Conformational Analysis of the Sodium/12-Crown-4 Complex:  Photoionization and ab Initio Molecular Orbital Studies

Abstract

The molecular complexes formed between sodium atoms and 12-crown-4 molecules were generated in a flow reactor and studied with photoionization mass spectroscopy. The photoionization threshold energies of these complexes, which are dependent on the complex conformations, were obtained from the analysis of the photoionization efficiency spectra. Ab initio molecular orbital calculations were performed on the possible conformers of these complexes and their corresponding ionic states. With the help of theoretical calculations, the photoionization threshold energy of the C 4 conformer of Na(12-crown-4) was determined to be 3.01 ( 0.02 eV, and the C s conformer to be 3.36 ( 0.04 eV. The photoionization threshold energy of the C i conformer was estimated to be 3.82 ( 0.04 eV. The conformation-dependent valence electron spatial distributions, bond dissociation energies, and photoionization threshold energies of the Na(12-crown-4) complex could be rationalized and classified in the framework of the general properties of the complexes formed between the sodium atoms and Lewis base molecules.

Conformational Analysis of the Molecular Complexes of Sodium with Methanol and 1,2-Ethanediol: Photoionization and ab Initio Molecular Orbital Studies

“…Generally speaking, for the diol complex, the HF ionization energies are lower than the corresponding MP2 energies by about 0.15 eV and the MP2 energies are in turn less than the corresponding B3PW91 values by about 0.23 eV. Since it has been demonstrated that the ionization energies calculated by the B3PW91 method are in better agreement with the experimental measurements, , the B3PW91 ionization energies shall be adapted exclusively for the following discussion on the ionization energies. The HF and MP2 ionization energies are served as references.…”

“…The details of the experimental setup, which mainly consists of a photoionization mass spectrometer coupled with a flow reactor, have been described in previous publications. − , In the following, only the experimental conditions, which were relevant to the present experiment, are mentioned briefly. The sodium vapor was generated in an oven heated to 616 K. An argon flow, which constituted a partial pressure of about 570 mTorr in the flow reactor, carried the sodium vapor into the flow tube and reacted with diol vapor.…”

“…Since it has been demonstrated that the ionization energies calculated by the B3PW91 method are in better agreement with the experimental measurements, 3,4 the B3PW91 ionization energies shall be adapted exclusively for the following discussion on the ionization energies. The HF and MP2 ionization energies are served as references.…”

“…It appears that the general physical properties of these multidentate complexes, whose geometric structures apparently lie between the simplest form of the complexes and the solvated-like higher cluster systems, could be understood and fitted into the general picture of this class of molecular system. [4][5][6][7][8][9][10][11] Despite the above general relationship of the physical properties among the complexes, by a closer examination of each complex, one would find that the conformation forms, interaction strengths, ionization threshold energies, and other physical properties do vary as either the Lewis base molecule or the alkali metal atom being replaced by even similar elements or compounds. Among the simplest bifunctional Lewis bases, the complex formed from 1,2-ethanediol exhibits the most complicated conformation structures.…”

“…In the past few years, molecular complexes formed between the alkali metal atoms and multifunctional Lewis bases, such as K/ethylenediamine, K/1,2-ethanediol (eo), Na/1,2-dimethoxyethane (DME), and Na/12-crown-4, have been studied in this laboratory. − The conformation-dependent bond dissociation energies and photoionization threshold energies of these complexes were specifically emphasized in these works. It appears that the general physical properties of these multidentate complexes, whose geometric structures apparently lie between the simplest form of the complexes and the solvated-like higher cluster systems, could be understood and fitted into the general picture of this class of molecular system. − …”