Abstract:We report proton transfer in the complex H(3)N...HCl to form the ion pair NH(4)(+)Cl(-), which is favored inside the C(60) cage according to quantum chemical calculations. The results show that the NH(4)(+)Cl(-)@C(60) is stable with an interaction energy of -2.78 kcal mol(-1). Compared with the complex H(3)N...HCl without proton transfer, it is found that the C(60) cage plays the role of a catalyst for proton transfer. In NH(4)(+)Cl(-)@C(60) a negative charge area in the C(60) cage is near the cation NH(4)(+) … Show more
“…Ma et al . have reported a similar result 31 .Figure 2MP2/aug-cc-pVTZ level asymmetric single-well potential energy surface (rigid) of H 2 O ··· HCl (left) and H 2 OH + ··· Cl − (right), showing a proton bound to and transferred from the Cl − species, respectively (PBE/6-311 G(d, p) geometry was used for the rigid scan). Bond distances are in Å and the ∠O ··· H–Cl and ∠O – H ··· Cl bond angles in deg.…”
Section: Resultssupporting
confidence: 64%
“…We estimated the binding energies of the H 2 O···HF dimer in the absence and in the presence of the C 70 cage at various levels of theory, including [CCSD(T)/aug-cc-pVTZ], as was done in previous studies on other systems 13,25,28,31 . From the sign and magnitudes of the uncorrected (Δ E ) and basis set corrected (Δ E (BSSE)) binding energies (Table S1), it is quite apparent that the isolated H 2 O ··· HF dimer is less stable (<1 kcal mol −1 at all levels of theory) than in H 2 O ··· HF@C 70 ; this is accompanied by the O ··· H bond contraction.…”
When acids are supplied with an excess electron (or placed in an Ar or the more polarizable N
2
matrix) in the presence of species such as NH
3
, the formation of ion-pairs is a likely outcome. Using density functional theory and first-principles calculations, however, we show that, without supplying an external electron or an electric field, or introducing photo-excitation and -ionization, a single molecule of HCl or HBr in the presence of a single molecule of water inside a C
70
fullerene cage is susceptible to cleavage of the σ-bond of the Brønsted-Lowry acid into X
−
and H
+
ions, with concomitant transfer of the proton along the reaction coordinate. This leads to the formation of an X
−
···
+
HOH
2
(X = Cl, Br) conjugate acid-base ion-pair, similar to the structure in water of a Zundel ion. This process is unlikely to occur in other fullerene derivatives in the presence of H
2
O without significantly affecting the geometry of the carbon cage, suggesting that the interior of C
70
is an ideal catalytic platform for proton transfer reactions and the design of related novel materials. By contrast, when a single molecule of HF is reacted with a single molecule of H
2
O inside the C
70
cage, partial proton transfers from HF to H
2
O is an immediate consequence, as recently observed experimentally. The geometrical, energetic, electron density, orbital, optoelectronic and vibrational characteristics supporting these observations are presented. In contrast with the views that have been advanced in several recent studies, we show that the encaged species experiences significant non-covalent interaction with the interior of the cage. We also show that the inability of current experiments to detect many infrared active vibrational bands of the endo species in these systems is likely to be a consequence of the substantial electrostatic screening effect of the cage.
“…Ma et al . have reported a similar result 31 .Figure 2MP2/aug-cc-pVTZ level asymmetric single-well potential energy surface (rigid) of H 2 O ··· HCl (left) and H 2 OH + ··· Cl − (right), showing a proton bound to and transferred from the Cl − species, respectively (PBE/6-311 G(d, p) geometry was used for the rigid scan). Bond distances are in Å and the ∠O ··· H–Cl and ∠O – H ··· Cl bond angles in deg.…”
Section: Resultssupporting
confidence: 64%
“…We estimated the binding energies of the H 2 O···HF dimer in the absence and in the presence of the C 70 cage at various levels of theory, including [CCSD(T)/aug-cc-pVTZ], as was done in previous studies on other systems 13,25,28,31 . From the sign and magnitudes of the uncorrected (Δ E ) and basis set corrected (Δ E (BSSE)) binding energies (Table S1), it is quite apparent that the isolated H 2 O ··· HF dimer is less stable (<1 kcal mol −1 at all levels of theory) than in H 2 O ··· HF@C 70 ; this is accompanied by the O ··· H bond contraction.…”
When acids are supplied with an excess electron (or placed in an Ar or the more polarizable N
2
matrix) in the presence of species such as NH
3
, the formation of ion-pairs is a likely outcome. Using density functional theory and first-principles calculations, however, we show that, without supplying an external electron or an electric field, or introducing photo-excitation and -ionization, a single molecule of HCl or HBr in the presence of a single molecule of water inside a C
70
fullerene cage is susceptible to cleavage of the σ-bond of the Brønsted-Lowry acid into X
−
and H
+
ions, with concomitant transfer of the proton along the reaction coordinate. This leads to the formation of an X
−
···
+
HOH
2
(X = Cl, Br) conjugate acid-base ion-pair, similar to the structure in water of a Zundel ion. This process is unlikely to occur in other fullerene derivatives in the presence of H
2
O without significantly affecting the geometry of the carbon cage, suggesting that the interior of C
70
is an ideal catalytic platform for proton transfer reactions and the design of related novel materials. By contrast, when a single molecule of HF is reacted with a single molecule of H
2
O inside the C
70
cage, partial proton transfers from HF to H
2
O is an immediate consequence, as recently observed experimentally. The geometrical, energetic, electron density, orbital, optoelectronic and vibrational characteristics supporting these observations are presented. In contrast with the views that have been advanced in several recent studies, we show that the encaged species experiences significant non-covalent interaction with the interior of the cage. We also show that the inability of current experiments to detect many infrared active vibrational bands of the endo species in these systems is likely to be a consequence of the substantial electrostatic screening effect of the cage.
