Six cobalt(<sc>ii</sc>), zinc(<sc>ii</sc>), nickel(<sc>ii</sc>) and copper(<sc>ii</sc>) complexes based on bis-benzimidazolyl bidentate ligands with phenolyl ether linkers: synthesis, structural studies and recognition of HSO4-

Three bis-benzimidazolyl bidentate ligands with phenolyl ether linkers, 1,n-bis[2-(1H-1,3-benzimidazol-1-ylmethyl)phenoxy]alkane (L-1: n = 1, L-2: n = 3, L-3: n = 4), and their six metal complexes were synthesized by the reactions of the respective ligands with metal salts. The six metal complexes included two cobalt(ii) complexes ([Co(L-1)(NO3)(2)] (1) and [Co(L-3)(L-A)](n) (6) (L-A = maleate)), two copper(ii) complexes ([Cu(L-1)(SO4)](2) (4) and [Cu(L-3)(SO4)](2) (5)), one zinc(ii) complex ([Zn(L-1)(NO3)(2)] (2)) and one nickel(ii) complex ([Ni(L-2)(NO3)(2)] (3)). Complexes 1 and 2 had one 16-membered macrometallocycle, and complex 3 had one 18-membered macrometallocycle. In complexes 4 and 5, two SO42- joined two macrometallocycles together (16-membered macrometallocycle for 4 and 19-membered macrometallocycle for 5). In complexes 1-5, each macrometallocycle was constructed from one ligand and one metal ion. In complex 6, 19-membered macrometallocycles were connected together by maleate groups (L-A) to form a 1D polymeric chain, where each 19-membered macrometallocycle was constructed from one L-3 and one Co(ii) ion. In crystal packings of complexes 1-6, H-bonds, pi-pi interactions and C-H & ctdot;pi contacts participated in the formation of 2D supramolecular layers and 3D supramolecular architectures. The conformations of complexes 1-6 were also analyzed. Additionally, the recognition performance of complex 1 as a chemosensor for HSO4- was studied through fluorescence spectra, UV/vis spectra, H-1 NMR titrations, HRMS spectra and IR spectra. The large binding constant (1.81 x 10(4) M-1) showed that there was a strong acting force between 1 and HSO4-, and the low detection limit (1.40 x 10(-7) mol L-1) indicated that the detection of 1 for HSO4- was sensitive. The experimental results showed that complex 1 can effectively differentiate HSO4- from other anions.