catena-Poly[[triaquachlorido-μ3-malonato-cerium(III)] hemihydrate]

The asymmetric unit of the title compound, {[Ce(C3H2O4)Cl(H2O)3]·0.5H2O}n, contains a Ce3+ atom coordinated by a chloride anion, three water molecules and a malonate ligand, and one water molecule of crystallization with a factor of occupancy of 50%. The malonate ligand is bonded to three different symmetry-related metal atoms yielding a one-dimensional coordination polymer running parallel to the a axis. A supramolecular network composed of strong and highly directional O—H⋯O and O—H⋯Cl hydrogen bonds ensures a close and effective packing of adjacent polymeric chains.

The asymmetric unit of the title compound, {[Ce(C 3 H 2 O 4 )Cl-(H 2 O) 3 ]Á0.5H 2 O} n , contains a Ce 3+ atom coordinated by a chloride anion, three water molecules and a malonate ligand, and one water molecule of crystallization with a factor of occupancy of 50%. The malonate ligand is bonded to three different symmetry-related metal atoms yielding a onedimensional coordination polymer running parallel to the a axis. A supramolecular network composed of strong and highly directional O-HÁ Á ÁO and O-HÁ Á ÁCl hydrogen bonds ensures a close and effective packing of adjacent polymeric chains.
Data collection: APEX2 (Bruker, 2006); cell refinement: SAINT-Plus (Bruker, 2005); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: DIAMOND (Brandenburg, 2009) (Shi et al., 2008). Following our continuous interest in the preparation and study of the properties of metal-organic frameworks based on phosphonates (Cunha-Silva et al., 2009;Cunha-Silva et al., 2007;Paz et al., 2005;Paz et al., 2004), and our recent motivation to employ microwaves as an alternative heating source (Klinowski et al., 2010), we decided to test the afore-  Table 1), the Ce1-Cl1 bond is considerably longer [2.9086 (6) Table 2). The hydrogen bonding interactions can be divided in three different types concerning the connectivity in relation to the polymeric chain. Intra-chain hydrogen bonds add stability to the coordination polymer by connecting three adjacent metal centres through a O3W···O2W···Cl chain (blue dashed lines in Figure 2). The other two types of hydrogen bonds involve the crystal packing of adjacent coordination polymers: inter-chain interactions (green dashed lines in Figures   2 and 3) connect coordinated water molecules (O1W and O3W) of one polymer to the oxygen atoms of malonato ligands (O2 and O4, respectively) of an adjacent polymer; the second type of inter-chain interactions occur via the half-occupied crystallization water molecule (O4W) forming O4···O4W···Cl1 chains (pink dashed lines in Figures 2 and 3). The extensive supplementary materials sup-2 hydrogen bonding network described above leads to a series of strong connections among adjacent coordination polymers as depicted in Figure 3.

Experimental
The title compound was prepared following the procedure described elsewhere (Shi et al., 2008), while replacing hydrothermal heating by microwave heating (Klinowski et al., 2010). The reactive homogeneous suspension was transferred to a 10 ml IntelliVent reactor which was placed inside a CEM Focused Microwave TM Synthesis System Discover S-Class equipment. The reaction took place with constant magnetic stirring (controlled by the microwave equipment) and by monitoring the temperature and pressure inside the vessel. Experimental conditions: i) temperature of 120 °C; ii) power of 50 W; iii) reaction time of 45 minutes of microwave irradiation. A constant flow of air (ca 10 psi) ensured a close control of the temperature inside the vessel. After reacting a colourless solution was obtained. The resulting solution was then left to stand at ambient temperature until large block crystals grew by slow evaporation of the solvent over a period of six months.

Refinement
C-bound H atoms were located at their idealized positions and were included in the final structural model in riding-motion approximation with C-H distances of 0.99 Å. The isotropic displacement parameters for these atoms were fixed at 1.2×U eq of the carbon atom to which they are attached.
All hydrogen atoms associated with the water molecules were directly located from difference Fourier maps and included in the structure with the O-H and H···H distances restrained to 0.95 (1) and 1.55 (1) Å, and with U iso fixed at 1.5×U eq of the O atom to which they are attached. Fig. 1. Asymmetric unit of the title compound showing all non-hydrogen atoms as displacement ellipsoids drawn at the 50% probability level and hydrogen atoms as small spheres with arbitrary radius [symmetry codes: (i)2 -x, -y, 2 -z; (ii)1 -x, -y, 2 -z]. The water molecule of crystallization, with fractional occupancy, is also depicted. For clarity, the coordination sphere of Ce1 was completed by generating by symmetry the remaining oxygen atoms.