N-Methylmorpholine betaine hydrochloride (MMB·HCl) forms a 3:2 inclusion compound with acetonitrile. The crystal structure of the compound has been determined at 100 K from a twinned crystal to be trigonal with the space group P3; a=b=16.767(2), c=6.996(1)Å,γ=120°. The host framework is constructed from the ionic pairs formed by the chlorine anion and the protonated, at the carboxylate group, betaine cation. The cation and anion are joined by the O–H⋯Cl− hydrogen bond of the length 2.974(2) Å and angle 173(3)°. The guest molecules are included in two kinds of channels formed in the host matrix. The narrow channel runs parallel to the z axis at x=2/3, y=1/3 and is filled with acetonitrile molecules situated at the three-fold axis. The second channel, also parallel to the z axis, joins large cavities with the center at 0,0,1/2 of 3 symmetry. The cavity accommodates two guest molecules which exhibit disorder in the crystal. There are only van der Waals interactions between the host and the guest. FTIR spectra of MMB·HCl and its deuterated analog have been discussed.

The 1:1 and 2:1 complexes of trigonelline (TRG) with HBr, HI, HNO 3 , HClO 4 and HBF 4 have been synthesized and their FTIR, 1 H and C NMR spectra were analyzed. The 1:1 complexes are divided into two groups. The first group includes complexes with HBr, HI and HNO 3 , in which a proton is transferred from the acid to TRG and the anions are bonded with the carboxylic group, COOH...X - (1). The second comprises complexes with HClO 4 and HBF 4 , with two molecules of protonated TRG forming dimer, like benzoic acid, and the anions interacting exclusively with the positively charged nitrogen atoms (2). All 2:1 complexes crystallized with one water molecule and their FTIR spectra are of HadŽi type iii, characterized by an intense broad (continuum) absorption below 1600 cm - 1 typical of a short-strong hydrogen bond (SSHB) with a delocalized proton and a single vC=O band. In these complexes the water molecule interacts electrostatically with one positively charged nitrogen atom and the anions with the second one (3). The water molecule additionally forms a hydrogen bond with Br, I and NO 3 ions. The proton and carbon chemical shifts of the complexes in D 2 O have been determined and discussed.

Three types of crystalline complexes of N-methylmorpholine betaine (MMB) with phenols (1:1, 1:2, 2:1) were prepared and their FTIR spectra were studied as a function of the acidity of phenols. The variations of absorption in the 3000–2000 and 1600–400cm−1 regions with pKa values of phenols in the 1:1 complexes reflect the formation of the molecular complex (A–H⋯B) and hydrogen-bonded ion pair (A−⋯HB+). In the 1:2 complexes the betaine carboxylate group is linked to two phenol molecules forming two different hydrogen bonds. The FTIR spectra are less affected by proton donor properties of phenol. In the 2:1 complex of MMB with picric acid two molecules of MMB are bridged by hydrogen bond and form a homoconjugated cation. The FTIR spectrum shows a broad (continuum) absorption in 1500–400cm−1 region, which suggests a strong hydrogen bond.

Several 1:1 and 2:1 complexes of N-methylmorpholine betaine (MMB, N-(carboxymethyl)– N-methylmorpholinium inner salt) with HCl, HBr, HNO3, HBF4, HI and HClO4 were synthesized and their FTIR, 1H and 13C NMR spectra were investigated. In the 1:1 complexes, MMB·HX, a proton is transferred from the acid to the betaine molecule and both the νOH and νCO frequencies vary with the proton acceptor properties of the anion. The spectra of the 2:1 complexes, (MMB)2H·X, show a broad and intense νOHO stretching absorption in the 1500–400cm−1 range which is slightly affected by the anion and are similar to that for the type A acid salts of carboxylic acids. The crystal structure of bis(N-methylmorpholine betaine) hydrochloride [(MMB)2H·Cl] was solved by X-ray diffraction as monoclinic, space group C2/c, a=23.113(2)Å, b=6.9404(6)Å, c=10.800(1)Å, β=94.450(7)°, Z=4. The carboxylate groups of a pair of MMB are bridged by a hydrogen atom to form a dimeric cation [(MMB)2H]+ with a very strong, linear and symmetrical O⋯H⋯O hydrogen bond of the length 2.435(2)Å. The centers of cations and anions are located in special positions, in the inversion centers and on twofold axes, respectively.

