Showing papers on "Stability constants of complexes published in 2000"
TL;DR: The stability constants demonstrated substantial deviation from Irwing-Williams series reported for divalent ions, and some of the factors affecting the stability constants such as cation exchange capacity of humus soil, molecular radius, and molecular surface area of humic molecules were estimated.
280 citations
TL;DR: In this paper, the authors measured the stoichiometry and thermo- dynamic stabilities of the uranyl-surface complexes of Bacillus subtilis using batch experiments in 0.1 M NaClO4 as a function of pH, time and solid:solute ratio at 25 °C.
Abstract: Uranyl adsorption onto the Gram-positive soil bacterium Bacillus subtilis was measured using batch experiments in 0.1 M NaClO4 as a function of pH, time, and solid:solute ratio at 25 °C. The experimental data were interpreted using a surface complexation approach. The experimental measurements constrain the stoichiometry and thermo- dynamic stabilities of the important uranyl-surface complexes. The U adsorption data require two separate adsorption reactions, with the uranyl ion forming surface complexes with the neutral phosphate functional groups and the deprotonated carboxyl functional groups of the bacterial cell wall: R−POH0 + UO22+ ⇔ R−POH−UO22+ (log K = 11.8 ± 0.2) and R−COO- + UO22+ ⇔ R−COO−UO2+ (log K = 5.4 ± 0.2). These new stability constants, in conjunction with other experimental and predicted stability constants, may be incorporated in surface complexation models to determine the mobility and fate of U in bacteria-bearing water−rock systems.
161 citations
TL;DR: In this paper, the aqueous speciation, formation constants, and solution structure were determined for a new insulin-mimetic organic vanadium(V) compound (ammonium (dipicolinato)oxovanadate(V)).
Abstract: The aqueous speciation, formation constants, and solution structure were determined for a new insulin-mimetic organic vanadium(V) compound (ammonium (dipicolinato)oxovanadate(V)). The solution properties of the system were characterized by using potentiometry, 1H, 13C, and 51V NMR 1D and 2D spectroscopy, and UV/visible spectroscopy. These studies were conducted using the crystalline compound as well as combinations of the free ligand and the metal salt. The major complex is most stable in the acidic pH range, although it does protonate at low pH. It protonates at pH ∼1 and decomposes below pH 0. The dipic ligand is coordinated in a tridentate manner throughout the pH range studied. Protonation at low pH takes place on one of the oxo groups. Dynamic processes were explored using 1H and 13C EXSY NMR spectroscopy. VO2dipic- was found to exchange between the complex and the ligand at high and at low pH values. In the intermediate-pH range, no evidence for exchange processes was obtained, documenting the inert...
145 citations
TL;DR: Glass electrode potentiometric titrations have been used to re-determine the formation constants of both the Fe(III)- and Fe(II)-citrate systems and redox equilibria of iron are included in large models of blood plasma for the first time.
142 citations
TL;DR: In this article, the interaction between polyvinylpyrrolidone (PVP) and metal cations has been studied in absolute ethanol and water at room temperature and atmospheric pressure.
Abstract: The interaction between polyvinylpyrrolidone (PVP) and metal cations has been studied in absolute ethanol and water at room temperature and atmospheric pressure. The UV-VIS and IR absorption spectra of metal cations, PVP and PVP-M n + (M n + =Fe 3+ , Co 2+ , Ni 2+ ) were given. It was shown that PVP and metal cations formed unstable complexes, and the coordination stability constants were determined according to the Miller–Dorough method. The stability constants of PVP-Fe 3+ and PVP-Co 2+ were lower than 10 and 0.6, respectively, and that of PVP-Ni 2+ was too low to be estimated. The solid complexes of PVP-Fe 3+ and PVP-Co 2+ were also synthesized under proper conditions.
114 citations
TL;DR: In this article, the stability constants of thorium(IV) hydrolysis species have been measured at 15, 25, and 35°C (in 1.0 mol dm−3 NaClO4) using both potentiometry and solvent extraction.
Abstract: The stability constants of thorium(IV) hydrolysis species have been measured at15, 25, and 35°C (in 1.0 mol dm−3 NaClO4) using both potentiometry and solventextraction. The results indicate the presence of the monomeric speciesTh(OH)3+, Th(OH)2+2, Th(OH)+3, and Th(OH)4, in addition to the polymericspecies Th4(OH)8+8 and Th6(OH)9+15. The polymeric species were found to beimportant, although the total thorium concentration was limited to 0.01–0.1mmol-dm−3. The solvent extraction measurements required the use of acetylacetone.As such, the stability constants of thorium(IV) with acetylacetone were alsomeasured using both potentiometry and solvent extraction. All logarithms of thestability constants were found to be linear functions of the reciprocal absolutetemperature indicating that ΔHo and ΔSo of reaction are both independent oftemperature (over the temperature range examined in the study).
