J. Phys. Chem. 1993,97, 6590-6591
6590
A Cyclic Hydrogen-Bonded System with Collective Proton Motion in Bis[3,3’-(2,2‘-dihydroxybiphenyl)]methane BogumiI Brzezinski,?Piotr Radziejewskif Jerzy Olejnik,t and Georg Zundel’a Faculty of Chemistry, A . Mickiewicz University, Grunwaldzka 6, PL-60780 Poznah, Poland, and Physikalisch-Chemisches Inrtitut. Universitat Miinchen, Theresienstrasse 41, 0-80333 Munich 2, Germany Received: November 30, 1992
Bis[3,3’-(2,2’-dihydroxybiphenyl)]methane (BBPM) was synthesized. It was studied by osmometry and by IH NMR and FTIR spectroscopies. Furthermore, the monotetrachloroaurate of BBPM was also investigated. BBPM is a monomer in acetonitrile solution. Within this molecule the four OH groups form a cyclic hydrogenbonded structure in which a collective proton fluctuation occurs. In the case of the monotetrachloroaurate the cyclic structure is more stable, the additional OH group is also hydrogen-bonded, and its proton is involved in the collective proton fluctuation, as in the case of crown ethers. Introduction All structurally symmetrical hydrogen-bonded chains cause continua in the infrared spectra.ld These continua indicate that these systems show large proton polarizability due to collective proton motion.’ Recently we investigated the tetrabutylammonium salts of 1,11,12,13,14-pentahydroxypentacene3and 1,11,12,13,14pentahydr~xymethylpentacene.~ In these compounds open chains with four intramolecular hydrogen-bonded OH groups are present, which show large proton polarizability due to collective proton motion. In the following study we investigated a new compound with four OH groupswhich form a cyclichydrogen-bonded system.
Experimental Section The monotetrachloroaurate of BBPM was prepared by adding of equimolar amounts of the 0.1 mol dm-3 acetonitrile solution of HAuC14 to a solution of BBPM in 100%ethanol. The solvents were removed under reduced pressure, and the solid residue was dissolved in acetonitrile. All solvents were stored over 3-A molecular sieves. All preparations and transfers of solutions were carried out in a carefully dried glovebox. 1HNMR spectra were recorded in acetonitrilbd3 or in DMSOd6 solutions (0.1 mol dm-3) with a Varian Gemini VT 300 spectrometer at 298 K and calibrated against TMS as internal standard. TheIRspectra were takenofthesamplesat 293 Kinacetonitrile solutions(0.1 mol dm-3) with a FTIR spectrometer,Bruker Model IFS 113v, using a cell with Si windows (sample thickness 0.260 mm, detector DTGS, resolution 2 cm-1). Bis [3,3’-(2,2’-dihydroxybiphenyl)]methane was synthesizedas follows: Diethylamine (2.8 cm3, 0.054 mol) and 40 p L of 10% aqueous NaOH were added slowly, on cooling, to a suspension of paraformaldehyde (0.84 g, 0.054 mol) in methanol (10 cm3). The clear solution formed was then transferred to a dropping funnel and added during 30 min to a stirred solution of 2,2’biphenol ( 5 g, 0.027 mol) in 10 cm3 of methanol. The reaction mixture was let for 14 days at room temperature and then cooled to 0 OC. The precipitate formed was filtered off, washed with a saturated NaHCO3 solution (3 X 10 cm3), water (3 X 10 cm3), and then 1% hydrochloric acid (3 X 10 cm3) and water again (3 X 10 cm3). Yield 1.25 g (5%); mp = 94-96 OC. Found: C = 78.02, H = 5.22. CzsHz004 requires C = 78.1 1, H = 5.24. The osmoticcoefficientswere measured by vapor pressure osmometry t A. Mickiewicz University. t Universit&tMIinchen.
TABLE I: ‘€I NMR Chemical Shifts (6, ppm) of BBPM, Its MonotetracbloroaurateSalt, and 2,2’-Bipbenol compound solvent OH rinltorotons‘ CH2 BBPM DMSO-d6 8.27(4)b 6.42-6.55 m (6) 473(2) . . ., 6.70-6.90 m (8) BBPM CD&N 11.67(4) 6.45-6.57 m (6) 4.72(2) 6.77-6.95 m (8) BBPM + HAuCL CDsCN 11.82(5) 6.49-6.62m (6) 4.71(2) 6.78-6.96m (8) 2,2’-biphenol CDCls 5.65(2) H-3,3’ 7.01 (2) H-4,4’ 7.32 (2) H-5.5’ 7.05 (2) H-6,6’ 7.27 (2) a m = multiplet. * In brackets the number of protons. in acetonitrilesolutionwith a Knauer osmometer. The instrument was calibrated against benzil.
