The structure has a very pronounced two dimensional character, with a separation of hydrophobic n-alkyl chains from the carboxylate groups, the Co2+ cations and the water of crystallisation. <...> The structure is discussed in respect of the structures of other known compositionally related compounds, including the dihydrate Co(C12H20O4)(H2O)2. <...> The interest in the chemical and physical properties of transition metal coordination networks (now often referred to as MOFs — metal organic frameworks) is rapidly increasing. <...> In the design of new materials there are many strategies and parameters that can be exploited. <...> We can use ligands with well defined chelating coordination modes to produce well defined arrays of metal ions, whether they are discreet clusters [ 7 ] or infinite arrays [ 8 ]. <...> This is certainly seen with aryl carboxylate ligands such as the rigid 1,2,4,5-benzene tetracarboxylate [ 9 ]. <...> With alkyl carboxylates we introduce a conformational flexibility to the ligand, and we also introduce the hydrophobic alkyl-alkyl interactions which when the alky chain is long enough, result in a layered 2D lamella character to a material. <...> Powder X-ray diffraction was performed using a Bruker D5000 instrument with CuKh radiation. <...> Hydrogen atoms on the alkyl chain were fixed in ideal geometries and refined in riding mode, while the hydrogen atoms of water molecules (involved in hydrogen bonding) were located in the difference map and refined freely. <...> For example, a slight excess of Co(II) ions results in crystals large enough for single crystal structural determination. <...> Microanalysis and powder X-ray diffraction show that this synthetic method produces a mixture of crystals of the trihydrate Co[O2C(CH2)10CO2](H2O)3 (1) and the dihydrate [ 14 ]. <...> The structure of 1 has a 2D character, consisting of alternating layers of the fully extended dicarboxylate ligand and layers of metal ions (Fig. 1). <...> This is not at all surprising given the amphiphilic nature of the ligand, with a long hydrophobic alkyl section and the hydrophilic carboxylate groups at each end. <...> View along the crystallographic b axis of 1, showing the segregation of the components into hydrophobic layers containing the alkyl chains which alternate with polar layers containing the carboxylate groups, the Co(II) ions and water molecules Fig <...>