Transition metal ions and amides. VIII. Discrimination between different models for the complexation of Cu2+ with N,N′-diglycyl 1, 2-ethanediamine,N, N′-diglycyl-1, 3-propanediamine and glycine ethylamide by potentiometric or by spectrophotometric titration

The complexation of Cue²⁺ with 1, 8-diamino-3, 6-diaza-2, 7-octanedione (? N, N′-diglycyl-1, 2-ethanediamine, DED) and with 1, 9-diamino-3, 7-diaza-2, 8nonanedione (? N, N′-diglycyl-1, 3-propanediamine, DPD) has been studied by potentiometric and by spectrophotometric titration. With both ligands L the complexation to Cue²⁺ leads to relatively complicated equilibria with CuLH³⁺, CuL²⁺, CuLH^?2, and dimeric Cu₂L complexes. With DED, another dimeric species, Cu₂L₂H, is formed in addition. Independent numerical treatment of spectrophotometric and poteritiometric titrations was used to obtain a satisfactory model for the complexation and to test the relative discriminatory power of the two methods. Titrations of glycine ethylamide (GEA) were used as an additional test and as a model for DED and DPD. It was shown that in each case spectrophotometric titrations give results of similar reproducibility and have a discriminatory power equal to or better than potentiometric titrations, provided that optimum mathematical algorithms are used in the numerical treatment.     

Chiral Diaminodiamide Copper(II) Complexes for the Enantioselective Recognition of Amino Acids: Synthesis of the Ligands and Formation Constants

(S,S)-N,N′ -Bis(aminoacyl)ethane- and (S,S)-N,N′ -bis(aminoacyl)propanediamines (AA-NN-2 and AA-NN-3, respectively, AA = alanine, phenylalanine, valine) were synthesized as the dihydrochlorides, and their complexes with Cu(II) studied potentiometrically. Since these ligands in the presence of Cu(II) are able to perform chiral resolution of D ,L -dansylamino acids in HPLC (reversed phase), in a certain pH range (6.5–8.5), it is important to know the equilibria existing between ligands and copper in aqueous solution. For AA-NN-2, four species, CuLH³⁺, CuL²⁺, Cu₂L₂H, and CuLH_?2, were detected, whereas for AA-NN-3, only CuLH³⁺, CuL²⁺, and CuLH_?2 were found. The aim is to find out which complexes may be involved in the recognition process.     

Complex formation equilibria of L-Amino-Acid amides with copper(II) in aqueous solution

Protonation and Cu(II) complexation equilibria of L -phenyhilaninamide, N²-methyl-L-phenylalaninamide, N², N²-dimethyl-L-phenylalaninamide, L -valinamide, and L -prolinamide have been studied by potentiometry in aqueous solution. The formation constants of the species observed, CuL²⁺, CuL, CuLH, CuL₂H and CuL₂H_?2, are discussed in relation to the structures of the ligands. Possible structures of bisamidato complexes are proposed on the ground of VIS and CD spectra. Since Cu(II) complexes of the present ligands (pH range 6–8) perform chiral resolution of dansyl- and unmodified amino acids in HPLC (reversed phase), it is relevant for the investigation of the resolution mechanism to know which are the species potentially involved in the recognition process.     

Stabilities and Redox Properties of Cu(I) and Cu(II) Complexes with Macrocyclic Ligands Containing the N2S2 donor Set

The complexation of Cu(I) and Cu(II) by a series of 12-, 14- and 16-membered macrocyclic ligands 1–6 containing the N₂S₂ donor set has been studied potentiometrically, spectrophotometrically and voltammetrically. In the case of Cu(II), mononuclear complexes CuL²⁺ with stability constants of 10¹⁰–10¹⁵ are formed. In addition, partially hydrolyzed species Cu(L)OH⁺ are observed at pH > 10 for the 12-membered ligands. For Cu(I), beside the specis CuL⁺ with stabilities of 10¹²–10¹⁴, the unexpected formation of protonated species CuLH²⁺ was detected. In contrast to the well-known general trends in coordination chemistry, the stability of these protonated species increases relative to that of the complexes with the neutral ligand when the ring size and concomitantly the distance between neighbouring donor atoms is decreased. From the stability constants of the Cu(I)- and Cu(II)-complexes the redox potentials have been calculated and are compared to the values of E^1/2 obtained by cyclic voltammetry. Despite the identical donor set the Cu(II)/Cu(I) redox potentials of the complexes are spanning a range of 340 mV or six orders of magnitude in relative stability, reflecting the importance of subtle differences in steric requirements.     

