Borate-based ligands with two soft heterocycle/thione groups and their sodium and bismuth complexes

Abstract

Two novel sodium complexes [NaBb] (1) (Bb = dihydrobis(2-mercapto-benzimidazolyl)borate) and [NaBt^Me] (2) (Bt^Me = dihydrobis(2-mercapto-4-methylthiazolyl)borate) have been prepared and characterized by using two heterocycles, 2-mercapto-benzimidazole and 2-mercapto-4-methylthiazole, as well as NaBH₄ as precursors. The dipodal boron centred soft ligands Bb and Bt^Me were prepared in situ. The reactivity of [NaBb] (1) and [NaBt^Me] (2) towards Bi(III) ions has been studied. The resulting complex [BiBb₂Cl] (3) contains an MS₄ core with κ³-S,S,H coordination mode, while the complex [BiBt^Me₃] (4) with an MS₆ core adopts a coordination mode κ²-S,S. A reaction of BiCl₃ with the heterocyclic precursors 2-mercapto-benzimidazole (L¹) and 2-mercapto-4-methylthiazole (L²) was also attempted; this afforded the monomeric [BiL¹₄Cl₂][BiL¹₂Cl₄] (5) and dimeric [BiL²₂(μ-Cl)Cl]₂ (6) bismuth complexes. The bismuth complexes possess distorted octahedral geometries except 3 for which a face-capped octahedron is found. The presence of (B)H⋯Bi interactions has been identified by X-ray diffraction in 3 with a H⋯Bi distance of 2.58(1) Å which is uniquely short and unprecedented. Two of the synthesized complexes (4 and 5) have been investigated by luminescence spectroscopy. They feature emission bands in the solid state at room temperature at 674 (4) and 586 nm (5), which are hypsochromically shifted in (frozen) ethanolic solutions at 77 K to 618 and 537 nm, respectively.