Coordination polymers and molecular complexes of group 13 metal halides with bis-pyridylethane: comparison with rigid N-containing ligands

Abstract

A systematic structural study of novel complexes formed by aluminium and gallium trihalides with 1,2-bis(4-pyridyl)ethane (bpa) is performed. The complexes were synthesized using a solvent-free melt reaction approach and crystallized by sublimation in vacuum. Ionic coordination polymers (CPs) [MCl₂(bpa)₂]⁺[MCl₄]⁻, M = Al (1) or Ga (2), exhibit isostructural one-dimensional networks. Ionic CP 3 [AlBr₂(bpa)₂]⁺Br⁻ has a 1 : 2 composition and possesses a cationic part analogous to 1 and 2, featuring a modulated structure, in which the entire polymer chain and/or the positions of the bromido ligands are displaced according to a harmonic law. In the ionic CP [Ga₂Br₄(bpa)₅]²⁺[GaBr₄]₂⁻·bpa (4) featuring a 2 : 3 composition, the [Ga₂Br₄(bpa)₅]²⁺ cation forms a 2D polymer framework, in which {GaBr₂}⁺ nodes are linked by the μ-bpa spacers forming 1D chains that are further interconnected by μ-bpa ligands of every second metal center. In the case of the 2 : 1 ratio, irrespective of the Lewis acid, molecular complexes [(MX₃)₂(bpa)] (MX₃ = AlCl₃ (5), AlBr₃ (6), GaCl₃ (7), and GaBr₃ (8)) were obtained. Solid-state structures of complexes 1–8 were determined for the first time.