Werner Lippens

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.

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.

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.

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.

Charge transfer spectra of organometallic complexes—II. Determination of the donor site in trialkyltinhalides

Abstract The charge transfer spectra of several trialkyltiniodide- and bromide-iodine systems are presented. Interpretation of the blue shift, the charge transfer band maximum and the formation constant data leads to the conclusion that, on complexation with iodine, the halide atom is the preferred donor site in the trialkyltinhalide molecule.

Charge-transfer spectra of organometallic complexes. I: Formation constants for complexes of trialkyltiniodides with iodine in carbon tetrachloride solutions

Abstract A charge-transfer complex is formed as reaction intermediate in the iodinolysis of R 3 SnI (R = CH 3 , C 2 H 5 , n -C 3 H 7 , iso -C 3 H 7 , n -C 4 H 9 , iso -C 4 H 9 and sec -C 4 H 9 ) in CCl 4 solutions. By means of the spectrophotometric molar ratio method and by the detection of an isosbestic point at 510 nm, the complex species was identified as a 1 : 1 molecular adduct between the alkyltiniodide and iodine. Formation constants of the complex were calculated using a non-linear regression analysis of absorbancy measurements on the perturbed iodine band. With the aid of these constants, the maxima of the charge-transfer peaks (u.v. region) and blue shifted iodine peaks (visible region) could be accurately determined.

Metal-ion complexation in aqueous solutions of 1 - thia-4,7-diazacyclononane-, 1-thia-4,8-diazacyclodecane and 2,5-diazahexane-N,N′-diacetic acid

The stability constants of the macrocyclic 1-thia-4,7-diazacyclononane-and 1-thia-4,8-diazacyclodecane-N,N′-diacetic acid (H2L1 and H2L2) and of the open-chain 2,5-diazahexane-N,N′-diacetic acid (H2L3) with MgII, CaII, SrII, BaII, MnII, CoII, NiII, CuII, ZnII, CdII, PbII and LaIII have been determined in aqueous solution (25 °C, 0.1 mol dm–3 KNO3) by pH potentiometry, and in some cases in combination with visible absorption spectrophotometry. The complexation enthalpies with CuII have been determined by adiabatic calorimetry. The electronic absorption spectra of the complexes of CuII and NiII were also recorded. All metal-ion complexes with H2L1 are stronger than with H2L3, even for the harder metal ions. The presence of the thioether donor particularly enhances covalent bonding with CuII as indicated by a higher heat of complexation, a more favourable entropy change and a stronger ligand-field strength. The change in stability of the complexes upon replacing H2L1 with a five-membered chelate ring between the metal ion and the two tertiary nitrogens, by H2L2 having a six-membered one, is dependent on the metal-ion size. The larger metal ions are destabilised relative to the small metal ions: the metal ion size-based selectivity for this pair of ligands is controlled by the chelate-ring size. Binding of CuII by H2L2 is sterically much more efficient than by H2L1 and is evidenced by a higher heat of complexation and a stronger ligand field.

Charge transfer spectra of organometallic complexes—III. Energy contributions to the formation of a donor—acceptor complex and to the electron transfer in the interaction between trialkyltin iodides and iodine in carbon tetrachloride solutions☆

Abstract The enthalpies of formation for charge transfer complexes of the type [R 3 SnI.I 2 ] (R = CH 3 , C 2 H 5 , n -C 3 H 7 , n -C 4 H 9 ) have been measured by calorimetry. The data are analysed using Mullikens resonance structure theory, to produce the different energy contributions to the formation of and the charge transfer interaction in these products. The use of cyclic voltammetry and photoelectron spectroscopy to assess the donor properties of R 3 SnI ligands is discussed.

Protonation and metal-ion complexation in aqueous solution by pyridine-containing hexaaza macrocycles

The protonation as well as the metal-binding constants with Ni2+, Cu2+, Zn2+, Cd2+ and Pb2+ for the macrocyclic hexadentate ligands L1{3,6,14,17,23,24-hexaazatricyclo[17.3.1.1.8,12]tetracosa-1(23),8,10,12(24),19,21-hexaene} and L2{3,7,15,19,25,26-hexaazatricyclo[19.3.1.19,13]hexacosa-1(25),9,11,13(26),21,23-hexaene} have been determined at 25 °C in 0.1 mol dm–3 KNO3 or KCl. The heats of protonation and of complexation with Cu2+, Cd2+ and Pb2+ were determined calorimetrically. The value for the fourth protonation step of L1 showed a medium dependency, being much higher in KNO3(aq) than in KCl (aq). The crystal structure of [H4L1][NO3]4 was determined and consists of discrete centrosymmetric three-ring tetrapositive cations and two crystallographically independent nitrate ions. Hydrogen bonds between the four endo-nitrogens of the eighteen-atom ring and the nitrate ions are formed. Mononuclear 1 : 1 metal-ion complexes were identified with L1 and L2. Electronic spectral data indicate octahedral six-co-ordination for the complexes of Cu2+ and Ni2+ with L1 and L2. Copper(II) also forms a monoprotonated mononuclear complex and a dinuclear complex with L2. The metal-ion affinities of L1 are compared to those of the fully saturated 1,4,7,10,13,16-hexaazacyclooctadecane L3 using thermodynamic and electronic spectral data. The larger stability of Cu2+ with L1 relative to L3 is entirely due to a more favourabLe entropy change, indicating that ligand pre-organization is the main reason for the increased stability. The metal-ion affinity of L2 is lower than that of L1 due to the less exothermic heats of complexation.