X-RAY, FOURIER-TRANSFORM INFRARED, H-1 AND C-13 NUCLEAR-MAGNETIC-RESONANCE, AND PM3 STUDIES OF (N-H...N)-H...O)- INTRAMOLECULAR HYDR OGEN BONDS IN A COMPLEX OF 1,8-BIS(DIMETHYLAMINO)NAPHTHALENE WITH MALEIC-ACID( AND (O)

The crystal structure of the title compound has been determined by X-r ay analysis. The intramolecular hydrogen bond lengths are 2.606(3) ang strom for the (NHN)+ bridge in protonated 1,8-bis(dimethylamino)naphth alene cation (DMAN+H) and 2.401(4) angstrom for the (OHO)- bridge in t he hydrogen maleate anion (HM-), The H-bonds are asymmetrical and not strictly linear: NHN, 157(3)-degrees and OHO, 170(5)-degrees. The geom etries of the N-H ... N and 0-H ... 0 bridges of the investigated cati on and anion are dominated by the spherical repulsions of their consti tuent atoms. The overlapping bands in the absorbance IR spectra of pot assium hydrogen (deuteron) maleate are separated in the second-derivat ive spectra. The strong mixing of the in-plane modes with skeletal mod es in the hydrogen maleate ion causes a larger separation (DELTAnu alm ost-equal-to 115 cm-1) of the nu(C=0) bands in comparison with those i n other type A acid salts containing intermolecular hydrogen bonds (DE LTAnu almost-equal-to 20-35 cm-1). The observed lack of solvent effect on the IR absorption suggests that the hydrogen bonds in tetrabutylam monium hydrogen maleate and 1,8-bis(dimethylamino)naphthalene hydrogen maleate are not extremely polarizable. H-1 and C-13 NMR chemical shif ts of the investigated compound were measured and identified in two-di mensional (2D) experiments. The H-1 NMR spectra show two narrow signal s at ca. 19.5 and 18.7 ppm due to the OHO and NHN protons, respectivel y. The structural parameters of the cation and anion were also determi ned by quantum-mechanical calculations with the semiempirical MNDO-PM3 method.