95 citations
TL;DR: In this article, a series of azo metal chelate dyes have been synthesized and the UV-Vis absorption spectra of the azo dye and its metal complexes were measured.
94 citations
TL;DR: In this paper, the influence of EDTA speciation on its utilization by the EDTA-degrading bacterial strain DSM 9103 was investigated, and the data suggest that these EDTA chelates were not used directly by the cells but that they had to dissociate prior to degradation.
Abstract: Ethylenediaminetetraacetate (EDTA), an industrially important chelating agent, forms very stable complexes with di- and trivalent metal ions, and in both wastewater and natural waters it is normally present in the metal-associated form. Therefore, the influence of EDTA speciation on its utilization by the EDTA-degrading bacterial strain DSM 9103 was investigated. EDTA-grown cells harvested from the exponential phase of a batch culture were incubated with 1 mM of various EDTA species and the EDTA concentration in the assay was monitored as a function of time. Uncomplexed EDTA as well as complexes with low stability constants (MgEDTA2-, CaEDTA2-, and MnEDTA2-, stability constant < 1016) were found to be readily degraded to completion at a constant rate. For more stable EDTA chelates (i.e. chelates of Co2+, Cu2+, Zn2+, and Pb2+) the data suggest that these complexes were not used directly by the cells but that they had to dissociate prior to degradation. The rate of this dissociation step possibly determined...
88 citations
TL;DR: In this paper, the aqueous complexation reactions of trivalent actinide and lanthanide cations with hexadentate ligand N,N,N′, N′-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) have been characterized using potentiometric and spectroscopic techniques in 0.1 M NaClO4.
74 citations
TL;DR: In this paper, a solvent extraction separation of uranium with a crown hydroxamic acid 5, 14-N, N′-hydroxyphenyl-4, 15-dioxo-1,5,14,18-tetraaza hexacosane (NHDTAHA) in the presence of cerium, thorium and lanthanides is described.
73 citations
TL;DR: In this article, the macrocyclic ligand cucurbituril and aliphatic alcohols, acids and nitriles have been studied using calorimetric titrations.
TL;DR: The experimental data show a good fit to the calculated speciation model, even for the less abundant species, and diperoxovanadates are the favoured species at pH 2-10, when sufficient peroxide is present.
TL;DR: In this paper, the hydrogen peroxide decomposition kinetics were investigated for both free and complexed iron catalysts with DTPA, EDTA, EGTA, and NTA as ligands.
Abstract: The hydrogen peroxide decomposition kinetics were investigated for both “free” iron catalyst [Fe(II) and Fe(III)] and complexed iron catalyst [Fe(II) and Fe(III)] complexed with DTPA, EDTA, EGTA, and NTA as ligands (L). A kinetic model for free iron catalyst was derived assuming the formation of a reversible complex (Fe–HO2), followed by an irreversible decomposition and using the pseudo-steady-state hypothesis (PSSH). This resulted in a first-order rate at low H2O2 concentrations and a zero order rate at high H2O2 concentrations. The rate constants were determined using the method of initial rates of hydrogen peroxide decomposition. Complexed iron catalysts extend the region of significant activity to pH 2–10 vs. 2–4 for Fenton's reagent (free iron catalyst). A rate expression for Fe(III) complexes was derived using a mechanism similar to that of free iron, except that a L–Fe–HO2 complex was reversibly formed, and subsequently decayed irreversibly into products. The pH plays a major role in the decomposition rate and was incorporated into the rate law by considering the metal complex specie, that is, EDTA–Fe–H, EDTA–Fe–(H2O), EDTA–Fe–(OH), or EDTA–Fe–(OH)2, as a separate complex with its unique kinetic coefficients. A model was then developed to describe the decomposition of H2O2 from pH 2–10 (initial rates = 1 × 10−4 to 1 × 10−7 M/s). In the neutral pH range (pH 6–9), the complexed iron catalyzed reactions still exhibited significant rates of reaction. At low pH, the Fe(II) was mostly uncomplexed and in the free form. The rate constants for the Fe(III)–L complexes are strongly dependent on the stability constant, KML, for the Fe(III)–L complex. The rates of reaction were in descending order NTA > EGTA > EDTA > DTPA, which are consistent with the respective log KMLs for the Fe(III) complexes. Because the method of initial rates was used, the mechanism does not include the subsequent reactions, which may occur. For the complexed iron systems, the peroxide also attacks the chelating agent and by-product-complexing reactions occur. Accordingly, the model is valid only in the initial stages of reaction for the complexed system. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 24–35, 2000
TL;DR: In this article, the inclusion of tetramethylammonium cation (TEMA) by the water soluble calixarene hosts 1-8 was studied at neutral pH by 1H NMR spectroscopy and compared with that of the ditopic trimethylanilinium (TMA).
