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The aggregation of molecules is usually associated with a specific type of interaction, which can be altered by thermodynamic conditions. Under normal conditions, the crystal structure of selenourea, SeC(NH2)2, phase α is trigonal, space group P31, Z = 27. Its large number of independent molecules (Zα′ = 9) can be associated with the formation of an NH...N hydrogen bond substituting one of 36 independent NH...Se hydrogen bonds, which prevail among intermolecular interactions. Phase α approximates the trigonal structure with a threefold smaller unit cell (Z = 9), which in turn approximates another still threefold smaller unit cell (Z = 3). The temperature‐induced transformations of selenourea have been characterized by calorimetry and by performing 21 single‐crystal X‐ray diffraction structural determinations as a function of temperature. At 381.0 K, phase α undergoes a first‐order displacive transition to phase γ, with space group P3121 and Z reduced to 9, when the NH...N bond is broken and an NH...Se bond is formed in its place. Previously, an analogous competition was observed between NH...N and NH...O hydrogen bonds in high‐pressure phase III of urea. The lattice vectors along the (001) plane in low‐ and high‐temperature phases of selenourea are related by a similarity rule, while the lattice dimensions along direction c are not affected. This similarity rule also applies to the structures of phase γ and hypothetical phase δ (Z = 3). The thermally controlled transition between enantiomorphic phases of selenourea contrasts with its high‐pressure transition at 0.21 GPa to a centrosymmetric phase β, where both the NH...Se and NH...N bonds are present. The compression and heating reduce the number of independent molecules from Z′ = 9 in phase α, to Z′ = 2 in phase β and to Z′ = 1.5 in phase γ. [ABSTRACT FROM AUTHOR]

The 1:1 complex of N -methylmorpholinium-acetate, MMB, with hydrobromic acid ( 1 ) has been investigated by single-crystal X-ray analysis, infrared spectroscopy and theoretical calculations. The proton-transfer complex has been observed in the crystalline state, with the COO H⋯Br hydrogen bond with the O⋯Br distance of 3.107(2) Å. In the structure optimized at the B3LYP/6-311++G(d,p) levels of theory the proton is closer to the bromide anion, with the Br H⋯OOC distance of 3.069 Å. The potential energy distributions (PED) have been used for the assignments of IR bands. The experimental and theoretical infrared spectra have been discussed. [ABSTRACT FROM AUTHOR]

The structure of bis(4-trimethylammoniumbenzoate) hydroiodide hydrate 1 has been studied by X-ray diffraction, B3LYP/6–311G(d,p) calculations, FTIR, Raman and NMR spectroscopic techniques. The crystal is polar in monoclinic space group Cc. Two 4-trimethylammoniumbenzoate moieties are joined by a short and asymmetric hydrogen bond of 2.45(2) Å. Water molecules are gradually released from the structure, causing shifts in the position of iodine anions, which induces their disorder. The water molecule interacts with 4-trimethylammoniumbenzoate moiety and iodide anion via two O(3)–H(1)⋯O(1) and O(3)–H(2)⋯I(1) hydrogen bonds of lengths 2.70(3) and 3.51(1) Å. Hydrogen bonds in theoretically predicted structures of 2 and 3 (in vacuum), and 4 , 5 (in DMSO) optimized by the B3LYP/6-311G(d,p) approach are slightly longer than in crystal 1 . The FTIR spectrum of 1 shows a broad and intense absorption in the 1500–400 cm −1 region, typical of short hydrogen bonds assigned to the ν as (OHO) + γ (OHO) vibrations. The correlations between the experimental 13 C and 1 H chemical shifts ( δ exp ) of the investigated compound in DMSO and the GIAO/B3LYP/6-311G(d,p) magnetic isotropic shielding constants ( σ calc ) calculated by using the screening solvation model (COSMO) are linear, δ exp = a + b σ calc , and they well reproduce the experimental chemical shifts. [ABSTRACT FROM AUTHOR]

