The sandwich complex commo-[3,3′-Fe{1-(C₄H₃S)-1,2-C₂B₉H₁₀}₂]^–1 and its tetrathiafulvalenium salts [ttf]₅[Fe(C₂B₉H₁₀C₄H₃S)₂]₂2 and [ttf][Fe(C₂B₉H₁₀C₄H₃S)₂]3 were synthesised in order to study the effect of the thiophene (C₄H₃S) group on the crystal packing, electrical and magnetic properties of ttf–metallacarborane salts. The crystal structure of 2 features unusual two-dimensional networks of ttf units which extend in the a and c directions. Each ttf sheet contains stacked trimers of ttf units, which propagate along the a direction, and bridging ttf units, which lie between the ttf stacks approximately orthogonally to the ttf units within the trimers. The trimers are linked along the c direction via short S ⋯ S contacts (3.56 Å) with these bridging ttf units. In contrast, the crystal structure of compound 3 contains discrete stacked dimers of [ttf]˙⁺ cations. Whilst crystals of 2 are semiconducting (σ_{300 K}= 2 × 10^–3 S cm^–1) with an activation energy of 0.22 eV, those of 3 are insulating (σ_{290 K}⩽ 10^–7 S cm^–1). Both compounds exhibit weak ferromagnetic interactions between the unpaired spins of their [Fe(C₂B₉H₁₀C₄H₃S)₂]^– anions, with small positive Weiss constants of 1.9 and 0.5 K respectively.