Short N<sup>+</sup>—H...Ph hydrogen bonds in ammonium tetraphenylborate characterized by neutron diffraction

Steiner, Thomas; Mason, Sax A.

doi:10.1107/s0108768199012318

Cited by 35 publications

(25 citation statements)

References 19 publications

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“…This mode of interaction is similar to that involving the CH 3 CN solvent in 1a, and is also topologically similar to the Ar‚‚‚H-X-H‚‚‚Ar interactions found in water (X ) O) 35 and dichloromethane (X ) C) 36 inclusion complexes of calixarenes and in ammonium tetraphenylborate (X ) N). 37 Despite being "charge-assisted", the distances from the cation to the aryl rings of the anion are slightly greater than those of the CH 3 CN-anion interactions found in 1a, presumably reflecting the greater steric bulk of the Ph 3 PEt + cation. The C-H‚‚‚π bonded cation interacts further, with O1 of a neighboring anion via one aryl para C-H group, completing the polymeric supramolecular structure shown in Figures 7 and 8.…”

Section: Resultsmentioning

confidence: 94%

On the Reliability of C−H···O Interactions in Crystal Engineering: Synthesis and Structure of Two Hydrogen Bonded Phosphonium Bis(aryloxide) Salts

Broder

Davidson

Forsyth

et al. 2002

Crystal Growth & Design

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W This paper contains enhanced objects available on the Internet at http://pubs.acs.org/crystal. ABSTRACT: Two related phosphonium aryloxides, [Ph 3 PCH 3 ] + 2 [CH 2 (C 6 H 2 -3,5-tert-butyl-4-O) 2 ] 2-, 1a, and [Ph 3 -PC 2 H 5 ] + 2 [CH 2 (C 6 H 2 -3,5-tert-butyl-4-O) 2 ] 2-, 1b have been synthesized by protonation of nonstabilized phosphorus ylides with 4,4′-methylenebis(2,6-di-tert-butylphenol) LH 2 . The crystal structures of 1a and 1b have been determined by single-crystal X-ray diffraction, and that of 1b has also been determined by low-temperature (20 K) neutron diffraction. Both crystallize as CH 3 CN solvates, and both exhibit polymeric supramolecular structures via extensive C-H‚‚‚O hydrogen bonding. The predominant structural motif is chelation of the aryloxide oxygen atom of the anion by phosphonium alkyl and aryl C-H groups, such as has been previously observed for phosphonium monoaryloxide salts. The use of this motif as a supramolecular synthon in crystal engineering is explored. In the case of 1a, in addition to the expected intermolecular C-H‚‚‚O hydrogen bonding pattern, C-H‚‚‚π interactions between the anion and this solvent are observed. In the structure of 1b, C-H‚‚‚π interactions between the cation and anion lead to an unpredicted supramolecular structure. The possible significance of this feature is discussed the context of the general use of weak hydrogen bonds in crystal engineering.

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Section: Resultsmentioning

confidence: 94%

On the Reliability of C−H···O Interactions in Crystal Engineering: Synthesis and Structure of Two Hydrogen Bonded Phosphonium Bis(aryloxide) Salts

Broder

Davidson

Forsyth

et al. 2002

Crystal Growth & Design

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“…Previously, only presumptions about the geometry of the motions of the donor and acceptor of the aromatic H bond had been reported. Calculations and structural studies 3,[23][24][25][26][27] have indicated that the directionality of the aromatic H bond is extremely flexible. Our study provides now more precise information, showing that the donor rotates in a specific way, and the acceptor undergoes strongly damped librational mo- tion with a partially diffusive character.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

“…3 Such a symmetry would be respected by considering reorientations of the C 3 molecular axis. It follows that the EISF associated to such a model can be approximated by a tetrahedral jump model ͑T d ͒ given by 17,18 A 04 ͑Q͒ = 1 4…”

Section: A Ammonium Reorientationsmentioning

confidence: 99%

The dynamical properties of the aromatic hydrogen bond in NH4(C6H5)4B from quasielastic neutron scattering

Jalarvo¹,

Desmedt

Lechner³

et al. 2006

The Journal of Chemical Physics

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NH 4 ͑C 6 H 5 ͒ 4 B represents a prototypical system for understanding aromatic H bonds. In NH 4 ͑C 6 H 5 ͒ 4 B an ammonium cation is trapped in an aromatic cage of four phenyl rings and each phenyl ring serves as a hydrogen bond acceptor for the ammonium ion as donor. Here the dynamical properties of the aromatic hydrogen bond in NH 4 ͑C 6 H 5 ͒ 4 B were studied by quasielastic incoherent neutron scattering in a broad temperature range ͑20ഛ T ഛ 350 K͒. We show that in the temperature range from 67 to 350 K the ammonium ions perform rotational jumps around C 3 axes. The correlation time for this motion is the lifetime of the "transient" H bonds. It varies from 1.5 ps at T = 350 K to 150 ps at T = 67 K. The activation energy was found to be 3.14 kJ/ mol, which means only 1.05 kJ/ mol per single H bond for reorientations around the C 3 symmetry axis of the ammonium group. This result shows that the ammonium ions have to overcome an exceptionally low barrier to rotate and thereby break their H bonds. In addition, at temperatures above 200 K local diffusive reorientational motions of the phenyl rings, probably caused by interaction with ammonium-group reorientations, were found within the experimental observation time window. At room temperature a reorientation angle of 8.4°± 2°and a correlation time of 22± 8 ps were determined for the latter. The aromatic H bonds are extremely short lived due to the low potential barriers allowing for molecular motions with a reorientational character of the donors. The alternating rupture and formation of H bonds causes very strong damping of the librational motion of the acceptors, making the transient H bond appear rather flexible.

