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

Admixture of a N3S(thioether) ligand having two internal hydrogen bond donors (pbnpa: N-2-(phenylthio)ethyl-N,N-bis-((6neopentylamino-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)CuCl]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 (up tack) > 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.