Coordination compounds in a pentacyclic aromatic system from 2-aminobenzothiazole derivatives and transition metal ions

Herein we report the syntheses and structural analyses of coordination compounds derived from 2-(2-benzothiazolylamino)benzothiazole, bis-btz (1), 2-(2-aminobenzothiazolylamino)benzoxazole, btz-boz (2) and 2-(2-benzothiazolylamino) benzimidazole, btz-bz (3). Ligands 1–3 are aromatic heterocycles prepared from 2-aminobenzothiazole that differ by the heteroatom (S, O, N) at position 12. These heterocycles were reacted with cobalt(II), nickel(II), and zinc(II) acetates; in addition, ligand 1 with mercury(II) acetate. The coordination compounds were characterized in the solid state by UV–Vis–NIR reflectance spectra, IR, X-ray diffraction and mass spectrometry. Unusual electronic spectra of Co2+ and Ni2+ compounds, indicated the participation of the metal ion in the ligand electronic delocalization. The N–H group was, in all cases, deprotonated and coordination to the metal ion occurs through the nitrogen atoms N(3) and N(13), forming a six-membered ring in a planar pentacyclic aromatic system. A distorted tetrahedral geometry is stabilized for ML2 complexes (M2+ = Co, Ni, Zn; L = 1–3) and for the (bis-btz)2Hg2+ compound, while nickel in [Ni(btz-boz)2(MeOH)] is square pyramidal and octahedral in [Ni(L)(OAc)(MeOH)2] (L = 1–3). Solid state structures showed 1D and 2D supramolecular arrangements.

Graphical abstractThe syntheses and structural analyses of coordination compounds derived from 2-(2-benzothiazolylamino)benzothiazole (1), 2-(2-aminobenzothiazolylamino)benzoxazole (2) and 2-(2-benzothiazolylamino)benzimidazole (3) with Co(II), Ni(II), and Zn(II) acetates and ligand 1 with Hg(II) acetate are reported. Three different geometries for the metal atoms were found: a distorted tetrahedron (for ML2 Co, Ni, Zn and Hg), a square pyramid [for Co and Ni in NiL2(MeOH)] and an octahedron for Ni(L)(OAc)(MeOH)2.Figure optionsDownload full-size imageDownload as PowerPoint slide