Poly[diaquabis(mu3-2,2-dimethylpropanedioato)calcium(II)copper(II)].

The title complex, CaCu(C(5)H(6)O(4))(2)(H(2)O)(2), is the first heterobimetallic complex based on a substituted malonate dianion. The Cu(II) cation and two independent 2,2-dimethylmalonate (or 2,2-dimethylpropanedioate) dianions build up a robust dianionic Cu(C(5)H(6)O(4))(2) complex, which acts as a building block to coordinate to four Ca(2+) cations. Each Cu(II) centre is in a four-coordinate square plane of dimethylmalonate O atoms, while each Ca(II) atom is in an eight-coordinate distorted bicapped trigonal-prismatic environment of six O atoms from four different dimethylmalonate groups and two water molecules. This arrangement creates a two-dimensional layer connectivity of the structure. The dianionic Cu(C(5)H(6)O(4))(2) units are involved in different intermolecular hydrogen-bonding interactions with water molecules via the formation of hydrogen-bonded rings of graph sets R(1)(2)(8) and R(6) within this layer. The crystal was nonmerohedrally twinned by rotation about [011] with a major twin volume fraction of 0.513 (3).