Palladium(II) halide complexes of N,N,S-tridentate Schiff bases: synthesis, structural studies in solution and solid state, and analysis of Hirshfeld surfaces

Abstract

The synthesis and characterization of bromo-and iodo complexes of Pd(II) containing tridentate anionic Schiff bases, derived from the opening of 2-R-2-(2-pyridyl)benzothiazoline precursors (R = H, 1; R = Me, 2; R = C6H5, 3; R = C5H4N, 4) is described. The Pd(L n )X] complexes [for X = Br: n = 1 (1a), n = 2 (2a), n = 3 (3a), and n = 4, (4a); for X = I: n = 1 (1b), n = 2 (2b), n = 3 (3b), and n = 4 (4b)] were characterized in solution and in solid state by NMR and IR spectroscopy and by elemental analyses. In all complexes the corresponding anionic Schiff ligand {L n } − displayed a  2 NS-tridentate coordination mode. X-ray diffraction studies of [Pd(L 3 )Br] (3a), [Pd(L 3 )I] (3b), [Pd(L 4 )Br] (4a) and [Pd(L 4 )Br] (4b) complexes showed the formation of two five-membered chelate rings, with a distorted square planar geometry around the Pd(II) cation. Crystal structures of 3a, 3b, 4a, and 4b are stabilized by non-classical C-H•••, C-H•••S, and C-H•••X hydrogen bonding. For 3a, 3b, 4a, and 4b the Hirshfeld surface analysis allowed identify to the H•••H contacts as the predominants, and the C-H•••S or C-H••• non-classical hydrogen bonding as the stacking major contributions.