The 1:2 complex of 1,4-dimethylpiperazine mono-betaine (MBPZ) with squaric acid (H2SQ) has been characterised by single-crystal X-ray analysis, FTIR and NMR spectroscopies, and by DFT calculations. The crystals are monoclinic, space groupP21/c. Two MBPZ cations and four hydrogen squarate anions (HSQ− ) are linked by strong O(1)–H…O(13) (2.525(4) Å), O(14)–H…O(21) (2.511(4) Å) and N(4)–H…O(23) (2.607(3) Å) hydrogen bonds into a cyclamer. In turn, the cyclamers are linked into a helixthrough two O(24)–H…O(11) hydrogen bonds of 2.516(4) Å. The piperazinium ring has a chair conformation with N(4)–CH3and N(1)–CH2COOH substituents in the equatorial positions, and N(1)–CH3in the axial position. The FTIR spectrum is consistent with the crystal data. Two models of the 1:2 complex of MBPZ with H2SQ have been optimised at the B3LYP/6-311++G(d,p) level of theory and have been used to calculate harmonic IR frequencies. One of the models (2) is dominated by electrostatic attraction between NH(4)+and HSQ− , whereas in the other (3) squaric acid interacts with a zwitterionic MBPZ through the O–H…O and O–H…N hydrogen bonds. [ABSTRACT FROM PUBLISHER]

The main directions and achievements in the research on transformations of hydrogen-bonds during the last decade have been briefly outlined. [ABSTRACT FROM AUTHOR]

A novel and unique crystalline three-component complex was formed of 2-(1-piperidine)ethanol, p -hydroxybenzoic acid and water at the ratio 1:1:1. Its structure has been determined by single-crystal X-ray diffraction. This is an example of a hydrogen-bonded interaction between amino alcohol and benzoic acid molecules. Water acts as a bridge between molecules. The molecules are linked through medium-strong OH⋯O hydrogen bonds from 2.665(6) to 2.813(6) Å and NH⋯O one 2.744(5) Å in length. The molecular structure of 2-(1-piperidinium)ethanol p -hydroxybenzoate hydrate has been characterized by FTIR and Raman spectra and optimized at the B3LYP/6−311++G(d,p) level of theory. The potential energy distributions (PED) have been used to assign the vibrational spectra. Charge delocalization was analyzed using the natural bond orbital (NBO) methods. [ABSTRACT FROM AUTHOR]

( R / S )-Piperidine-3-carboxylic acid (P3C, nipecotic acid) forms a stable 1:1 hydrogen-bonded complex with 2,6-dichloro-4-nitrophenol (DCNP). Both, in crystal and in the optimized theoretically structure by the B3LYP/6-311 + +G(d,p) approach the proton is transferred from DCNP to P3C. The ( R ) and ( S )-stereoisomersic complexes of piperidinium-3-carboxylic acid 2,6-dichloro-4-nitrophenolate, P3C + H·DCNP − , aggregate into centrosymmetric cyclic dimers through the COOH⋯O − and N + H⋯ONO hydrogen bonds of 2.57(1) and 3.06(1) Å, respectively, which in turn are linked into a ladder-type cyclamer through the C H⋯Cl hydrogen bonds of 3.71(1) Å. The title compound is characterized by single-crystal X-ray analysis, Raman and FTIR spectroscopies. The structures of the complexes of the ratio 1:1 (monomer), 2:2 (dimer) and 4:4 (cyclamer) of P3C + H·DCNP − units are optimized by the B3LYP/6-311 + + G(d,p) approach and compared with the solid-state experimental structure. Detail interpretation of the vibrational spectra has been carried out by computing Potential Energy Distribution (PED). Charge delocalization has been analyzed using the Natural Bond Orbital (NBO) method. [ABSTRACT FROM AUTHOR]