Results and Discussion We studied bis [3,3’(2,2’-dihydroxybipheny1)lmethane (BBPM) and its monotetrachloroaurate by osmometric measurements, 1H NMR, and FTIR spectroscopy. The determined osmotic coefficient for BBPM 0.1 mol dm-3 acetonitrile solution was 0.98, indicating that BBPM exists as monomer in this solution. The lH NMR data of BBPM and its monotetrachloroaurate in acetonitrile-d3solution are given in Table I. For comparison the chemical shifts of the protons of 2,2’-biphenol and of BBPM in a DMSO-d6 solution are also shown. The chemical shift of the protons of the four OH groups of BBPM amounts to 11.67 ppm in acetonitrile-d3. This value of the chemical shift observed for the BBPM hydroxyl groups is almost twice of the corresponding shift for 2,2’-biphenol. Thus, in BBPM relatively strong intramolecular hydrogen bonds are formed. The chemical shift of the OH protons in BBPM in DMSO-d6 solution amounts to 8.27 ppm indicating, that in DMSO-ds the intramolecular hydrogen bonds are broken and the OH groups form less strong hydrogen bonds to DMSO-ds molecules. This result is confirmed by the IR spectrum. The IR spectrum of an acetonitrile solution of BBPM is shown in Figure 1 (solid line), and that of BBPM monotetrachloroaurate is given in Figure 2 (solid line). In both figures for comparison the spectrum of 2,2’-biphenol is also given. To improve the comparability, the concentration of 2,2‘-biphenol is twice. Figure 1 shows that BBPM in acetonitrile causes a continuum of relatively weak intensity and a very weak band at about 3385 cm-l. The weak band proves that a very small amount of the OH groups are bonded to acetonitrile. The continuum caused by
0022-365419312097-6590$04.00/0 Q 1993 American Chemical Society
The Journal of Physical Chemistry, Vol. 97, No. 25, 1993 6591
A Cyclic Hydrogen-Bonded System 0
band at about 3385 cm-l is no longer found. The continuum caused by the BBPM monotetrachloroaurate is much more intense,
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WAVENUMBER 1/CM Figure 1. FTIR spectra of (-) BBPM (concentration 0.1 mol dm-3) and for comparison of (- - -) 2,2’-biphcnol (concentration0.2 mol dm-’), both in acetonitrile.
and no band of a free OH group is observed. The reason for this intensity increase of the continuum is the fact that the cyclic hydrogen-bondedstructure is now positively charged. Therefore, the dipole moment fluctuations are larger, and hence, the transition dipolemoments of the hydrogen-bonded structure are also larger. The fact that after protonation no stretching vibration band of a free OH group is observed shows that this OH group forms hydrogen bonds, too, and its proton is also involved in the collective fluctuation of the protons in the cyclic ring, as in the case of protonated crown ethers:
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WAVENUMBER I /CM Figure 2. FTIR spectra (-) a 1:l complex of BBPM with HAuCL (concentration 0.1 mol dm-3) and for comparison of (- - -) 2,2’-biphenol (concentration 0.2 mol cm-9, both in acetonitrile.
BBPM demonstrates that in this molecule the OH groups build up a cyclic ring with relatively strong hydrogen bonds in which a collective proton motion occurs:
This additional hydrogen bond can be formed since both parts of the molecule are folded toward each other.
Conclusions The BBPM molecule exists in acetonitrile as monomer. It forms a cyclic hydrogen-bonded structure in which the four OH groups are involved almost completely. Within this structure a collective proton motion occurs. In BBPM monotetrachloroaurate the collectiveproton motion is favored in the cyclic structure. The additional OH group forms hydrogen bonds, and hence it is also involved in the collective proton fluctuation.
Acknowledgment. Our thanks are due to the Polish Committee for Scientific Research (KBN), Research Project No. 2 0709 91 01, the Deutsche Forschungsgemeinschaft, and the Fonds der Chemischen Industrie for providing facilities for this work. We are also grateful to the EEC program No. SCI-0229. The ’H NMR spectrum of BBPM-HAuCb complex shows only one signal of five protons, shifted toward lower field (1 1.82 ppm) when compared with the four OH protons signal of pure BBPM (1 1.67 ppm). This observation demonstrates that all five protons are strongly hydrogen-bonded. This signal may be assigned to a cyclic hydrogen-bonded structure including four OH groups of BBPM and one proton of HAuCl4. Such situation can only be realized when a ringlike structure similar to that in protonated crown ethers is built up. The ring protons signals of BBPM shift only slightly after protonation, and they are not characteristic. The above 1H NMR results are further supported by the FTIR studies. Figure 2 shows that with the protonation of BBPM a
References and Notes (1) Brzezinski, B.;KrHmer, R.; Zundel,G. Chem. Phys. Lett. 1986,124, 395.
(2) Brzezinski, B.; Krlmer, R.; Zundel, G. J. Phys. Chem. 1987, 91, 3077. (3) Brzezinski, B.; Zundel, G.; Krlmer, R. Chem. Phys. Lett. 1989,157, 512. (4) Brzezinski, B.; K r h e r , R.; Zundel, G. Chem. Phys. Lett. 1991,178, 138. ~. .
(5) Brzezinski, B.; Maciejewska, H.; Zundel, G.; KrHmer, R. J. Phys. Chem. 1990, 94, 528. (6) Brzezinski, B.; Maciejewska, H.; Zundel, G. J. Phys. Chem. 1990, 94, 6983. (7) Zundel, G.; Ekkert, M. J. Mol. Struct. (THEOCHEM)1988, 200, 7016.
