Mononuclear zinc(II), cadmium(II), cobalt(III) and di-nuclear nickel(II) complexes of a 14pi electron diimine ligand: Syntheses, structures, photoluminescence and DFT investigations

• Fluorescent complexes of 14π electron diimine ligand.
• Mononuclear Zn(II), Cd(II), Co(III) and di-nuclear Ni(II) complexes.
• Syntheses, structures, spectra and DFT investigations.

Three types of fluorescent coordination complexes of an unsymmetrical diimine ligand (LNNOH) with conjugated 14π electrons (14πe) are reported [LNNOH = (E)-2-((phenyl(pyridin-2-yl)methylene) amino)phenol]. The complexes are: [M(LNNO−)X] [M = Zn, X = Cl, 1; M = Zn, X = Br, 2; M = Cd, X = Cl, 3], [Co(LNNO−)2]Cl, [4]Cl and [Ni2(LNNOH)2(LNNO−)2]Cl2, [5]Cl2. The complexes were substantiated by elemental analyses, IR, 1H NMR, mass and UV–Vis spectra including the single crystal X-ray structure determinations of [4]Cl·H2O and [5]Cl2·2H2O. Complexes 1–3 and [4]Cl are brightly fluorescent in fluid solutions (CH2Cl2: 1, λex = 475, 507 nm, λem = 520, 551 nm, Φ = 0.037, τav = 2.6 ns; 2, λex = 474, 507 nm, λem = 519, 552 nm, Φ = 0.027, τav = 2.4 ns; 3, λex = 474, 507 nm, λem = 518, 551 nm, Φ = 0.01, τav = 2.0 ns; [4]Cl, λex = 472, 505 nm, λem = 518, 551, 601 nm, Φ = 0.06, τav = 3.9 ns) while [5]Cl2 is weakly emissive (CH2Cl2: λex = 472, 506 nm, λem = 520, 557, 595 nm, Φ = 0.002, τav = 1.9 ns). Variable temperature magnetic measurement and Mulliken atomic spin densities obtained from unrestricted density functional theory (DFT) calculation on [5]2+ cation, are consistent with the existence of weakly interactive (J = +2.318) two Ni(II) ions. Time dependent (TD) DFT calculations on 1 and [4]+ authenticated the intra-ligand πphenolato → πdiimine∗ transitions for 1–3 and both intra- and inter-ligand πphenolato → πdiimine∗ transitions for [4]Cl as the origins of the emissive excitations.

Syntheses, molecular structures, spectra and DFT calculations of three types of fluorescent complexes, [M(LNNO−)X] [M = Zn, X = Cl, 1; M = Zn, X = Br, 2; M = Cd, X = Cl, 3], [Co(LNNO−)2]Cl, [4]Cl and [Ni2(LNNOH)2(LNNO−)2]Cl2, [5]Cl2 incorporating a diimine ligand (LNNOH) with conjugated 14π electrons are reported.Figure optionsDownload as PowerPoint slide