Adamantane-1-ammonium acetate

In the title compound, C10H18N+·C2H3O2 −, the ammonium H atoms of the cation are linked to three acetate anions via N—H⋯O hydrogen bonds, forming a chain structure extending along the b axis.

In the title compound, C 10 H 18 N + ÁC 2 H 3 O 2 À , the ammonium H atoms of the cation are linked to three acetate anions via N-HÁ Á ÁO hydrogen bonds, forming a chain structure extending along the b axis.

Comment
It is well established that 1-aminoadamantane hydrochloride (amantadine hydrochloride: trade name Symmetrel) is effective in the prevention and treatment of the influenza (A) virus (Hoffmann, 1973;Dolin et al., 1982;Bright et al., 2005). However recent studies suggest that the virus is becoming increasingly resistant to this anti-influenza drug (Betakova, 2007). The investigation of new derivatives of this compound is still important. Here we report the crystal structure of adamantane-1ammonium acetate (I), illustrated in Fig. 1.
The asymmetric unit of (I) contains an adamantane-1-ammonium cation and an acetate anion. In the cation, the exocyclic C-N bond is 1.500 (3) Å. The C-C bonds of the adamantane skeleton range from 1.527 (3) to 1.537 (3) Å, with a mean value of 1.531 Å. The C-C-C bond angles range from 109.05 (18) to 110.10 (18) °, with a mean value of 109.5 °, which is in good agreement with the value for a tetrahedral angle. In the anion, the C(sp3)-O distances of 1.266 (3) and 1.240 (3) Å are in the range of values given in the literature (Orpen et al., 1989).
The crystal structure is stabilized by a network of intermolecular charge assisted carbonyl-to-amine hydrogen bonds. All ammonium hydrogen atoms are involved in hydrogen bonding with the oxygen atoms of the acetate anion (Table 1). The hydrogen-bonding scheme can be described as a nine membered ring motif with graph-set notation R 3 4 (10) (Bernstein et al., 1995). This results in the formation of a one-dimensional chain structure parallel to the b axis of the unit cell (Fig. 2).

Experimental
Adamantadine hydrochloride (10 mg) was dissolved in three drops of glacial acetic acid and deionized water. The solution was allowed to undergo slow evaporation. Single crystals of (I) suitable for X-ray diffraction anlaysis precipitated after a few days.

Refinement
The ammonium H atoms were placed according to the observed electron density and allowed to refine freely. A distance constraint was placed on one of the N-H bonds [N1-H1C, 0.95 (2) Å]. The remaining H atoms were positioned geometrically and allowed to ride on their respective parent atoms, with C-H bond lengths of 0.99 (aromatic CH) 1.00 (methine CH), 0.99 (methylene CH 2 ) and 0.98 Å (methyl CH 3 ), and with U iso (H) = 1.2 or 1.5 times U eq (C).