Dichlorido{2-[3-(dimethylammonio)propyliminomethyl]phenolato}zinc(II) hemihydrate

The title complex, [ZnCl2(C12H18N2O)]·0.5H2O, is a mononuclear zinc(II) compound derived from the zwitterionic form of the Schiff base 2-[3-(dimethylamino)propyliminomethyl]phenol. The ZnII atom is four-coordinated by the imine N and the phenolate O atoms of the Schiff base ligand, and by two chloride ions, in a distorted tetrahedral coordination geometry. The dimethylammonio group is disordered over two positions with site occupancies of 0.51 (3) and 0.49 (3). In the asymmetric unit, there is also a disordered water molecule with a partial occupancy of 0.5. In the crystal structure, the water molecules are linked to the Schiff base complex molecules through intermolecular N—H⋯O hydrogen bonds. Molecules are further linked through additional intermolecular N—H⋯O hydrogen bonds, forming chains running along the b axis.

Schiff bases have widely been used as versatile ligands in coordination chemistry (Biswas et al., 2008;Wu et al., 2008;Kawamoto et al., 2008;Ali et al., 2008;Habibi et al., 2007), and their metal complexes are of great interest in many fields (Chen et al., 2008;Yuan et al., 2007;Tomat et al., 2007;Darensbourg & Frantz, 2007). Zinc(II) is an important element in biological systems and functions as an active site of hydrolytic enzymes, such as carboxypeptidase and carbonic anhydrase where it is in a hard-donor coordination environment of nitrogen and oxygen ligands (Lipscomb & Sträter, 1996).
Recently, we have reported some Schiff base complexes (Zhu & Yang, 2008a,b,c,d). In this paper, the synthesis and structural characterization of a new zinc(II) complex ( Fig. 1) of the Schiff base ligand 2-[(3-dimethylaminopropylimino)methyl]phenol is reported.
The zinc(II) atom in the title compound is four-coordinated by the imine N and phenolate O atoms of the zwitterionic form of the Schiff base ligand, and by two Clions in a tetrahedral coordination geometry. The coordinate bond lengths (Table 1) are typical and comparable to the corresponding values observed in other similar zinc(II) Schiff base complexes Wei et al., 2007;Qiu, 2006a,b).
In the crystal structure, the water molecules are linked to the Schiff base complex molecules through intermolecular N-H···O hydrogen bonds ( Table 2). The molecules are further linked through intermolecular N-H···O hydrogen bonds (Table   2), forming chains running along the b axis (Fig. 2).

Experimental
The Schiff base compound was prepared by the condensation of equimolar amounts of salicylaldehyde with N,N-dimethylpropane-1,3-diamine in a methanol solution. The complex was prepared by the following method: to an anhydrous methanol solution (5 ml) of ZnCl 2 (13.7 mg, 0.1 mmol) was added a methanol solution (10 ml) of the Schiff base compound (20.6 mg, 0.1 mmol) with stirring. The mixture was stirred for 30 min at room temperature and filtered. Upon keeping the filtrate in air for a few days, colourless block-shaped crystals were formed at the bottom of the vessel on slow evaporation of the solvent.

Refinement
H atoms bound to C and N atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C-H distances in the range 0.93-0.97 Å, N-H distances of 0.91 Å, and with U iso (H) = 1.2U eq (C,N) and 1.5U eq (methyl C). The dimethylammmonium group is disordered over two distinct sites, with occupancies of 0.51 (3) and 0.49 (3), respectively. The lattice water molecule is also disordered, with an occupancy restrained to 0.50. The water H atoms were placed at calculated positions and refined with the O-H and H···H lengths constrained to 0.85 (1) and 1.37 (2) Å, respectively, and with the isotropic thermal parameter fixed at 0.08 Å 2 .
supplementary materials sup-2 Figures Fig. 1. The molecular structure of the title compound with ellipsoids drawn at the 30% probability level. Only the major component of disorder is shown.

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 > 2sigma(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.

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