Bis(2,9-dimethyl-1,10-phenanthrolin-1-ium) hydrogen (S,S)-tartrate nonahydrate

The asymmetric unit of the title compound, 2C14H13N2 +·2C4H5O6 −·9H2O, contains two cations and two anions in addition to nine molecules of water. Each of the hydrogen tartrate anions is hydrogen bonded to itself by translation along [100] in a head-to-tail fashion via a short hydrogen bond with donor–acceptor distances of 2.473 (4) and 2.496 (4) Å. A large number of intermolecular O–H⋯O, N—H⋯O and C–H⋯O hydrogen-bonding interactions, as well as π–π stacking [centroid–centroid distances in the range 3.642 (3) to 3.866 (3) Å], play an important role in the crystal structure.

The asymmetric unit of the title compound, 2C 14 H 13 N 2 + Á-2C 4 H 5 O 6 À Á9H 2 O, contains two cations and two anions in addition to nine molecules of water. Each of the hydrogen tartrate anions is hydrogen bonded to itself by translation along [100] in a head-to-tail fashion via a short hydrogen bond with donor-acceptor distances of 2.473 (4) and 2.496 (4) Å . A large number of intermolecular O-HÁ Á ÁO, N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen-bonding interactions, as well asstacking [centroid-centroid distances in the range 3.642 (3) to 3.866 (3) Å ], play an important role in the crystal structure.

Comment
We recently reported the structure of the trihydrate of a salt formed by proton transfer from D-tartaric acid to phenanthroline (Derikvand & Olmstead, 2010). An interesting feature of this structure was the existence of a short hydrogen bond between adjacent tartrate anions. There are many other proton transfer structures of tartaric acid, for example, (Paixão et al., 1999;Ryttersgaard & Larsen, 2003;Bai et al., 2005;Zhang et al., 2006;Smith, et al., 2006;Suresh et al., 2006;Wang et al., 2008;Su et al., 2009), some of which feature similar short hydrogen bonds. The title structure contains two protonated cations of 2,9-dimethyl-1,10-phenanthroline (neocuproine), two anions of mono-deprotonated D-tartaric acid and nine water molecules. As shown in Fig. 1, one of the protons of the tartaric acid carboxylic groups has been transferred to one of the nitrogen atoms of the 2,9-dimethyl-1,10-phenanthroline molecule. The structure reveals a pattern similar to that seen in the previous structure of (phen)(D-tartrate) . 3H 2 O. In particular, the carboxylic acid group at one end of the tartrate anion is hydrogen bonded to the deprotonated carboxylic acid group of an adjacent tartrate anion in a linear, head-to-tail fashion.
Each of the two tartrate anions in the asymmetric unit displays this kind of hydrogen bond (Fig. 2). These hydrogen bonds are short (O···O distances of 2.473 (4) Å and 2.496 (4) Å), and are propagated by unit translations of the anions along the a-direction. In addition, the O-H distance is longer, the H···O distance is shorter and the O-H···O angle is more linear than other O-H···O interactions in the structure. A large number of additional hydrogen bonding interactions are also present.
It is notable that crystal growth along the a-direction is clearly preferred. In the crystal used for data collection, the longest dimension, 0.53 mm, corresponds to the [100] direction. The two shorter dimensions, 0.05 mm and 0.06 mm, correspond to [010] and [001], respectively. Details of the O-H···O, N-H···O and C-H···O hydrogen bonds are given in Table 1. As was seen in the structure containing phen, the cationic dmpH + units are stacked together via π-π interactions. The centroid-centroid distances fall in the range 3.642 (3) Å to 3.866 (3) Å. The overall packing of the structure is depicted in Fig. 3.

Experimental
To an aqueous solution of D-tartaric acid (75 mg, 1 mmol) in water (10 ml) was added a solution of 2,9-dimethyl-1,10-phenanthroline (100 mg, 1 mmol) in methanol (10 ml) in a 1:1 molar ratio. The solution was stirred for 1 h. By slow evaporation of the solvent at room temperature, colorless needles were obtained after 1 week.