Conformational Study of the Structure of 12-crown-4−Alkali Metal Cation Complexes (original) (raw)
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The structure and binding energies of 12-crown-4 and benzo-12-crown-4 complexes with Li + , Na + , K + , Zn 2+ , Cd 2+ , and Hg 2+ were investigated with ab initio calculations using Hartree-Fock approximation and second-order perturbation theory. The basis set used in this study is lanl2mb. The structure optimization of cation-crown ether complexes was evaluated at HF/lanl2mb level of theory and interaction energy of the corresponding complexes was calculated at MP2/lanl2mb level of theory (MP2/lanl2mb//HF/lanl2mb). Interactions of the crown et hers and the cations were discussed in term of the structure parameter of crown ether. The binding energies of the complexes show that all complex formed from transition metal cations is more stable than the complexes formed from alkali metal cations.
Anion-induced structural diversity in 12-crown-4 complexes of transition metal salts
2001
The synthesis and X-ray crystal structures of eight transition metal complexes of 12-crown-4 are reported. These are: [Mn(H 2 O) 6 ][Mn(12-crown-4) 2 ] 2 (ClO 4 ) 6 ·6H 2 O (1), [Ni(H 2 O) 6 ](ClO 4 ) 2 ·12-crown-4 (2), [Zn(12-crown-4) 2 ] 2 [Zn(H 2 O) 6 ](ClO 4 ) 6 ·(12crown-4) 2 ·(H 2 O) 2 (3), [Mn(12-crown-4) 2 ][MnCl 4 ]·H 2 O (4), [Co(12-crown-4)Cl(H 2 O)] 2 (ClO 4 )·H 2 O (5), [Zn(12-crown-4) 2 ][ZnCl 3 (H 2 O)] 2 , [Cu(Br) 2 (12-crown-4)] (7) and [Cd(12-crown-4)(NO 3 ) 2 ] (8). Depending on the identity of the counter anion, the structures fall into three groups: (1) hydrogen bonded polymers; (2) sandwich M(12-crown-4) 2 cations alternating with transition metal containing anions; and (3) neutral molecular species incorporating 12-crown-4. : S 0 2 7 7 -5 3 8 7 ( 0 1 ) 0 0 9 0 7 -X
Conformational Study of the Structure of Free 12-Crown-4
The Journal of Physical Chemistry A, 2004
A conformational search at the MM3 level was performed for 12-crown-4 (12c4) whereby 180 conformations were predicted. To determine the lowest energy conformations and to get a more accurate energy order of the predicted conformations, geometry optimization was performed for the 180 conformations at the HF/STO-3G level and for the 100 lowest energy conformations, according to HF/STO-3G energy order, at the HF/4-31G and HF/6-31+G* levels. Some of the 100 conformations had equal energies at the three abovementioned levels and consequently 37 conformations were excluded. Further computations were performed for the 20 lowest energy unique conformations, according to the MP2/6-31+G*//HF/6-31+G* energy order, at the B3LYP/6-31+G*, MP2/6-31+G*//B3LYP/6-31+G*, and MP2/6-31+G* levels. Good agreement was found between the energy order of the conformations at the MP2/6-31+G*//HF/6-31+G* and MP2/6-31+G*// B3LYP/6-31+G* levels and that at the MP2/6-31+G* level, the most accurate level considered in this work. The relative energies of the predicted conformations at the MP2/6-31+G*//B3LYP/6-31+G* level are close to those at the MP2/6-31+G* level, to within 0.1 kcal/mol at most. This is with the exception of only two conformations. This suggests that the cheaper MP2/6-31+G*//B3LYP/6-31+G* level may be used to determine the relative energy order of conformations of larger molecules where the MP2/6-31+G* computations are prohibitively expensive. The closeness of the MP2/6-31+G*//B3LYP/6-31+G* and MP2/6-31+G* relative energies is shown to be a reflection of the closeness of the B3LYP6-31+G* and MP26-31+G* optimized geometries. For the two conformations where the difference of the relative energies was larger than 0.1 kcal/mol, large differences between some of the B3LYP/6-31+G* and MP2/6-31+G* ring dihedral angles were found. The calculated results show that the correlation energy is necessary to obtain an accurate energy order of the predicted conformations. A rationalization of the energy order of some of the predicted conformations in terms of the CH‚‚‚O interactions is given.
