A.M. Goeminne

Ab initio conformational analysis of ethylene glycol and 1,3-propanediol

Abstract In this study we report the results of an ab initio investigation of the conformational properties of ethylene glycol and 1,3-propanediol. We performed HF/6-31++G ∗∗ optimizations of the geometries of 10 ethylene glycol conformers, and HF/4-31+G ∗ optimizations of 23 1,3-propanediol conformers. In the case of ethylene glycol we found the lowest energy conformers to have a gauche OCCO arrangement, stabilized by intramolecular hydrogen bonding. In case of 1,3-propanediol the lowest energy conformers have gauche OCCC arrangements. Intramolecular hydrogen bonding also plays an important role in this molecule. In both molecules we found that the ab initio results agree relatively well with available experimental data. It was also found that the conformational trends in the smaller ethylene glycol molecule are maintained in the larger 1,3-propanediol molecule. The introduction of Moller-Plesset second order electron correlation strengthens the intramolecular hydrogen bonding and the gauche-effect in both molecules.

The dinuclear copper(II) complex of the hexaaza macrocyclic ligand 3,6,9,17,20,23-hexaaza-tricyclo[23.3.1.111,15]triaconta-1(29),11(30),12,14,25,27-hexaene as a host for alanine, valine, leucine, norleucine, norvaline and serine anions

Abstract The hexaaza macrocyclic ligand 3,6,9,17,20,23-hexaazatricyclo[23.3.1.111,15]triaconta-1(29),11(30),12,14,25,27-hexaene (L), which forms strong dinuclear Cu(II) complexes, can act as a host for several anionic guests. The guests under investigation are the amino acids alanine, valine, leucine, norleucine, norvaline and serine. The host–guest interactions were investigated by conventional potentiometric pH-metry, by spectrophotometric titrations in 2:1:1 molar ratio for Cu(II), L and guest and by IR spectroscopy. In aqueous solution three ternary species are formed as a result of coordinate bonding, Coulombic attraction and hydrogen bond formation between the host and guest. The stability constants as well as the calculated equilibrium constants for the species are reported. It was found that the norleucine anion has the largest affinity for the dinuclear Cu(II) complex. The large inductive effect and the linear structure of its side chain is suggested to be responsible.

EQUILIBRIUM STUDIES OF COPPER(II) AND OF NICKEL(II) COMPLEXES WITH SULPHIDE CONTAINING α,ω-DIAMINES

Abstract The complex formation of Cu2+ and Ni2+ with 1,7-diaza-4-thiaheptane (2,2-NSN), 1,8-diaza-4-thiaoctane (2,3-NSN), 1,9-diaza-4-thianonane (2,4-NSN) and 1,9-diaza-5-thianonane (3,3-NSN) has been studied potentiometrically at 25°C in 0.5 mol dm−3 (K)NO3 medium. The formation constants of the CuL2+ complexes with the four ligands are 9.02, 10.03, 9.49 and 9.79 respectively. In these 1:1 complexes the ligands can be facially disposed. 2,2-NSN and 2,3-NSN also form a CuL2 2+ complex with log K2=5.24 and 2.86 respectively, whereas the hydrolysis constants of the [Cu(OH)L]+ species with the same ligands are 5.90 and 4.60. 2,3-NSN also forms the species CuHL3+ and CuHL2 3+, with protonation constants 4.77 and 9.7 respectively. With Ni2+ only 5,5- and 5,6-membered chelate ring systems are formed. With 2,2-NSN log K1=7.377 and log K2=6.142. With 2,3-NSN log > K1=5.989 and log K2=3.86. There is a six co-ordinate environment about the metal ion in the NiL2 2+ complexes. The Ni(II) complexes of the latter ligan...

Aqueous solution study of Cu(II) and Ni(II) complexes of macrocyclic oxa- and thia-containing trans-dioxo-tetraamines.

