Zur Stabilität der Metallkomplexe von Methantriessigsäure und cis,cis-1,3,5-Cyclohexantricarbonsäure

The stabilities of the Mn²⁺-, Co²⁺-, Ni²⁺-, Cu²⁺- and Zn²⁺-complexes with 2-(carboxymethyl)glutaric acid ( 2 ) and cis,cis-1,3,5-cyclohexanetricarboxylic acid ( 3 ) were measured potentiometrically at 25° and I = 0.5 (KNO₃). Beside the complexes ML^? protonated species MLH and MLH are also formed. Their stability constants are given in Table 1. A comparison between the stabilities of 2 or 3 and those of acetate, as a model for a monocarboxylate, or succinate and glutarate, as examples for dicarboxylates, indicates that in all species only one carboxylate is strongly bound whereas the second and third ones are probably not. The observation that Δlog K₁ = log K ? log K as well as Δlog K₂ = log K ? log K are practically constants with values of 0.34 ± 0.05 and 0.49 ± 0.07, respectively, for both ligands and the five metal ions studied is also in line with the proposed monodentate structures of the complexes ML^?, MLH and MLH.     

Über Chalkogenolate. 82 [1]. N-Hydroxycarbamate und Ester der N-Hydroxycarbamidsäure und -carbimidsäure

On Chalcogenolates. 82. N-Hydroxy Carbamates and Esters of N-Hydroxy Carbamic Acid and Carbamic Acid The reaction between hydroxylammonium chloride, CO₂, and the corresponding hydroxide leads to N-hydroxy carbamates Esters of N-hydroxy carbamic acid have been prepared by reaction of N-hydroxy carbamates with alkyl bromide. – At room temperature the ethyl ester decomposes and forms the ester of N-hydroxy carbimic acid HO? N?C(OC₂H₅)₂. The prepared compounds have been characterized by different methods.     

The Series of Rare Earth Complexes [Ln2Cl6(μ‐4,4′‐bipy)(py)6], Ln=Y,Pr, Nd,Sm‐Yb: A Molecular Model System for Luminescence Properties in MOFs Based on LnCl3 and 4,4′‐Bipyridine

A series of 12 dinuclear complexes [Ln₂Cl₆(μ‐4,4′‐bipy)(py)₆], Ln=Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, ( 1 – 12 , respectively) was synthesized by an anhydrous solvothermal reaction in pyridine. The complexes contain a 4,4′‐bipyridine bridge and exhibit a coordination sphere closely related to luminescent lanthanide MOFs based on LnCl₃ and 4,4‐bipyridine. The dinuclear complexes therefore function as a molecular model system to provide a better understanding of the luminescence mechanisms in the Ln‐N‐MOFs ${\hbox{}{{\hfill 2\atop \hfill \infty }}}$ [Ln₂Cl₆(4,4′‐bipy)₃] ? 2(4,4′‐bipy). Accordingly, the luminescence properties of the complexes with Ln=Y, Sm, Eu, Gd, Tb, Dy, ( 1 , 4 – 8 ) were determined, showing an antenna effect through a ligand–metal energy transfer. The highest efficiency of luminescence is observed for the terbium‐based compound 7 displaying a high quantum yield (QY of 86 %). Excitation with UV light reveals typical emission colors of lanthanide‐dependent intra 4f–4f‐transition emissions in the visible range (Tb^III: green, Eu^III: red, Sm^III: salmon red, Dy^III: yellow). For the Gd^III‐ and Y^III‐containing compounds 6 and 1 , blue emission based on triplet phosphorescence is observed. Furthermore, ligand‐to‐metal charge‐transfer (LMCT) states, based on the interaction of Cl^? with Eu^III, were observed for the Eu^III compound 5 including energy‐transfer processes to the Eu^III ion. Altogether, the model complexes give further insights into the luminescence of the related MOFs, for example, rationalization of Ln‐independent quantum yields in the related MOFs.     