Copper Catalysed Oxygenation of Bis (2-pyridyl) methane and 6-Methyl-bis (2-pyridyl)methane to the Corresponding Ketones

The ligands (L) bis (2-pyridyl) methane (BPM) and 6-methyl-bis (2-pyridyl)methane (MBPM) form the three complexes CuL²⁺, CuL, and Cu₂L₂H with Cu²⁺. Stability constants are log K₁ = 6.23 ± 0.06, log K₂ = 4.83 ± 0.01, and log K (Cu₂L₂H + 2H²⁺ ? 2 CuL²⁺) = ?10.99 ± 0.03 for BPM and 4.56 ± 0.02, 2.64 ± 0.02, and ?11.17 ± 0.03 for MBPM, respectively. In the presence of catalytic amounts of Cu²⁺, the ligands are oxygenated to the corresponding ketones at room temperature and neutral pH. With BPM and 2,4,6-trimethylpyridine (TMP) as the substrate and the buffer base, respectively, the kinetics of the oxygenation can be described by the rate law with k₁ = (5.9 ± 0.2) · 10^?13 mol l^?1 s^?1, k₂ = (4.0 ± 0.6) · 10^?4 mol^?1 ls^?1, k₃ = (1.1 ± 0.1) · 10^?12 mol l^?1 s^?1, and k₄ = (9 ± 2) · 10^?14 mol l^?1 s^?1.     

Cuprous complexes and dioxygen. VIII. Steric factors controlling one- or two-electron reduction of O2 by cuprous complexes with substituted imidazoles

In aqueous acetonitrile (AN), Cu (I) forms the complexes Cu(AN)L⁺ and CuL with a series of substituted imidazoles (L). Stability constants logK of Cu(AN)⁺ + L ? Cu(AN)L⁺ and logβ₂ were near 5 and 12, resp., log units for all ligands. The rate of autoxidation is described by ?d[O₂]/dt=[CuL]²[O₂](k_a/(1+k_b[CuL]) + (k_c[L]+k_d)/([CuL] + k_e[Cu])), implying competition between one- or two-electron reduction of O₂. The value of k_c decreases from 5500M ^?2S ^?1 for unsubstituted imidazole to about 40M ^?2S ^?1 for 2-methylimidazole or 1,2-dimethyl-imidazole and essentially zero for the corresponding 2-ethyl-derivatives. On the other hand, k_a and k_b are much less influenced by the nature of the ligands, all values being near 5 · 10⁴M ^?2S ^?1 and 10³M ^?1, respectively, for the complexes with the last four bases. Thus rather subtle sterical changes may strongly influence the relative importance of different pathways in the reduction of dioxygen by cuprous complexes.     

Cuprous complexes and dioxygen. Part 11. Concomitant one- and two-electron reduction of O2 by the Cu ion

The autoxidation of Cu^I in aqueous MeCN has been studied using a Clark oxygen electrode in the presence and absence of Cu¹¹. The reaction is inhibited by Cu¹¹ in the pH range of 0.5 to 5.0, reaching a lower limiting value at the highest concentrations. The reaction order changes from 1 to 2 with respect to Cu^I under the influence of Cu²⁺ ion. Detailed kinetics analysis of a total of 275 measurements has shown that an unstable primary adduct CuO⁺₂ decomoses to give ^.O or HO, depnding on pH, and also reacts directly with a second Cu⁺ ion, avoiding one-electrton reduction of O₂ by this path. Reaction of HO is faster with Cu^I than with Cu¹¹ by a factor of 20, and single-electron transfer within CuO⁺₂ to Cu²⁺ and ^.O predominates over reaction with a second copper ion for [Cu^I_tot] < 2. 10^?3M in the absence of Cu²⁺. The most likely value for the reaction of ^.O with Cu^I is 5.3 · 10⁸ M ^?1S^?1, but even this high rate constant is at the limit of significance. All secondary reactions followinfg the initial formation of CuO⁺₂ are shown to be very fast, a fact that should be properly considered in the discussion of mechanisms of copper-catalyzed oxidations and oxygenations.     

