A novel blue luminescent high-spin iron(III) complex with interlayer O–H⋯Cl bridging: Synthesis, structure and spectroscopic studies

A blue luminescent high-spin (s = 5/2) iron(III) complex, [FeIII(HL1)2]Cl (2), was synthesized with the acyclic tridentate salicylaldehyde 2-pyridyl hydrazone ligand, H2L1 (1), and it can subsequently be deprotonated and methylated into blue luminescent iron(III) complexes, [FeIII(L2)2]Cl (3) and [FeIII(MeL1)2]Cl (4) respectively. On excitation at 390 nm, the ligand and the complexes display fluorescence in the blue region (λem = 440–450 nm) of the spectrum. The association constant, (Kass = 4.6421 × 104 at 298 K) and the thermodynamic parameters for complex 2 have been determined by UV–Vis spectroscopy. The iron(III)–iron(II) reduction potentials lie near – 0.2 V versus SCE. The X-ray crystal structure of the complex, [FeIII(HL1)2]Cl · H2O (2), was determined, revealing meridional binding of the two ligands affording a cis-FeN4O2 geometry with alternate chlorine and water molecules at the interface of the main molecule, resulting in interesting interlayer O–H⋯Cl bridging.

The acyclic tridentate salicyl-2-pyridyl hydrazone afforded a blue luminescent high-spin iron(III) complex (s = 5/2, λex = 390 nm, λem = 449 nm) with interesting interlayer O–H⋯Cl bridging. Deprotonation and insertion of a nucleophile in the ligand frame significantly modulates the photophysical and chemical properties of the complex. Moreover, the ligand and its iron(III) complex undergo photoinduced intramolecular azo-imine tautomerism.Figure optionsDownload as PowerPoint slide