Influence of the substituents on the electronic and electrochemical properties of a new square-planar nickel-bis(quinoxaline-6,7-dithiolate) system: Synthesis, spectroscopy, electrochemistry, crystallography, and theoretical investigation

Ramababu Bolligarla, Samala Nagaprasad Reddy, Gummadi Durgaprasad, Vudagandla Sreenivasulu, Samar K. Das

Research output: Contribution to journalArticlepeer-review

11 Scopus citations

Abstract

We describe the synthesis, crystal structures, electronic absorption spectra, and electrochemistry of a series of square-planar nickel- bis(quinoxaline-6,7-dithiolate) complexes with the general formula [Bu 4N]2[Ni(X26,7-qdt)2], where X = H (1a), Ph (2a), Cl (3), and Me (4). The solution and solid-state electronic absorption spectral behavior and electrochemical properties of these compounds are strongly dependent on the electron donating/accepting nature of the substituent X, attached to the quinoxaline-6,7-dithiolate ring in the system [Bu4N]2[Ni(X26,7-qdt)2]. Particularly, the charge transfer (CT) transition bands observed in the visible region are greatly affected by the electronic nature of the substituent. A possible explanation for this influence of the substituents on electronic absorption and electrochemistry is described based on highest occupied molecular orbital (HOMO) to lowest unoccupied molecular orbital (LUMO) gaps, which is further supported by ground-state electronic structure calculations. In addition to this, the observed CT bands in all the complexes are sensitive to the solvent polarity. Interestingly, compounds 1a, 2a, 3, and 4 undergo reversible oxidation at very low oxidation potentials appearing at E1/2 = +0.12 V, 0.033 V, 0.18 V, and 0.044 V vs Ag/AgCl, respectively, in MeOH solutions, corresponding to the respective couples [Ni(X26,7-qdt) 2]-/[Ni(X26,7-qdt)2]2-. Compounds 1a, 3, and 4 have been characterized unambiguously by single crystal X-ray structural analysis; compound 2a could not be characterized by single crystal X-ray structure determination because of the poor quality of the concerned crystals. Thus, we have synthesized the tetraphenyl phosphonium salt of the complex anion of 2a, [PPh4]2[Ni(Ph 26,7-qdt)2]·3DMF (2b) for its structural characterization.

Original languageEnglish
Pages (from-to)66-76
Number of pages11
JournalInorganic Chemistry
Volume52
Issue number1
DOIs
StatePublished - 7 Jan 2013
Externally publishedYes

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