Spectroscopic and magnetic properties of solvatochromic complex of Cu2+ and novel 3H-indolium derivative

• Complex of Cu (II) and novel indolium derivative has been synthesised.
• Its spectral and magnetic properties were studied in depth.
• Unusual stoichiometry of Cu (II) heterochelate was determined and confirmed.
• Its vis absorption spectra exhibit distinct polarity dependence.

A new solvatochromic complex of copper (II) and 3H-indolium (HQIndol) with the formula (HQIndol)3Cu has been synthesised and characterised by elemental analysis, UV–vis, IR spectroscopies, electron paramagnetic resonance (EPR), and static magnetic susceptibility and conductance measurements. The stoichiometry of complex has been determined as 1:3 (M:L) and the binding constant was calculated to be 5.86 × 1016 mol−1 L at 25 °C in CH3OH. Magnetization measurements indicate that (HQIndol)3Cu sample is paramagnetic with spin S = 1/2 for which phase transition from paramagnetic to antiferromagnetic has been registered at TN = 2.5 K. The symmetry of the EPR spectrum points to elongated tetragonal octahedral geometry of the complex. Examined heterochelate exhibits solvatochromic properties. Blue shift of the vis absorption band with increased solvent polarity is observed, Δν‾max in examined solvents amounts to 1466 cm−1.

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