• Structure of 8 - hydroxyquinoline betaine monohydrate was solved by X-ray. • The one proton of disordered water molecules is shared between two half-occupied sides. • Three broad bands classify the FTIR spectrum as the ABC type. • PED are used to assign the bands in the vibrational spectrum. • Hirshfeld surface, Mulliken atomic charges, MEP, HOMO-LUMO were computed. • The assignment of 1H and 13C resonance signals are based on the 2D measurements. Molecular structure and properties of 8-hydroxyquinoline betaine monohydrate (1-carboxymethyl-8-hydroxyquinolinium inert salt monohydrate) were studied by X-ray diffraction, DFT calculations, FTIR and NMR spectra. In the crystals, 8-hydroxyquinoline betaine and water are bonded by an intermolecular and asymmetric COO···H 2 O hydrogen bond of 2.782(3) Å. The water molecules are disordered so that one of the proton is shared between two half occupied sites. The hydroxyl group of quinoline is bonded to the neighboring molecule by the O−H···OOC hydrogen bond of 2.571(3) Å. The molecular geometry, Hirshfeld surface, Mulliken atomic charge distribution, molecular electrostatic potential, frontier molecular orbitals, vibrational wavenumbers, magnetic isotropic shielding constants were determined using the density functional theory (DFT/B3LYP) with 6–311++G(d,p) basis set. The FTIR spectrum shows a characteristic ABC structure, typical of medium-short hydrogen bonds. The potential energy distribution (PED) was used to assign the bands in the vibrational spectrum. 1H and 13C NMR spectra were analyzed. [Display omitted] [ABSTRACT FROM AUTHOR]

The crystals of 5,5′-dibromo-3-diethylaminomethyl-2,2′-biphenol N-oxide were studied by X-ray and FT-IR spectroscopy. Within this molecule two short OHO intramolecular hydrogen bonds are formed. The NO⋯H+⋯O− bond between the OH and the N-oxide groups is very strong, of 2.419(7) A˚ between the oxygen atoms. The proton potential of this hydrogen bond is flat, broad and has probably no barrier—consequently it could not be located from X-ray diffraction data. The other hydrogen bond formed between two hydroxyl groups appears asymmetrical from FT-IR spectra, and shows also relatively limited proton polarizability. The molecular conformation is non-planar, due to strong overcrowding effect between the oxygen atoms involved in the hydrogen bonds. [Copyright &y& Elsevier]

Abstract 2-(Quinuclidinium)-alkanocarboxylates co-crystallize with 2,6-dichloro-4-nitrophenol at the ratios 1:1 and 1:2 depending on the alkyl-chain lengths. The obtained complexes have been characterized by single-crystal X-ray diffraction, UV–vis, FTIR and NMR spectroscopy. The compounds 2-(quinuclidinium)-acetate and 2-(quinuclidinium)-propionate form complexes with 2,6-dichloro-4-nitrophenol at the stoichiometric ratio 1:2, while 2-(quinuclidinium)-butyrate and 2-(quinuclidinium)-valerate at ratio 1:1. Three crystal structures of compounds of these series were determined, but no single crystals of sufficient quality could be obtained of the 2-(quinuclidinium)-butyrate complex. The B3LYP/6-311++G(d,p) approach has been used to determine structures of their isolated molecules and to interpret the IR and UV–vis spectra. Diagrams of the HOMO and LUMO of molecules have been obtained. Graphical abstract Image 1 Highlights • Quiniclidinium-alkanocarboxylates form H B complexes with 2,6-dichloro-4-nitrophenol. • Lower homologues form molecular complexes at the 1:2 ratio. • Longer homologues form proton transfer 1:1 complexes. • Molecular structures were solved by X-ray diffraction and optimized by DFT methods. • UV–vis, FTIR and NMR spectra were measured. [ABSTRACT FROM AUTHOR]