Poly(vinylamine) complexes with f‐block salts from the lanthanide series that exhibit significant glass‐transition temperature enhancement

Six f‐block salts from the lanthanide series form complexes with poly(vinyl amine) and increase the glass‐transition temperature of the polymer. Results for poly(vinylamine) complexes with EuCl₃(H₂O)₆ and TbCl₃(H₂O)₆ surpass those for d⁷ cobalt complexes that were studied previously. The glass‐transition temperature increases by 49 °C per mol % Eu³⁺ and 50 °C per mol % Tb³⁺, up to 2 mol % of the f‐block cations. At 5 mol % Eu³⁺, T_g is slightly higher than 250 °C with no visual evidence of thermal degradation of either component in the complex. This corresponds to a T_g enhancement of almost 200 °C with respect to the undiluted polymer. The increases in T_g for these lanthanide complexes with poly(vinylamine) obey the following trend: up to 2 mol % of the f‐block cation. With the exception of Gd(CH₃COO)₃, which contains different anionic ligands than all of the other trichlorides, this trend correlates inversely with the highest dehydration/dehydrochlorination temperature of each undiluted lanthanide salt, as measured via calorimetry above the melting point and verified by thermogravimetry. Waters of hydration and amino sidegroups undergo ligand substitution in the coordination sphere of the lanthanides. Since lanthanide cations are classified as hard acids, it is not unreasonable that they form complexes with the nitrogen lone pair in the amino sidegroup of the polymer, which is classified as a hard base. Micro‐clustering of several amino side groups reduces chain mobility significantly in the vicinity of each metal center, produces coordination crosslinks, and increases T_g. Complementary solution studies reveal that hydrogels form with swelling ratios between 20 and 50 at Eu³⁺ mole fractions between 0.01 and 0.05 with respect to poly(vinylamine). Infrared spectroscopic observations suggest that the amino nitrogen lone pair in poly(vinylamine) interacts with these lanthanide metal centers. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1931–1938, 2000     

Komplexone VL. Reaktionsenthalpie und -entropie bei der Bildung der 1 : 1-Komplexe der Seltenen Erdionen mit 1,3-Diaminopropan-N,N, N′, N′-tetraacetat

The stability constants of the 1 :1 complexes of trimethylenediamine-N, N, N′ N′ tetraacetate ‘TMTA’ with rare earth trivalent cations have been checked. The heats involved in complex formation have been determined. The thermodynamic data show a similar trend as for those of the EDTA complexes, but the discontinuities in the plots ΔH vs. 1/r and ΔS vs. 1/r are displaced towards lower values of 1/r. A change of the coordination number and of the number of coordinated water molecules for the complexes along the series La³+ – Lu³⁺ is suggested. The simultaneous presence in solution of species differing only in the number of bonded H₂O for some members of the series has been confirmed by spectrophotometric measurements in the temperature range 2 to 70°. All facts support the conclusion that in dilute solution all SE^III aquo ions exhibit the same coordination number.     

Analysis of Lanthanide π-Complexes Containing N,P, and As Atoms

A sampling comprising 92 LnC _n H _m Q _k -complexes (Ln = Sc, Y, or lanthanides; Q = N, P, As) was used to analyze the influence of the nature, the oxidation state, and the coordination number of the central Ln atom and the nature of the Q atom on the parameters of the lanthanide action area. The effect of steric factors on the stability of complex groups and on the presence (or absence) of agostic interactions in the structures of these complexes was studied. A number of crystal structure features found previously for lanthanide -complexes of a different stoichiometric composition was confirmed for the structures of the given complexes.     

Koordinationszahl und nephelauxetischer Effekt von Komplexen der Lanthaniden

The Eu^IIIEDTA complex exhibits a strong temperature dependence of its absorption band at 395 nm in dilute aqueous solution. Similar but much weaker effects can be observed in solutions of SmEDTA and GdEDTA, whereas EDTA complexes of the other lanthanide ions as well as the aquo ions of the whole series show no significant change of their absorption spectra in nation number along the series of the lanthanide EDTA complexes that takes place from Sm to Tb at room temperature. It can be concluded from the nephelauxetic effect that the coordination number decreases with increasing atomic number. The coordination numbers of the aquo ions are the same for all trivalent lanthanide ions in dilute solutions.     

