New cobalt(II) coordination complex for adsorption of Rhodamine B dye and its mechanistic pathway

[Display omitted] •The crystal structure of new mononuclear, mixed-ligand Co(II) complex is determined.•The maximum adsorption capacity of the complex reached 194.4 mg/g for Rhodamine B dye.•The plausible mechanism is electrostatic interaction, hydrogen bonding, and π-π interaction.•The kinetic study investigation provided, Qe = 207.3 mg/g. A new mixed-ligand cobalt complex with the general formula [Co(H2O)(teaH3)(4-NBA)]·(4-NBA)·H2O (1), where (teaH3 = triethanolamine and 4-NBA = 4-nitrobenzoate), has been successfully synthesized and characterized. In this complex, triethanolamine acts as a tetradentate ligand and the 4-NBA act as monodentate ligands. The cobalt metal ion in the complex has a coordination number of 6 with a slightly distorted octahedral geometry. Furthermore, some intramolecular and intermolecular interactions have been observed in 1. Moreover, the kinetic studies on the rate of adsorption confirm that the Pseudo Second Order model accurately predicted the absorption of RhB by the complex. The higher R-squared value and the close agreement between the calculated (Qe = 207.3 mg/g) and experimental (194.4 mg/g) values indicate a satisfactory match. The hydrogen bonding interactions and other weaker electrostatic interactions between the complex and the RhB molecule enhance this adsorption.