Conformational Study of the Structure of 12-crown-4−Alkali Metal Cation Complexes

El-Azhary, Adel A.; Al-Kahtani, A. A.

doi:10.1021/jp052605t

Cited by 23 publications

(22 citation statements)

References 54 publications

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“…Table 1 shows the geometry of this conformation at the B3LYP and MP2 levels using the 6-31+G* basis set. The details of the MP2 computations are as given in ref 31. It can be noticed from the data in Table 1 that there is an increase of the displacement of the metal cation out of the ring plane, M-O bond length, where M refers to alkali metal cation, by the increase of the metal cation size.…”

Section: Resultsmentioning

confidence: 99%

“…31 Cartesian coordinate force fields were calculated, at the corresponding optimized geometries, for six of the eight predicted conformations. The other two conformations have C 1 symmetry and were not considered.…”

Section: Computational Detailsmentioning

confidence: 99%

“…The other two conformations have C 1 symmetry and were not considered. The six conformations considered have symmetries of, in energy order, C 4 , C s , C s , C 2V , C 2V , and C s , as detailed in ref 31. Notice that for the Li + complex in all levels considered in ref 31, except at the HF/3-21G level, the energy order of the first C 4 and second C s conformations is reversed and the third C s conformation collapses to the second C s conformation.…”

Section: Computational Detailsmentioning

confidence: 99%

“…16,30 In a continuing study, conformational analysis of 12c4-alkali metal cation complexes was performed. 31 The study predicted eight possible conformations of these complexes. It was concluded that the C 4 conformation is the lowest energy conformation of the 12c4-Na + , K + , Rb + and Cs + complexes.…”

Section: Introductionmentioning

confidence: 99%

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Experimental and Theoretical Study of the Vibrational Spectra of 12-Crown-4−Alkali Metal Cation Complexes

2006

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The vibrational, Raman, and IR, spectra of the five 12-crown-4 (12c4) complexes with Li+, Na+, K+, Rb+, and Cs+ alkali metal cations were measured. Except for a small shift of the position of some bands in the vibrational spectra of the Li+ complex, the vibrational spectra of the five complexes are so similar that it is concluded that the five complexes exist in the same conformation. B3LYP/6-31+G* force fields were calculated for six of the eight predicted conformations in a previous report (J. Phys. Chem. A 2005, 109, 8041) of the 12c4-Li+, Na+, and K+ complexes that are of symmetries higher than the C1 symmetry. These six conformations, in energy order, are of C4, Cs, Cs, C(2v), C(2v), and Cs symmetries. Comparison between the experimental and calculated vibrational frequencies assuming any of the above-mentioned six conformations shows that the five complexes exist in the C4 conformation. This agrees with the fact that the five alkali metal cations are larger than the 12c4 ring cavity. The B3LYP/6-31+G* force fields of the C4 conformation of the Li+, Na+ and K+ complexes were scaled using a set of eight scale factors and the scale factors were varied so as to minimize the difference between the calculated and experimental vibrational frequencies. The root-mean-square (rms) deviations of the calculated frequencies from the experimental frequencies were 7.7, 5.6, and 5.1 cm(-1) for the Li+, Na+, and K+ complexes, respectively. To account for the earlier results of the Li+ complex that the Cs conformation is more stable than the C4 conformation by 0.16 kcal/mol at the MP2/6-31+G* level, optimized geometries of the complex were calculated for the C4 and Cs conformations at the MP2/6-311++G** level. The C4 conformation was calculated to be more stable than the Cs conformation by 0.13 kcal/mol.

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Section: Resultsmentioning

confidence: 99%

Section: Computational Detailsmentioning

confidence: 99%

Section: Computational Detailsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Experimental and Theoretical Study of the Vibrational Spectra of 12-Crown-4−Alkali Metal Cation Complexes

2006

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“…The lowest energy complex Li(12С4) + has a pyramidal structure with С 4 symmetry and a large deviation of the Li atom from the plane passing through four O atoms. 30 The choice of the structure with S 4 sym metry for calculations of the Li(12С4) + complex is due to the fact that the geometry of this conformer best matches that of 12С4, namely, the Li + ion is also within the macrocycle cavity.…”

Section: Figmentioning

confidence: 99%