Abstract: The inclusion of symmetrical tetramethylammonium cation (TEMA) by the water soluble calixarene hosts 1–8 was studied at neutral pH by 1H NMR spectroscopy and compared with that of the ditopic trimethylanilinium cation (TMA). The hosts blocked in the cone conformation and bearing sulfonate groups at the upper rim (2, 3, 5, 7 and 8) bind selectively the aromatic portion of TMA, whereas compound 4 which lacks sulfonate groups interacts only with the charged head group of TMA. The conformationally mobile compound 1 and the partial cone calixarene 6 include TMA cation in an unselective fashion. TEMA is complexed by hosts 1–7, but not by the tetraether-tetrasulfonate receptor 8. The binding constants for all the systems, as determined by 1H NMR spectroscopy, show that inclusion is favoured by the presence of the sulfonate groups and that the complexes of the conformationally mobile receptor 1 with both guests are more stable. The thermodynamic parameters of inclusion determined by direct calorimetry for 2–TEMA and 4–TEMA systems show that in both cases the inclusion process is enthalpically driven and that the greater stability constant observed for 2–TEMA with respect to that of 4–TEMA mainly results from a less unfavourable entropic contribution, suggesting that in the 2–TEMA complex the charged sulfonate groups cause a better desolvation of the host–guest system upon inclusion.
TL;DR: Electrospray ionization (ESI)/quadrupole ion trap mass spectrometry is used to evaluate the heavy metal binding selectivities of five caged crown ethers and two polyether reference compounds in methanol solution with the aim of developing this method for the rapid screening of binding selectivity of new synthetic ligands.
Abstract: Electrospray ionization (ESI)/quadrupole ion trap mass spectrometry is used to evaluate the heavy metal binding selectivities of five caged crown ethers and two polyether reference compounds in methanol solution. The binding preferences for Hg2+, Pb2+, Cd2+, and Cu2+ were analyzed by comparison of ESI mass spectral intensities with the aim of developing this method for the rapid screening of binding selectivities of new synthetic ligands. The cage compounds preferentially bind Hg2+, except for the cage cryptand derivative, which favors Pb2+. The preference for Hg2+ stems from the favorable positioning of the nitrogen or sulfur atoms for linear coordination of Hg2+, whereas the cryptand derivative favors Pb2+ because of its larger cavity size. The counterions of the metal salts influence the type of complexes observed in the ESI mass spectra because the strengths of the metal−anion bonds affect retention of the anion in the complexes.
TL;DR: In this article, the acid-base properties of diatom suspensions with proton were characterized from titration curves with copper, which allowed us to determine the specific adsorption of copper in a heterogeneous adorption model.
TL;DR: The highest formation constant is observed for the dicopper cryptate of a pyridine-spaced cryptand, suggesting involvement in complexation of donors from the spacer link, making it a possible candidate for treatment of copper-excess pathology.
Abstract: Complexation and protonation equilibria were studied in aqueous solution for a new range of aminocryptand ligands, N(CH2CH2NHCH2RCH2NHCH2CH2)3N, (R = m-xylyl, p-xylyl, 2,5-furan, 2,6-pyridine) and demonstrate that stability constants for first transition series ions Co2+ to Zn2+ are relatively high. X-ray crystallography shows that the cryptands are reasonably well preorganized for complexation. The furan-spaced cryptand L6.H2O crystallizes in the rhomobohedral space group R3 (no. 148) with a = 14.645(1), b = 14.645(1), and c = 25.530(4) A, whereas the m-xylyl-spaced cryptand L4 crystallizes in the triclinic space group P1 (no. 2) with a = 9.517(1), b = 15.584(2), and c = 23.617(4) A. The highest formation constant (log beta21 = 33.07) is observed for the dicopper cryptate of a pyridine-spaced cryptand, suggesting involvement in complexation of donors from the spacer link. This pyridine-spaced host also shows good selectivity for copper(II) over zinc(II), making it a possible candidate for treatment of copper-excess pathology.
