Poly[[dodeca-aqua-bis-(μ(3)-pyridine-2,6-dicarboxyl-ato)tetra-kis-(μ(2)-pyridine-2,6-dicarboxyl-ato)tri-calciumdieuropium(III)] 10.5-hydrate].

In the title compound, {[Ca(3)Eu(2)(C(7)H(3)NO(4))(6)(H(2)O)(12)]·10.5H(2)O}(n), the Eu(III) ion is nine-coordinated by three tridentate pyridine-2,6-dicarboxyl-ate (PDA) ligands, forming a [Eu(PDA)(3)](3-) building block. The Ca(2+) ions adopt two types of coordination geometries. One Ca(2+) ion, lying on a twofold rotation axis, is eight-coordinated by four carboxyl-ate O atoms from four PDA ligands and four water mol-ecules, and the other two Ca(2+) ions, each lying on an inversion center, are six-coordinated by two carboxyl-ate O atoms from two PDA ligands and four water mol-ecules. The carboxyl-ate groups bridge the Eu(III) and Ca(2+) ions into a three-dimensional porous framework, with channels extending along [010] and [001] in which lattice water mol-ecules are located. Two of the lattice water mol-ecules are disordered over two sets of sites with equal occupancy and one water mol-ecule is 0.25-occupied. Numerous O-H⋯O hydrogen bonds involving the water mol-ecules and carboxyl-ate O atoms are present.

In the title compound, {[Ca 3 Eu 2 (C 7 H 3 NO 4 ) 6 (H 2 O) 12 ]Á-10.5H 2 O} n , the Eu III ion is nine-coordinated by three tridentate pyridine-2,6-dicarboxylate (PDA) ligands, forming a [Eu(PDA) 3 ] 3À building block. The Ca 2+ ions adopt two types of coordination geometries. One Ca 2+ ion, lying on a twofold rotation axis, is eight-coordinated by four carboxylate O atoms from four PDA ligands and four water molecules, and the other two Ca 2+ ions, each lying on an inversion center, are sixcoordinated by two carboxylate O atoms from two PDA ligands and four water molecules. The carboxylate groups bridge the Eu III and Ca 2+ ions into a three-dimensional porous framework, with channels extending along [010] and [001] in which lattice water molecules are located. Two of the lattice water molecules are disordered over two sets of sites with equal occupancy and one water molecule is 0.25-occupied. Numerous O-HÁ Á ÁO hydrogen bonds involving the water molecules and carboxylate O atoms are present.
heterometal-organic frameworks associated with lanthanide and alkaline earth ions are rather rare, only Ln-Ba complexes based on pyridine-2,6-dicarboxylic acid ligand were reported (Zhao, Zuo et al., 2009). In this paper, we report the synthesis and crystal structure of the title compound, using the hydrothermal method with pyridine-2,6-dicarboxylic acid.
In the title compound, the Eu III ion coordinates with three PDA ligands in a tridentate mode, forming a [Eu(PDA) 3 ] 3building block. The remaining coordination sites in the [Eu(PDA) 3 ] 3unit coordinate with Ca 2+ ions. The Ca 2+ ions adopt two types of coordination geometry, as shown in Fig. 1 (Fig. 2).

Refinement
H atoms bonded to C atoms were positioned geometrically and refined using a riding model, with C-H = 0.95 Å and U iso (H) = 1.2U eq (C). H atorms of water molecules were found from difference Fourier maps and refined with a distance sup-2 Acta Cryst. (2012). E68, m685-m686 restraint of O-H = 0.85 (1) Å and with U iso (H) = 1.2U eq (O). O22 and O23 atoms were disordered over two sets of positions with occupancy factors of 0.5:0.5, respectively. The occupancy factor of the lattice water O24 was set to 0.25.
H atorms of disordered water molecules O22, O23 and O24 were not included. The highest residual electron density was found 2.36 Å from H5 atom and the deepest hole 0.78 Å from Eu1 atom.

Figure 1
The asymmetric unit of the title compound. Displacement ellipsoids are drawn at the 30% probability level. Lattice water molecules and H atoms are omitted and C atoms are not labeled for clarity. [Symmetry codes:

Figure 2
The three-dimensional structure of the title compound viewed along the b axis. Lattice water molecules and H atoms are omitted for clarity.

Crystal data
[Ca 3 Eu 2 (C 7 H 3 NO 4 ) 6 (H 2 O) 12 ]·10.5H 2 O M r = 1820.14 Monoclinic, P2/c Hall symbol: -P 2yc a = 16.070 (4) Å b = 9.471 (2) Å c = 23.540 (6)  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.