Bis(μ-3-nitrophthalato-κ2 O 1:O 2)bis[(thiourea-κS)zinc] dihydrate

In the title complex, [Zn2(C8H3NO6)2(CH4N2S)4]·2H2O, the carboxylate groups of the 3-nitrophthalate ligands coordinate in a bis-monodentate mode to the ZnII cations. This results in the formation of a centrosymmetric dimer containing two ZnII cations with distorted tetrahedral geometries provided by the O atoms of two different 3-nitrophthalate dianions and the S atoms of two non-equivalent coordinated thiourea molecules. The crystal structure exhibits N—H⋯O and O—H⋯O hydrogen bonds which link the dimers into a three-dimensional network.

In the title complex, [Zn 2 (C 8 H 3 NO 6 ) 2 (CH 4 N 2 S) 4 ]Á2H 2 O, the carboxylate groups of the 3-nitrophthalate ligands coordinate in a bis-monodentate mode to the Zn II cations. This results in the formation of a centrosymmetric dimer containing two Zn II cations with distorted tetrahedral geometries provided by the O atoms of two different 3-nitrophthalate dianions and the S atoms of two non-equivalent coordinated thiourea molecules. The crystal structure exhibits N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds which link the dimers into a threedimensional network.
The Zn atom shows a distorted tetrahedral coordination comprised of two O atoms from the carboxylate groups of two different 3-nitrophthalates and two S atoms of two non-equivalent coordinated thiourea molecules. The packing is stabilized by weak intra-and intermolecular N-H···O and O-H···O hydrogen bond.(see Table 1). A packing diagram is shown in Fig. 2.

Experimental
Zinc oxide (0.21 g, 2.5 mmol) was added to a stirred solution of 3-nitrophthalic acid (0.53 g, 2.5 mmol) in boiling water (20.0 ml) over a period of 40 min following which thiourea (0.30 g, 4 mmol) was added to the solution. After filtration, slow evaporation over a period of a week at room temperature provided colorless needle crystals of (I).

Refinement
The H atoms of the water molecule were found in difference Fourier maps. However, during refinement, they were fixed at O-H distances of 0.85 Å and their U iso values were set at 1.5 U eq (O). The H atoms of C-H and N-H groups were treated as riding, with C-H = 0.93 Å, and U iso (H) = 1.2 U eq (C) and N-H = 0.90 Å, and U iso (H) = 1.2 U eq (N). The C10, N3, N4 unit shows a rotational disorder about the C10-S2 bond. A simple split-atom model for the two nitrogen atoms is used in refinement of this structure. Each of the N atoms bonded to C10 is disordered over at least two sites. Refined occupancy factors for atoms N3/N3′ and N4/N4′ were 0.53 (3):0.47 (3).   The packing diagram of (I) showing the hydrogen-bonding interactions. For clarity, the minor components have been omitted. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.35 e Å −3 Δρ min = −0.50 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.