TL;DR: In this article, the complexation of trivalent lanthanides with aliphatic dicarboxylic acids (malonic, succinic, glutaric and adipic) was studied at 25°C and 0.1 M (NaClO4) ionic strength by luminescence and absorption spectroscopy.
TL;DR: In this article, the interaction of amino acids with the major constituents of natural waters has been studied potentiometrically by determining protonation constants at different ionic strengths (e.g., I ≤ 5.6 mol (kg H 2 O) −1 (NaCl)) and in artificial seawater (containing Na +, K +, Ca 2+, Mg 2+, Cl − and SO 4 2− ) at different salinities.
TL;DR: In this article, the authors examined the complexation of β-cyclodextrin (β-CD) with 6-p-toluidinylnaphthalene-2-sulfonate (TNS), a fluorescent probe for exploring hydrophobic regions of several biological substances.
TL;DR: In this paper, the ionic strength dependence of rare earth elements (YREE) formation constants in perchlorate solution for ionicstrengths between 0 and 6 molar was expressed as logFβ1 (M, μ) =logFβ 1o (M) −3.066 μ0.5/(1 + 1.769 μ 0.5)+ 0.1645 μ.
Abstract: Formation constants for the complexation of yttrium and rare earth elements(YREE) by fluoride ions have been measured at 25°C. The ionic strength (μ)dependence of YREE formation constants in perchlorate solution for ionicstrengths between 0 and 6 molar can be expressed aslogFβ1 (M, μ) =logFβ1o (M) −3.066 μ0.5/(1 + 1.769 μ0.5)+ 0.1645 μwhere logFβ1o(M) represents MF2+formation constants at zero ionic strength.The logFβ1o(M) results obtained inthis work are: Y(4.46), La(3.62), Ce(3.86),Pr(3.84), Nd(3.82), Sm(4.15), Eu(4.27), Gd(4.24), Tb(4.37), Dy(4.39), Ho(4.28),Er(4.27), Tm(4.29), Yb(4.39), and Lu(4.25). The relative magnitudes of YREEformation constants are independent of ionic strength. The pattern oflogFβ1(M,μ),formation constants obtained in this work [relative magnitudes oflogFβ1o (M)],exhibits a shallow minimum between Dy and Yb. In contrast to the smoothpattern of stability constants expected if fluoride were to interact with bare ions(with monotonically decreasing crystal radii between La and Lu), theinteractionof F− with YREEs, which have extensive hydration spheres[M(H2O)8–93+] resultsin a relatively complex pattern of lanthanide stability constants. The fluoridecomplexation behavior of yttrium differs distinctly from the behavior of any rareearth. Although the crystal radius of Y3;pl is approximately equalto that of Ho3+,differences in the covalence/ionicity of Y3+ relative to therare earths leads to aYF2+ stability constant that exceeds that of any rare earthelement (REE).
TL;DR: Electrospray ionization (ESI) mass spectra of ternary complexes of Cu(2+) and 1,10-phenanthroline with the 20 essential amino acids (AA) were investigated quantitatively and a weak correlation was found between DeltaF and the ESI efficiencies that showed that amino acids with hydrophobic side-chains were ionized more efficiently.
Abstract: Electrospray ionization (ESI) mass spectra of ternary complexes of Cu(2+) and 1,10-phenanthroline with the 20 essential amino acids (AA) were investigated quantitatively. Non-basic amino acids formed singly charged complexes of the [Cu(AA - H)phen](+) type. Lysine (Lys) and arginine (Arg) formed doubly charged complexes of the [Cu(HAA - H)phen](2+) type. Detection limits were determined for the complexes of phenylalanine (Phe), glutamic acid (Glu) and Arg, which were at low micromolar or submicromolar concentrations under routine conditions. Detection limits of low nanomolar concentrations are possible for amino acids with hydrophobic side-chains (Phe, Tyr, Trp, Leu, Ile) as determined for Phe. The efficiencies for the formation by ESI of gaseous [Cu(AA - H)phen](+) ions were determined and correlated with the acid-base properties of the amino acids, ternary complex stability constants and amino acid hydrophobicities expressed as the Bull-Breese indices (DeltaF). A weak correlation was found between DeltaF and the ESI efficiencies for the formation of gaseous [Cu(AA - H)phen](+) [Cu(HAA - H]phen](2+) and [AA + H](+) ions that showed that amino acids with hydrophobic side-chains were ionized more efficiently. In the ESI of binary and ternary amino acid mixtures, the formation of gas-phase Cu-phen complexes of amino acids with hydrophobic side-chains was enhanced in the presence of complexes of amino acids with polar or basic side-chains. An interesting enhancement of the ESI formation of [Cu(Glu - H)phen](+) was observed in mixtures. The effect is explained by ion-cluster formation at the droplet interface that results in enhanced desorption of the glutamic acid complex.