A novel anhydrous 1:1 and 2:1 complexes of quinoline betaine (QB) with perchloric acid have been prepared and their structures determined by X-ray diffraction. The 1:1 complex betaine is protonated and the carboxylate group forms a hydrogen bond with the ClO4 ion: O⋯O distance is 2.820(3)Å. In the 2:1 complex, the carboxylate group of a pair of QB molecules are bridged by a proton to form dimeric cation in non-planar configuration, [(QB)2H]+, featuring a very strong hydrogen bond of the length 2.453(3)Å. The FTIR spectrum of the 1:1 complex shows a strong absorption at ca. 3100cm−1 due to the νOH vibration. Broad and intense absorption in the 1500–400cm−1 region in the spectrum of the 2:1 complex is typical for the very short hydrogen bonds. B3LYP calculations predict slightly shorter hydrogen bonds with different orientation of the ring vs. COOH group than these observed in crystals.

The following isostructural complexes: [C5H5N+(CH2)(n)COO](2)HX and [C6H5(CH2)(n)COO](2)HK (n = 1-4) were synthesised and their FTIR spectra analysed. In these two series hydrogen-bonded units are similar, although they differ in that one is zwitterion. Most of the spectra are of Hadzi type (iii), characterised by an intense broad (continuum) absorption below 1600 cm(-1) typical for a short-strong hydrogen bonds, and a single nu C=O band. The O ... O distances in [C5H5N+CH2COO](2)HCl-. H2O and [C6H5CH2COO](2)HK are 2.436(6) Angstrom [Chen and Mak, J. Mol. Struct. 221 (1990) 265] and 2.443(4) Angstrom [Speakman, Structure and Bonding 12 (1972) 141], respectively, and their spectra are very similar. Addition of methylene groups breaks this similarity, as only complexes containing pyridine ring are non-linear as results of the attractive Coulombic interaction between the oppositely charged groups. Counterions interact with N+ atoms and have negligible effect on the OHO bridge, and as the result the spectra are comparable, and the O ... O distance would be also comparable. The O ... O distance in [C5H5N+CH2CH2COO](2)HBr is 2.450(6) Angstrom [Chen and Mak, Acta Cryst. Sect. C 50 (1993) 1807]. All the complexes containing phenyl ring are probably linear and the K+ ion interacts with the oxygen atoms of the carboxylate groups. On addition of methylene groups contacts of K+ ion with carboxylate groups become non-equivalent and the broad absorption moves to the higher wave numbers. This indicates that hydrogen bonds become longer and the H-bonded proton is closer to one of the carboxylate group. In the spectrum of [C6H5(CH2)(4)COO](2)HK both the nu C=O and nu(as)COO bands, respectively, at 1707 and 1641 cm(-1) were found. (C) 1999 Elsevier Science B.V. All rights reserved.

A complex of pyridine N-oxide (PyO) with 2,6-dichloro-4-nitrophenol (DCNP) was studied by X-ray diffraction, FT-IR spectroscopy and quantum-mechanical calculations with the DFT and semiempirical methods. The crystals of the PyO . DCNP are triclinic, space group P (1) over bar, a = 6.833(1) Angstrom, b = 8.717(2) Angstrom, c = 11.482(2) Angstrom, alpha = 98.93(2)degrees, beta = 93.63 (1)degrees, gamma = 109.12(2)degrees, V = 633.6(3) Angstrom(3), Z = 2. The molecules of the complex are joined by the N-O ... H-O hydrogen bond with the O ... O distance of 2.476(2) Angstrom, and the O(4)... H(1)-O(1) angle of 165.1 degrees. The dihedral angle between the planes of the bridged pyridine and phenyl rings is 71.8 degrees. The weak C-H ... O, C-H ... Cl interactions and stacking forces stabilize three dimensional packing pattern. The SAM1 and DFT methods predict one minimum for B ... H-A form, while the PM3 method predicts two minima, the deeper one for B ... H-A complex and the shallower one for B+-H ... A(-) form. For the most stable complexes the predicted O ... O distances are longer than the experimental value by 0.141, 0.067 and 0.231 Angstrom, respectively for the DFT, SAM1 and PM3 methods. The calculated bond lengths, except N(1)-O(4), are longer than those fi om the X-ray as results of intermolecular interactions in the crystal. The SAM1 geometry of PyO . DCNP is slightly better than this obtained by the PM3 method and it is recommended as input in nb initio calculations. The protonic broad absorption in the 1500-250 cm(-1) region is typical for such a short hydrogen bond and the proton motion may be described by a potential curve with an asymmetric double minimum. Proton motion in the bridge is faster than the time range of IR spectroscopy.

