Bagchi Sukanya, Kamilya Sujit, Mehta Sakshi, Mandal Subhankar, Bandyopadhyay Arka, Narayan Awadhesh, Ghosh Subrata, Mondal Abhishake
Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India.
Dalton Trans. 2023 Aug 15;52(32):11335-11348. doi: 10.1039/d3dt01707a.
A series of mononuclear manganese(III) complexes Mn(X-sal-323) (X = 5 Cl, 1; X = 5 Br, 2; X = 3,5 Cl, 3; X = 3,5 Br, 4; and X = 5 NO, 5), containing hexadentate ligands prepared using the condensation of ,'-bis(3-aminopropyl)ethylenediamine and 5- or 3,5-substituted salicylaldehyde, has been synthesized. Variable temperature single-crystal X-ray diffraction, magnetic, spectroscopic, electrochemical, and spectroelectrochemical analyses, and theoretical calculations have been used to explore the role of various ligand substituents in the spin-state switching behavior of the prepared manganese(III) complexes. All five complexes consist of an analogous distorted octahedral monocationic MnNO surrounding offered by the flexible hexadentate ligand and ReO as the counter anion. However, a disordered water molecule was detected in complex 4. Complexes 1 (X = 5 Cl) and 5 (X = 5 NO) show gradual and complete spin-state switching between the high-spin (HS) ( = 2) and the low-spin (LS) ( = 1) state with values of 146 and 115 K respectively, while an abrupt and complete transition at 95 K was observed for complex 2 (X = 5 Br). Alternatively, complex 3 (X = 3, 5 Cl) exhibits an incomplete and sharp transition between the HS and LS states at 104 K, while complex 4 (X = 3, 5 Br) (desolvated) remains almost LS up to 300 K and then displays gradual and incomplete SCO at a higher temperature. The nature of the spin-state switch and transition temperature suggest that the structural effect (cooperativity) plays a more significant role in comparison with the electronic effect coming from various substituents (Cl, Br, and NO), which is further supported by the detailed structural, electrochemical, and theoretical studies.
通过1,2'-双(3-氨丙基)乙二胺与5-或3,5-取代水杨醛缩合制备了一系列含有六齿配体的单核锰(III)配合物Mn(X-sal-32,3)（X = 5-Cl，1；X = 5-Br，2；X = 3,5-Cl，3；X = 3,5-Br，4；X = 5-NO₂，5）。采用变温单晶X射线衍射、磁性、光谱、电化学和光谱电化学分析以及理论计算等方法，探究了各种配体取代基在制备的锰(III)配合物自旋态转换行为中的作用。所有这五种配合物均由一个类似的扭曲八面体单核阳离子MnNO₆构成，由柔性六齿配体提供配位环境，ReO₄作为抗衡阴离子。然而，在配合物4中检测到一个无序水分子。配合物1（X = 5-Cl）和5（X = 5-NO₂）分别在146 K和115 K时，在高自旋(HS)（S = 2）和低自旋(LS)（S = 1）状态之间呈现逐渐且完全的自旋态转换，而配合物2（X = 5-Br）在95 K时观察到突然且完全的转变。另外，配合物3（X = 3,5-Cl）在104 K时在HS和LS状态之间呈现不完全且急剧的转变，而配合物4（X = 3,5-Br）（去溶剂化）在高达300 K时几乎保持LS状态，然后在更高温度下呈现逐渐且不完全的自旋交叉（SCO）。自旋态转换的性质和转变温度表明，与来自各种取代基（Cl、Br和NO₂）的电子效应相比，结构效应（协同性）起着更重要的作用，详细的结构、电化学和理论研究进一步支持了这一点。
