The reaction between Ln(NO₃)₃·xH₂O, Cs₃[W^V(CN)₈]·H₂O and 2,2′:6′,2″-terpyridine (terpy) leads to the original isomorphous cyano-bridged [Ln^III(terpy)(DMF)₄][W^V(CN)₈]·6H₂O [Ln = Gd (1), Sm (2)] 1-D chains. The crystal structures of {Ln^IIIW^V} chains 1 and 2 consist of alternating {[W(CN)₈]} and {[Ln(terpy)]} building blocks. The neighbouring 1-D chains are weakly linked through π–π stacking interactions of the aromatic rings leading to 2-D supramolecular layers. The layers are linked through hydrogen bonds between H₂O molecules and terminal cyano ligands. Magnetic studies revealed a weak antiferromagnetic coupling (J = −2.3(2) K) within the {Gd^IIIW^V} chains in 1. The positive effective coupling constant J = +2.0(5) K between the total angular momentum of the Sm(III) centre and the spin of the W(V) ion is equivalent to an antiferromagnetic character of the spin coupling between both centres in the {Sm^IIIW^V} chains of 2. The magnetic measurements suggest that they display an isolated magnetic chain behaviour.