Ghosh Subrata, Bagchi Sukanya, Kamilya Sujit, Mehta Sakshi, Sarkar Debopam, Herchel Radovan, Mondal Abhishake
Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India.
Department of Inorganic Chemistry, Faculty of Science, Palacký University, CZ-771 46 Olomouc, Czech Republic.
Dalton Trans. 2022 May 17;51(19):7681-7694. doi: 10.1039/d2dt00660j.
Four mononuclear manganese(III) complexes coordinated with photo-active hexadentate azobenzene ligands, Mn(5azo-sal-323) (X = Cl, 1; X = BF, 2; X = ClO, 3; X = PF, 4), were prepared. The impact of various counter anions on the stabilization and switching of the spin state of the manganese(III) center was explored through detailed magneto-structural investigation using variable temperature single-crystal X-ray diffraction, magnetic, spectroscopic, and spectroelectrochemical studies, along with theoretical calculations. All four complexes consisted of an isostructural monocationic distorted octahedral MnNO coordination environment offered by the hexadentate ligand and Cl, BF, ClO, and PF as counter anions respectively. Complex 1 with a spherical Cl counter anion showed a reversible and gradual spin-state switching between low-spin (LS) ( = 1) and high-spin (HS) ( = 2) states above 400 K, where non-covalent cation-anion interactions played a significant role in stabilizing the LS state. While, irrespective of the shape of the counter anion, complexes 2-4 remained in the HS state throughout the measured temperature range of 300-2 K, where strong π-π interaction between the azobenzene motifs among cationic units played a substantial role in stabilizing the HS state. Furthermore, magnetic data analyses revealed significantly large zero-field splitting in the = 1 state for 1 ( = 19.4 cm, / = 0.008) in comparison with that in the = 2 state for 2-4 ( = 3.99-4.97 cm, / = 0.002-0.195). Spectroelectrochemical investigations revealed the quasi-reversible reduction and oxidation of the manganese(III) center to manganese(II) and manganese(IV), respectively. A detailed theoretical calculation at the DFT and CASSCF level of theory was carried out to better understand the magneto-structural correlation.
制备了四种与光活性六齿偶氮苯配体配位的单核锰（III）配合物，即Mn(5azo-sal-323)（X = Cl，1；X = BF，2；X = ClO，3；X = PF，4）。通过使用变温单晶X射线衍射、磁性、光谱和光谱电化学研究以及理论计算进行详细的磁结构研究，探索了各种抗衡阴离子对锰（III）中心自旋态的稳定和转换的影响。所有四种配合物均由六齿配体提供的等结构单核阳离子畸变八面体MnNO配位环境以及分别作为抗衡阴离子的Cl、BF、ClO和PF组成。具有球形Cl抗衡阴离子的配合物1在400 K以上显示出低自旋（LS）（S = 1）和高自旋（HS）（S = 2）状态之间的可逆且逐渐的自旋态转换，其中非共价阳离子-阴离子相互作用在稳定LS状态中起重要作用。而无论抗衡阴离子的形状如何，配合物2-4在300-2 K的测量温度范围内均保持在HS状态，其中阳离子单元之间的偶氮苯基序之间的强π-π相互作用在稳定HS状态中起重要作用。此外，磁性数据分析表明，与2-4的S = 2状态（D = 3.99-4.97 cm-1，giso = 0.002-0.195）相比，1的S = 1状态（D = 19.4 cm-1，giso = 0.008）具有明显大的零场分裂。光谱电化学研究表明，锰（III）中心分别向锰（II）和锰（IV）的准可逆还原和氧化。在DFT和CASSCF理论水平上进行了详细的理论计算，以更好地理解磁结构相关性。
