Bis(1-methylpiperazine-1,4-diium) tetrabromidocuprate(II)

The title compound, (C5H14N2)[CuBr4], was synthesized by hydrothermal reaction of CuBr2 with 1-methylpiperazine in an HBr/water solution. Both amine N atoms are protonated. The Cu—Br distances in the tetrahedral anion are in the range 2.3809 (11)–2.4131 (11) Å. In the crystal, moderately strong and weak intermolecular N—H⋯Br hydrogen bonds link the anion and cation units into an infinite two-dimensional network parallel to the ab plane.


Experimental
Crystal data (C 5

Comment
Amino derivatives of piperazine have found a wide range of applications in material science, due to their magnetic, fluorescent and dielectric properties. There has also been an increased interest in the preparation of amino coordination compounds (Aminabhavi et al. 1986;Dai & Fu 2008a;Dai & Fu 2008b;Fu, et al. 2009). We report here the crystal structure of the title compound, bis-(1-methylpiperazine-1,4-diium) tetrabromide copper(II).
The asymmetric unit is composed of one CuBr 4 2anion and one 1-methylpiperazine-1,4-diium cation ( Fig.1). Both amine N atoms are protonated, indicating thus two positive charges on the cation that balance the two negative charges on the CuBr 4 2anion. Geometric parameters of the title compound are in the normal range.
In the crystal structure, all H atoms of the amine groups are involved in intermolecular N-H···Br hydrogen bonds with the bond angles ranging from 132.7° to 154.3° and N···Br distances from 3.339 (6)Å to 3.457 (5)Å, respectively. Following the survey by Brammer et al. (2001) the N2-H2D···Br1 and N2-H2D···Br2 H-bonds should be considered to be clearly weaker than the N2-H2C···Br3 and N1-H1···Br4 interactions ( Table 1). The hydrogen bonds link the cations and anions into an infinite two-dimensional network parallel to the ab-plane (Fig.2). The chlorine analogue of the title compound is reported elsewhere in this issue (Peng, 2011).

Refinement
All H atoms attached to C atoms were fixed geometrically and treated as riding on the parent atoms with C-H = 0.97 Å (methylene) and C-H = 0.96 Å (methyl) with U iso (H) = 1.2U eq (methylene) and U iso (H) = 1.5U eq (methyl). The positional parameters of the H atoms (N1, N2) were initially refined freely, subsequently restrained using a distance of 0.90 Å and in the final refinements treated in riding motion on their parent nitrogen atoms with U iso (H)=1.2U eq (N). Bis(1-methylpiperazine-1,4-diium) tetrabromidocuprate(II) Crystal data (C 5

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.