Nonlinear-Optical Properties of 伪-Diiminedithiolatonickel(II) Complexes Enhanced by Electron-Withdrawing Carboxyl Groups

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• 作者：Luca Pilia ; Maddalena Pizzotti ; Francesca Tessore ; Neil Robertson
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：May 5, 2014
• 年：2014
• 卷：53
• 期：9
• 页码：4517-4526
• 全文大小：520K
• 年卷期：v.53,no.9(May 5, 2014)
• ISSN：1520-510X

文摘

We report the synthesis, characterization, nonlinear-optical (NLO) properties, and density functional theory (DFT) calculations for three nickel diiminedithiolate complexes [Ni(4,4鈥?R₂carboxy-bpy)(L)] [R = methyl, L = 1,2-benzenedithiolate (bdt), 1; R = ethyl, L = 5,6-dihydro-1,4-dithine-2,3-dithiolate (dddt), 2; R = ethyl, L = 1-(N-methylindol-5-yl)ethene-1,2-dithiolate (mi-5edt), 3]. The crystal structure of 1 shows a square-planar coordination for the nickel ion and bond distances consistent with a diiminedithiolate description for the complex. For all complexes, the cyclic voltammetry measurements show two reversible reduction processes (鈭?.353/鈥?.380 V and 鈭?798/鈥?.830 V, respectively) and an anodic wave (+0.372/+0.601 V). The UV鈥搗is spectra present a band around 600鈥?00 nm (蔚 = 4880鈥?000 dm³ mol^鈥? cm^鈥?) mainly attributed to a charge-transfer highest occupied molecular orbital (HOMO)鈥搇owest unoccupied molecular orbital (LUMO) transition, which shows a large negative solvatochromic shift, characteristic of push鈥損ull complexes, and is responsible for the NLO properties of these molecules. The charge-transfer character of this electronic transition is confirmed by DFT calculations, with the HOMO mainly centered on the dithiolate moiety and the LUMO on the bpy ligand, with important contribution given by the carboxyl groups (鈮?3%). Small contributions from the nickel(II) ion are present in both of the frontier orbitals. The carboxyl groups enhance the optical properties of this class of complexes, confirmed by comparison with the corresponding unsubstituted compounds. The second-order NLO properties have been measured by an electric-field-induced second-harmonic-generation technique using a 10^鈥? M solution in N,N-dimethylformamide and working with a 1.907 渭m incident wavelength, giving for 渭尾_1.907 (渭尾₀) values of 鈭?095 (鈭?81), 鈭?760 (鈭?54), and 鈭?650 (鈭?18) 脳 10^鈥?8 esu for 1鈥?b>3, respectively. These values are among the highest in the class of square-planar push鈥損ull complexes, similar to those found for dithionedithiolate compounds. Moreover, spectroelectrochemical experiments demonstrate the possibility of using these complexes as redox-switchable NLO chromophores.