X-RAY, FTIR, H-1 AND C-13 NMR, PM3 AND AM1 STUDIES OF (N-H...N)(-H...O)(-) HYDROGEN-BONDS IN A COMPLEX OF 1,8-DIAMINONAPHTHALENE WITH MALEIC-ACID - PROTON CAVITY AND BASICITY OF PROTON SPONGES() AND (O)

The crystal structure of the title complex has been determined by X-ra y analysis. All H atoms were located and refined isotropically; R = 0. 041 for 1595 observed reflections. The intramolecular hydrogen bonds a re asymmetrical and are characterized by the following distances and a ngles: 2.670 (3) Angstrom and 146 (3)degrees for the (NHN)(+) bridge i n the protonated 1,8-diaminonaphthalene cation (DAN(+)H) and 2.423 (2) Angstrom and 177 (3)degrees for the (OHO)(-) bridge in the hydrogen m aleate anion (HM(-)). The N+H3 group is engaged in two intermolecular bonds with the anion [N+(H)...O distances 2.794 (2) and 2.856 (3) Angs trom]. The interactions of the NH2 group with the anion are weaker [N( H)...O distances 3.078 (3) and 3.225 (3) Angstrom]. Most of the bond d istances and angles in DAN(+)H HM(-) are very similar to those in the complex of 1,8-bis(dimethylamino)naphthalene with maleic acid, DMAN(+) H HM(-). The deformations of the naphthalene skeleton in DAN(+)H HM(-) and DMAN(+)H HM(-) are also comparable. In DMAN(+)H, the proton is lo cated in a cavity formed by four methyl groups, therefore, its exchang e is slow on the NMR timescale. in DAN(+)H the proton is not inside a cavity and the exchange becomes rapid. Although spherical repulsions a re not negligible, the cavity is of prime importance for the large bas icity of DMAN. The PM3 method reproduces correctly the cation structur e and its interactions with the anion but the O...O distance in the an ion is too long. The AM1 method failed to reproduce the structure of t he complex correctly.