Benzothiadiazolyl-pyridine and-2,2′-bipyridine Ligands for Luminescent and Magnetic Complexes

Two new luminescent ligands, 4-(2-pyridine)-7-methyl-2,1,3-benzothiadiazole (L1) and 4-(2,2-bipyridine)-7-methyl-2,1,3-benzothiadiazole (L2), based on 2,1,3-benzothiadiazole and pyridine or bipyridine were obtained by Suzuki coupling reactions. DFT and TD-DFT type calculations have been performed on L1 and L2 in order to assign their experimental UV-visible and emission bands. Reaction of L1 and L2 with metal(II) chlorides (M=Zn, Mn, Cu) provided the neutral complexes of formulas [ZnL1Cl2] (1), [Zn(L1)2Cl2] (2), [ZnL2Cl2] (3), [MnL2Cl2] & sdot; 0,5CH2Cl2 (4) and [CuL2Cl2] & sdot; H2O (5) which have been structurally characterized. The Zn(II) ions in 1 and 2 are four-coordinate in somewhat distorted tetrahedral N2Cl2 surroundings with L1 adopting bidentate (1) and monodentate (2) coordination modes. Complexes 3-5 are isostructural and their metal atoms are five-coordinate in distorted square pyramidal environments with three nitrogen atoms from the tridentate L2 ligand and a chlorine building the basal plane and another chlorine atom occupying the apical position. The three Zn(II) complexes are strongly luminescent in solution and the solid state, while the cryomagnetic study of the paramagnetic compounds 4 and 5 in the temperature range 2.9-300 K shows a Curie-Weiss behaviour typical of small antiferromagnetic interactions which are mediated by weak intermolecular contacts. Luminescent zinc(II) and paramagnetic copper(II) and manganese(II) complexes have been prepared with unprecedented benzothiadiazolyl-pyridine and -2,2 '-bipyridine ligands.image

Automated summary

Two new luminescent ligands were successfully synthesized through Suzuki coupling reactions. DFT and TD-DFT calculations were performed to analyze the UV-visible and emission bands. The experimental results revealed the coordination modes and structural characteristics of the ligands with metal ions. The products showed strong luminescence properties in solution and the solid state, and magnetic studies indicated small antiferromagnetic interactions in some of the compounds.