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Ion-pair charge transfer complexes with intense near IR absorption: Syntheses,crystal structures,electronic spectra and DFT calculations
Authors:Bing-Qian Yao  Jia-Sen Sun  Zheng-Fang Tian  Xiao-Ming Ren  Da-Wei Gu  Lin-Jiang Shen  Jingli Xie
Institution:1. Department of Applied Chemistry, College of Science, Nanjing University of Technology, Nanjing 210009, PR China;2. Coordination Chemistry Institute and State Key Lab, Nanjing University, Nanjing 210093, PR China;3. Department of Applied Physics, College of Science, Nanjing University of Technology, Nanjing 210009, PR China;4. School of Chemistry and Bio21 Institute, The University of Melbourne, Parkville Vic 3010, Australia
Abstract:Five ion-pair complexes, consisting of R-benzylidene-1-aminopyridinium derivatives and Ni(mnt)2]2− (R = p-nitro (1), p-methyl (2), p-bromo (3), p-chloro (4) and m-nitro (5); mnt2− = maleonitriledithiolate), were synthesized and structurally characterized. As for 1, it is interesting to observe a large deviation from square-planar coordination geometry for the Ni atom, while no deviation is observed in the other four complexes. In the solid state, UV–Vis–NIR spectra of 25 show similar properties with intense absorption in the 200–750 nm and moderate near IR absorption in the 750–1000 nm region, whereas 1 exhibits an intense absorption from UV/Visible to near-IR region (200–1100 nm). This unique spectral feature of 1 is attributed to its distinctive structural differences from 2 to 5, namely the strong intermolecular packing interactions between anions and cations, as well as a significant deviation from the planarity of the anion. Based on DFT and TDDFT calculations, near-IR absorbance bands in 15 were assigned to combined transitions of d–d, MLCT and π–π in the Ni(mnt)2]2− anion as well as the ion-pair charge transfer (IPCT) from the anionic HOMO to the cationic LUMO. The IPCT band position in acetonitrile is independent of the substituent group feature in benzene ring of cations for 15, which could be interpreted that the substituent group in benzene ring only has a minor contribution to the cationic LUMO.
Keywords:Ion-pair  Charge transfer  Crystal structure  DFT calculation
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