Bis(μ-iminodiacetato)bis[(2,2′-diamino-4,4′-bi-1,3-thiazole)lead(II)] tetrahydrate

In the crystal structure of the title compound, [Pb2(C4H5NO4)2(C6H6N4S2)2]·4H2O, the dinuclear PbII complex molecule is centrosymmetric. The Pb atom is chelated by a tridentate iminodiacetate anion (IDA) and a diaminobithiazole (DABT) ligand, while a carboxylate O atom from an adjacent IDA anion further bridges the Pb atom with a longer Pb—O bond [2.892 (3) Å]. The lone-pair electrons of the Pb atom occupy an axial site in the Ψ-pentagonal-bipyramidal coordination polyhedron. The IDA anion displays a facial configuration: its chelating five-membered rings assume an envelope configuration. Within the DABT ligand, the two thiazole rings are twisted relative to each other, making a dihedral angle of 9.51 (17)°. Extensive N—H⋯O, O—H⋯O and weak C—H⋯O hydrogen bonding helps to stabilize the crystal structure.

The molecular structure of the title compound is shown in Fig. 1. The dinuclear Pb II complex molecule is centro-symmetric. Each Pb atom is chelated by a tridentate iminodiacetate anion (IDA) and a diaminobithiazole (DABT) ligand, and one carboxyl O atom from the adjacent IDA anion further bridges the Pb atom. The lone-pair electrons of the Pb atom occupy an axial site in the distorted Ψ-pentagonal bipyramidal coordination geometry, which is similar to that found in Pb II complexes reported previously (Lacouture et al., 2001;Jones et al., 1988). The longer Pb-O(bridge) bond distance (Table   1) is comparable to 2.968 (4) Å found in a related Pb complex (Inoue et al., 1993). The IDA displays a facial configuration, its both chelating five-membered rings assume the envelope configuration. Within the DABT ligand, the two thiazole rings are twisted to each other with a dihedral angle of 9.51 (17)°, it agrees with 14.7 (3) and 9.5 (2)° found in transition metal complexes of DABT Zhang et al., 2006).
The extensive N-H···O, O-H···O and weak C-H···O hydrogen bonding helps to stabilize the crystal structure (Table   2).

Experimental
An aqueous solution (20 ml) containing DABT (0.20 g, 1 mmol) and Pb(NO 3 ) 2 (0.33 g, 1 mmol) was mixed with another aqueous solution (10 ml) of H 2 IDA (0.13 g, 1 mmol) and NaOH (0.08 g, 2 mmol). The mixture was refluxed for 5 h. The solution was filtered after cooling to room temperature. Single crystals were obtained from the filtrate after one week.

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Pb 0.545731 (18)