Experimental Evidence for Unusual Protonation of Tetraethyl p-tert-Butylcalix[4]arene Tetraacetate and the Most Probable Structure of the Resulting Complex

Using ¹H and ¹³C NMR, FT IR spectroscopy together with quantum mechanical DFT calculations, we show that tetraethyl p-tert-butylcalix[4]arene tetraacetate (1) forms a stable equimolecular complex with proton in the form of hydroxonium ion in acetonitrile-d ₃. Protons for this complex were offered by hydrogen bis(1,2-dicarbollyl) cobaltate (HDCC) and converted to hydroxonium ions by traces of water. The complex 1·H₃O⁺ adopts a slightly asymmetric conformation, which is distinctly more cone-like than ligand 1. According to spectral evidence, the hydroxonium ion H₃O⁺ is bound mainly to three of the phenoxy oxygen atoms of 1 by strong hydrogen bonds leaving the ester carbonyl groups, which are the usual coordination site for metal cations, free. Theoretical DFT calculations support the bonding to phenoxy oxygen atoms but slightly prefer a structure with one of the carbonyls being involved in the coordination.     

A Proton Complex of p-tert-Butylcalix[4]arene-tetrakis(N,N-dimethylthioacetamide): NMR Evidence and Probable Structure

Using ¹H and ¹³C NMR together with density functional theoretical (DFT) calculations, it is shown that p-tert-butylcalix[4]arene-tetrakis(N,N-dimethylthioacetamide) (1) forms a stable equimolecular complex with proton in the form of hydroxonium ion in nitrobenzene-d ₅. Protons were offered by hydrogen bis(1,2-dicarbollyl) cobaltate (HDCC) and converted to hydroxonium ions by traces of water. The complex 1·H₃O⁺ adopts a slightly asymmetric but rapidly motionally averaged conformation, which is distinctly more cone-like than ligand 1. The hydroxonium ion H₃O⁺ is bound partly to thiocarbonyl sulphur atoms and partly to phenoxy oxygen atoms of 1 by strong hydrogen bonds and other electrostatic interactions.

     

Contribution to the Protonation of a Calix[4]arene: DFT Calculated Structure of Protonated p-tert -Butylcalix[4]arenetetrakis( N , N -diethylacetamide)

By using DFT calculations, the most probable structure of the p-tert-butylcalix[4]arenetetrakis(N,N-diethylacetamide) · H₃O⁺ complex species was derived. In this complex, the hydroxonium ion H₃O⁺ is predominantly bound by strong hydrogen bonds to three phenoxy oxygens of the ligand and partly to the remaining phenoxy oxygen atom by two somewhat weaker hydrogen bonds. Besides, the H₃O⁺ cation is also bound to two carbonyl oxygens of the mentioned ligand by further two weaker hydrogen bonds.     

Contribution to the Protonation of a Calix[4]arene: DFT Calculated Structure of Protonated <Emphasis Type="Italic">p-tert</Emphasis>-Butylcalix[4]arenetetrakis(<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-diethylacetamide)

Summary. By using DFT calculations, the most probable structure of the p-tert-butylcalix[4]arenetetrakis(N,N-diethylacetamide) · H₃O⁺ complex species was derived. In this complex, the hydroxonium ion H₃O⁺ is predominantly bound by strong hydrogen bonds to three phenoxy oxygens of the ligand and partly to the remaining phenoxy oxygen atom by two somewhat weaker hydrogen bonds. Besides, the H₃O⁺ cation is also bound to two carbonyl oxygens of the mentioned ligand by further two weaker hydrogen bonds.     

DFT-calculated structure of protonated tetraphenyl p - tert -butylcalix[4]arene tetraketone

Using DFT calculations, two of the most probable structures (A, B) of the tetraphenyl p-tert-butylcalix[4]arene tetraketone·H₃O⁺ cationic complex species were derived. The hydroxonium ion H₃O⁺, placed in the coordination cavity formed by the calix[4]arene lower-rim groups, is bound by strong hydrogen bonds to the phenoxy oxygen atoms of the calix[4]arene ligand (structures A, B) and also to one carbonyl oxygen (structure B).     

Protonation of electroneutral p-tert-butylcalix[4]arenetetraacetic acid

Abstract  

Using ¹H NMR spectroscopy together with density functional theoretical calculations, it is shown that electroneutral p-tert-butylcalix[4]arenetetraacetic acid forms an equimolar complex with a proton in the form of the H₃O⁺ ion in nitrobenzene-d ₅. Protons were offered by hydrogen bis(1,2-dicarbollyl)cobaltate and converted to hydroxonium ions by traces of water. In the resulting complex, the H₃O⁺ cation is bound by strong hydrogen bonds to two phenoxy oxygen atoms of the parent calix[4]arene ligand and to one carbonyl oxygen of the corresponding COOH group of this ligand.     

