Bis(cyclohexylammonium) terephthalate

In the title molecular salt, 2C6H11NH3 +·C8H4O4 2−, the terephthalate dianion is close to being planar (r.m.s. deviation = 0.049 Å). In the crystal, the cations and anions are linked by N—H⋯O hydrogen bonds into (010) sheets. Of the four terephthalate O atoms, two accept two hydrogen bonds each and two accept one hydrogen bond each.

In the title molecular salt, 2C 6 H 11 NH 3 + ÁC 8 H 4 O 4 2À , the terephthalate dianion is close to being planar (r.m.s. deviation = 0.049 Å ). In the crystal, the cations and anions are linked by N-HÁ Á ÁO hydrogen bonds into (010) sheets. Of the four terephthalate O atoms, two accept two hydrogen bonds each and two accept one hydrogen bond each.

Meng Ting Han Comment
At present, much attention in ferroelectric material field is focused on developing ferroelectric pure organic or inorganic compounds (Haertling et al. 1999;Homes et al. 2001). Recently we have reported the synthesis of a variety of compounds Hang et al., 2009), which have potential piezoelectric and ferroelectric properties. In order to find more dielectric ferroelectric materials, we investigate the physical properties of the title compound (Fig. 1). The dielectric constant of the title compound as a function of temperature indicates that the permittivity is basically temperature-independent (dielectric constant equaling to 0.26 to 0.79), suggesting that this compound should be not a real ferroelectrics or there may be no distinct phase transition occurred within the measured temperature range. Similarly, below the melting point (higher than 533 K) of the compound, the dielectric constant as a function of temperature also goes smoothly, and there is no dielectric anomalyobserved (dielectric constant equaling to 0.26 to 0.79). Herein, we report the synthesis and crystal structure of the title compound.
The molecular structure of the title compound is shown in Fig. 1. There are one C 8 H 4 O 4 2anion and two cyclohexanamine cation in the asymmetric unit. All cyclohexanamine rings are, of course, chair conformation. As can be seen from the packing diagram ( Fig. 2), molecules are connected via intermolecular N-H···O hydrogen bonds to form a twodimensional plane. Dipole-dipole and van der Waals interactions are effective in the molecular packing.

Experimental
A mix of cyclohexylamine (0.461 g, 0.01 mol) and terephthalic acid (0.8307 g, 0.005 mol) in water (20 ml) was stirred until clear. After several days, the title compound was formed and recrystallized from solution to afford colourless prisms.

Computing details
Data collection: CrystalClear (Rigaku, 2005); cell refinement: CrystalClear (Rigaku, 2005); data reduction: CrystalClear (Rigaku, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure:   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 O1