Piperazinediium tetrachloridozincate(II)

In the title compound, (C4H12N2)[ZnCl4], the Zn atom adopts a slightly distorted tetrahedral geometry. In the crystal, the dication and dianion interact by way of N—H⋯Cl and N—H⋯(Cl,Cl) hydrogen bonds to result in a layered network propagating in (010). The hydrogen-bonding network is unbalanced, with three Cl atoms accepting two hydrogen bonds each and one Cl atom not accepting any hydrogen bonds: the latter shows the shortest Zn—Cl bond length. The crystal studied was found to be an inversion twin.

In the title compound, (C 4 H 12 N 2 ) [ZnCl 4 ], the Zn atom adopts a slightly distorted tetrahedral geometry. In the crystal, the dication and dianion interact by way of N-HÁ Á ÁCl and N-HÁ Á Á(Cl,Cl) hydrogen bonds to result in a layered network propagating in (010). The hydrogen-bonding network is unbalanced, with three Cl atoms accepting two hydrogen bonds each and one Cl atom not accepting any hydrogen bonds: the latter shows the shortest Zn-Cl bond length. The crystal studied was found to be an inversion twin.

Comment
As part of our ongoing investigations of hydrogen bonding networks in molecular salts containing metal-chlorido complexes, (Bremner & Harrison, 2003), we now report the structure of the title compound, (I). The structure of a monohydrate containing the same cation and anion was reported previously (Kefi & Nasr, 2005).
The Zn atom in (I) adopts a slightly distorted tetrahedral coordination arising from four chloride ions (Table 1, Fig. 1) and the organic dication adopts a typical chair geometry with normal bond lengths and angles (Allen et al., 1995), the two nitrogen atoms being displaced from the mean plane of the four carbon atoms by -0.654 (7)Å and 0.685 (6)Å for N1 and N2, respectively.
In the crystal of (I), the components interact by way of simple N-H···Cl and bifurcated N-H···(Cl,Cl) hydrogen bonds (Table 2), such that each NH 2 group forms one simple and one bifurcated bond. Some of the bifurcated H···Cl contacts are relatively long, but still significantly shorter than the H···Cl van der Waals' contact distance of 2.95 Å.
This hydrogen-bond connectivity results in a layered network propagating in (010) (Fig. 2). It is notable that this H bonding arrangement is unbalanced (Wilkinson & Harrison, 2007), with Cl1, Cl2 and Cl4 accepting two hydrogen bonds each, whereas Cl3 does not accept any H bonds. This may correlate with the fact that the Zn1-Cl3 bond length in (I) is the shortest of the four zinc-chloride links. Within the layers, various graph-set motifs (Bernstein et al., 1995) are apparent, including R 2 2 (6) and R 4 4 (14) loops.
In (C 4 H 12 N 2

Experimental
In an attempt to prepare a zinc-arsenite open-framework compound, ZnO, As 2 O 3 and piperazine hexahydate were dissolved in a 1:1:1 molar ratio in dilute HCl solution. Colourless slabs of (I) grew as the water slowly evaporated, accompanied by octahedra of As 2 O 3 .

Refinement
The H atoms were placed in idealized locations (C-H = 0.99 Å, N-H = 0.92 Å) and refined as riding with U iso (H) = 1.2U eq (carrier).
supplementary materials sup-2 Figures   Fig. 1. View of the molecular structure of (I) showing 50% displacement ellipsoids (arbitrary spheres for the H atoms) with the hydrogen bonds indicated by double dashed lines. Fig. 2. Part of an (010) hydrogen bonded sheet in the structure of (I) with the hydrogen bonds shown as double dashed lines. All the carbon-bound H atoms are omitted for clarity. Symmetry codes as in Table 2.