Metal complexes with macrocyclic ligands. XVI. Spectrophotometric and thermodynamic studies of solvents and unidentate ligands interaction with the pentacoordinate Co2+-, Ni2+- and Cu2+-complexes of 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane

The interaction of solvents and of unidentate ligands such as N, SCN^?, OCN^? and OH^? with the Co²⁺-, Ni²⁺ and Cu²⁺-complexes of 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (TMC) have been studied by Spectrophotometric and calorimetric techniques. The spectra in different solvents (Table 2) show that the Ni²⁺- and probably also the Cu²⁺-complex with TMC exist as square planar or pentacoordinate species or as a mixture of both, depending on the donor properties of the solvent. The [Co(TMC)]²⁺-complex is pentacoordinate in all the solvents studied. Ternary complexes [M(TMC)X]ⁿ⁺ are also formed by the unidentate ligands X = N, OCN^?, OH^?, F^? and NH₃ and their stability constants have been determined. Interesting is the high selectivity of [Ni(TMC)]²⁺ towards the addition of a further donor (Table 3). Only small ligands such as those listed above form stable adducts, whereas the larger ones such as imidazole or pyridine do not. This is a consequence of the special structure of the complex and of the trans-I-(RSRS)- conformation of the ligand in these complexes. Since the four methyl groups are all on the side of the macrocycle to which the additional unidentate ligand binds, steric interaction between the four methyl groups and the larger ligands prevents the formation of the adducts. The calorimetric measurements show that the stability of the complexes [M(TMC)X]ⁿ⁺ is due to both an enthalpic and entropic contribution which differ in their magnitude (Table 4). This indicates that several antagonistic factors are important in determining the overall stability.     

Das erste Alkali-Erdalkali-Oxocuprat(II,III): NaBa2Cu22+Cu3+O6

The first Alkaline Alkaline-Earth Oxocuprate (II, III): NaBa₂Cu₂²⁺Cu³⁺O₆ The compound NaBa₂Cu₃O₆ was prepared by heating of Na₂O₂, BaO₂, Cu₂O in closed Ag-tubes. X-ray single crystal investigations led to orthorhombic symmetry, space group D-Fmmm; a = 8.4229; b = 11.4418; c = 14.4063 Å; Z = 8. Cu²⁺ and Cu³⁺ show square planar polygones of four and Na⁺ trigonal prisms of six O^2?. The two barium point positions show coordination numbers C.N. = 8 and 6 + 4. The crystal structure is discussed.     

Cuprous complexes and dioxygen,VII. Competition between one- and two-electron reduction of O2 in the autoxidation of Cu(1-methyl-2-hydroxymethyl-imidazole)2+

The complexation of 1-methyl-2-hydroxymethyl-imidazole (L) with Cu(I) and Cu(II) has been studied in aqueous acetonitrile (AN). Cu(I) forms three complexes, Cu(AN)L⁺, CuL₂⁺, and Cu(AN)H_?1L, with stability constants logK(Cu(AN)⁺ + L ? Cu(AN)L⁺) = 4.60 ± 0.02, logβ₂ = 11.31 ± 0.04, and logK(Cu(AN)H_?1L+H⁺ ? Cu(AN)L⁺) = 10.43 ± 0.08 in 0.15M AN. The main species for Cu(II) are CuL²⁺, CuH_?1L⁺, CuH_?1L₂⁺, and CuH_?2L₂. The autoxidation of CuL₂⁺ was followed with an oxygen sensor and spectrophotometrically. Competition between the formation of superoxide in a one-electron reduction of O₂ and a path leading to H₂O₂ via binuclear (CuL₂)₂O was inferred from the rate law with k_a = (2.31 ± 0.12) · 10⁴M ^?2S ^?1, k_b = (1.0 ± 0.2) · 10³M ^?1, k_c = (2.85 ± 0.07) · 10²M ^?2S ^?1, k_d = 3.89 ± 0.14M ^?1S ^?1, k_e = 0.112 ± 0.004, k_f = (2.06 ± 0.24) · 10^?10M S ^?1, k_g = (1.35 ± 0.07) · 10^?7 S ^?1, and k_h = (6.8 ± 1.4) · 10^?7M ^?1 S ^?1.     