Abstract Four macrocyclic trans-dioxo-tetraamines containing sulphur or oxygen as additional donors have been prepared: 1-oxa-3,14-dioxo-4,7,10,13-tetraazacyclopentadecane, 1-thia-3,14-dioxo-4,7,10,13-tetraazacyclopentadecane, 1-oxa-3,16-dioxo-4,8,11,15-tetraazacycloheptadecane and 1-thia-3,16-dioxo-4,8,11,15-tetraazacycloheptadecane. Their protonation as well as their metal binding properties with Cu2+ and Ni2+ have been determined at 25°C in 0.10 mol dm−3 KNO3. The complexation process was investigated by potentiometric, calorimetric and UV/VIS-spectroscopic titrations. IR-spectroscopy was used to establish the involvement of the amido groups in the coordination. Oxidation of the complexes to the trivalent state of the metal ion was also investigated by cyclic voltammetry. Metal ion complexation promotes the deprotonation of the amide nitrogens, resulting in a neutral complex with four nitrogen donors and a MLH-2 stoichiometry at pH 8. Additional complexes with stoichiometry ML and MLH-1 were needed to describe the complexation in the pH range 2–11. Their stability constants were calculated. The presence of oxygen or sulphur donors as well as ring enlargement influence the complexation properties. The electronic spectra indicate rather distorted tetragonal coordination geometries for the Cu(II)-complexes. The Ni(II)-complexes are all square–planar with the exception of an equilibrium between a square–planar and an octahedral form for NiL1H−2. All complexes are easily but irreversibly oxidized to the trivalent state of the metal ion.

Ab initio and molecular mechanics study of 1,2-dimethoxyethane and 12-crown-4

Abstract Ab initio calculations have been carried out on a number of selected conformations of 12-crown-4. The selection of conformers was based on the low energy conformations of 12-crown-4 as obtained using molecular mechanics calculations (MM3). Extensive conformational searching within the molecular mechanics method was performed using two different approaches. The 23 lowest lying minima were submitted to ab initio calculations using different qualities of basis sets. Basis set choice was based on calculations on 1,2-dimethoxyethane and ethylene glycol as typical building blocks of the macrocycles. The highest level calculations on the crown ether are Hartree–Fock 6-31G** calculations. Results are discussed in terms of energies, geometries and intramolecular interactions.

COMPLEX FORMATION BETWEEN 1-AZA-4-THIAPENTANE, 1,4-DIAZA-7-THIAOCTANE AND 2-HYDROXYETHYLTHIOETHYLAMINE, AND HYDROGEN IONS, COPPER(II) AND NICKEL(II) IONS IN AQUEOUS SOLUTION A Potentiometric and Calorimetric Investigation

Abstract The behaviour of 1-aza-4-thiapentane, 1,4-diaza-7-thiaoctane and 2-hydroxyethylthioethylamine in aqueous solution in equilibria with protons, and Cu(II) and Ni(II) ions has been investigated potentiometrically and calorimetrically. The protonation constants for the ligands, and the stability constants for their complexes at 25° C in 0.5 M KNO3 are reported, together with the corresponding thermodynamic parameters δG°, δH° and δS°. It is found that the presence of a thioether group in the aliphatic chain of the ligands lowers the basicity of the aminogroups. The complexes are less stable than their polyamine analogues: N-methylethylenediamine, diethylene-triamine and N-(2-hydroxyethyl)ethylenediamine. The reduced stability is due mainly to an unfavourable entropy change during complexation, although their heats of formation are also less exothermic.

