We present the synthesis and characterisation of a novel series of lanthanide complexes bearing long aliphatic chains, obtained by post-functionalisation of LnL (Ln = Tb–Tm and Y, H₃L = tris(((3-formyl-5-methylsalicylidene)amine)ethyl)amine) via Schiff-base reaction with 1-octadecylamine. Crystal structures show that the first coordination sphere is not radically perturbed by the post-functionalisation although the trigonal symmetry is lost. Post-derivatisation influences the static magnetic properties of the Kramers and non-Kramers ions differently, with the non-Kramers ions most sensitive to derivatisation. The observed differences likely stem from changes in eigenvector composition as luminescence spectra showed minor modifications of the energy spectra upon derivatisation.