Copper(II) complexes of potentially terdentate N2-[(R)-2-hydroxypropyl]- and N2-[(S)-2-hydroxypropyl]-(S)-phenylalaninamide for chiral recognition: Synthesis of the Ligands and Formation Constants

Copper(II) complexes of the ligands N²-[(R)-2-hydroxypropyl]- and N²-[(S)-2-hydroxypropyl]-(S)-phenylalaninamide performed chiral separation of N-dansyl-protected and unmodified amino acids in HPLC (reversed phase). With the aim of investigating which species are potentially involved in the discrimination mechanism, the two ligands were synthesized and their complexation equilibria with Cu²⁺ studied by potentiometry and spectrophotometry in aqueous solution up to pH 11.7. The formation constants of the species observed, [CuL]²⁺, [CuL₂]²⁺, [CuLH_–1]⁺, [CuL₂H_–1]⁺, [CuL₂H_–2], and [CuL₂H_–3]^?, were quite similar for both compounds and were compared to those of (S)-phenylalaninamide. Most probably, in [CuL₂H_–3]^? the ligands behave as terdentate, with the deprotonated OH group occupying an apical position.     

Stability of disubstituted copper complexes in the gas phase analyzed by electrospray ionization mass spectrometry

A series of nitrogen ligand (L)/copper complexes of the type [Cu^IL]⁺, [Cu^IIL(X)]⁺ and [Cu^IL₂]⁺ (X = Cl^–, BF, acac^–, CH₃COO^– and SO₃CF) was studied in the gas phase by electrospray ionization mass spectrometry. The following ligands (L) were employed: 1,12‐diazaperylene (dap), 1,1′‐bisisoquinoline (bis), 2,2′‐bipyridine (bpy), 1,10‐phenanthroline (phen), 2,11‐disubstituted 1,12‐diazaperylenes (dap), 3,3′‐disubstituted 1,1′‐ bisisoquinoline (bis), 5,8‐dimethoxy‐substituted diazaperylene (meodap), 6,6′‐ dimethoxy‐substituted bisisoquinoline (meobis) and 2,9‐dimethyl‐1,10‐phenanthroline (dmphen). Collision‐induced decomposition measurements were applied to evaluate the relative stabilities of the different copper complexes. The influence of the spatial arrangement of the ligands, of the type of substituents and of the counter ion of the copper salts employed for the complexation was examined. Correlations were found between the binding constants of the [ML₂]⁺ complexes in solution and the relative stabilities of the analogous complexes in the gas phase. Furthermore, complexation with the ligands 2,11‐dialkylated 1,12‐diazaperylenes [alkyl = ethyl (dedap) and isopropyl (dipdap)] was studied in the solvents CH₃OH and CH₃CN. Copyright © 2010 John Wiley & Sons, Ltd.     

Cuprous complexes and dioxygen. IX. Formation of a unique trimeric species Cu3L and Ligand Oxidation (L  cis,cis-1, 3, 5-cyclohexanetriamine)

The complexation of Cu⁺ by the potentially tripod like ligand cis, cis-1, 3, 5 cyclohexanetriamine (chta) has been studied potentiometrically in aqueous acetonitrile (an). The expected tetracoordinated species Cu (chta) ? (an)⁺ was formed only at rather high pH with log K (Cu (an)⁺ + chta ? Cu (chta) · (an)⁺) = 6.94. Quite unexpectedly the most stable complex in neutral solution was the trimetric species Cu³ (chta) with log K (3 Cu⁺ + 2 chta ? Cu³ (chta)) = 31.75. In addition, the ternary complexes Cu (LH²) · (an)³⁺ and Cu (LH) · (an)²⁺ (L = chta) are formed at low pH. From model considerations, Cu³ (chta) must contain two ligand molecules with all amino groups in equatorial position, linked by three linearly coordinated Cu⁺-ions. Cu₃ (chta)³⁺₂ shows no measurable reactivity towards dioxygen. At pH values above 9, very rapid O₂-uptake due to Cu (chta) · (an)⁺ is observed. In this reaction, Cu⁺-autoxidation is stoichiometrically coupled to ligand oxidation, followed by a much slower Cu-catalyzed secondary reaction of the primary oxidation product of chta. Hydrogen peroxide and likely also superoxide, are involved in the coupled Cu⁺/ligand oxidation.     

