Indium Complexes With 2-((Pyridin-4-ylmethylene)amino)phenols: Synthesis, Structure and Spectroscopic Properties

Abstract

Reactions of Schiff base ligands HL^1–4 (wherein HL¹ is 2-((pyridin-4-ylmethylene)amino)phenol, HL² is 4-methyl-2-((pyridin-4-ylmethylene)amino)phenol, HL³ is 4‑chloro-2-((pyridin-4-ylmethylene)amino)phenol, HL⁴ is 4-nitro-2-((pyridin-4-ylmethylene)amino)phenol) with Me₃In in a molar ratio of 1:1 lead to the formation of dimethylindium complexes of the general formula (L^1–4)InMe₂ (1–4). The molecular structures of 1–4 have been determined by single crystal X-ray analysis. In the crystal, all complexes form centrosymmetric dimers via coordination of bridging μ²-O atoms of the phenolate fragment to the metal atom of the neighboring molecule. The crystal packing of 1–4 represents infinite chains due to short contacts between each indium in the dimer and the pyridine nitrogen of the adjacent dimeric molecule. UV–vis absorption spectra of 1–4 have been recorded in various organic solvents. The position of the absorption band assigned to intraligand charge transfer (ILCT) in the UV–vis absorption spectra of 1–4 depends on the nature of the substituent in the phenolate moiety of L^1–4 and shifts hypsochromically with increasing of the electron acceptor properties of the substituents in the Schiff bases. The HOMO-LUMO energy gap calculated from the CV measurements for 1–3 also narrows with the introduction of the electron donor substituents in the ligand L. All complexes show fluorescence with broad emission bands in the range of 500–700 nm both in Me-THF solution and in the solid state.