Boron-centered soft ligands based on tetrazole units and their complexes with sodium, potassium and bismuth ions

Abstract

The syntheses of Na(Ttt^Me) (1), K(Ttt^Me) (2), K(Btt^Me) (3), and Na(Btt^Ph) (4) are reported, where (Ttt^Me)⁻ and (Btt^R)⁻ (R = Me, Ph) are tri- and di-substituted boron-centered soft ligands; they were produced by the reaction of NaBH₄ and KBH₄ with the corresponding tetrazole heterocycles: 1-methyl-5-thiotetrazole (L¹H) and 1-phenyl-5-thiotetrazole (L²H). The syntheses of Na(Ttt^Me) (1) and K(Ttt^Me) (2) were carried out following Trofimenko's protocol. The anion (Ttt^Me)⁻ is a typical Janus scorpionate ligand. Na(Ttt^Me) (1) and Na(Btt^Ph) (4) were reacted with Bi(CH₃COO)₃ to observe the coordination pattern of these ligands towards bismuth ions. These reactions afforded the complexes [Bi(Ttt^Me)₂(CH₃COO)] (5), [Bi(L²)₂]₂ (6a, 6b) and [Bi(L²)₃] (7). The products were characterized by NMR spectroscopy, elemental analyses and mass spectrometry. Solid state structures were determined by X-ray diffraction of single crystals of 1, 2, 3, 4, 5, 6a, 6b and 7. M(Ttt^Me) (M = Na (1), K (2)) and K(Btt^Me) (3) exhibit sheet-like structures. The alkali metal complexes 1–4 dissociate in solution as observed in ¹H, ¹³C NMR and ¹H diffusion NMR experiments. Negative mode ESI-MS data also indicate the presence of monomers. Both the sodium salts of (Ttt^Me)⁻ and (Btt^Ph)⁻ as well as the Bi complexes 5 and 7 were investigated by absorption and emission spectroscopy.