Spectroscopic differences between heterocyclic benzothiazoline, -thiazole and imine containing ligands and comparison of the Co and Cu pyridine benzothiazole and imine complexes

Five heterocyclic benzothiazoline and -thiazole analogs have been synthesized and characterized by 1H NMR and IR spectroscopy. The analogs fall into two different classes, (a) those which contain one benzothiazoline group adjacent to the heterocyclic ring system (starting with 2-pyridinecarboxaldehyde, 2-thiophenecarboxaldehyde or 2-furaldehyde), and (b) those which have two benzothiazoline substituents (starting with 2,6-pyridinecarboxaldehyde and 2,5-thiohenecarboxaldehyde). In addition, the imine containing ligands, bis-2-[(pyridin-2-ylmethylene)-imino]-benzenethiol disulfide (PyIS)2 and bis-2-[(thiophen-2-ylmethylene)-imino]-benzenethiol disulfide(ThIS)2, were prepared starting with the disulfide of 2-aminothiophenol. Each species has been characterized by 1H NMR and IR spectroscopies. Ligation reactions with 2-(2-pyridyl)benzothiazoline (Py(Bt)) and Cu(OAc)2·1H2O resulted in the formation of a dinuclear species containing two copper ions, two ligand frames and two acetate groups, [Cu(PyAS)(OAc)]2 (1). Both copper ions are five-coordinate and bonded to one monodentate acetate, one ligand frame (NNS) and one bridging thiolate. Ligation reaction with 2-(2-pyridyl)benzothiazole (Py(oBt)) and CoCl2·xH2O or Cu(BF4)2·xH2O resulted in the formation of a six-coordinate, octahedral Co(II) complex, cis-[Co(Py(oBt)2Cl2] (2) and a five coordinate Cu(II) complex, [Cu(Py(oBt))2(OH2)](BF4) (3), respectively. All complexes have been characterized by X-ray crystallography as well as UV–Vis and IR spectroscopy.

Graphical abstractFive heterocyclic benzothiazoline and -thiazole analogs were synthesized and characterized. Ligation reactions with 2-(2-pyridyl)benzothiazoline and 2-(2-pyridyl)benzothiazole with Cu salts yielded a species (left) containing a 1:1 metal to ligand ratio with bridging thiolato groups and a mononuclear Cu species with two N,N bonded ligands frames per metal center (right), respectively.Figure optionsDownload full-size imageDownload as PowerPoint slide