Poly[[tri-μ-aqua-dodecaaquatris(μ3-1-hydroxyethylidene-1,1-diphosphonato)tricalcium(II)tripalladium(II)] pentahydrate]

The asymmetric unit of the title compound, {[CaPd{CH3OHC(PO3)2}(H2O)5]·5/3H2O}n, consists of one half of the complex [Pd{CH3OHC(PO3)2}]2− anion (point group symmetry m..), one Ca2+ cation [site symmetry (.2.)] that is surrounded by three water molecules (one of which is on the same rotation axis) and by three disordered lattice water molecules. The anions form a trinuclear metallocycle around a crystallographic threefold rotation axis. The cations are related by a twofold rotation axis to form a [Ca2(H2O)10]2+ dimer. The slightly distorted square-planar coordination environment of the PdII atoms in the complex anions is formed by O atoms of the bidentate chelating phosphonate groups of the 1-hydroxyethylidene-1,1-diphosphonate ligands. In the crystal, cations are bound to anions through —Ca—O—P—O— bonds, as well as through O—H⋯O hydrogen bonds, resulting in a three-dimensional polymer. The structure is completed by five disordered solvent molecules localized in cavities within the framework.

The asymmetric unit of the title compound, {[CaPd{CH 3 OHC(PO 3 ) 2 }(H 2 O) 5 ]Á5/3H 2 O} n , consists of one half of the complex [Pd{CH 3 OHC(PO 3 ) 2 }] 2À anion (point group symmetry m..), one Ca 2+ cation [site symmetry (.2.)] that is surrounded by three water molecules (one of which is on the same rotation axis) and by three disordered lattice water molecules. The anions form a trinuclear metallocycle around a crystallographic threefold rotation axis. The cations are related by a twofold rotation axis to form a [Ca 2 (H 2 O) 10 ] 2+ dimer. The slightly distorted square-planar coordination environment of the Pd II atoms in the complex anions is formed by O atoms of the bidentate chelating phosphonate groups of the 1-hydroxyethylidene-1,1-diphosphonate ligands. In the crystal, cations are bound to anions through -Ca-O-P-O-bonds, as well as through O-HÁ Á ÁO hydrogen bonds, resulting in a three-dimensional polymer. The structure is completed by five disordered solvent molecules localized in cavities within the framework.
Supporting information for this paper is available from the IUCr electronic archives (Reference: BR2239).  (Szabo et al., 2002). Also in the last years, there has been a surge of interest in palladium complexes as a prospective antitumor preparation (Abu-Surrah et al., 2008, Curic et al., 1996. The title compound crystallized in centric space group P6/mcc. The square-planar environment of palladium atoms in the complex anion [Pd 3 {CH 3 OHC(PO 3 ) 2 } 3 ] 6is formed by coordination of the oxygen atoms of the chelating phosphonic groups of the ligand. By crystallographic threefold rotation axis it completed to trinuclear species with equilateral triangle geometry ( Fig.1). Palladium atoms slightly deviate from the oxygen mean-planes towards the triangle center by 0.12 Å.
The range of Pd -O bond distances of 2,006 (2) -2,010 (2)Å as well cis O-Pd-O angles ranging from 85.78 (9)° to 92.91 (13)° are in a good agreement with literature values (Babaryk et al., 2012 and references therein). CH 3 and OH groups of the HEDP are statistically disordered over two positions with equal occupation numbers.
As it shown on Fig. 2, each Ca atom of the complex binuclear cation is surrounded by eight oxygen atoms (six from water molecules, comprising two bridging ones, and two from phosphonic groups of the trinuclear clusters) in the form of a slightly distorted, bi-capped trigonal prism. (Hammerl et al., 2002). The Ca -O bond distances were observed within the range of 2,416 (3) -2,538 (3)Å. Calcium coordinated by eight water molecules is well known in the literature, and the distances of the bridging and nonbridging oxygen atoms found here agree well with the previously reported values (Müller et al., 1972). Each binuclear cation linked to four trinuclear anions of adjacent layers through -Ca-O-P-O-bonds

Experimental
A solution of AgNO 3 (0.3398 g, 2.0 mmol) in H 2 O (5 ml) was added to a solution of PdCl 2 (0.0885 g, 0.5 mmol) in hydrochloric acid (0.1M, 10 ml) and the resulting solution stirred at 276 K for 30 min under protection from light until AgCl was precipitated and filtered off. Hydroxyethylidenediphosphonic acid (0.112 g, 0.5 mmol) and CaCO 3 (0.05 g, 0.5 mmol) were added to filtrate. The resulting solution was stirred for 1 h at 276 -277 K and left staying overnight at room temperature. The solvent was removed from resulting reaction mixture under reduced pressure leaving an yellow solid, which was washed twice with methanol and diethyl ether and dried under vacuum. Yellow rectangular crystals of the title compound suitable for crystallographic study were produced by slow evaporation of a water solution at room temperature.

Refinement
The structure was solved by the direct method. H atoms of methyl groups were placed at calculated positions and treated as riding on the parent atoms, with U iso (H) = 1.5 U eq (C). H atoms near of the O4A and O4B atoms, and H atoms of water molecule were located in a difference Fourier map and further refined with SADI instruction to the restraint that they should be equal within about 0.02 Å and U iso (H) = 1.5Ueq(O). The OH and CH 3 groups near C(1) carbon atom are disordered over two position with occupancy factor 0.25 and 0.25 respectively. Oxygen atoms of the water solvent molecules O8, O9, O10 were refined isotropically-O8 is statistically disordered with occupancy 1/2 and it position depends on the disorder of the above mentioned OH group; O9 is situated at the origin (0, 0, 0) with 1/12 multiplicity;     Crystal packing of title compound, in a projection along the c axis. Solvate molecules as well as hydrogen bonds are omitted for clarity. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger. Geometric parameters (Å, º)