We show the key role that the size and shape of the solvent molecules may play in the dimensionality and structure of a series of lanthanoid-chloranilato coordination polymers. We report the synthesis, structure and magnetic properties of six different coordination polymers prepared with Er(iii) and chloranilato (C6O4Cl22- = 3,6-dichloro-2,5-dihydroxy-1,4-benzoquinone) and six different solvents: [Er2(C6O4Cl2)3(H2O)6]·10H2O (1), [Er2(C6O4Cl2)3(FMA)6]·4FMA·2H2O (2) (FMA = formamide = NH2CHO), [Er2(C6O4Cl2)3(DMSO)4]·2DMSO·2H2O (3) (DMSO = dimethy sulfoxide = Me2SO), [Er2(C6O4Cl2)3(DMF)6] (4) (DMF = dimethylformamide = Me2NCHO), [Er2(C6O4Cl2)3(DMA)4] (5) (DMA = dimethylacetamide = Me2NC(Me)O) and [Er2(C6O4Cl2)3(HMPA)(H2O)3]·H2O (6) (HMPA = hexamethylphosphormamide = (Me2N)3PO). We show how the different solvent molecules modulate and determine important structural parameters such as the coordination number and geometry, the shape and distortions of the cavities, the presence of solvent molecules in these cavities, the interlayer space and even the dimensionality of the structure.