Hemi- and holo-directed lead(ii) complexes in a soft ligand environment

Abstract

To investigate the geometry and stereochemical activity of the lone pair at the lead atom, lead(II) complexes (1–10) with one tripodal (L¹), one dipodal (L²) boron-centred soft ligand and eight other small soft heterocyclic ligands, 2-mercaptobenzimidazole (L³), 2-mercapto-5-methylbenzimidazole (L⁴), 3-mercapto-1,2,4-triazole (L⁵H), 3-mercapto-4-methyl-1,2,4-triazole (L⁶), 2-mercapto-1,3,4-thiadiazole (L⁷H), 2-mercapto-5-methyl-1,3,4-thiadiazole (L⁸H), 5-mercapto-1-methyltetrazole (L⁹H) and 2-mercapto-4-phenylthiazole (L¹⁰H) were prepared. The structures of these complexes were elucidated on the basis of X-ray crystallography, elemental analyses as well as ¹H NMR, ¹H DOSY, ¹³C NMR and ²⁰⁷Pb NMR spectroscopy. The coordination numbers of these complexes vary from 4 to 8. The majority of the complexes are polymeric and possess a hemi-directed environment around the lead atoms. Solution studies revealed that most of the complexes are dissociated in highly polar solvents. Most of the complexes are emissive both under ambient conditions and at 77 K in the solid state. However, no obvious relationship between their solid state structures and luminescence behaviour with respect to the nature of the excited state could be identified.