Hydrothermal syntheses and crystal structures of three zinc succinates: Zn(C₄H₄O₄)-a, Zn(C₄H₄O₄)-b and K₂Zn(C₄H₄O₄)₂

Three zinc succinate coordination polymers have been synthesised hydrothermally. Two polymorphs of Zn(C4H4O4) adopt three-dimensional structures consisting of tetrahedral Zn atoms isolated from each other via bis-bidentate succinate moieties. The polymorphs differ in the conformation of the succinate group, the alpha form (I) having syn-periplanar geometry whereas the beta form (II) has anti-periplanar geometry. K2Zn(C4H4O4)(2) (III) has a layered structure also composed of isolated tetrahedral Zn units. In this case the two crystallographically distinct succinate groups, one of each conformer, have bis-monodentate coordination, acting as both inter- and intra-layer bridges between neighbouring Zn-containing layers. The 'double' zinc succinate layers are separated along the b-axis by interlayer potassium ions.