Lanthanide(III) Complexes of 2‐[4,7,10‐Tris(phosphonomethyl)‐1,4,7,10‐tetraazacyclododecan‐1‐yl]acetic Acid (H7DOA3P): Multinuclear‐NMR and Kinetic Studies

The protonation constants of 2‐[4,7,10‐tris(phosphonomethyl)‐1,4,7,10‐tetraazacyclododecan‐1‐yl]acetic acid (H₇DOA3P) and of the complexes [Ln(DOA3P)]^4? (Ln=Ce, Pr, Sm, Eu, and Yb) have been determined by multinuclear NMR spectroscopy in the range pD 2–13.8, without control of ionic strength. Seven out of eleven protonation steps were detected (pK =13.66, 12.11, 7.19, 6.15, 5.77, 2.99, and 1.99), and the values found compare well with the ones recently determined by potentiometry for H₇DOA3P, and for other related ligands. The overall basicity of H₇DOA3P is higher than that of H₄DOTA and trans‐H₆DO2A2P but lower than that of H₈DOTP. Based on multinuclear‐NMR spectroscopy, the protonation sequence for H₇DOA3P was also tentatively assigned. Three protonation constants (pK_MHL, pK_MH2L, and pK_MH3L) were determined for the lanthanide complexes, and the values found are relatively high, although lower than the protonation constants of the related ligand (pK , pK , and pK ), indicating that the coordinated phosphonate groups in these complexes are protonated. The acid‐assisted dissociation of [Ln(DOA3P)]^4? (Ln=Ce, Eu), in the region c_H+=0.05–3.00 mol dm^?3 and at different temperatures (25–60°), indicated that they have slightly the same kinetic inertness, being the [Eu(H₂O)₉]³⁺ aqua ion the final product for europium. The rates of complex formation for [Ln(DOA3P)]^4? (Ln=Ce, Eu) were studied by UV/VIS spectroscopy in the pH range 5.6–6.8. The reaction intermediate [Eu(DOA3P)]* as ‘out‐of‐cage’ complex contains four H₂O molecules, while the final product, [Eu(DOA3P)]^4?, does not contain any H₂O molecule, as proved by steady‐state/time‐resolved luminescence spectroscopy.     

Structural and selectivity of 18-crown-6 ligand in lanthanide-picrate complexes

The selectivity factor in the separation of lanthanide could be associated with the coordination behaviour. Thus, we observed the study in the solid phase to understand the coordination pattern of Ln(III) with the 18-crown-6 (18C6) ligand. Good selectivity of the rigid 18C6 ligand toward Ln(III) depends on gradually smaller their ionic radii of Ln(III) in the complexes formation in the presence of picrate anion (Pic⁻), i.e. lanthanide contraction and steric effects as clearly shown in the series of [Ln(Pic)₂(18C6)]⁺(Pic)⁻ {Ln = La, Ce, Pr, Nd, Sm, Gd} and [Ln(Pic)₃(OH₂)₃] · 2(18C6) · 4H₂O {Ln = Tb, Ho} complexes. The La-Gd complexes crystallized in an orthorhombic with space group Pbca, while the Ho complex crystallized in triclinic with space group . The lighter lanthanides complexes [La-Sm] had a 10-coordination number from the 18C6 ligand and the two picrates, forming a bicapped square-antiprismatic geometry. Meanwhile, the middle lanthanide complex [Gd] had a nine-coordination number from the 18C6 ligand and the two picrates, forming a tricapped trigonal prismatic geometry. The heavier lanthanide [Ho] is rather unique, since Ho(III) coordinated with nine oxygen atoms from three picrates and three water molecules in the opposite direction whereas three 18C6 molecules surrounded in the inner coordination sphere, forming a trigonal tricapped prismatic geometry. The 18C6 ligand is effective in controlling the molecular geometry and coordination bonding of Ln-O and can use a crystal engineering approach. No dissociation of Ln-O bonds in solution was observed in NMR studies conducted at different temperatures. The photoluminescence spectrum of the Pr complex has typical 4f-4f emission transitions, i.e. ³P₀ → ³F₂ (650 nm), ¹D₂ → ³F₂ (830 nm) and ¹D₂ → ³F₄ (950 nm).     