TL;DR: Solid complexes of N-βD and β-cyclodextrin exhibited higher rates of dissolution and dissolution efficiency values than the corresponding physical mixtures and pure drug and higher dissolution rates were observed with kneaded complexes than with those prepared by coevaporation.
Abstract: Complex formation of nimesulide (N) and beta-cyclodextrin (beta CD) in aqueous solution and in solid state and the possibility of improving the solubility and dissolution rate of nimesulide via complexation with beta CD were investigated. Phase solubility studies indicated the formation of a 1:1 complex in solution. The value of the apparent stability constant Kc was 158.98 M-1. Solid inclusion complexes of N and beta CD were prepared by kneading and coevaporation methods. Differential scanning calorimetry (DSC) studies indicated the formation of solid inclusion complexes of N-beta CD at a 1:2 molar ratio in both the methods. Solid complexes of N-beta D (1:1 and 1:2 M) exhibited higher rates of dissolution and dissolution efficiency values than the corresponding physical mixtures and pure drug. Higher dissolution rates were observed with kneaded complexes than with those prepared by coevaporation. Increases of 25.6- and 38.7-fold in the dissolution rate were observed, respectively, with N-beta CD 1:1 and 1:2 kneaded complexes.
TL;DR: In this paper, the authors used steadystate fluorescence and molecular mechanics to study the inclusion complexes of dimethyl 2,6-naphthalenedicarboxylate (DMN) with α-and β-cyclodextrins (CDs).
Abstract: Steady-state fluorescence and molecular mechanics have been used to study the inclusion complexes of dimethyl 2,6-naphthalenedicarboxylate (DMN) with α- and β-cyclodextrins (CDs). Emission spectra of DMN show two bands whose ratio is very sensitive to the medium polarity. From the change of this ratio with CD concentration and temperature, the stoichiometry, the formation constants, and the changes of enthalpy and entropy upon inclusion of complexes formed were obtained. Stoichiometry depends on the host CD used. The estimated formation constants at 25 °C were (8.2 ± 0.6) × 105 M-2 for DMN:αCD2 and 1311 ± 57 M-1 for DMN:βCD. A dependence of the thermodynamic parameters ΔH° and ΔS° on the temperature was also found. Both complexes showed a negative ΔCp°. In addition, DMN seems to be a good probe for estimating microenvironmental polarity. Molecular mechanics calculations were also employed to study the formation of 1:1 and 1:2 complexes of DMN with both α- and βCDs. The study was mainly performed in the pr...
TL;DR: In this article, a new range of lanthanide compounds of the formula Ln(HL)3(NO3)3, where Ln=La, Ce, Nd, SmLu, Y; HL=C6H5C(O)N(H)P(O)[N(CH2CH3)2]2]
TL;DR: It is found that the competition of the Bd and Bn ligands for the formation of ternary species with a specific substrate is strongly dependent on the p[H].
