The first structurally characterized sulfonamide derivatized Zn(II)-dipicolylamine complexes with eight membered chelate rings. Synthetic and structural studies

Abstract

Di(2-picolyl)amine has attracted a great deal of attention as the most popular chelating group in synthesizing biological sensors to detect zinc(II) ions. This study reveals the first structurally characterized zinc complexes of the sulfonamide derivatized di(2-picolyl)amine (dpa) moiety with a rare eight membered chelate ring. The novel synthesized zinc(II) complexes; Zn(N(SO2R1dpa)Cl2 (C1), Zn(N(SO2R2dpa)Cl2 (C2), Zn(N(SO2R3dpa)Cl2 (C3), where R1 = 1-naphthalene, R2 = 2-naphthalene, R3 = 5-(dimethylamino)naphthalene were characterized using single crystal X-ray diffraction analysis, 1H NMR, FTIR, UV–Visible and fluorescence spectroscopy. Structural analysis showed that the complexes possess distorted tetrahedron geometry around the zinc centre and that the zinc metal centre is bound to the two pyridyl nitrogens of the dpa group in a bidentate fashion creating a large eight membered chelate ring. The signal attributed to the methylene group (CH2) in the free ligand spectra remains a singlet in the 1H NMR spectra of the zinc complexes but has shifted more downfield. Spectral studies of the complexes revealed that the complexes are fluorescent at concentrations of 0.1 mM with intense fluorescence peaks (C1: 335 nm, C2: 343 nm and C3: 528–551 nm) and, thus, can be further investigated on their potential to be used as imaging agents or biological sensors.