DFT-calculated structure of protonated tetraphenyl <Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">tert</Emphasis>-butylcalix[4]arene tetraketone

Using DFT calculations, two of the most probable structures (A, B) of the tetraphenyl p-tert-butylcalix[4]arene tetraketone·H₃O⁺ cationic complex species were derived. The hydroxonium ion H₃O⁺, placed in the coordination cavity formed by the calix[4]arene lower-rim groups, is bound by strong hydrogen bonds to the phenoxy oxygen atoms of the calix[4]arene ligand (structures A, B) and also to one carbonyl oxygen (structure B). Correspondence: Emanuel Makrlík, Faculty of Applied Sciences, University of West Bohemia, Pilsen, Czech Republic.     

Theoretical study on the protonation of cucurbit[6]uril

Abstract  

The most probable structures of the cucurbit[6]uril·H₃O⁺ and cucurbit[6]uril·(H₃O⁺)₂ cationic complex species have been derived by quantum mechanical DFT calculations. In these two complexes, each of the H₃O⁺ ions is bound by three strong linear hydrogen bonds to three carbonyl oxygen atoms of the parent macrocycle.     

Theoretical study on the protonation of bambus[6]uril

Abstract  

Quantum mechanical density functional theory (DFT) calculations were used to derive the most probable structures of the bambus[6]uril·H₃O⁺ and bambus[6]uril·(H₃O⁺)₂ cationic complex species. In these two complexes, each of the considered H₃O⁺ ions is bound by three strong linear hydrogen bonds to the three corresponding carbonyl oxygens of the parent macrocyclic receptor.     

Experimental evidence, stability, and the most probable structure of protonated p-tert-butylcalix[4]arenetetrakis(N,N-dimethylacetamide)

Abstract  

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium H₃O⁺(aq) + 1·Na⁺(nb) \leftrightarrows \leftrightarrows 1·H₃O⁺ (nb) + Na⁺ (aq) taking place in the two-phase water–nitrobenzene system (1 = p-tert-butylcalix[4]arenetetrakis(N,N-dimethylacetamide); aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K _ex (H₃O⁺, 1·Na⁺) = −0.1 ± 0.1. Further, the stability constant of the 1·H₃O⁺ complex in water-saturated nitrobenzene was calculated for a temperature of 25 °C as log β _nb (1·H₃O⁺) = 10.9 ± 0.2. By using quantum mechanical DFT calculations, the most probable structure of the 1·H₃O⁺ cationic complex species was derived. In this complex, the hydroxonium ion H₃O⁺ is bound partly to one phenoxy oxygen atom and partly to two carbonyl oxygens of 1 by strong hydrogen bonds and obviously by other electrostatic interactions.     

A solid‐state oxidation of 1,1,3,3‐tetramethylguanidinium 4‐methylbenzenesulfinate to 1,1,3,3‐tetramethylguanidinium 4‐methylbenzenesulfonate

The organic acid–base complex 1,1,3,3‐tetramethylguanidinium 4‐methylbenzenesulfonate, C₅H₁₄N₃⁺·C₇H₇O₃S⁻, was obtained from the corresponding 1,1,3,3‐tetramethylguanidinium 4‐methylbenzenesulfinate complex, C₅H₁₄N₃⁺·C₇H₇O₂S⁻, by solid‐state oxidation in air. Comparison of the two crystal structures reveals similar packing arrangements in the monoclinic space group P2₁/c, with centrosymmetric 2:2 tetramers being connected by four strong N—H...O=S hydrogen bonds between the imine N atoms of two 1,1,3,3‐tetramethylguanidinium bases and the O atoms of two acid molecules.     

Regioselective Long‐Range Proton Transfer in New Rifamycin Antibiotics: A Process in which Crown Ethers Act as Stronger Brønsted Bases than Amines

Water‐mediated proton transfer in six new derivatives of 3‐formylrifamycin SV that contain crown, aza‐crown, and benzo‐crown ether rings were investigated by FTIR and NMR spectroscopy. ¹H–¹H COSY couplings provide evidence for the formation of zwitterionic structures of the aza‐crown and crown ether derivatives of rifamycin, in which a proton from one of the phenolic groups is transferred to tertiary and secondary nitrogen atoms. The increased intensity of the continuous absorption in the mid‐infrared region together with the NMR data indicate proton transfer from the phenol group of the rifamycin core to the cavity of the benzo‐crown ether ring. This proton transfer is achieved by formation of hydronium (H₃O⁺) or Zundel ions (H₅O₂⁺), which form intermolecular hydrogen bonds with the oxygen atoms of the crown ether. DFT calculations are in agreement with the spectroscopic data and allow visualization of the structures of all new rifamycin derivatives, characterized by different intramolecular protonation sites.     