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“…The T-shaped structure of the 2-butyne·HCl complex (B) [11] and the π-face structure of NH 4 + ⋯C 6 H 6 (C) [12] have been confirmed in the solid state by X-ray crystallography although, in the H 3 O + ·3C 6 H 6 cation, [13] the O-H bonds are directed more closely to carbon atoms than to the centroid of benzene. More generally, the X-H⋯π hydrogen bonding interaction has become widely recognized as a weak but prevalent intermolecular interaction in small molecule crystallography.…”

Section: Introductionmentioning

confidence: 90%

“…This is in line with neutron diffraction data where N-H vectors of the N + -H⋯phenyl interaction between an NH 4 + ion and phenyl groups are time-averaged orientation is the centroid of the phenyl rings whereas the 50% probability ellipsoids of the N-H vector samples the entire face of the aromatic ring. [12] In the 1:1 complexes formed by cyclic molecules with a pair of conjugated C=C bonds, the functionality acts as a single C=C-C=C chromophore. The absorption of this chromophore for the free (non-complexed) L molecule has two νC=C bands (1603 and 1578 cm −1 ) of medium to low intensity.…”

Section: π-Hydrogen Bondingmentioning

confidence: 99%

The Basicity of Unsaturated Hydrocarbons as Probed by Hydrogen‐Bond‐Acceptor Ability: Bifurcated NH⁺⋅⋅⋅π Hydrogen Bonding

Stoyanov

Stoyanova

Reed

2008

Chemistry A European J

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The competitive substitution of the anion in contact ion pairs of the type [Oct 3 NH + ]B(C 6 F 5 ) 4 − by unsaturated hydrocarbons L in accordance with the equilibrium Oct 3 NH + ⋯Anion − + nL ↔ [Oct 3 NH + ⋯L n ]Anion − has been studied in CCl 4 solution. On the basis of equilibrium constants K and shifts of νNH to low frequency, it is established that complexed Oct 3 NH + ⋯L n cations with n = 1 and 2 are formed, having unidentate and bifurcated N-H + ⋯π hydrogen bonds, respectively. Bifurcated H-bonds to unsaturated hydrocarbons have not been observed previously. The unsaturated hydro-carbons studied include benzene and methylbenzenes, fused-ring aromatics, alkenes, conjugated dienes, and alkynes. From the magnitude of the red shifts in N-H stretching frequencies, ΔνNH, a new scale for ranking the π-basicity of unsaturated hydrocarbons is proposed: fused-ring aromatics ≤ benzene < toluene < xylene < mesitylene < durene < conjugated dienes ∼ 1-alkynes < pentamethylbenzene < hexamethyl-benzene < internal alkynes ∼ cyclo-alkenes < 1-methylcycloalkenes. This scale is relevant to the discussion of π complexes for incipient protonation reactions and to understanding N-H + ⋯π hydrogen bonding in proteins and molecular crystals.

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Short N⁺—H...Ph hydrogen bonds in ammonium tetraphenylborate characterized by neutron diffraction

Cited by 35 publications

References 19 publications

On the Reliability of C−H···O Interactions in Crystal Engineering: Synthesis and Structure of Two Hydrogen Bonded Phosphonium Bis(aryloxide) Salts

On the Reliability of C−H···O Interactions in Crystal Engineering: Synthesis and Structure of Two Hydrogen Bonded Phosphonium Bis(aryloxide) Salts

The dynamical properties of the aromatic hydrogen bond in NH4(C6H5)4B from quasielastic neutron scattering

The Basicity of Unsaturated Hydrocarbons as Probed by Hydrogen‐Bond‐Acceptor Ability: Bifurcated NH⁺⋅⋅⋅π Hydrogen Bonding

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Short N+—H...Ph hydrogen bonds in ammonium tetraphenylborate characterized by neutron diffraction

Cited by 35 publications

References 19 publications

On the Reliability of C−H···O Interactions in Crystal Engineering: Synthesis and Structure of Two Hydrogen Bonded Phosphonium Bis(aryloxide) Salts

On the Reliability of C−H···O Interactions in Crystal Engineering: Synthesis and Structure of Two Hydrogen Bonded Phosphonium Bis(aryloxide) Salts

The dynamical properties of the aromatic hydrogen bond in NH4(C6H5)4B from quasielastic neutron scattering

The Basicity of Unsaturated Hydrocarbons as Probed by Hydrogen‐Bond‐Acceptor Ability: Bifurcated NH+⋅⋅⋅π Hydrogen Bonding

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Short N⁺—H...Ph hydrogen bonds in ammonium tetraphenylborate characterized by neutron diffraction

The Basicity of Unsaturated Hydrocarbons as Probed by Hydrogen‐Bond‐Acceptor Ability: Bifurcated NH⁺⋅⋅⋅π Hydrogen Bonding