Cation–anion interactions involving hydrogen bonds. Syntheses, Structures and spectroscopic studies of [H2dam][BiIIIPh(O2CCF3)4], [Hpy]2[BiIIIPh(O2CCF3)4] and [H2dam][BiIII(O2CCF3)5](dam = diamine, py = pyridine)

Abstract

New anionic bismuth(III) complexes [H₂dam][BiPh(O₂CCF₃)₄]1, [HPy]₂[BiPh(O₂CCF₃)₄]1g and [H₂dam][Bi(O₂CCF₃)₅]2(dam = diamine, py = pyridine) have been synthesised by the reaction of BiPh₃with trifluoroacetic acid and diamines or pyridine. The crystal structures of [H₂dam][BiPh(O₂CCF₃)₄][dam = Me₂N(CH₂)₃NMe₂1a, Me₂NCH₂CH(OH)CH₂NMe₂1b, Me₂N(CH₂)₄NMe₂1c, Me₂N(CH₂)₂NMe₂1d or N,N,N′,N′-tetramethyl-1,4-phenylenediamine 1f], 1g, and [H₂teed][Bi(O₂CCF₃)₅]2e[teed = Et₂N(CH₂)₂NEt₂] have been determined by single-crystal X-ray diffraction analyses. The structure of the [BiPh(O₂CCF₃)₄]^2– anion in the solid state has been found to be dependent on the structure of the protonated diamine or pyridine. In 1a–1c it has a cup-like structure with the Bi^III adopting a square-pyramidal geometry, while in 1d it has an irregular shape with the Bi^III of approximate pentagonal-pyramidal geometry The [BiPh(O₂CCF₃)₄]^2– anion in 1f and 1g has intermediate structure between the ‘cup’ and the pentagonal pyramid. Compound 2e has an irregular polyhedral geometry and the bismuth is surrounded by ten oxygen atoms. The structural variations observed in these compounds are attributed to hydrogen-bonding interactions between the anion and the cation, and the stacking of aromatic rings in the crystal lattice. The solution behaviour of [BiPh(O₂CCF₃)₄]^2– has been examined by ¹H NMR spectroscopic analysis. In cases where the dam is an aliphatic diamine, compound 1 is in equilibrium with [H₂dam][Bi(O₂CCF₃)₄]₅]2 and [Hdam][BiPh₂(O₂CCF₃)₂]3, except for 1b which undergoes irreversible decomposition in solution. When dam is an aromatic diamine or pyridine the [BiPh(O₂CCF₃)₄]^2–anion is stable in solution. Solvent molecules such as tetrahydrofuran or acetone have been found to affect the equilibrium between compounds 1 and 2 and 3.