Three-dimensional frameworks built from piperazine-2,5-dione and simple metal salts (M = Co, Ni, Cu and Ag)

Compounds trans-tetraaquadichloridocobalt(II)-piperazine-2,5- dione (1/1), [CoCl2(H2O)(4)]center dot C4H6N2O2, (I), and trans-tetraaquadichloridonickel( II)-piperazine-2,5-dione (1/1), [NiCl2( H2O)(4)]center dot C4H6N2O2, (II), are isomorphous. In each structure, the metal complex and the piperazinedione unit both lie across centres of inversion in the space group P2(1)/n. The [MCl2(H2O)(4)] units (M = Co or Ni) are linked by O-H center dot center dot center dot Cl hydrogen bonds into sheets of R-2(2)(8) and R-4(2)(12) rings, and these sheets are linked by the piperazinedione components via a combination of O-H center dot center dot center dot O and N-H center dot center dot center dot Cl hydrogen bonds into a three-dimensional framework. In catena-poly[[[transdiaquacopper( II)]-di-mu-chlorido] piperazine-2,5-dione solvate], {[CuCl2(H2O)(2)]center dot C4H6N2O2}(n), (III), the metal ion and the piperazine unit both lie across centres of inversion in the space group I2/a. The coordination polymer forms chains of centrosymmetric [CuCl2(H2O)(2)] units running parallel to [010] and these are linked by the piperazinedione units into a three-dimensional framework structure. In poly[mu(3)-nitrato-mu 2-piperazine- 2,5-dione-silver(I)], [Ag(NO3)(C4H6N2O2)](n), (IV), the silver and nitrate ions lie on mirror planes in the space group Pnma, while the piperazinedione unit lies across a centre of inversion. The compound is a coordination polymer containing five-coordinate approximately square-pyramidal Ag, in which the ligating O atoms are derived from three different nitrate ligands and two different piperazinedione ligands. The ionic components form sheets in which each anion is coordinated to three different cations, and these sheets are linked into a three-dimensional framework by the organic ligands, each of which coordinates to two different Ag centres. The significance of this study lies in its demonstration of a wide variety of framework types built from a common and very simple organic component with simple metal salts.