Evaluation of the influence of a thioether substituent on the solid state and solution properties of N3S-ligated copper(ii) complexes

Abstract

Admixture of a N₃S(thioether) ligand having two internal hydrogen bond donors (pbnpa: N-2-(phenylthio)ethyl-N,N-bis-((6-neopentylamino-2-pyridyl)methyl)amine; ebnpa: N-2-(ethylthio)ethyl-N,N-bis-((6-neopentylamino-2-pyridyl)methyl)amine) with equimolar amounts of Cu(ClO₄)₂·6H₂O and NaX (X = Cl⁻, NCO⁻, or N₃⁻) in CH₃OH/H₂O yielded the mononuclear Cu(II) derivatives [(pbnpa)Cu–Cl]ClO₄ (1), [(ebnpa)Cu–Cl]ClO₄ (2), [(pbnpa)Cu–NCO]ClO₄ (3), [(ebnpa)Cu–NCO]ClO₄ (4), [(pbnpa)Cu–N₃]ClO₄ (5), and [(ebnpa)Cu–N₃]ClO₄ (6). Each complex was characterized by FTIR, UV-VIS, EPR, and elemental analysis. Complexes 1, 2, 3 and 6 were characterized by X-ray crystallography. The structural studies revealed that [(pbnpa)Cu–X]ClO₄ derivatives (1, 3) exhibit a distorted square pyramidal type geometry, whereas [(ebnpa)Cu–X]ClO₄ complexes (2, 6) may be classified as distorted trigonal bipyramidal. EPR studies in CH₃OH/CH₃CN solution revealed that 1–6 exhibit an axial type spectrum with g_∥ > g_⊥ > 2.0 and A_∥ = 15–17 mT, consistent with a square pyramidal based geometry for the Cu(II) center in each complex. A second species detected in the EPR spectra of 2 and 6 has a smaller A_∥ value, consistent with greater spin delocalization on to sulfur, and likely results from geometric distortion of the [(ebnpa)Cu(II)–X]⁺ ions present in 2 and 6.