An Ab Initio Investigation of the Structure and Alkali Metal Cation Selectivity of 18-Crown-6
Journal of the American Chemical Society, 1994
We present an ab initio, quantum mechanical study of 18-crown-6 (18~6) and its interaction with the alkali metal cations Li+, Na+, K+, Rb+, and Cs+. Geometries, binding energies, and binding enthalpies are evaluated at the restricted Hartree-Fock (RHF) level using standard basis sets (3-21G and 6-31+G*) and relativistic effective core potentials. Electron correlation effects are determined at the MP2 level, and wave function analysis is performed by the natural bond orbital (NEiO) and associated methods. The affinity of 18c6 for the alkali metal cations is quite strong (50-100 kcal mol-', depending on cation type), arising largely from the electrostatic (ionic) interaction of the cation with the nucleophilic ether backbone. Charge transfer (covalent bonding) contributions are somewhat less important, only 20-50% as strong as the electrostatic interaction. Agreement of the calculated binding enthalpies and experimentally determined quantities is rather poor. For example, the binding energy for K+/18c6 (-71.5 kcal mol-') is about 30 kcal mol-' stronger than that determined by experiment, and it is not clear how to reconcile this difference. Our calculations clearly show that solvation effects strongly influence cation selectivity. Gas-phase 18c6 preferentially binds Li+, not K+ as found in aqueous environments. We show, however, that K+ selectivity is recovered when even a few waters of hydration are considered.
Ab initio investigation of the structure and alkali metal cation selectivity of 18-crown-6
J Am Chem Soc, 1994
We present an ab initio, quantum mechanical study of 18-crown-6 (18~6) and its interaction with the alkali metal cations Li+, Na+, K+, Rb+, and Cs+. Geometries, binding energies, and binding enthalpies are evaluated at the restricted Hartree-Fock (RHF) level using standard basis sets (3-21G and 6-31+G*) and relativistic effective core potentials. Electron correlation effects are determined at the MP2 level, and wave function analysis is performed by the natural bond orbital (NEiO) and associated methods. The affinity of 18c6 for the alkali metal cations is quite strong (50-100 kcal mol-', depending on cation type), arising largely from the electrostatic (ionic) interaction of the cation with the nucleophilic ether backbone. Charge transfer (covalent bonding) contributions are somewhat less important, only 20-50% as strong as the electrostatic interaction. Agreement of the calculated binding enthalpies and experimentally determined quantities is rather poor. For example, the binding energy for K+/18c6 (-71.5 kcal mol-') is about 30 kcal mol-' stronger than that determined by experiment, and it is not clear how to reconcile this difference. Our calculations clearly show that solvation effects strongly influence cation selectivity. Gas-phase 18c6 preferentially binds Li+, not K+ as found in aqueous environments. We show, however, that K+ selectivity is recovered when even a few waters of hydration are considered.
American Journal of Research …, 2013
In this account 12-crown-4 (12c4), 15-crown-5 (15c5) and 18-crown-6 (18c6), their cluster complexes with Li+, Na+, K+ with general chemical formula as [M(crown ether)]+ and the water solvated complexes of Li+, Na+, K+ are theoretically studied. The chemical properties of crown ether complexes of Li, Na and K cations are compared with those of water-solvated complexes of these species. The B3LYP/6-31+G(d,p) level of calculation has been used for obtaining equilibrium geometries and Rho(r) functions (electron density distributions). By the aid of fundamental physical theorems implemented in the Quantum Theory of Atoms in Molecules (QTAIM), the structures and the physical nature of the chemical bonds have been determined for the abovementioned species at the B3LYP/6-31+G(d,p)computational level. These results establish the Metal-oxygen in all complexes in this work as ionic. Also Li+, Na+ and K+ have coordination number of 4 with 12c4 and possess the coordination number of 5 with 15c5. But the Li+ shows the coordination number of 3 with 18c6 crown ether and Na+ and K+ exhibits the coordination number of 6.
