Ethylenediammonium dichloride

The title ionic compound, C2H10N2 2+·2Cl−, crystallizes with a center of symmetry within the cation. Each of the positively charged ammonium ends of the molecule is trigonally hydrogen bonded to three different chloride counter-ions, while each of the chloride ions is trigonally hydrogen bonded to three different ethylenediammonium cations. The hydrogen-bonding network leads to stabilization of the structure.

The title ionic compound, C 2 H 10 N 2 2+ Á2Cl À , crystallizes with a center of symmetry within the cation. Each of the positively charged ammonium ends of the molecule is trigonally hydrogen bonded to three different chloride counter-ions, while each of the chloride ions is trigonally hydrogen bonded to three different ethylenediammonium cations. The hydrogen-bonding network leads to stabilization of the structure.
Data collection: APEX2 (Bruker, 2006); cell refinement: APEX2; data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.  Ethylenediamine has been used for approximately one century in the preparation of many metal coordination complexes, such as tris(ethylenediamine)cobalt(III) chloride (Warner, 1912). This is an important precursor to many polymers, chelating agents and pharmaceuticals, including drug design (Kotti, et al., 2006). Since it is a widely used building block in the synthesis of many materials, its structure is of interest. However, it exists as a liquid at room temperature, with a melting point of 282K. We report herein the crystal structure of the dichloride salt of ethylenediamine.

Structure Reports Online
Ethylenediammonium dichloride (I) crystallizes with a center of symmetry in the ethylene moiety. Fig. 1 shows the dication with one chloride counterion hydrogen bonded at each terminal nitrogen atom; however, there are three such chloride ions surrounding each N atom. The angles around both N1 and C1 are essentially tetrahedral, with the N1-C1-C1[1 -x,1/2 + y,2.5 -z] angle = 109.68 (18)°, and the angles around N1 range from 102 (2) to 115 (2) °.  Table 1). Protonation occurs at both ammonium sites in the molecule (the 2nd is centrosymmetrically related); as a result, each nitrogen is also trigonally H bonded to three symmetry-related chlorides. This H bonding fixes both the chloride anions and the organic dication very rigidly in the lattice. Therefore, through symmetry, there exist six N-H···Cl bonds for each molecule, which leads to a great degree of stabilization in the structure.

Experimental
Compound (I) was prepared by mixing 2.5 ml of ethylenediamine with 62 ml of water. Then 7.5 ml of 12 M HCl were added and this mixture was stirred in an ice bath at 273K until a white precipitate formed. The white precipitate was filtered and washed 3 times with methyl alcohol. The product was dissolved in water and then 12 M HCl was added until precipitation just began; a small quantity of water was then added to redissolve the precipitate. This mixture was allowed to evaporate slowly and large colorless needles of (I) formed, which were used directly for X-ray analyis.

Refinement
All H atoms for (I) were found in electron density difference maps. The ammonium and methylene Hs' fractional coordinates were allowed to refine, but their isotropic thermal parameters were set at U iso (H) = 1.5U eq (N) and 1.2U eq (C).
supplementary materials sup-2 Figures   Fig. 1. The molecluar structure of (I), with its numbering; one-half of the molecule is generated through a center of symmetry at 1/2,1/2,1/2 in the chosen unit cell. The H bonds to the chlorides are shown as dashed lines. Displacement ellipsoids are drawn at the 80% probability level. Fig. 2. A partial packing diagram for (I), with extracellular molecules, illustrating the trigonal hydrogen bonding of the chloride ion to three different ethylenediammonium cations. Also the three H atoms of the ammonium are bound to three different chloride counterions. All of the cations lie on centers of symmetry, at 1/2,1/2,1/2 and 1/2,0,0. Displacement ellipsoids are drawn at the 80% probability level.