Complexes of betaine (BET) with 2,6-dichloro-4-nitrophenol (DCNP), pentachlorophenol (PCP) and trifluoroacetic, trichloroacetic, dichloroacetic, chloroacetic and maleic acids and of pyridine betaine (PBET) with DCNP in solution and in the solid state were studied by UV and FTIR spectroscopies and X-ray analysis. The crystal of BET·DCNP is triclinic, space group P1̄, a = 7.1770(10) Å, b = 10.001(2) Å, c = 11.241(2) Å, α = 108.81(3)°, β = 100.06(3)°, γ = 106.82(3)°, Z = 2; the final R value is 0.033 for 1871 observed reflections. Protonated betaine and 2,6-dichloro-4-nitrophenolate are linked by an O(2)Htctdot;O(1) hydrogen bond with an Otctdot;O distance of 2.424(3) Å and the O(2)Htctdot;O(1) angle is 159(3)°. The broad absorption in the solid state FTIR spectra of the investigated complexes varies with ΔpKa, and is typical of complexes with strong hydrogen bonds. The UV spectra of phenol complexes in acetonitrile show a typical absorption for Btctdot;HA and B+Htctdot;A− species. In less polar dichloromethane, only molecular complexes are present. An exception is PBET·DCNP, where B+Htctdot;A− species appear in both solvents. The agreement between the UV and IR data is good.

Complexes of five pyridines and nine pyridine N-oxides with 2,6-dichloro-4-nitrophenol (DCNP) in solution and the solid state were studied by Fourier transform IR and UV spectroscopy, by quantum-mechanical calculations with the semiempirical parametric method 3 (PM3) and by X-ray analysis.The crystals of the 1 : 1 complex of 4-methoxy-2,6-dimethylpyridine N-oxide with DCNP are monoclinic, space group P2(1)/n, a = 4.5936(5) Angstrom, b = 21.953(3) Angstrom, c = 15.664(2) Angstrom, beta = 92.87(1)degrees, V = 1577.6(8) Angstrom(3), Z = 4. The molecules of the complex are joined together by an N+O-H ... O- hydrogen bond with an O ... O distance of 2.425(3) Angstrom, a C-O- distance of 1.286(3) Angstrom and a (N+O)-H ... O- angle of 152.9 degrees.The PM3 method predicts for all the investigated complexes two minima, the deeper one for B ... HA complexes and the shallower one for the B+-H ... A(-) forms. For the 4-methylpyridine complex the N+-H ... O- distance is reproduced correctly but for the 4-methoxy-2,6-dimethylpyridine N-oxide complex the N+-H ... O- distance is too long, The predicted hydrogen-bond angles differ from the experimental values by more than 10 degrees.In solid state complexes of pyridines the N ... O distances and the broad absorption due to a protic vibration are not directly related to Delta pK(a). This is due to the crystal packing forces. In solution the broad absorption varies with Delta pK(a). A band in the 3500 cm(-1) region due to the solvated phenol is present in all investigated complexes in solution. Absorption in the 3000-2000 cm(-1) region of pyridine complexes is more intense than that of the pyridine N-oxides, in agreement with the difference in N ... O and N-O ... O distances. The broad absorption in the spectra of pyridine complexes is more influenced by solvent effects than in the pyridine N-oxide complexes.The UV spectra of the pyridine complexes show two bands due to B ... H-A (305-315 nm) and B+-H ... A(-) (382-395 nm) forms. The UV spectra of complexes of pyridine N-oxides of intermediate strengths in CH2Cl2 are not combinations of the spectra of phenol and phenolate, The band in the intermediate position denotes that neither species close to phenol nor to phenoxide ion is present. In these complexes the proton is probably localized in a single minimum and the minimum moves from the donor to the acceptor or, what is more probable, reorganization of the solvent molecules around the complex is faster than the time range of UV spectroscopy. In acetonitrile the situation is quite different as two bands are present, in agreement with a prototropic equilibrium. Effects of solvent, concentration and stoichiometry on interactions of DCNP with pyridines and pyridine N-oxides are compared and discussed. An extended mechanism of the proton-transfer reaction is proposed.

Trimethylamine N-oxide and 4-dimethylamine-2,6-dimethylpyridine N-oxide form three types of crystalline complexes with perchloric acid, with the base-to-acid ratio 1:1, 2:1 and 3:2, which are easily distinguished by their IR absorption. The asymmetric unit of the P1 unit cell contains two (Me3NO)3·(HClO4)2 formula units. Each of the formula units assembles into a (Me3NO)32H+ dication and two independent ClO−4 anions which show no H-bond interactions with the cationic components. The oxygen atom of a central trimethylamine N-oxide molecule accepts hydrogen bonds from two protonated trimethylamine N-oxide cations with O...O distances in the range 2.537(5) – 2.562(7) Å. The O...HO bonds are linear and formed along direction of the two electron lone-pairs on the oxygen atom. In acetonitrile solutions the 3:2 complexes exist as mixtures of the 1:1 and 2:1 complexes.

