Piperazine-1,4-diium bis[tetrachloridoaurate(III)] dihydrate

In the title compound, (C4H12N2)[AuCl4]2·2H2O, the AuIII atom has a square-planar geometry. The piperazinium dication lies on an inversion centre and adopts a typical chair conformation. In the crystal, a combination of N—H⋯O, N—H⋯Cl and O—H⋯Cl hydrogen bonds results in the formation of a three-dimensional network.

In the title compound, (C 4 H 12 N 2 )[AuCl 4 ] 2 Á2H 2 O, the Au III atom has a square-planar geometry. The piperazinium dication lies on an inversion centre and adopts a typical chair conformation. In the crystal, a combination of N-HÁ Á ÁO, N-HÁ Á ÁCl and O-HÁ Á ÁCl hydrogen bonds results in the formation of a three-dimensional network.

S1. Comment
The asymmetric unit of the title compound consists of a discrete [AuCl 4 ]complex anion, one water molecule and onehalf of a diprotonated piperazinium dication (Fig. 1). The Au atom in the tetrachloridoaurate anion exhibits a squareplanar coordination. A similar geometry has been observed, for exemple, in tetraphenylantimony(V) tetrachloroaurate (Sharutin et al., 2008) and bipyridinium tetrachloroaurate (Zhang et al., 2006). The Au-Cl bond lengths are in the range of 2.2802 (6) -2.2842 (7) Å. In the crystal structure, the anions are stacked into columns along the a axis, parallel to each other. The distances between anion planes are ca. 3.734 and 3.999 Å. The organic piperazinium dication lies at an inversion centre and adopts a typical chair geometry with normal valence bond lengths (Allen et al., 1987) and angles, as observed in the structures of piperazinediium tetrachloridozincate (Sutherland & Harrison, 2009) and piperazinediium tetrachloridozincate monohydrate (Kefi & Nasr, 2005).
The piperazinium dications and water molecules are linked by intermolecular bifurcated N-H···O hydrogen bonds to form chains proagagting along the [100] direction (Fig. 2). The water-piperaziniun chains and the anion stacks form a three-dimensional framework (Fig. 3) via bifurcated N-H···Cl and O-H···Cl hydrogen bonds (Table 1).

S2. Experimental
The chemicals used were of reagent grade. Ciprofloxacin hydrochloride (37 mg, 0.1 mmol) and gold(III) chloride (AuCl 3 30 mg, 0.1 mmol) were dissolved in 10 ml of 32% of HCl. Yellow crystals of the title compound, suitable for X-ray analysis, were obtained by slow evaporation in air at rt, after a few days.

S3. Refinement
The water H-atoms were located from difference electron-density maps and were refined with distance restraints of O-H  The asymmetric unit of the title compound, showing 50% displacement ellipsoids (arbitrary spheres for the H atoms).    A view along the a axis of the crystal packing of the title compound, with the hydrogen bonds shown as dotted lines. All the C-bound H atoms have been omitted for clarity. Symmetry codes are the same as in Table 1.

Piperazine-1,4-diium bis[tetrachloridoaurate(III)] dihydrate
Crystal data (C 4  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.002 Δρ max = 1.36 e Å −3 Δρ min = −0.75 e Å −3 Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.01512 (17) 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.

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