Dihydrocyclam dimaleate [H2(cyclam)(maleate)2]

The asymmetric unit of the title molecular salt [systematic name: 1,4,8,11-tetraazacyclotetradecane-1,8-diium bis(3-carboxyprop-2-enoate)], C10H26N4 2+·2C4H3O4 −, contains two half-cations (both completed by crystallographic inversion symmetry) and two maleate anions. The cyclam macrocycles adopt trans-III conformations, supported by two intramolecular N—H⋯O hydrogen bonds. The O-bonded H atom of each maleate ion is disordered over two positions with an occupancy ratio of 0.61 (5):0.39 (5): each one generates an intramolecular O—H⋯O hydrogen bond. In the crystal, the cations are linked to the anions by N—H⋯O hydrogen bonds, generating [001] chains.


Comment
Cyclam is doubly protonated in [H 2 (cyclam)(maleate) 2 ], resulting in a maleate monoanion. The di-protonated cyclam [C 10 H 26 N 4 ] 2+ exhibits bond distances and angles in the range usually found in the literature (Melson, 1979). The two additional protons on N1 and N1A are trans to each other and interact through hydrogen bonds with the nonprotonated N2 and N2A nitrogen atoms [N1···N2= 2.800 (1) Å, N3···N4= 2.805 (1) Å]. The diprotonated macrocycle adopts an quadrangular (3,4,3,4)-C conformation ( Fig. 1) according to Dale's nomenclature [(Dale, 1973and 1976, (Hancock et al., 1996], where the exo-cyclic nitrogen atom N2 is located two bonds away from the adjacent corner atoms C9A and C11, while the amine nitrogen atom N1A is located one bond away from the corresponding corner atom C9A and two bonds away from C11A. According to the stereochemical classification of 1,4,8,11 tetraazacyclotetradecane introduced by Bosnich et al. (1965), the cyclam ring adopts a trans-III geometry type, which, according to molecular mechanics MMcalculations, is the most stable among the five possible configurations (Bandoli et al., 1993). In the crystal structure, intramolecular hydrogen bonds occur, linking carboxylate O atoms in each maleate ion. The H3C and H7A atoms are involved in these bonds and maintain the charge balance by bridging two carboxylate groups within the structure. The

Experimental
0.2 g (1 mmol) of cyclam C 10 H 24 N 4 was dissolved 25 ml of water-ethanol mixture 1:1 (v/v) and 0.233 g (2 mmol) of maleic acid C 4 H 4 O 4 , in 25 ml of the same solvent. The solutions were combined, and the mixture was refluxed for 3 h, before to be deposited to set at room conditions. Prismatic coloreless crystals were obtained which were washed with a water (80%) /ethanol (20%) (v:v) solution. program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication:

Computing details
SHELXL97 (Sheldrick, 2008).  The molecular structure of the title compound, with hydrogen bonds shown as dashed lines. Anisotropic displacement parameters drawn at the 50% probability level.

Figure 2
Inter-molecular H-bonds between cyclam and maleate ion.  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 Occ. (