G. G. Herman

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.

Host-guest interaction between the dinuclear copper(II) complex of 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 and malonate, maleate, fumarate, pyrophosphate and orthophosphate anions

Abstract The hexaaza macrocyclic ligand 3,6,9,17,20,23-hexaazatricyclo[23.3.1.1]triaconta-1(29),11(30),12,14,25,27-hexaene (L), forms strong dinuclear complexes, as well as several protonated and hydroxo chelates, with Cu(II) ions. The host-guest interactions between the dinuclear copper(II) complexes of L and malonate, maleate, fumarate, pyrophosphate and orthophosphate anions were investigated by potentiometric conventional pH-metry as well as by spectrophotometric titrations in 2:1:1 molar ratio for Cu(II), L and guest. Several ternary complexes are found in aqueous solution as a result of coordinate bonding, hydrogen bond formation and Columbic attraction between the host and guest. The stability constants for all the species found are reported. The dinuclear copper(II) complex of L shows stronger complexation with the maleate anion than with malonate and fumarate anions. It is suggested that the presence of the double bond in maleate offers a more favourable geometry for coordination to the Cu 2 L host. Complexation with pyrophosphate and orthophosphate anions show little difference in stability. The big, flexible, pyrophosphate anion probably coordinates outside the macrocycle.

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...

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.

Characterisation of the sol–gel process in the superconducting NdBa2Cu3O7−y system

The objective of this paper is to obtain a better insight into the sol–gel mechanism of water-based precursors for the development of thin NdBa2Cu3O7−y (NBCO) superconducting films. The influence of metal complexation behaviour on the formation of transparent and homogenous gels after the combination of different metal salts and ligands has been studied for several metal salts (Cu2+, Nd3+ and Ba2+). Two inorganic aqueous sol–gel precursors have been studied: a metal nitrate–citric acid-based and a metal acetate–triethanolamine-based solution. The characteristics of the precursor solution are based on the determination of the stability constants by the computer program Superquad. The prediction of the complex stability in this solution was related to the complexation of the three metal ions (Cu2+, Nd3+ and Ba2+) with a certain ligand. IR-spectroscopy was used for the determination of the gel. This resulted in a better understanding of the composition of the solution and could be used for preparation of more stable sol–gel precursors for the synthesis of homogeneous end products. These sol–gel systems were used for the deposition of highly textured superconducting thin films on SrTiO3 substrates by dip-coating. Using detailed thermal analysis, it is shown that the morphology of the films can be optimised by adjusting the parameters during thermal treatment, resulting in dense and highly textured thin films. Special attention is given to the microstructure of the thin film because of its relevance to the superconducting transport properties of the coated conductor system.

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.

Sulphurnitrogen chelating agents. Part I. Some copper(II) complexes of sulphur-containing α,ω-diamines

Abstract Some series of five- and six-coordinated complexes of general formulate Cu{R2N(CH2)nS(CH2)mNH2}X2 or CU{R2N(CH2)nS(CH2)mNH2}ZY (n, m = 2 or 3; R = CH3 or H; X = NO−3, Cl−, Br−, ClO−4; Z = OAc−, NO−4, OH−) have been prepared and characterized. Structure assignment of the complexes is based on their conductivities in methanol, on their I.R. and electronic spectra. Dependent on the anion the n,m-R2NSN ligand may be facially or meridionally disposed around the central Cu(II) ion. The parallelism between the electronic spectra of the Solid {Cu(n,m-R2NSN)OAc}ClO4 complexes and the electronic spectra of the corresponding {Cu(n,m-R2NSN)3H2O}2+ species in aqueous solution suggests structural similarity.

Potentiometric, calorimetric and nuclear magnetic resonance studies of the protonation in aqueous solution of 1-thia-4,7-diazacyclononane-N,N′-diacetic acid, 1-thia-4,8-diazacyclodecane-N,N′-diacetic acid and related open-chain diaminocarboxylic acids

The acid-base properties in aqueous solution of 1-thia-4,7-diazacyclononane -N,N′-diacetic acid (TNODA) and 1-thia-4,8-diazacyclodecane-N,N′-diacetic acid (TDEDA) have been investigated in 0.1 mol dm−3 KNO3 at 25°C. The protonation constants were determined by conventional pH potentiometry. The protonation enthalpy changes were obtained by adiabatic calorimetry. The corresponding entropy changes were calculated. For TNODA: log KH1 = 11.63, log KH2 = 4.05, log KH3 = 1.8; ΔH°1 = −41.4 kJ mol−1, ΔH°2 = −0.5 kJ mol−1, ΔH°3 = 4.2 kJ mol−1; ΔS°1 = 83.5 J mol−1 K−1, ΔS°2 = 75.8 J mol−1 K−1, ΔS°3 = 48.5 J mol−1 K−1. For TDEDA: log KH1 = 12.9, log KH2 = 3.95, log KH3 = 2.0; ΔH°2 = 0.2 kJ mol−1, ΔH°3 = 3.2 kJ mol−1; ΔS°2 = 76.2 J mol−1 K−1, ΔS°3 = 50 J mol−1 K−1. The protonation sequence of the cyclic diaminocarboxylates was established by 1H NMR spectroscopy. The results indicate that the first proton is added to a tertiary amino group, whereas the second and the third are added to the two carboxylate groups. The second amino group of TDEDA is only protonated in strong acid medium. Reduced solvation of the cyclic diaminocarboxylates as compared with their open-chain counterparts explains the increase in basicity at the first protonation step upon acetate substitution on the second amino group of the parent cyclic diamines. The acid-base properties of the open-chain diaminocarboxylates 2,5-diazahexane-N,N′-diacetic acid and 5-thia-2,8-diazanonene-N,N′-diacetic acid were also investigated under the same experimental conditions for comparison purposes.

Cu(II) and Ni(II) complexes of N,N'-bis(2-aminoethyl)-oxamide and N,N'-bis(3-aminopropyl) oxamide: a potentiometric and spectrophotometric study

Abstract Extensive potentiometric and spectrophotometric (visible region) data resulted in the unravelling of the complete details of complex formation of N,N′-bis(2-aminoethyl) oxamide (L1) and N,N′-bis(3-aminopropyl) oxamide (L2). This study reveals both similarities and differences in complex formation for these ligands. Earlier reports gave evidence for the formation of a Cu3L2H-4 complex of L2. We show that L1 forms a Cu2L2H2 complex. This difference in behaviour is due to a decrease in stability of the CuLH-2 complex of L2 compared to that of L1. The complexation of Ni2+ by L1 is also discussed.