Poly[diaquabis(μ2-5-carboxy-2-propyl-1H-imidazole-4-carboxylato-κ3 N 3,O 4:O 5)lead(II)]

In the title complex, [Pb(C8H9N2O4)2(H2O)2]n, the eight-coordinate PbII atom lies on a twofold rotation axis and adopts a slightly distorted square-antiprismatic N2O6 coordination geometry. The ligand donor atoms are the tertiary N atoms of the imidazole rings and the carboxylate O atoms of two chelating 5-carboxy-2-propyl-1H-imidazole-4-carboxylate ligands, the carboxy O atoms of two additional imidazole ligands and two water O atoms. The carboxy O and the N,O-chelate systems also link adjacent PbII atoms, forming a two-dimensional layer structure, with four individual PbII atoms located at the corners of a square. These layers are further interconnected by an extensive array of O—H⋯O and N—H⋯O hydrogen bonds into a three-dimensional network.

In the title complex, [Pb(C 8 H 9 N 2 O 4 ) 2 (H 2 O) 2 ] n , the eightcoordinate Pb II atom lies on a twofold rotation axis and adopts a slightly distorted square-antiprismatic N 2 O 6 coordination geometry. The ligand donor atoms are the tertiary N atoms of the imidazole rings and the carboxylate O atoms of two chelating 5-carboxy-2-propyl-1H-imidazole-4-carboxylate ligands, the carboxy O atoms of two additional imidazole ligands and two water O atoms. The carboxy O and the N,Ochelate systems also link adjacent Pb II atoms, forming a twodimensional layer structure, with four individual Pb II atoms located at the corners of a square. These layers are further interconnected by an extensive array of O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds into a three-dimensional network.

Comment
It is well known that 4,5-imidazoledicarboxylic acid, a rigid N-heterocyclic dicarboxylic acid has great potential as a ligand in coordination complexes and for hydrogen bond formation. Imidazoledicarboxylate complexes have been found to exhibit useful properties, such as magnetism and porosity (Cao et al., 2002;Rajendiran et al., 2003). We have therefore reacted the 2-propyl-1H-imidazole-4,5 dicarboxylic acid ligand with Pb(NO 3 ) 2 under hydrothermal conditions to obtain a new Pb II complex and its structure is reported here.
In the title complex, [Pb(C 8 H 9 N 2 O 4 ) 2 (H 2 O) 2 ] n , the eight coordinate Pb II atom lies on a two-fold rotation axis and adopts a slightly distorted square-antiprismatic N 2 O 6 coordination geometry. The ligand donor atoms are the N1 atoms of the imidazole rings and the carboxylate O1 atoms of two chelating 5-carboxy-2-propyl-1H-imidazole-4-carboxylato ligands, the O4 carboxy oxygen atoms of two additional imidazole ligands and two O5 water molecules. The O1 and N1 atoms of the chelate systems also link adjacent Pb II centres forming a two-dimensional layer structure, with four individual Pb II atoms located at the corners of a square. These layers are further interconnected by an extensive array of O-H···O and N-H···O hydrogen bonds into a three-dimensional network.

Experimental
A mixture of Pb(NO 3 ) 2 (0.5 mmol, 0.07 g) and 2-propyl-1H-imidazole-4,5-dicarboxylic acid(0.5 mmol, 0.99 g) in 15 ml of H 2 O solution was sealed in an autoclave equipped with a Teflon liner (25 ml) and then heated at 373k for 3 days. Crystals of the title compound were obtained by slow evaporation of the solvent at room temperature.

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). H atoms of the water molecule were located in a difference map and were allowed to ride on the parent atom, with U iso (H)=1.2 U eq . supplementary materials sup-2 Figures Fig. 1. The structure of the title compound, showing the atomic numbering scheme. Non-H atoms are shown with 30% probability displacement ellipsoids(H atoms are omitted for clarity). [Symmetry codes: (i) 1-x, y, 1.5-z; (ii) -0.5+x, 0.5+y, z; (iii) 0.5+x, 0.5+y, z; (iv) 0.5+x, -0.5+y, z; (v) 0.5-x, -0.5+y, 1.5-z] Crystal data [Pb(C 8

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 Rfactors(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.