The complex of 2-(hydroxymethyl)-1-methyl-piperidine [2-(1-methyl-piperidine)-methanol] (MPMe) and p -hydroxybenzoic acid (HBA) crystallizes as a hydrate. HBA interacts through the OH···O and NH···O hydrogen bonds with MPMe. The water mediated hydrogen-bonded bridge molecules MPMe and HBA. The structure of 2-(hydroxymethyl)-1-methyl-piperidinium p -hydroxybenzoate hydrate has been characterized by X-ray diffraction, FTIR and NMR spectroscopy and optimized at the B3LYP/6-311++G(d,p) level of theory. The potential energy distributions, PED, have been used to assign the vibrational spectra. The GIAO/B3LYP/6-311++G(d,p) calculated magnetic isotropic shielding constants have been used to interpret the chemical shifts in the 1 H and 13 C NMR spectra. [ABSTRACT FROM AUTHOR]

The molecular complex of N -ethyl-3-hydroxypyridinium hydrogen squarate has been obtained and characterized by single-crystal X-ray diffraction, B3LYP/6-311++G(d,p) calculations, Raman, FTIR and NMR spectra. The complex is built of OH⋯O hydrogen-bonded dimer involving two anions and two cations. In order to establish a tautomeric equilibrium between 3-phenolic and 3-pyridone forms in N -ethyl-3-oxopyridinium unit in the complex, additionally N -ethyl-3-oxopyridinium has been studied by the same experimental and theoretical methods. The potential energy distributions (PED) have been used to assign the vibrational spectra. Charge delocalization has been analyzed using the Natural Bond Orbital (NBO) method. [ABSTRACT FROM AUTHOR]

The molecular structure of 1,2-di(3-hydroxymethylpyridinium)ethane dibromide ( 1 ) has been characterized by X-ray diffraction, B3LYP/6-311++G(d,p) calculations, FTIR, Raman and NMR spectra. The crystals are monoclinic, space group C2/c . 1,2-Di(3-hydroxymethylpyridinium)ethane dication and hydrogen-bonded bromide anions in crystals are located at the inversion center. The both CH 2 OH groups are engaged in two equal length hydrogen bonds with bromide anions. Two structures ( 2 ) and ( 3 ) were optimized at the B3LYP/6-311++G(d,p) level of theory. The optimized complex ( 2) resembles the crystal structure, while complex ( 3 ) is preferred energetically. The O⋯Br − hydrogen bonds distances are: 3.289(2) Å in crystals ( 1 ), but in the optimized structures ( 2 ) and ( 3 ) they are 3.303 Å and 3.461 Å, respectively. The investigated complex is additionally stabilized by the N + ⋯Br − electrostatic attractions. The potential energy distributions (PED) were used for the assignments of IR and Raman frequencies in the experimental and calculated spectra of the title compound. The FTIR spectrum of ( 1 ) is consistent with the X-ray results. Interpretation of the 1 H and 13 C NMR spectra in DMSO- d 6 has been based on 2D experiments. The calculated GIAO/B3LYP/6-311++G(d,p) magnetic shielding constants have been used to predict 1 H and 13 C chemical shifts for the optimized structures of ( 2 ) and ( 3 ). [ABSTRACT FROM AUTHOR]

The molecular structure of 1:1 complex formed between the naturally occurring polyether ionophore, called lasalocid acid (LAS) and propargylamine (PROP) is studied by X-ray, FT-IR, 1 H NMR, 13 C NMR and ESI-MS methods. The complex formed between deprotonated LAS acid and protonated PROP molecule is stabilized by intra- and inter-molecular hydrogen bonds. The protons of the protonated amine group are hydrogen bonded to etheric and hydroxyl oxygen atoms of the LAS anion. The similarity of the FT-IR spectra of the LAS–PROP complex in solid state and in solution demonstrated that the molecular structures of the complex in both states are comparable. It is shown that LAS in solution can form concurrent complexes with metal cations (M = Li + , Na + , K + ) and amine existing in equilibrium. Analysis of the structures of lasalocid complexes is important for a better understanding of the antibacterial and anticancer properties of lasalocid acid. [ABSTRACT FROM AUTHOR]