Ab initio conformational analysis of the chelating bidentate ligands ethylenediamine and 1,3-propanediamine

Abstract We report the results of an ab initio investigation of the conformational properties of ethylenediamine and 1,3-propanediamine. We have carried out 6-31++G∗∗ optimizations of the geometries of ten ethylenediamine conformers and 4-31+G∗ optimizations of 25 1,3-propanediamine conformers. In the case of ethylenediamine we find the lowest energy conformers to have a gauche NCCN arrangement, stabilized by internal hydrogen bonding. In the case of 1,3-propanediamine the lowest energy conformer was also found to be stabilized by internal hydrogen bonding. Our results for ethylenediamine agree well with available experimental data. It was also found that the conformational trends in the smaller ethylenediamine molecule are still present in the larger 1,3-propanediamine molecule. The introduction of Moller-Plesset second-order electron correlation strengthens the gauche effect in both molecules.

Zinc complexation of 3,6,9,17,20,23-hexaazatricyclo[23.3.1.111,15]triaconta-1(29),11(30),12,14,25,27-hexaene and its molecular recognition of anions

Abstract The hexaaza macrocyclic ligand 3,6,9,17,20,23-hexaazatricyclo[23.3.1.1 11,15 ]triaconta-1(29),11(30),12,14,25,27-hexaene (L), forms both mono- and dinuclear species, as well as several protonated and hydroxo chelates with Zn(II) ions. These cationic species can bind inorganic and organic anions through coordination and hydrogen bonding. Stability constants of the mononuclear Zn(II) complexes of L as well as their interaction with maleate, pyrophosphate and norleucine anions have been measured potentiometrically and for norleucine also by means of 1 H NMR. From these results it can be observed that all the anion complexes formed present 1:1 stoichiometry, which seems to be the preferred binding mode for charged anions. The complexation with Zn(II) ions shows an explicit preference to form hydroxo species which is also seen for the studied host–guest complexation. Remarkable is the existence of a dinuclear host–guest complex with pyrophosphate and norleucine anions which prevents the formation of hydroxo complexes till higher pH.

THE THERMODYNAMICS OF PROTONATION OF SOME SULPHIDE CONTAINING DIAMINES IN AQUEOUS SOLUTION

Abstract The protonation properties of 1,7-diaza-4-thiaheptane, 1,8-diaza-4-thiaoctane, 1,9-diaza-4-thianonane and 1,9-diaza-5-thianonane have been investigated potentiometrically and calorimetrically at 25°C in 0.5 mol dm−3 (K)NO3 solution. Values for the protonation constants and for the thermodynamic functions δH° and δS° were determined. The results have been discussed. It has been found that the place of the thioether group in the aliphatic chain, connecting the two aminogroups, predominantly determines the behaviour of the diamines when protonated.

Metal ion complexation studies in an aqueous solution of 1-thia-4,7-diazacyclononane, 1- thia-4,8-diazacyclodecane and 5-thia-2,8- diazanonane

Abstract The stability constants of the macrocyclic 1-thia-4,7- diazacyclononane ([9]aneN 2 S) and 1-thia-4,8-diazacyclodecane ([10]aneN 2 S) and of the open-chain 5-thia-2,8-diazanonane (atan) with cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II) and lead(II) have been determined in aqueous solution (25°C, 0.1 mol dm −3 KNO 3 ) by pH potentiometry. The complexation enthalpies with copper(II) have been determined by adiabatic calorimetry. The electronic spectra of the copper(II) and nickel(II) complexes were recorded. The magnitude of the macrocyclic effect for the copper(II) complexes is dependent upon the choice of the open-chain reference ligand and is analysed for its enthalpic and entropic contributions: a positive entropy contribution is found irrespective of the reference ligand, while the enthalpy contribution may be exothermic or endothermic. The metal ion size-based selectivity upon increase in the chelate ring size from five-membered in [9]aneN 2 S to six-membered in [10]aneN 2 S is controlled by the macrocyclic ring size: the largest drop in stability is observed for the smaller metal ions [copper(II) and nickel(II)] when [9]aneN 2 S is replaced by [10]aneN 2 S in the 1: 1 complexes. This drop in stability in the case of the 1: 1 complex with copper(II) is entirely due to an unfavourable entropy change, the complexation heat and the LF strength being higher for [10]aneN 2 S than for [9]aneN 2 S.