Coordination networks incorporating the in situ generated ligands [OC(CO2)3]4− and [OCH(CO2)2]3−

A coordination polymer of composition [Zn6(C4O7)(C3HO5)3(H2O)6](H3O)·8H2O separates in crystalline form from basic aqueous reaction mixtures at 40 °C containing Zn(II) together with either dihydroxyfumaric acid or diketosuccinic acid. [Mn6(C4O7)(C3HO5)3(H2O)6](H3O)·8H2O can be obtained under analogous conditions using diketosuccinic acid but not when dihydroxyfumaric acid is used as the starting material. The zinc and manganese products are cubic with space group P213 [a  =16.807(8) Å (Zn) and 17.2584(10) Å (Mn)]. The unusual C4O74− component of these compounds is the new oxyanion of carbon, [OC(CO2)3]4− arising via a metal-promoted benzilic acid-type rearrangement. The C3HO53− component is the trianion of hydroxymalonic acid generated by the decarboxylation of C4O74−. The structures of these two compounds consist of cubane-like units inter-linked via C3HO53− bridges into a 3D network with the intrinsically chiral (10,3)-a   topology. In the case of zinc, the crystalline product that separates under somewhat more forcing conditions contains no C4O74− but only its decarboxylation product C3HO53−, the composition being [Zn3(C3HO5)2(H2O)6]·2H2O. This compound crystallises in the monoclinic space group P21/c with unit cell dimensions a=9.8346(11) Å, b=5.4564(6) Å, c=14.9897(16) Å and β  =105.400(2)°. The C3HO53− unit plays the same triply chelating role seen in the above two compounds, giving rise in this case to a 2D coordination polymer with the (6,3) topology. The sheet structure adopts a strongly undulating character reminiscent of corrugated galvanised sheet. Multiple intra-sheet and inter-sheet hydrogen bonds are present. Basic aqueous solutions containing diketosuccinic acid and zinc(II) under even more forcing conditions (sealed tube, 130 °C) yield the ultimate decomposition product, oxalate, in the crystalline form of the known Zn(C2O4)(H2O)2.