Crystal Structure and Behavior in Solution of [Cu(HBPA)₂]Cl₂·4H₂O [HBPA = (2-hydroxybenzyl-2-pyridylmethyl)amine]

Abstract

The crystal structure of [Cu(HBPA)₂]Cl₂·4H₂O [HBPA = (2-hydroxybenzyl-2-pyridylmethyl)amine] revealed an octahedral geometry around Cu(II). The mononuclear complex crystallizes in the triclinic space group P2₁/n with cell lengths of a = 7.3705 (6), b = 9.7695 (6), c = 20.2314 (15) Å and with cell angles of α = 90, β = 100.264 (3) and γ = 90º. The coordination plane is comprised of two secondary amine and two pyridine nitrogens, the phenol oxygen atoms are coordinated in the protonated form and occupy the axial sites. Investigations in solution (MeOH and DMF) by electronic spectroscopy and electrochemical studies suggest effect of the solvents on the structure, indicating the partial coordination of the axial ligands as phenolate, resulting in the formation of distinct species in solution. Addition of base enables the effective coordination of phenol group as phenolate, as observed by the increase of the intensity of the band at 429 nm and the formation one only compound in DMF solution, according to cyclic voltammetry studies.

Graphical Abstract

Herein we describe the crystal structure of [Cu(HBPA)₂]Cl₂·4H₂O [HBPA = (2-hydroxybenzyl-2-pyridylmethyl)amine].The coordination plane is comprised of two secondary amine and two pyridine nitrogens, the phenol oxygen atoms are coordinated in the protonated form and occupy the axial sites. Investigations in solution by electronic spectroscopy and electrochemical studies suggest effect of the solvent; the addition of base enables the effective coordination of phenol group as phenolate, resulting in one only compound in solution.