Structure, biological and electrochemical studies of transition metal complexes from N,S,N′ donor ligand 8-(2-pyridinylmethylthio)quinoline

Abstract

The semirigid tridentate 8-(2-pyridinylmethylthio)quinoline ligand (Q1) is shown to form the structurally characterized transition metal complexes [Cu(Q1)Cl 2] ( 1), [Co(Q1)(NO 3) 2] ( 2), [Cd(Q1)(NO 3) 2] ( 3), [Cd(Q1)I 2] ( 4). [Cu(Q1) 2](BF 4) 2·(H 2O) 2 ( 5), [Cu(Q1) 2](ClO 4) 2·(CH 3COCH 3) 2 ( 6), [Zn(Q1) 2](ClO 4) 2(H 2O) 2 ( 7), [Cd 2(Q1) 2Br 4] ( 8), [Ag 2(Q1) 2(ClO 4) 2] ( 9), and [Ag 2(Q1) 2(NO 3) 2] ( 10). Four types of structures have been observed: ML-type in complexes 1– 4, in which the anions Cl −, NO 3 − or I − also participate in the coordination; ML 2 − type in complexes 5– 7 without direct coordination of the anions BF 4 − or ClO 4 − and with more (Cu 2+) or less (Zn 2+) distorted bis- fac coordinated Q1; M 2 L 2 -type in complex 8, in which two Br − ions act as bridges between two metal ions; and M 2 (μ-L) 2-type in complexes 9 and 10, in which the ligand bridges two anion binding and Ag–Ag bonded ions. Depending on electron configuration and size, different coordination patterns are observed with the bonds from the metal ions to N pyridyl longer or shorter than those to N quinoline. Typically Q1 acts as a facially coordinating tridentate chelate ligand except for the compounds 9 and 10 with low-coordinate silver(I). Except for 6 and 8, the complexes exhibit distinct constraining effects against both G(+) and G(-) bacteria. Complexes 1, 3, 4, 5, 7 have considerable antifungal activities and complexes 1, 5, 7, and 10 show selective effects to restrain certain botanic bacteria. Electrochemical studies show quasi-reversible reduction behavior for the copper(II) complexes 1, 5 and 6.