J. Phys. Chem. 1995,99, 14667-14677 14667 ESCA, Solid-state NMR, and X-ray Diffraction Monitor the Hydrogen Bonding in a Complex of 1,s-Bis(dimethy1amino)naphthalene with 1,ZDichloromaleic Acid Krzysztof WozniakJ?' Heyong He,' Jacek Klinowski,*9* William Jones,# and Tery L. Barr* Department of Chemistry, Universiv of Warsaw, 02-093 Warszawa, ul. Pasteura I, Poland, Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 IEW, U.K., and Department of Materials, Laboratory f o r Surface Studies, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53201 Received: June 13, 1995; In Final Form: August 1, 1995@ The complex of 1,8-bis(dimethylamino)naphthalene (DMAN) with 1,2-dichloromaleic acid (ClMH2) has been examined by electron spectroscopy (ESCA), X-ray diffraction at 120 and 293 K, and I3C and 'H MAS NMR at 123 and 293 K. The complex contains two strong, asymmetric, ionic hydrogen bonds, [N-H.**N]' and [O-H.*O]-. The asymmetry results from asymmetric intermolecular interactions of the oxygen atoms of the carboxylic groups. Well-resolved I3C MAS NMR spectra of a DMAN salt show separate signals from protonated "almost symmetrical" carbons. The difference between the binding energies of core (and valence) electrons of the donor and acceptor atoms is a good measure of the strength of hydrogen bonds. The influence of hydrogen bonding on the binding energies of core electrons of the atoms of the ClMH- anion decreases with the increased distance from the [0-H- 01- hydrogen bond site. Introduction Electron spectroscopy for chemical analysis (ESCA) is known to be a powerful method of surface analysis.'-3 A sample is irradiated with monoenergetic soft X-rays (A1 Ka or Mg Ka), and the energies of emitted electrons are monitored. The photons penetrate the outermost layer of the solid to the depth of ca. 1 - 10 pm and interact with atoms in that surface region via the photoelectric effect causing electrons to be emitted. The kinetic energy of the emitted electrons is KE=hv - BE - Qs where hv is the energy of the photon, BE is the binding energy of the atomic orbital from which the electron originates, and QS is the spectrometer work function. Since each type of atom can give rise to a variety of different ions, there is a corre- sponding variety of kinetic energies of emitted electrons. Although ionization occurs up to a depth of a few micrometers, only electrons emitted within tens of angstroms below the surface can leave the sample and be detected. Other electrons lose energy while passing through the solid. Thus ESCA is well attuned to the observation of surface phenomena. The aim of this work is to examine the influence of strong hydrogen bonds on the binding energies of the core electrons of atoms involved in hydrogen bonding and atoms which are remote from the hydrogen bond sites. We have selected a complex of the aromatic diamine 1 ,8-bis(dimethy1amino)- naphthalene (DMAN) with 1,2-dichloromaleic acid (ClMH2) (Figure 1). DMAN belongs to the class of compounds with extremely high basicity constants and proton affinities, known as proton sponges. With mineral or organic acids, proton sponges form very stable ionic complexes containing intramo- lecular [N *He ON]+ hydrogen bonds. Proton sponges have attracted considerable attention, particularly since the reviews by Staab4 and Aldes appeared, and more than 70 X-ray structures have been published. Intramolecularly hydrogen- + University of Warsaw. * University of Cambridge. 9 University of Wisconsin-Milwaukee. @ Abstract published in Advance ACS Absfracfs, September 15, 1995. 0022-365419512099-14667$09.00/0 0 Hllb 3 H5 H4 Figure 1. Numbering scheme and atomic displacement parameters for the DMANH+ and ClMH- ions at 120 K. The ellipsoids are drawn at the 50% probability level. bonded proton sponges have been the subject of more than 100 papers. The DMAN molecule itself has been studied by X-ray diffraction,6v7 solid-state NMR,7-9 NQR7,I0," at 293 K and low temperatures and ab-initio computational methods.I2 The Cambridge Structural Databa~e'~ contains nearly 50 structures involving the hydrogen maleate anion and its deriva- tives, including the complexes of maleic acid with 1,8- diamin~naphthalene'~ and 1,8-bi~(dimethylamino)naphthalene.'~ Ab-initio computational methods were also used to study this model moiety.l6.l7 One can expect the [N-H.*N]+ hydrogen bond in the DMANH+ cation and the [0-H- 01- hydrogen bond in the ClMH- anion to influence significantly the ESCA spectra of the DMANHTlMH- complex. Experimental Section Synthesis. DMANH+ClMH- was prepared by mixing ma- leic acid with DMAN in acetonitrile. The product was then recrystallized from methanol. X-ray Diffraction. Crystals of DMAN suitable for X-ray work were grown from heptane by slow evaporation. X-ray measurements were made on a Rigaku AFC7R diffractometer using monochromated Mo Ka radiation in the w-28 scan mode. Three standard reflections were monitored for every 100 reflections collected, and none showed a significant decrease 0 1995 American Chemical Society