Poly[[dodecaaquahexakis(μ2-pyridine-2,5-dicarboxylato)tricopper(II)diytterbium(III)] dihydrate]

The asymmetric unit of the title heterometallic coordination polymer, {[Cu3Yb2(C7H3NO4)6(H2O)12]·2H2O}n, contains one YbIII and two CuII atoms. The CuII atom that is located on an inversion center is N,O-chelated by two pyridine-2,5-dicarboxylate (pdc) anions in a square-planar geometry; the Cu atom located on a general position is N,O-chelated by two pdc anions in the basal plane and is further coordinated by a water O atom at the apical position in a distorted square-pyramidal geometry. The Yb(III) atom is eight coordinated in a distorted square-antiprismatic geometry formed by three carboxylate O atoms from three pdc anions and five water molecules. The pdc anions bridge adjacent Yb(III) and Cu(III) atoms, forming a three-dimensional polymeric structure. The crystal structure contains extensive O—H⋯O hydrogen bonds. π–π stacking is present in the crystal structure, the shortest centroid–centroid distance between parallel pyridine rings of adjacent molecules being 3.646 (3) Å.


S1. Comment
Many studies concering the use of pdc as a ligand toward transition metal (Wen et al., 2007) and /or rare earth transition metal (Wei et al., 2005;Huang et al., 2008) have shown that a great variety of polymeric structures can be obtained as a result of the differnet coordination modes of the pdc ligands.
The asymmetric unit of the title heterometallic coordination polymer, [Cu 3 Yb 2 (C 7 H 3 NO 4 ) 6 (H 2 O) 12 .4H 2 O] n ,contains one Yb III and two Cu II atoms, three pyridine-2,5-dicarboxylate (pdc) anions and six water molecules. One Cu II atom is located on an located on an inversion center and is N,O-chelated by two pdc anions in the equatorial plane with square-planar geometry; the other Cu atom is N,O-chelated by two pdc anions in the coordination basal plane and coordinated by a carboxyl O atom at the apical position with a distorted square-pyramidal geometry [Cu-O = 2.374 (4) Å in the apical direction]. The Yb atom is eight coordinated with a distorted square-antiprismatic geometry formed by three carboxylate O atoms from three pdc anions and five water molecules (selected bond lengths are given in Table 1). The pdy anions bridge adjacent Yb and Cu atoms to form the three dimensional polymeric structure (Fig. 1).

S2. Experimental
A mixture of ytterbium chloride hexahydrate (0.2438 g, 0.25 mmol), copper acetate hydrate (0.050 g, 0.25 mmol), pyridine-2,5-dicarboxylic acid (0.0418 g, 0.25 mmol,) and 10 ml H 2 O were put in a 23-ml Teflon liner reactor and heated at 418 K in oven for 48 h. The resulting solution was slowly cooled to room temperature. The blue transparent single crystals of the title complex were obtained in 34.26% yield (based on Yb).

S3. Refinement
Water H atoms were placed in calculated positions and refined with the distances constrains of O-H = 0.82, and U iso (H)= 1.5U eq (O). Other H atoms were positioned geometrically with C-H = 0.93 Å and refined using a riding model,

Figure 2
The molecular packing for the title compound. Hydrogen bonds are shown as dashed lines.

Crystal data
[Cu 3 Yb 2 (C 7 H 3 NO 4 ) 6 where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 1.01 e Å −3 Δρ min = −1.68 e Å −3 Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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.