Nickel(II) Complex of a Hexadentate Ligand with Two o-Iminosemiquinonato(1−) π-Radical Units and Its Monocation and Dication
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- 作者：Akram Ali ; Debanjan Dhar ; Suman K. Barman ; Francesc Lloret ; Rabindranath Mukherjee
- 刊名：Inorganic Chemistry
- 出版年：2016
- 出版时间：June 20, 2016
- 年：2016
- 卷：55
- 期：12
- 页码：5759-5771
- 全文大小：776K
- 年卷期：0
- ISSN：1520-510X
文摘
Aerobic reaction of a hexadentate redox-active o-aminophenol-based ligand, H4L3 = N,N′-bis(2-hydroxy-3,5-di-tert-butylphenyl)-2,2′-diamino(diphenyldithio)-ethane, in CH3OH with NiII(O2CCH3)2·4H2O and Et3N afforded isolation of a reddish-brown crystalline solid [Ni(L3)] 1. Cyclic voltammetry (CV) experiment exhibits two oxidative responses at E1/2 = 0.09 and 0.53 V vs SCE (saturated calomel electrode). Chemical oxidation of 1 in air by [FeIII(η5-C5H5)2][PF6] and AgBF4 in CH2Cl2 led to the isolation of one-electron oxidized species [1]1+ as purple [1][PF6]·CH2Cl2 and two-electron oxidized species [1]2+ as dark purple [1][BF4]2·CH2Cl2, respectively. X-ray crystallographic analysis at 100(2) K unambiguously established that the ligand is present in [NiII{(LISQO,N)•–}{(LISQO,N)•–}{(LS,S)0}] 1, [NiII{(LIBQO,N)0}{(LISQO,N)•–}{(LS,S)0}][PF6]·CH2Cl2, and [NiII{(LIBQO,N)0}{(LIBQO,N)0}{(LS,S)0}][BF4]2·CH2Cl2, as monoanionic o-iminosemiquinonate(1−) π-radical (Srad = 1/2) (LISQ)•– and neutral o-iminoquinone (LIBQ)0 redox-levels. Complexes 1, [1][PF6]·CH2Cl2, and [1][BF4]2·CH2Cl2 possess an S = 2, 3/2, and 1 ground-state, respectively, established by temperature-dependent (2–300 K) magnetic behavior of 1 and [1][PF6]·CH2Cl2, and a μeff value of [1][BF4]2·CH2Cl2 at 300 K. Both 1 and [1][PF6]·CH2Cl2 exhibit ferromagnetic exchange-coupling between the two electrons of NiII and two/one ligand π-radicals, respectively. The redox processes are shown to be ligand-based. Spectroscopic and redox properties, and density functional theory (DFT) calculations at the CAM-B3LYP-level of theory adequately describe the electronic structure of 1, [1]1+, and [1]2+. The observed UV–vis–NIR absorptions for 1, [1][PF6]·CH2Cl2, and [1][BF4]2·CH2Cl2 have been assigned, based on time-dependent (TD)-DFT calculations.