Sulfide-based open-framework materials are intriguing compounds. Apart from the fact that they possess a very diverse and therefore interesting structural chemistry, these materials might act as next generation zeolites that combine physical properties typical for semiconductors.1 The first materials obtained with this in mind, which were based on germanium and tin sulfides, were discovered by Bedard et al. in 1989.2 Since then, one successful synthetic approach toward this class of compounds has been to generate inorganic frameworks by selfassembly reactions of molecular building blocks (e.g. [Ge4S10] and [AsS3]) with metal ions (e.g. Mn2+, Fe2+, Co2+, Cu+) at moderate temperatures (room temperature or mild hydro(solvo)thermal conditions) in the presence of organic template ions. The latter are incorporated into the “holes” and thus determine the “porosity” of the resulting frameworks. This approach let the field expand rapidly and compounds such as [Et4N]2Cu2Ge4S10, [Me4N]2MGe4S10 (M ) Mn,4,5 Fe,5,6 Co,5 Zn5), [Me4N]6(Cu0.44Ge0.56S0.73)Ge4S10, [Ph4P]Hg2As4S9, [Me4N]HgAs3S6, [Ph4P]InAs3S7, and [Me4N][Rb]BiAs6S12 were reported. On the other hand, extended structures are also accessible via condensation processes of molecular building blocks with themselves. Several of these “non-functionalized”10 germanium,11 tin,12-19 and antimony sulfides20,21 have been characterized. In contrast, the use of small alkali cations under similar synthetic conditions gives dense structures with extended inorganic frameworks. Examples include KCu2AsS3, KCu4AsS4, MAg2SbS4, and M2AgSbS4 (M ) Rb, K) as well as CsSb2Se4, Rb2Sn2Se5, Cs2Sn3Se7, and Cs4Sn5S12. In preceding papers,8,9 we have demonstrated that the AsS3 ligand is a powerful building block to form extended structures if it is reacted with metal ions (In3+, Bi3+, Hg2+) in the presence of organic templates. Here we report the interesting twodimensional material [Co(en)3]CoSb4S8 (1) which was prepared by heating CoBr2 with Na3SbS3 and ethylenediamine (en) in H2O at 130 °C.29 The green-black compound is insoluble in all common organic solvents. [Co(en)3]CoSb4S8 consists of isolated [Co(en)3] cations and “porous” non-centrosymmetric layers of composition