物晶体结构,它表现出高度扭曲的六坐标几何形状和螺旋配体构象。铁( II )络合物在室温下在溶液中是高自旋的,但1[BF 4 ] 22[BF 4 ] 2在冷却时经历热自旋交叉平衡。所有化合物在室温下在溶液中均表现出基于配体的发射。气相 DFT 计算主要再现了配合物的自旋态特性,但显示出由于空间拥挤分子中的分子内、配体间色散相互作用而产生的小异常。
更新日期:2023-10-06
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