Heavier group 2 metal complexes with a flexible scorpionate ligand based on 2-mercaptopyridine

Abstract

We report the synthesis of novel alkaline earth metal complexes [κ²-SS-(Bmp)₂M(THF)_n] [M = Ca (2), Sr (3) n = 2; M = Ba (4), n = 3] of a flexible dihydrobis(2-thiopyridone)borate (Bmp) ligand based on 2-mercaptopyridine. Complexes 2–4 were isolated in good yield by the reaction between sodium dihydrobis(2-thiopyridone)borate, [{(Bmp)Na(THF)}₂]_n (1) and the corresponding alkaline earth metal diiodides in toluene at ambient temperature. The solid-state structures of the strontium and barium complexes, complexes 3 and 4 respectively, were established using single-crystal X-ray diffraction analysis. The solid-state structure of sodium complex 1 was also confirmed using X-ray techniques. The solid-state structures of complexes 3 and 4 revealed that the Bmp ligand coordinates through sulphur atoms to the metal ions in κ² fashion. The strontium ion is attached symmetrically and the barium ion is asymmetrically linked with the Bmp ligand, manifesting the 2-thiopyridone and pyridine-2-thiolate tautomeric form of the Bmp ligand. The strontium ion in complex 3 adopts a distorted octahedral geometry whereas the geometry around the barium ion can best be described as a distorted pentagonal bipyramidal. Both complexes 3 and 4 also have a short B⋯H⋯M interaction due to the presence of the BH₂ group in the ligand. In the solid state, sodium complex 1 is polymeric in nature and in the asymmetric unit each sodium ion is bonded to two sulphur atoms through η¹ and μ² modes. The adjacent BH₂ group is also linked with each sodium ion through hydrogen atoms via μ² and η¹.