Abstract: The host-guest interactions between ortho- (Ph), pyro- (Pp), and tripolyphosphate (Tr) anions together with ATP (At), ADP (Ad), and AMP (Am) nucleotides and the hexaazamacrocyclic ligand 3,7,11,19,23,27-hexaazatricyclo[27311(13,17)]triaconta- 1(32),13,15,17(34),29(33),30-hexaene (Bn) have been investigated by potentiometric equilibrium methods. Ternary complexes are formed in aqueous solution as a result of hydrogen bond formation and Coulombic attraction between the host and the guest. Formation constants for all the species obtained are reported. The selectivity of the Bn ligand with regard to the phosphate and nucleotide substrates is discussed and illustrated with species distribution diagrams. A comparison of the present results with those obtained for the similar but smaller macrocyclic ligand 3,6,9,17,20,23- hexaazatricyclo[23311(11,15)]triaconta-1(29),11(30),12,14,25,27-hexaene (Bd) is also discussed. It is found that the competition of the Bd and Bn ligands for the formation of ternary species with a specific substrate is strongly dependent on the p[H]. The crystal structure of the compound [(H6Bn)(H2PO4)6]2H2O with empirical formula C28H68N6O26P6 has been solved by means of X-ray diffraction analysis. The compound belongs to the triclinic P1 space group with Z = 1, a = 8892(2) A, b = 9369(4) A, c = 16337(8) A, alpha = 7372(4) degrees, beta = 8301(4) degrees, and gamma = 6481(3) degrees. The phosphate counterions are found to bridge adjacent layers of macrocyclic molecules through an extensive hydrogen-bonding network
TL;DR: In this paper, the complexation of the praseodymium(III) ion with d -gluconic acid was studied by potentiometry, UV-Vis spectrophotometry, circular dichroism (CD) experiments and 1H and 13C NMR.
TL;DR: The equilibrium formation constants of manganese(II) chloride complexes have been determined spectrophotometrically in the temperature range from 25°C to 300°C at saturated water vapour pressure at chloride concentrations from 0.022 to 0.80 mol kg −1.
TL;DR: In this article, it was shown that molybdenum(VI) forms a mononuclear 1:1 complex with glutamic acid of the type MoO3L-2 at pH 5.8.
Abstract: The complexation of molybdenum(VI) with glutamic acid was investigated in aqueous solution ranging in pH from 4 to 9, using polarimetric and spectrophotometric techniques. The composition of the complex was determined by the continuous variations method. It was shown that molybdenum(VI) forms a mononuclear 1:1 complex with glutamic acid of the type MoO3L-2 at pH 5.8. The protonation constants of glutamic acid (using the potentiometric technique) and the stability constant of the complex (using the spectrophotometric technique) were determined at 25 °C and at ionic strengths ranging from (0.1 to 1.0) mol dm-3 sodium perchlorate. The dependence of the protonation of glutamic acid and the stability constants of the complex on ionic strength is described by a Debye−Huckel-type equation.
TL;DR: The ligands described in this work are part of a new class of heteropodate ligands which exploit the various chelating properties of several binding units within a single tripodal ligand and allow for systematic variation of the properties for medical or other applications.
Abstract: New ligands based on hydroxypyridinonate (HOPO) and other bidentate ligands are explored as iron(III) sequestering agents. These are based on the N,N',N"-tris[(3-hydroxy-1-methyl- 2-oxo-1,2-didehydropyrid-4-yl)-carboxamidoethyl]amine (TREN-Me-3,2-HOPO) platform in which one Me-3,2-HOPO ligand group is substituted with either a 2-hydroxyisophthalamide (TREN-Me-3,2-HOPOIAM) or a 2,3-dihydroxyterephthalamide (TREN-Me-3,2-HOPOTAM) moiety. The ferric complexes have been prepared and structurally characterized by X-ray diffraction: Fe[TREN-Me-3,2-HOPOIAM] crystallizes in the monoclinic space group C2/c with cell parameters a = 18.1186(3) A, b = 17.5926(2) A, c = 25.0476(2) A, beta = 98.142(1) degrees, Z = 8. Fe[TREN-Me-3,2-HOPOTAM]- crystallizes in the monoclinic space group C2/c with cell parameters a = 31.7556(12) A, b = 14.0087(6) A, c = 22.1557(9) A, beta = 127.919(1) degrees, Z = 8. The aqueous coordination chemistry of these ligands with both the ferric and ferrous redox states of iron has been examined using spectroscopic and electrochemical methods, giving log formation constants of 26.89(3) (beta 110), 31.16(6) (beta 111) for the ferric TREN-Me-3,2-HOPOIAM complexes and 33.89(2) (beta 110), 38.45(2) (beta 111) for the ferric TREN-Me-3,2-HOPOTAM complexes. For the reduced (ferrous) complexes values of 10.03(9) (beta 110) and 13.7(2) (beta 110) were observed for the Fe[TREN-Me-3,2-HOPOIAM]- and Fe[TREN-Me-3,2-HOPOTAM]2- complexes, respectively. These data provide a complete description of metal-ligand speciation as a function of pH and of redox activity. The ligands described in this work are part of a new class of heteropodate ligands which exploit the various chelating properties of several binding units within a single tripodal ligand and allow for systematic variation of the properties for medical or other applications.