Protonated Tetramethyl p - tert -Butylcalix[4]arene Tetraketone: NMR Evidence and Probable Structures

Both NMR spectra in nitrobenzene-d ₅ and high-precision quantum mechanical DFT calculations proved that tetramethyl p-tert-butylcalix[4]arene tetraketone binds hydroxonium cation H₃O⁺ quite strongly to form an equimolar complex. Three different structures of the resulting complex species were indicated by the NMR spectra and the DFT calculations.     

Melamine-mediated self-assembly of a Cu(II)–methylmalonate complex assisted by π+–π+ and anti-electrostatic H-bonding interactions

A Cu(II)-methylmalonate complex, (C₃H₇N₆)₄[Cu(II)(C₄H₄O₄)₂](H₂O)₄Cl₂ (1) (where C₃H₇N₆ = protonated melamine, C₄H₄O₄ = methylmalonic acid), has been synthesized from aqueous media and its crystal structure was determined by single-crystal X-ray diffraction. The anionic Cu(II)-methylmalonate complex mediated formation of interesting supramolecular assemblies in the solid state by means of ionic interactions with protonated melamine. Moreover, other forces such as antielectrostatic H-bonding and π⁺–π⁺ interactions also play a crucial role in defining the final 3-D architecture of 1. An interesting stacking among protonated melamine molecules is studied by DFT calculations. Lattice water molecules and chlorides form various hydrogen bonds to take part in the self-assembly processes.     

Steric conditions and polarizability of structurally symmetrical interamoleculer hydrogen bonds in R-DI(α-pyridyl) hydroperchlorates

Seven R-di-(α-pyridyl) hydroperchlorates (R = (1) CH₂, (2) NH, (3) CO, (4) (CH₂)₂, (5) (CH₂)₃, (6) (CH₂)₄ and (7) S-S) were prepared and studied in acetonitrile-d₃ solutions by NMR and IR spectroscopy. With the hydroperchlorates of compounds 1 and 4, an equilibrium between non-hydrogen-bonded NH⁺ groups and intramolecular-bonded NH⁺ groups is present. With compounds 2, 3 and 5–7, the intramolecular hydrogen bonds are formed quantitatively. In compounds 4–7, the potential wells in these intramolecular structurally symmetrical N⁺H· N ? N · H⁺N bonds, are double minima. These hydrogen bonds are easily polarizable. With compounds 1–3, the distance between the N atoms given by the steric conditions of the molecules is smaller than with usual linear hydrogen bonds. Therefore, strong bent intramolecular structurally symmetrical hydrogen bonds are found, with relatively narrow single-minimum potential wells. These bonds cause a band in the region 3000–2500 cm^?1 instead of the continuum. Thus they are not easily polarizable.     

Protonated Tetramethyl <Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">tert</Emphasis>-Butylcalix[4]arene Tetraketone: NMR Evidence and Probable Structures

Summary. Both NMR spectra in nitrobenzene-d ₅ and high-precision quantum mechanical DFT calculations proved that tetramethyl p-tert-butylcalix[4]arene tetraketone binds hydroxonium cation H₃O⁺ quite strongly to form an equimolar complex. Three different structures of the resulting complex species were indicated by the NMR spectra and the DFT calculations.     

Syntheses and X-Ray Crystal Structures of Novel Oxonium Ion-12-Crown-4 Complexes Isolated From Liquid Clathrate Media

Abstract

The reactions of Mo(CO)₆ and W(CO)₆ with HCl_(g) in the presence of 12-crown-4 and H₂O have been investigated in toluene. For both reactions, two products were isolated, depending on the oxidation of the metal center. For molybdenum, the Mo^III species, [H₃O⁺ · 12-crown-4]₃[Mo₂Cl₉ ^3-], 1, was obtained from the liquid clathrate layer in the reaction mixture. Upon air oxidation of the reaction mixture, the Mo^v complex, [H₇O₃ ^? · H₄O₂ ⁺ · (12-crown-4)₂][MoOCl₄(H₂O)^?]₂, 2, rapidly formed. For tungsten, the W^II species, [(H₅O₂ ⁺)₂ · 12-crown-4][W(CO)₄Cl^? ₃]₂, 3, deposited from the liquid clathrate layer which upon oxidation formed the W^v complex, [H₃O⁺· 12-crown-4][WOCl₄(H₂O)^?], 4. These reactions were promoted by UV radiation and formed liquid clathrates almost immediately upon reaction. X-ray crystal structures were performed on each compound. Complexes 1 and 4 have H₃O⁺ oxonium ions involved in complex hydrogen bonded arrays with the 12-crown-4 acceptor molecules. The H₅O₂ ⁺ oxonium ions in 2 and 3 contain extremely short O…O separations, equivalent to the shortest O-H…O bonds known. Also isolated in complex 2 was the H₇O₃ ⁺ oxonium ion which contains an unusual linear O…O…O core.     

