The partial oxidation of [Ni-2(II/II)(RCS2)(4)] (R = Et (1), n-Pr (2), and n-Bu (3)) with iodine affords the MMX chain compounds [Ni-2(II/III)(RCS2)(4)I](infinity) (R = Et (4), n-Pr (5), and n-Bu (6)), respectively. The crystal structures of 4-6 consist of neutral one-dimensional (1-D) chains with a repeating -Ni-Ni-I- unit. The room-temperature (RT) structure of 4 indicates a charge-polarization (CP) state {-Ni(2.5-delta)+-Ni(2.5+delta)+I--Ni(2.5-delta)+ -Ni(2.5+delta)+-I- (delta << 0.5)} close to an averaged valence state judged by the Ni-I distances. In contrast, 5 and 6 exhibit a Vold periodicity of a -Ni-Ni-l- unit due to the disorder of the dithiocarboxylato ligands. Compounds 4-6 show typical semiconducting behavior and exhibit an intense sharp absorption band centered at 5400 cm(-1), which is attributed to a Mott-Hubbard gap due to a relatively large on-site Coulomb repulsion energy U of the nickel atoms. The high-temperature magnetic susceptibilities of 4-6 can be described by a 1-D Heisenberg antiferromagnetic chain model with vertical bar J vertical bar/k(B) ranging from 898(2) to 939(3) K. Compounds 4 and 5 undergo a spin-Peierls (SP) transition at relatively high T-sp = 47 and 36 K, respectively, which are accompanied by superlattice reflections corresponding to a 2-fold -Ni-Ni-l- period below T-sp. By determining the superstructure of 4 at 26 K, we conclude that the valence-ordered state changes from the CP in the RT phase to the altemate charge-polarization (ACP) state of -Ni(2.5-delta)+-Ni(2.5+delta)+-I--Ni(2.5-delta)+-I-Ni(2.5+delta)+-Ni(2.5 -delta)+-I- -in the SP phase. Such a spin-Peierls transition could not be observed for 6.