Stabilité en solution aqueuse de complexes de métaux lourds avec des ligands diaza-polyoxamacrocycliques

Stability in aqueous solution of some complexes of heavy metals with diaza-polyoxamacrocyclic ligands Stability of metal complexes (Mⁿ⁺ = Cu²⁺, Ni²⁺, Co²⁺, Zn²⁺, Pb²⁺, Ag⁺ and Cd²⁺) with five diaza-polyoxamacrocycles (L = [2.1.1], [2.2.1], [2.2.2], [2.1] and [2.2] ) have been determined at 25°, in 0.1 M Et₄N⁺ClO aqueous solutions, by means of potentiometric titrations. All cations form MLⁿ⁺ complexes; Cu²⁺ also forms the MHL⁽ⁿ⁺¹⁾⁺ protonated species with both [2.2.1] and [2.1.1] ligands. The stability of these complexes has been discussed in terms of structure and by considering the ionic radii of the cations together with the radii of the macrocyclic cavities. Different behaviour is observed between some of these complexes and the well known alkali and alkaline-earth cryptates, partly due to the more covalent nature of bonds formed by the investigated cations and the donor sites of the ligands. The effect of the substitution of two oxygen by two sulfur atoms in the pentadentate ligand [2.1] on the stability of the complexes is reported.     

Synthese und Kristallstruktur von Cu2PtIIPtS8

Synthesis and Crystal Structure of Cu₂Pt^IIPt S₈ (NH₄)₂PtCl₆ and Cu(CH₃COO)₂ were reacted at 380 K in a constant flow of H₂S in the molar ratio of 2:1. Subsequent annealing of the product in sealed quartz glass ampoules in the presence of CuS as a buffer for the sulfur activity (temperature range 770 to 870 K) yields Cu₂Pt₄S₈ as a polycrystalline, greyish black powder. Cu₂Pt₄S₈ crystallizes in the space group P2/n (No. 13) with the cell parameters a = 10.6478(2), b = 6.9350(1), c = 6.7411(1) Å, β = 91.942(1), Z = 2. The structure determination and refinement were performed by the means of x-ray powder diffraction data of this first copperthioplatinate. There are no isotypic compounds known, so far. According to the characteristic coordination of the metals by sulfur, the oxidation states are Cu^+I, Pt^+II and Pt^+IV, the compound may be formulated as Cu₂Pt^+IIPtS₈. Cu₂Pt₄S₈ exhibits diamagnetic and semiconducting properties.     

Metal Complexes with Macrocyclic Ligands. XIV. Formation,dissociation and metal exchange with an N2S2-macrocycle

10, 10, 12-Trimethyl-3,4-benzo-1,6-dithia-9,13-diazacyclopentadecen-dihydrochloride (LH, 2 ) and its Ni²⁺ complex were synthesized and their reactivity studied. The formation kinetics of 2 with Cu²⁺ were found to be a second order reaction between Cu²⁺ or CuACO⁺ and the monoprotonated form of the ligand LH⁺. The rate constant k = 29 M ^?1S ^?1 is 10⁵–10⁶ times smaller than those of monoprotonated tetraazamacrocycles either because of second bond formation or because of a strong electrostatic interaction between the positive charges of the Cu²⁺ and the ammonium group. The metal-metal exchange between NiL⁺ and Cu²⁺ was also investigated. The reaction is independent of [Cu²⁺] and has the same rate and activation parameters as the dissociation of NiL²⁺. In contrast to open chain ligands, no mixed complex CuNiL⁴⁺ as intermediate was observed.     

Potentiometric and spectrophotometric titration of Cu2+ complexes with N-isopropyl-2-methyl-1,2-propanediamine

The complexation of Cu²⁺ by N-isopropyl-2-methyl-1,2-propanediamine (L) has been studied by potentiometric and spectrophotometric titration. The dominant complexes formed in this system are [CuL]²⁺, [CuL₂]²⁺, [Cu₂L₂(OH)₂]²⁺, and [CuL(OH)₂]. The data were thoroughly tested for different models with [CuL(OH)]⁺, [CuL(OH)]⁺, [Cu(OH)]⁺, and [Cu₂(OH)₂]²⁺ as additional species. The importance of steric factors is indicated by the d-d* spectra: for [CuL₂]²⁺, (λ_max = 499 nm) the absorption maximum is shifted by 50 nm to high energies relative to [Cu(en)₂]²⁺, (λ_max = 549 nm), whereas the opposite is true for the 1:1 complexes ([CuL]²⁺ : λ_max = 712 nm,s [Cu(en)]²⁺ : λ_max = 660 nm).     

