See-Saw Ni(II) thiosemicarbazones, Energy and Photophysical Properties

Abstract

Depending on the orientation and nature of substituents, the properties of metal complexes decorated at the external periphery change. In this study, we present the synthesis, characterization, and emission properties of three thiosemicarbazone-based nickel complexes. Three ligands used in this study were (E)-2-(anthracen-9-ylmethylene)-N-(aryl)hydrazine-1-carbothioamide (aryl = 3-methoxyphenyl, 2,3-dichlorophenyl, and 2,4-dichlorophenyl), each of which forms a bis-chelated nickel complex. Depending on the substituent, the complexes had different orientations of the peripheral anthracenyl and aryl groups. In the case of aryl = 2,3- or 2,4-dichlorophenyl, the complexes had in-in orientation of the substituent rings across the central core, and the 3-methoxyphenyl-derived complex had the in-out orientation of the two aryl groups across the central core of the complex. In methoxyphenyl derived complex had N-H⋯S interaction, whereas in the dichlorophenyl group containing complexes, C-H⋯π, C-H⋯Cl and S⋯Cl interactions had stabilized particular forms in solid state, The theoretically optimized energies of the in-in, in-out, and out-out isomers of each complex have revealed two aspects: (a) the lowest energy isomers were not necessarily observed experimentally, (b) the HOMO and LUMO of the complexes were delocalized over metal and ligands. These observed isomers of the complexes were responsive to temperature, concentrations, and excitation wavelengths, which were reflected in emission spectra and proton NMR studies. The temperature-dependent NMR and emission of nickel complexes, as well as theoretically calculated HOMO-LUMO energy gaps, were reflected in the experimentally determined visible spectra and the dual emission peaks shown by the respective nickel complex.