“…35 Quantum chemical calculations show that C 60 catalyzes proton transfer between caged NH 3 and HCl to NH 4 + + Cl À . 36 The greatly improved resolution of the mass spectrometer used in the present study makes it possible to easily separate contributions from protonated, unprotonated and dehydrogenated ions for complexes containing up to three C 60 molecules. Ions are predominantly unprotonated if they contain n o 5 ammonia molecules; the ratio of protonated to unprotonated ions approaches B1 at n = 5 or 6.…”
Helium nanodroplets are co-doped with C(60) and ammonia. Mass spectra obtained by electron ionization reveal cations containing ammonia clusters complexed with up to four C(60) units. The high mass resolution of Δm/m≈ 1/6000 makes it possible to separate the contributions of protonated, unprotonated and dehydrogenated ammonia. C(60) aggregates suppress the proton-transfer reaction which usually favors the appearance of protonated ammonia cluster ions. Unprotonated C(x)(NH(3))(n)(+) ions (x = 60, 120, 180) exceed the abundance of the corresponding protonated ions if n < 5; for larger values of n the abundances of C(60)(NH(3))(n)(+) and C(60)(NH)(n-1)NH(4)(+) become about equal. Dehydrogenated C(60)NH(2)(+) ions are relatively abundant; their formation is attributed to a transient doubly charged C(60)-ammonia complex which forms either by an Auger process or by Penning ionization following charge transfer between the primary He(+) ion and C(60). The abundance of C(x)NH(3)(+) and C(x)NH(4)(+) ions (x = 120 or 180) is one to two orders of magnitude weaker than the abundance of ions containing one or two additional ammonia molecules. However, a model involving evaporation of NH(3) or NH(4) from the presumably weakly bound C(x)NH(3)(+) and C(x)NH(4)(+) ions is at odds with the lack of enhancement in the abundance of C(120)(+) and C(180)(+). Mass spectra of C(60) dimers complexed with water complement a previous study of C(60)(H(2)O)(n)(+) recorded at much lower mass resolution.
“…The well-known H 3 N−HCl and H 2 O−HCl acid−base pairs provide us with simple and prototypical examples to study proton-transfer reactions. As is known, single H 3 N−HCl and H 2 O−HCl pairs do not react to form ion pairs, H 4 N + Cl − and H 3 O + Cl − , in isolation. − However, if there is an external stimulus, such as, polar molecules, − ,− excess electrons, , or a nanoconfined environment, , the proton transfer could occur. Li et al and Bowen et al have shown that only a water molecule or an excess electron can trigger the proton transfer of H 3 N−HCl.…”
It is well-known that single H3N-HCl and H2O-HCl acid-base pairs do not react to form the ion pairs, H4N(+)Cl(-) and H3O(+)Cl(-), in isolation. On the basis of ab initio method, we propose a physical method of external electric field (Eext) to drive the proton transfer from acid (HCl) to base (NH3/H2O). Our results show that when Eext along the proton-transfer direction achieves or exceeds the critical electric field (Ec), the proton transfer occurs, such as, the Ec values of proton transfer for H3N-HCl and H2O-HCl are 54 × 10(-4) and 210 × 10(-4) au, respectively. And the degree of the proton transfer can be controlled by modulating the strength of Eext. Furthermore, we estimate the inductive strength of an excess electron (Ee) equivalent to the Eext = 125 × 10(-4) au, which is greater than the Ec (54 × 10(-4) au) of NH3-HCl but less than the Ec (210 × 10(-4) au) of H2O-HCl. This explains well the anion photoelectron spectroscopy [Eustis et al. Science 2008, 319, 936] that an excess electron can trigger the proton transfer for H3N-HCl but not for H2O-HCl. On the basis of the above estimation, we also predict that two excess electrons can induce H2O-HCl to undergo the proton transfer and form the ion pair H3O(+)Cl(-).
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