Influence of 2,2'-bipyridyl on the stability of Cu2+ -glycine-1:1 complexes

The stability constant of the Cu²⁺-2,2′-bipyridyl-glycine complex (log K = 7,88) was measured and compared with that of the binary Cu²⁺-glycine complex (log K = 8,27). The value Δ log K = ?0,4 (cf. equation (3)) is in the order which should be expected for the coordination of a mixed O? N-ligand to (Cu-Bipy)²⁺ which results in the formation of a ternary complex (cf. [1]).     

Metal Complexes with Macrocyclic Ligands. Part XLVI. Synthesis and structures of dinuclear metal complexes of bis-macrocycles having a pyrazole bridging unit

Three bis-macrocyclic ligands consisting of two N₃-, N₂S-, or NS₂-cyclononane rings, i.e., of two octahydro-1H-1,4,7-triazonine, octahydro-1,4,7-thiadiazonine, or hexahydro-5H-1,4-7-dithiazonine rings, connected by a 1H-pyrazolediyl unit were prepared. They form dinuclear Cu^II and Ni^II complexes which are able to bind one additional exogenous bridging molecule such as Cl^?, Br^?, N, SO, and 1H-pyrazol-1-ide. The structures determined by X-ray diffraction show that each Cu²⁺ is coordinated by the three donor atoms of the macrocyclic ring, by a pyrazolidodiyl N-atom, by an atom of the exogenous bridging ligand, and sometimes by a solvent molecule. In the majority of the Cu²⁺ cases, the metal ion exhibits square-pyramidal or trigonal-bipyramidal coordination geometry, except in the sulfato-bridged complex, in which one Cu²⁺ is hexacoordinated with the participation of a water molecule. The X-ray structure of the azide-bridged dinuclear Ni²⁺ complex was also solved and shows that both Ni²⁺ centres have octahedral coordination geometries. In all complexes, the 1H-pyrazolediyl group connecting the macrocycles is deprotonated and bridges the two metal centres, which, depending on the exogenous ligand, have distances between 3.6 and 4.5 Å. In the dinuclear Cu²⁺ complexes, antiferromagnetic coupling is present. The azido-bridged complex shows a very strong interaction with ?2J ≥ 1040 cm^?1; in contrast, the H-pyrazol-1-ide and chloride bridged species have ?2J values of 300 and 272cm^?1, respectively. Cyclic voltammetry of the Cu²⁺ complexes in MeCN reveals a strong dependence of the potentials Cu^II/Cu-^II → Cu^II/Cu^I → Cu^I/Cu^I on the nature of the donor atoms of the macrocycle as well as on the type of bridging molecule. The more S-donors are present in the macrocycle, the higher is the potential, indicating a stabilization of the Cu¹ oxidation state.     

Zur Kenntnis komplexer Fluoride mit Cu2+ und Pd2+: MPtF6 (M  Pd,Cu) und RbCuPdF5

On Complex Fluorides with Cu²⁺ and Pd²⁺: MPtF₆ (M ? Pd, Cu) and RbCuPdF₅ For the first time single crystals of PdPtF₆ (green), trigonal-rhomboedric, a = 503.8, c = 1431.6 pm, spcgr. R3 ? C (No. 148), Z = 3, CuPtF₆ (orange), triclinic, a = 495.2, b = 498.5, c = 962.4 pm, α = 89.98, β = 104.23, γ = 120.35°, spcgr. P1 ? C (No. 2), Z = 2 and RbCuPdF₅ (orange brown, in connection with investigations on M^IPd₂F₅ [1]), orthorhombic, a = 626.9, b = 719.9, c = 1076.3 pm, spcgr. Pnma? D (No. 62), Z = 4, four circle diffractometer data, have been obtained.