Über Chalkogenolate. 165. Umsetzungen von Hydrazin mit Kohlenstoffdisulfid. 4. Salze des S-Methylesters der N-Dithiomethylendithiocarbazidsäure

On Chalcogenolates. 165. Reactions of Hydrazine with Carbon Disulfide. 4. Salts of the S-Methyl Ester of N-Dithiomethylene-dithiocarbazic Acid The S-methyl ester of dithiocarbazic acid reacts with carbon disulfide in the presence of sodium or potassium hydride at ?15°C to yield the hitherto unknown salts of the S-methyl ester of N-dithiomethylene-dithiocarbazic acid. The prepared compounds , have been studied with chemical methods as well as with electron absorption, infrared, nuclear magnetic resonance (¹H and ¹³C), and mass spectra.     

Zum Zusammenhang zwischen Ligand-Acidität und Metallkomplex-Stabilität: Abnehmende Stabilität bei zunehmender Basizität

The increase of the stability of metal ion complexes with decreasing basicity of the ligands within different series is discussed with the help of the equation of IRVING & ROSSOTTI [4] [12] and explained in terms of the free energy G of the complexes.     

Understanding,Controlling and Programming Cooperativity in Self‐Assembled Polynuclear Complexes in Solution

Deviations from statistical binding, that is cooperativity, in self‐assembled polynuclear complexes partly result from intermetallic interactions ΔE^M,M, whose magnitudes in solution depend on a balance between electrostatic repulsion and solvation energies. These two factors have been reconciled in a simple point‐charge model, which suggests severe and counter‐intuitive deviations from predictions based solely on the Coulomb law when considering the variation of ΔE^M,M with metallic charge and intermetallic separation in linear polynuclear helicates. To demonstrate this intriguing behaviour, the ten microscopic interactions that define the thermodynamic formation constants of some twenty‐nine homometallic and heterometallic polynuclear triple‐stranded helicates obtained from the coordination of the segmental ligands L1 – L11 with Zn²⁺ (a spherical d‐block cation) and Lu³⁺ (a spherical 4f‐block cation), have been extracted by using the site binding model. As predicted, but in contrast with the simplistic coulombic approach, the apparent intramolecular intermetallic interactions in solution are found to be i) more repulsive at long distance ( > ), ii) of larger magnitude when Zn²⁺ replaces Lu³⁺ ( > ) and iii) attractive between two triply charged cations held at some specific distance ( <0). The consequences of these trends are discussed for the design of polynuclear complexes in solution.     

Gasförmige Komplexe von Trichloriden,Tetrachloriden und Pentachloriden mit Aluminiumchlorid

Gaseous Complexes of Trichlorides, Tetrachlorides, and Pentachlorides with Aluminium Chloride The equilibria have been determined with the solid chlorides TiCl₃, VCl₃, ScCl₃, NdCl₃, ZrCl₄, TaCl₅, (NbCl₅) (double cells which contain AlCl₃ and MCl_x respectively; mass spectrometer). The complexes contain 1 AlCl₃/MCl_x. ZrAl₂Cl₁₀ molecules also have been observed. With MoCl₃ and WCl₆ AlCl₃ complexes could not be found. The ΔHº and ΔSº values have been discussed in connection with literature data. Complexes containing more as 1 AlCl₃/LnCl₃ (Ln ? Nd, Sm, Gd) also are included in the discussion.     

