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.