Poly[diaquabis(μ-4-carboxy-2-propyl-1H-imidazole-5-carboxylato-κ3 N 3,O 4:O 5)calcium(II)]

In the title complex, [Ca(C8H9N2O4)2(H2O)2]n, the CaII atom is eight-coordinated in a distorted square-antiprismatic environment. The water-coordinated Ca atom is N,O-chelated by the monocarboxylate anion; the carboxyl –CO2 portion engaged in chelation bears an acid hydrogen. The free –CO2 portion engages in bonding to adjacent Ca atoms. The CaII centres are connected through the ligand, forming a layer structure; the layers are linked by hydrogen bonds into a three-dimensional network.

In the title complex, [Ca(C 8 H 9 N 2 O 4 ) 2 (H 2 O) 2 ] n , the Ca II atom is eight-coordinated in a distorted square-antiprismatic environment. The water-coordinated Ca atom is N,O-chelated by the monocarboxylate anion; the carboxyl -CO 2 portion engaged in chelation bears an acid hydrogen. The free -CO 2 portion engages in bonding to adjacent Ca atoms. The Ca II centres are connected through the ligand, forming a layer structure; the layers are linked by hydrogen bonds into a three-dimensional network.

Related literature
For the potential uses and diverse structrual types of structures containing metals and N-heterocyclic carboxylic acids, see: Liang et al. (2002); Net et al. (1989); Nie et al. (2007).

S1. Comment
Recently, structures containing metals and N-heterocyclic carboxylic acids has attracted much attention, they can function as a multidentate ligand, exhibiting diverse structrual type and can be potentially used as functional materials (Nie et al., 2007;Liang et al.,2002;Net et al., 1989). In this paper, we report the synthesis and structure of a new Ca(II) complex obtained from 2-Propyl-1H-imidazole-4,5-dicarboxy with metal salts under hydrothermal conditions.
As illustrated in figure 1, the title complex molecule is eight-coordinated by two chelating rings [Ca-N=2.5998 (15)Å and Ca-O=2.605 (5) Å] and two carboxylate O atoms from two different 2-Propyl-1H-imidazole-4,5-dicarboxylate ligands and two water molecules, exhibiting a distorted square antiprismatic structure, the title Complex displays an extended two-dimensional layer structure constructed of quasi-squares, with four Ca atoms at the corners and 2-Propyl-1H-imidazole-4,5-dicarboxylate anions at each edge as linkers connecting two Ca atoms. the edge lengthes are equal, with a value of 9.0901 (16) Å. the angles of the rhombus are 88.650 (2)° and 91.350 (5)° (Fig. 2). Two dimensional layers are further linked by hydrogen bonds (Table 1), forming a three-dimensional network (Fig. 3)

S2. Experimental
A mixture of Ca(II)chloride (0.5 mmol, 0.055 g) and 2-propyl-1H-imidazole-4,5-dicarboxylic acid(0.5 mmol, 0.99 g) in 10 ml of distilled water was sealed in an autoclave equipped with a Teflon liner (20 ml) and then heated at 433k for 3 days. Crystals of the title compound were obtained by slow evaporation of the solvent at room temperature.

S3. Refinement
Carbon and nitrogen bound H atoms were placed at calculated positions and were treated as riding on the parent C or N atoms with C-H = 0.93 Å, N-H = 0.86 Å, and with U iso (H) = 1.2 U eq (C, N). The water H-atoms were located in a difference map, and were refined with a distance restraint of O-H = 0.84 Å; their U iso values were refined.    View the three-dimensional network.

Poly[diaquabis(µ-4-carboxy-2-propyl-1H-imidazole-5-carboxylato-κ 3 N 3 ,O 4 :O 5 )calcium(II)]
Crystal data [Ca(C 8  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.29 e Å −3 Δρ min = −0.23 e Å −3 Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.0076 (9) 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.