Étude thermodynamique de la complexation des lanthanides trivalents avec l'acide hydroxyethyl-ethylenediaminetriacetique et d'autres acides aminoacetiques: III. Détermination des Constantes de Formation des Complexes Mixtes par Titrage Potentiométrique

A thermodyrmmic study of the complex formation of trivaient lanthanides with hydroxyethylethyienediaminetriacetic acid and other aminoacetic acids. Part III. The determination of the formation constants of mixed complexes by potentiometric titration.The partial stability constants of the mixed and 1:2 complexes Ln—HEDTA—L (where Ln = La, Ce,... and L = glycine, IMDA, NTA, HEDTA and EDTA) have been determined by potentiometric titration at 25°C and at a constant ionic strength of 1 (KCl). The changes in stability of the complexes studied (1:1, 1:2, mixed, protonated and unprotonated) vs. atomic number of the lanthanide are discussed. The changes observed in the trends of the partial and overall stability constants across the lanthanide series are attributed to the decrease in the number of water molecules in the 1:1 LnHEDTA ·xH₂O from x = 3 for light lanthanides to x = 2 for heavy ones. However, in this 1:1 complex, HEDTA seems to be a hexadeutate ligand in the La—Sm range of the series and a pentadentate ligand in the Gd—Lu range. Significant differences have been found between the complexes containing four nitrogen atoms, i.e. L = HEDTA, EDTA, and those with three nitrogen atoms i.e. L = glycine, IMDA, NTA.     

Lanthanide Contraction within a Series of Asymmetric Dinuclear [Ln2] Complexes

A complete isostructural series of dinuclear asymmetric lanthanide complexes has been synthesized by using the ligand 6‐[3‐oxo‐3‐(2‐hydroxyphenyl)propionyl]pyridine‐2‐carboxylic acid (H₃ L ). All complexes have the formula [Ln₂(H L )₂(H₂ L )(NO₃)(py)(H₂O)] (Ln=La ( 1 ), Ce ( 2 ), Pr ( 3 ), Nd ( 4 ), Sm ( 5 ), Eu ( 6 ), Gd ( 7 ), Tb ( 8 ), Dy ( 9 ), Ho ( 10 ), Er ( 11 ), Tm ( 12 ), Yb ( 13 ), Lu ( 14 ), Y ( 15 ); py=pyridine). Complexes of La to Yb and Y have been crystallographically characterized to reveal that the two metal ions are encapsulated within two distinct coordination environments of differing size. Whereas one site maintains the coordination number (nine) through the whole series, the other one increases from nine to ten owing to a change in the coordination mode of an NO₃^? ligand. This series offers a unique opportunity to study in detail the lanthanide contraction within complexes of more than one metal. This analysis shows that various representative parameters proportional to this contraction follow a quadratic decay as a function of the number n of f electrons. Slater’s model for the atomic radii has been used to extract, from these decays, the shielding constant of 4f electrons. The average of O???O distances within the coordination polyhedra shared by both metals and of the Ln???Ln separations follow also a quadratic decay, therefore showing that such dependence holds also for parameters that receive the contribution of two lanthanide ions simultaneously. The magnetic behavior has been studied for all nondiamagnetic complexes. It reveals the effect of the spin–orbit coupling and a weak antiferromagnetic interaction between both metals. Photoluminescent studies of all the complexes in the series reveal a single broad emission band in the visible region, which is related to the coordinated ligand. On the other hand, the Nd, Er, and Yb complexes show features in the near‐IR region due to metal‐based transitions.     