Acta crystallographica. Section E, Crystallographic communications, 2017
The structures of the alkali metal (K, Rb and Cs) complex salts with 4-amino-phenyl-arsonic acid (p-arsanilic acid) manifest an isotypic series with the general formula [M2(C6H7AsNO3)2(H2O)3], with M = K {poly[di-μ3-4-amino-phenyl-arsonato-tri-μ2-aqua-dipotassium], [K2(C6H7AsNO3)2(H2O)3], (I)}, Rb {poly[di-μ3-4-amino-phenyl-arsonato-tri-μ2-aqua-dirubidium], [Rb2(C6H7AsNO3)2(H2O)3], (II)}, and Cs {poly[di-μ3-4-amino-phenyl-arsonato-tri-μ2-aqua-dirubidium], [Cs2(C6H7AsNO3)2(H2O)3], (III)}, in which the repeating structural units lie across crystallographic mirror planes containing two independent and different metal cations and a bridging water mol-ecule, with the two hydrogen p-arsanilate ligands and the second water mol-ecule lying outside the mirror plane. The bonding about the two metal cations in all complexes is similar, one five-coordinate, the other progressing from five-coordinate in (I) to eight-coordinate in both (II) and (III), with overall M-O bond-length ranges of 2.694 ...
Geometries, interaction energies and complexation free energies of 18-crown-6 with neutral molecules
CrystEngComm, 2016
Although 18-crown-6 is renowned for its binding affinity to various metal and ammonium cations, the nature and strength of its binding with neutral guest molecules is relatively unexplored. Here we report a computational study of the host:guest geometries, interaction energies and Gibbs free energies of formation of 18-crown-6 with 49 neutral guest molecules in the gas phase, using the G4(MP2) composite method. Optimized geometries are in excellent agreement with those observed in crystals, with differences readily attributed to guest:guest interactions in the solid state. Host:guest interaction energies range from-13 to-103 kJ mol-1 , and the estimated Gibbs free energies of binding at 298 K correlate with the observation (or not) of the complexes in crystals. The electrostatic, dispersion, polarization and repulsion components of the interaction energy have also been estimated using the recently described CE-B3LYP model energies, providing insight into the binding nature between 18C6 and neutral molecules.
Journal of the American Chemical Society, 1976
Log K, AH, and AS values for the 1:1 reactions at 25 O C in aqueous solution of several uni-and bivalent cations with 15-crown-5, 18-crown-6, and the cis-syn-cis and cis-anti-cis isomers of dicyclohexo-18-crown-6 have been determined by a calorimetric titration procedure. The marked selectivity toward uni-and bivalent cations shown by 18-crown-6 is not found with 15-crown-5. TI+ forms more stable complexes than Rb+ (same crystal radius) with all three 18-crown-6 ligands. Favorable enthalpy and entropy changes contribute to this result. Ag+ forms more stable complexes than K + (approximately same crystal radius) with only the cis-syn-cis isomer. Unfavorable AH and favorable AS values characterize formation of this complex. Only NHd+, of the cations studied, forms a more stable complex with 15-crown-5 than with the 18-crown-6 ligands. For the 18-crown-6 set of ligands, cation selectivity, particularly for bivalent metal ions, is enhanced when dicyclohexo groups are present in the cis-syn-cis conformation, bqt is diminished when these groups are present in the cis-anti-cis conformation.