The crystal structure of the 4-methoxy-2,6-dimethylpyridine N-oxide·pentachlorophenol complex has been determined by X-ray analysis. The O ··· O distance is 2.439(6) Å, the OHO angle is 152.3° and the hydrogen-bonded proton is close to the phenol molecule. The FT-IR spectra of pentachlorophenol complexes with some substituted pyridine N-oxides in the solid state and seven aprotic solvents of different polarity (ϵ from 2.27 to 37.5) show a broad absorption. The broad absorption shows weak dependence upon solvent polarity and is classified as type (ii). UV spectra show that in the investigated complexes protons are not transferred from the phenol to the N-oxides. Formamide (ϵ = 111) is a much stronger proton acceptor than the pyridine N-oxides. Pentachlorophenol in formamide is converted to the phenolate ion.

The crystal structure of bis(pyridine betaine) hydrochloride-d1 monohydrate-d2 has been determined by X-ray analysis. The carboxylate groups of a pair of pyridine betaine molecules are bridged by a deuteron to form a centro-symmetric symmetric dimer featuring a very strong hydrogen bond of length 2.444(4) angstrom. The geometric mass effect (DELTAR almost-equal-to 0.008 angstrom) is well within the range observed for this type of hydrogen bond.The FT-IR spectra of polycrystalline 1:1 and 2:1 complexes of pyridine betaine with HNO3. HCl, HBr, HI, HO3SCF3, HClO4, HBF4, and H2SO4 have been investigated in the 4000 200 cm-1 range. In the 1:1 complexes a proton is transferred from the acid to the betaine molecule, C5H5N+CH2COOH . A-, and both the nuOH and nuC=O frequencies vary with the proton acceptor properties of the anion. The spectra of the 2:1 complexes show broad and intense O . H . O stretching absorptions in the 1500-200 cm-1 range which are slightly affected by the anion and are similar to that for type A acid salts of carboxylic acids. The skeletal vibrations of the betaine residue were identified by second derivative spectroscopy. Evidence based on the nuC=O vibration and deuteration suggests that the hydrogen bonds in [C5H5NCH2COO. H . OOCCH2NC5H5]+A- are described by single minimum potentials; nu(H) = 940 cm-1, nu(H)/nu(D) = 1.2. As betaines are widely distributed in plants and animal tissue and form complexes with strong hydrogen bonds, such bonds should be formed in biological systems.

The broad absorption in IR spectrum of pyridine N-oxide hemiperchlorate in the region of 1600-400 cm(-1), occurring due to the protic mode, was separated from the skeletal mode using relation A(CPA) A((BHB)A) - A(BHA) - A(B) and the following isotope ratios were obtained: nu'(H)/nu'(D) = 1.2, nu "(H)/nu "(D) = 1.19, A(H)/A(D) = 2.0 and P-H/P-D = 1.7. In the solid state these absorptions were separated using ClO4 band at 1100 cm(-1) as an internal standard and found to be nu'(H)/nu'(D) = 1.13 and nu "(H)/nu "(D) = 1.13. Sources of errors on the estimated spectroscopic parameters are discussed. .

The crystal structure of the title compound has been determined by X-ray analysis. The intramolecular hydrogen bond lengths are 2.606(3) angstrom for the (NHN)+ bridge in protonated 1,8-bis(dimethylamino)naphthalene cation (DMAN+H) and 2.401(4) angstrom for the (OHO)- bridge in the hydrogen maleate anion (HM-), The H-bonds are asymmetrical and not strictly linear: NHN, 157(3)-degrees and OHO, 170(5)-degrees. The geometries of the N-H ... N and 0-H ... 0 bridges of the investigated cation and anion are dominated by the spherical repulsions of their constituent atoms.The overlapping bands in the absorbance IR spectra of potassium hydrogen (deuteron) maleate are separated in the second-derivative spectra. The strong mixing of the in-plane modes with skeletal modes in the hydrogen maleate ion causes a larger separation (DELTAnu almost-equal-to 115 cm-1) of the nu(C=0) bands in comparison with those in other type A acid salts containing intermolecular hydrogen bonds (DELTAnu almost-equal-to 20-35 cm-1). The observed lack of solvent effect on the IR absorption suggests that the hydrogen bonds in tetrabutylammonium hydrogen maleate and 1,8-bis(dimethylamino)naphthalene hydrogen maleate are not extremely polarizable. H-1 and C-13 NMR chemical shifts of the investigated compound were measured and identified in two-dimensional (2D) experiments. The H-1 NMR spectra show two narrow signals at ca. 19.5 and 18.7 ppm due to the OHO and NHN protons, respectively. The structural parameters of the cation and anion were also determined by quantum-mechanical calculations with the semiempirical MNDO-PM3 method.