Zur Stabilität und Struktur der CuI-Komplexe des Imidazols und Histamins. Chemie des einwertigen Kupfers in homogener,polarer Lösung. 1. Mitteilung

Univalent copper is stabilized in aqueous medium by the non-protophilic ligand CH₃CN, allowing ligand displacement reactions to be investigated as if a stable Cu^I-hydrate did exist. Under these conditions the formation of Cu^I-complexes with imidazole and its derivatives has been studied in polar solution in the absence of Cu^II. Imidazole (ImH) acts upon Cu^I as a bidentate ligand forming polynuclear chains according to the equation Histamine reacts in the same way, i. e. the coordination number of Cu^I does not exceed 2; by comparison of the complexes of Cu^I with histamine and its N-methyl-derivatives it is shown that no six-membered chelate – which sterically would be possible – is built up. Trigonal as well as tetrahedral coordination of Cu^I – i. e. chelate formation – in dilute polar solutions are confined to π- or d-acceptor ligands, e. g. bipyridine or methionine. Conclusions are drawn from this on the requirements for redox-active copper in proteins.     

Electronic circular dichroism in the 4f-4f transitions of a series of cesium tetrakis (+)-3-heptafluorobutyrylcamphorate Ln(iii) complexes

For electronic circular dichroism in the 4f-4f transitions (4f-4f CD) of a series of nine tetrakis ((+)-3-heptafluorobutyrylcamphorato) Ln(III) complexes, Δ-SAPR-8-C(4)(llll) Cs[Ln((+)-hfbc)(4)]·H(2)O (Cs-Ln = Cs-Pr, -Nd, -Sm, -Eu, -Dy, -Ho, -Er, -Tm, -Yb), the spectroscopic observables such as the dissymmetry factor g = Δε/ε values with the intensities (Δε) of the CD components and the molar absorption intensities (ε) in the 4f-4f transitions between the (2S+1)L(J) levels are compared with each other to test the classification of the CD components in the relative order of the observables predicted in terms of the selection rule for 4f-4f transitions. The 4f-4f CD-based chiroptical spectra-structural relationship across the series of Δ-SAPR-8-C(4)(llll) lanthanide(iii) complexes is proposed: the signs of the 4f-4f CD or CPL in the hypersensitive transitions are related to the absolute configuration; Ln complexes with a negative CD component have the Δ-configuration around Ln(III) and vice versa.     

Complex rate law for the cerium(IV) oxidation of glycolic acid in the medium HClO4–Na2SO4–NaClO4

The kinetics of the cerium(IV) oxidation of glycolic acid have been studied in the medium HClO₄? Na₂SO₄? NaClO₄ at varying organic substrate (HL), hydrogen, and bisulfate ion concentrations at 25.0°C and ionic strength 2.0M. Under the experimental conditions used (0.03 ? [H⁺] ? 0.5M; 0.02 ? [HSO₄^?] ? 0.1M; 0.01 ? [HL] ? 0.1M) the observed pseudo-first-order rate constant k_obs has been found to follow the complex expression where the values of the various constants have been estimated by a nonlinear least-squares method. According to this expression the oxidation process occurs significantly through three simultaneous pathways. Moreover three equilibria involving cerium(IV) and HSO₄^? (or SO₄^2?) ions are important from a kinetic point of view, whereas only two equilibria involving the corresponding complexes with the organic substrate are predominant.     

HgAlCl5,g,Formeltyp der gasförmigen Komplexe MCl2 · nAlCl3 und die Koordination im festen Dichlorid

HgAlCl_5,g – Formula Type of the Gaseous Complexes MCl₂ · nAlCl₃ and Coordination in Solid Dichloride Mass spectroscopic measurements confirmed that the molecule HgAlCl₅ is formed by reaction of HgCl₂ with Al₂Cl₆. For the equilibrium HgCl_2,g + 0.5 Al₂Cl_6,g = HgAlCl_5,g the data ΔHº = ?5.3 (±2) kcal and ΔSº = ?18(±3) cal/K have been found. As expected the ΔH- and ΔS-data for the combination of the dimers to the (1:1) complex are approximately zero. A discussion shows that for the reactions (under comparable conditions in respect to P(Al₂Cl₆) and T) the size of n is determined by the “relative stability” of MCl_2,s, that is the coordination of M and Cl in the solid MCl₂. The different numbers of n in the gaseous complexes described in the literature are easy to understand in this way.