The 1:2 complex ( 1 ) of dimethylphenyl betaine (DMPB) with two molecules of 2,6-dichloro-4-nitro-phenol (DCNP) was prepared and characterized by X-ray diffraction, B3LYP/6-311++G(d,p) and B3LYP-D3/6-311++G(d,p)calculations, FTIR and NMR spectroscopies. The crystal is monoclinic, space group P 2 1 / c with Z = 4. The protons at the oxygen atoms of phenols are bonded to each oxygen atoms of the DMPB carboxylate group by two nonequivalent H-bonds with the O H⋯O distances of 2.473(5) and 2.688(4) Å. Both H-bonds in the optimized structures 2 (in vacuum), 3 (in DMSO solution) and dispersion-correlated functional (D3) 4 (in vacuum) are comparable and are slightly shorter than O(6) H(O6)⋯O(2) in the crystal. The FTIR spectrum of 1 shows a broad absorption in the 3400–2000 cm −1 region corresponding to a longer hydrogen bond and a broad absorption in the 1800–500 cm −1 region caused by the shorter H-bond. The relations between the experimental 13 C and 1 H chemical shifts ( δ exp ) of the investigated compound 1 in DMSO solution and GIAO/B3LYP/6-311++G(d,p) magnetic isotropic shielding constants ( σ calc ) obtained by using the screening solvation model (COSMO) for 3 are linear and reproduce well the experimental chemical shifts described by the equation: δ exp = a + b σ calc . [ABSTRACT FROM AUTHOR]

Abstract: Cyclic diamide of o-phthalic acid with 3,6-dioxa-octyl-1,8-diamine (CPhDA) was synthesised by a new method and its hydrate structure has been studied by X-ray diffraction, FT-IR, NMR and PM5 semiempirical methods. The crystal of this compound is orthorhombic, space group Pbcn, with a =16.7033(11), b =8.8823(5), c =19.6182(12) and Z =8. The IR spectrum of the crystal is consistent with the results obtained by the X-ray study and provides spectroscopic evidence for the formation of the H-bonded complex with water molecules. The calculated structure of the complex and the structural parameters are comparable with those determined by the X-ray method. [Copyright &y& Elsevier]

N- Methylpyrrolidine betaine (N- carboxymethyl- N- methyl-pyrrolidinium, inner salt, MPRB) cocrystallizes with p -hydroxybenzoic acid (HBA) at the 1:1 ratio. The complex is characterized by single-crystal X-ray diffraction, FTIR and NMR spectra. The pyrrolidinium ring adopts an envelope conformation with the methyl group in axial and the carboxymethyl substituent in the equatorial positions. In the cocrystal the COO⋯HO and COO⋯HOOC hydrogen bonds are of 2.574 (4) and 2.586 (4) Å, respectively. The molecular geometry, Hirshfeld surface, natural bond orbitals (NBO), molecular electrostatic potential (MEP), vibrational wavenumbers, magnetic isotropic shielding constants were performed using the density functional theory (DFT/B3LYP) with 6–311++G (d,p) basis set. The molecular structures of isolated 1:1 and 1:2 complexes were optimized. The potential energy distribution (PED) of the IR vibrational modes were used to assign the bands in the IR spectrum. Diagrams of the HOMO and LUMO of components and complex are presented. Theoretical and experimental results are in a good agreement. Image 1 • The 1:1 complex of N-methylpyrrolidine betaine with p -hydroxybenzoic acid was prepared. • Structure of complexes were characterized by X-ray diffraction, FTIR and NMR spectra. • The structures of 1:1 and 1:2 complexes were optimized by the B3LYP/6-311++G(d,p) approach. • The molecules are linked through the OH∙∙∙OOC and COOH∙∙∙OOC hydrogen-bonds. • The IR and NMR experimental and computed spectra were discussed. [ABSTRACT FROM AUTHOR]