FT-IR and Raman spectra of amylose-Rose Benagl in solution and in lyophilised samples were investigated. In the Rose Bengal molecule, the number and positions of active atoms, i.e., those that interact with amylose, were determined. The interaction with amylose was found not to affect the Rose Bengal quinonoidal structure. Results for the amylose complex show considerable hindrance of the rotational vibrations of amylose functional groups. Moreover, the influece of Rose Bengal on the infrared signals in the structuer-sensitive region (950–1200 cm−) was studied. The FT-IR results indicated the formation of a stiff amylose network induced by Rose Bengal molecules.

The shape of the second derivative of absorption in the carbonyl region of substituted picolinic acid N-oxides suggests that the intramolecular hydrogen bonds are described by a strongly asymmetrical quasi-single-minimum potential. The intensities of the hydrogen-bond modes in the investigated acids are very weak in comparison with similar short intermolecular hydrogen bonds. The in-plane hydrogen-bond mode is strongly mixed with the carbonyl mode and this is responsible for band structure in the 1700 cm−1 region.

The crystal structures of trifluoroacetic acid complexes with 4-NMe2-, 4-Me- and 4-CN-pyridines were determined by X-ray analysis; the N-H...O bonds are 2.724(3), 2.702(4) and 2.587(5) angstrom respectively. The H-bonds are nearly linear for 4-NMe2, 177(4)-degrees; 4-Me, 177(4)-degrees; and 4-CN, 174(6)-degrees.IR spectra (Nujol) show continuous absorption, whose intensity decreases with elongation of the H-bond length. The continuous absorption is not observed in D2O spectra. The solid-state spectra in the 1700 cm-1 region are more complex than those in D2O; the characteristic overtones of the pyridine rings borrow intensity from the continuous absorption via Fermi resonance. The overtones indicate modified structure in the 1700 cm-1 region. The results of both diffraction and FT-IR experiments are comparable.The structural parameters of the complexes were also determined by quantum-mechanical calculations with the semiempirical MNDO-PM3 method. A solvent effect was taken into account using a self-consistent reaction field theory.

A single carbonyl band in the second-derivative FTIR spectra of the equimolar mixtures of six substituted pyridine N-oxides with trifluoroacetic acid in dichloromethane implies that complexation is complete and hydrogen bonds are described by a strongly asymmetrical quasi-single minimum potential. The equimolar complexes interact with a second molecule of the acid, the second hydrogen bond causes only a minor effect on the first hydrogen bond and this effect is independent of proton-acceptor properties of N-oxides. The equimolar complexes interact also with a second molecule of N-oxide to form homoconjugated complex (BHB)+A-. This interaction is controlled by pK(a) of the N-oxide.

FTIR spectra of dichloracetic acid and its eight complexes with substituted pyridine N-oxides and N,N-dimethylaniline in dichloromethane-d2 are reported. 4-N,N-dimethylaminopyridine N-oxides form two types of complexes with dichloroacetic acid; the acid interacts with NO or Me2N groups. The shape of the second derivative of absorption in the carbonyl region implies that the hydrogen bonds are described by a strongly asymmetrical quasi-single minimum potential. The situation with regard to the observed carbonyl frequencies as related to conformational equilibria is reviewed.

The second derivative of FTIR spectra in the carbonyl—carboxyl region has been used in order to study the interaction of trifluoroacetic acid with eight R-pyridines in dichloromethane. In the case of the equimolar base—acid mixture, the following species (a) B · HA, (b) B · HA · HA, (c) B+H · A− and (d) B+H · A− · HA are recognized. All of the species are present in complexes of the medium strong pyridines (R = H or D, 3-Me and 4-Me). Two species (a) and (b) are found for complexes of the weakest, when R = 4-CN and 3-Br, and another two (c) and (d) for complexes of the strongest, when R = 3-NMe2 and 2,4,6-Me3, pyridines. Complete formation of the 1:1 complex requires an excess of pyridines. Fermi resonance of overtones due to pyridines and the acid with the continuous absorption is observed.