Protonated Co(III) Complexes with Ethylenediaminetetraacetic and S-Proline-N-Mono-3-propionic Acids. Crystal Structures of (H3O)[Co(HEdta)(CN)] · H2O and [Co(Promp)(HPromp)] · H2O

Crystal structures of [Co(Promp)(Hpromp)] · H₂O (I) (where Promp and Hpromp are deprotonated and monoprotonated anions of S-proline-N-mono-3-propionic acid) and (H₃O)[Co(Hedta)(CN)] · H₂O (II) (where HEdta is monoprotonated anion of ethylenediaminetetraacetic acid) are determined by X-ray diffraction method. The Co coordination octahedron in compound I is formed by two N atoms in trans-positions and by four O atoms of two tridentate ligands, i.e., anions of H₂Promp acid, one of which is fully deprotonated, while the other one has protonated carboxyl group of a six-membered aminopropionate metal cycle. Neutral [Co(Promp)(Hpromp)] complexes and water molecules are united by hydrogen bonds into chains along 2₁ screw axis. Crystals II consist of the complex anions [Co(Hedta)(CN)]⁻, hydroxonium cations, and water molecules. The Co coordination octahedron includes two N atoms and three O atoms of ion of ethylenediaminetetraacetic acid, whose one acetate group is not coordinated but protonated; cyanide ion lies in the NCoN plane. Crystals II contain two types of H₃O⁺ ions that are involved in hydrogen bonds in different way.__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 8, 2005, pp. 596–605.Original Russian Text Copyright © 2005 by Poznyak, Burshtein.     

Self‐assembly properties of Salamo‐type trinuclear Cu(II) and Co(II) complexes based on the regulation of H+/OHˉ

A novel naphthalenediol‐based bis(salamo)‐type tetraoxime compound (H₄L) was designed and synthesized. Two new supramolecular complexes, [Cu₃(L)(μ‐OAc)₂] and [Co₃(L)(μ‐OAc)₂(MeOH)₂]·4CHCl₃ were synthesized by the reaction of H₄L with Cu(II) acetate dihydrate and Co(II) acetate dihydrate, respectively, and were characterized by elemental analyses and X‐ray crystallography. In the Cu(II) complex, Cu1 and Cu2 atoms located in the N₂O₂ sites, and are both penta‐coordinated, and Cu3 atom is also penta‐coordinated by five oxygen atoms. All the three Cu(II) atoms have geometries of slightly distorted tetragonal pyramid. In the Co(II) complex, Co1 and Co3 atoms located in the N₂O₂ sites, and are both penta‐coordinated with geometries of slightly distorted triangular bipyramid and distorted tetragonal pyramid, respectively, while Co2 atom is hexa‐coordinated by six oxygen atoms with a geometry of slightly distorted octahedron. These self‐assembling complexes form different dimensional supramolecular structures through inter‐ and intra‐molecular hydrogen bonds. The coordination bond cleavages of the two complexes have occurred upon the addition of the H⁺, and have reformed again via the neutralization effect of the OH^?. The changes of the two complexes response to the H⁺/OH^? have observed in the UV–Vis and ¹H NMR spectra.     

INTERACTION OF METAL IONS WITH TWO NEW CALIX[4, 8]ARENE DERIVATIVES

Abstract

Two new calixarene derivatives: 5,11,17,23-tetra-t-butyl-25,26,27,28-tetrakis-(piperidinocarbo-nylmethyoxy)calix[4]arene (L⁴) and 5,11,17,23,29,35,41,47-octa-t-butyl-49,50,51,52,53,54,55, 56-octa-(piperidinocarbonylmethoxy)calix[8]arene (L⁸), which show good binding abilities to metal ions, were synthesized by the reaction of the corresponding calixarene derivatives with piperidine. The ligand L⁴ is capable of separating a tight ion-pair formed by Pb²⁺ and the picrate anion in THF. The interactions of the new ligands (Lⁿ n = 4, 8) with Na⁺, Pb²⁺ and Cd²⁺, in the presence or absence of picrate, were investigated by ¹H NMR and electrospray mass spectrometry. It is found that L⁴ reacts with these metal ions to form a unique complex which can be described as [M^m+L⁴]^m+ while L⁸ forms a variety of complexes depending on whether there are picrate anions in solution. [M^m+L⁸]^m+ is formed in the absence of the picrate, and two complexes, [PbL⁸]·CH₃CN·H₂O and [PbNaL⁸]³⁺, are formed in the presence of the picrate. The higher conformational flexibility and larger macro-ring size of L⁸ account for the fact that it forms a variety of complexes as compared with L⁴.