Partial Molar Volumes of Cobalt(III) Complexes. Part 3: Homologous Series of Aminopentaamminecobalt(III) Complexes

Partial molar volumes (V ₂°) have been determined at infinite dilution in aqueous solution at 20 °C for a series of octahedral N₆-coordinated cobalt(III) species having five-coordinated ammonia ligands along with an N-coordinated linear alkyl amine whose alkyl chain was varied from ethylamine to octylamine. The experimental values for V ₂° are consistent with the relative sizes of the ligands but show increasing deviations from those predicted by computer modeling, as the size of the cation increases, presumably due to the void space of the cation that increases with the size of the amine ligand. The value of the partial molar volume at infinite dilution increased by about 16 mL⋅mol⁻¹ with each added methylene group.     

Partial Molar Volumes and Refractions of Cobalt(III) Complexes, Part 1: Homologous Series of Hexaaminecobalt(III) Complexes

Both the partial molar volumes (V∘_solute) and refractions (R∘_solute) of the solute at infinite dilution have been determined for a series of four octahedral N₆-coordinated cobalt(III) species with increasing ligand size (ammonia, ethylenediamine, sepulchrate, and 1,2-diaminocyclohexane). The experimental values for V∘ _solute are consistent with the relative sizes of the ligands but show larger values than those generated by computer modeling as the size of the cation increases. This suggests that the void space of the cation increases with the size of the cation. It is proposed that increasing hydrophobicity of the alkane ligand frameworks contributes to larger volumes.     

Pyrrole Ligands. III. The Stability of Dipyrromethenato Complexes of Cu (II) and Ni (II) in Aqueous Solutions

The protonation and complex formation of the new ligand 3,3′, 5,5′-tetramethyl-dipyrromethene-4,4′-dicarboxylate in aqueous solutions was investigated by alkalimetric titrations and spectrophotometric measurements (25°, I = 1 (KNO₃)). The pK values for the N? H groups are 8.03 and 16.1 and logβ₂ of the complexes with Cu (II) and Ni (II) are 31.0 and 24.4, respectively. Comparison with other ligands shows that the dipyrromethenato group acts as a normal rigid aromatic dinitrogen ligand, despite the charge on one nitrogen atom.     

Cyclometallated Rhodium(III) Complexes with Diimine Ligands

The synthesis of a mononuclear Rh(III) complex, as a representative example of a series of related species, containing two cyclometallating ligands ppy (2-phenylpyridine) and one diimine bpy (2,2′-bipyridine) from a binuclear Cl-bridged compound is described. The absorption spectrum shows a maximum at 364 nm (ε = 7000), with a very weak shoulder (ε = 10) at 454 nm. This band is tentatively assigned to a metal-to-ligand charge-transfer transition. A reversible, one-electron reduction appears in the cyclic voltammogram at E_1/2 = ?1.41 V (vs. NHE) and a irreversible oxydation at E_p = + 1.1 V. A detailed NMR analysis including ¹³C-NMR, NOE, SFORD as well as deuteration of the bpy ligand indicates the formation of only one isomer, having a C₂ axis, bisecting the bpy ligand, with the two carbon ligands in cis-position. ¹⁰³Rh, ¹³C and ¹⁰³Rh,H couplings are observed.     

Acid–Basic Properties of Al(III), Ga(III), and In(III) Complexes with Octaphenyltetraazaporphine

Al(III), Ga(III), and In(III) complexes with octaphenyltetraazaporphine and halide axial ligands of the composition [(X)MTAP] (X = F, Cl, Br) and In(III) complexes with bidentate ligands of the composition [(Y)InTAP] (Y = nitrite (NO₂) and 2,3-naphthodiolate (NpO₂)) were synthesized. The acid–basic properties of the complexes were studied in the proton-donor media and the concentration stability constants of the acidic forms obtained at the first protonation stage were determined. The effect of the nature of a metal and extra ligand on the basic properties of meso-nitrogen atom in macrocyclic ligand was discussed.     

The Affinity of Gallium(III) and Indium(III) for Nitrogen Donor Ligands

Abstract

Dedicated to Professor Arthur Martell on the occasion of his seventy fifth birthday.

The complexes of In(III) and Ga(III) with a variety of nitrogen donor ligands were studied in aqueous solution by glass electrode potentiometry at 25°C in 0.1 M NaNO₃. The ligands were 2-aminomethylpyri-dine (AMPY), ethylenediamine (EN), N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine (THPED), and N,N-bis(2-hydroxyethyl)glycine (BICIN). A variety of mixed ligand complexes of the MLOH type were detected with many of the above ligands as L. The logK₁ values obtained were with Ga(III) 8.40 (AMPY), 7.94 (THPED) 12.72 (EN), and In(III) 7.6 (AMPY), 8.20 (THPED), and 7.06 (BICIN). These formation constants are discussed in relation to previous predictions that In(III) and Ga(III) would have a substantial chemistry with nitrogen donor ligands. Of particular interest is the Ga(III) system with EN, where a very stable Ga(EN)³⁺ complex is formed, but no higher complexes except for hydrolyzed species such as Ga(EN)OH²⁺ and Ga(EN)(OH)₂ ⁺.     

Complex Formation Equilibria of Unusual Seven Coordinate Fe(III) Complexes with DNA Constituents

Seven-coordinate Fe(III) complexes [Fe(dapsox)(H₂O)₂]⁺, where [dapsox = 2,6-diacetylpyridine-bis(semioxamazide)] is an equatorial pentadentate ligand with five donor atoms (2O and 3N), were studied with regard to their acid–base properties and complex formation equilibria. Stability constants of the complexes and the pK _a values of the ligands were measured by potentiometric titration. The interaction of [Fe(dapsox)(H₂O)₂]⁺ with the DNA constituents, imidazole and methylamine·HCl were investigated at 25 °C and ionic strength 0.1 mol·dm^?3 NaNO₃. The hydrolysis constants of the [Fe(dapsox)(H₂O)₂]⁺ cation (pK _a1 = 5.94 and pK _a2 = 9.04), the induced ionization of the amide bond and the formation constants of the complexes formed in solution were calculated using the nonlinear least-squares program MINIQUAD-75. The stoichiometry and stability constants for the complexes formed are reported. The results show the formation of 1:1 and 1:2 complexes with DNA constituents supporting the hepta-coordination mode of Fe(III). The concentration distributions of the various complex species were evaluated as a function of pH. The thermodynamic parameters ΔH° and ΔS° calculated from the temperature dependence of the equilibrium constants were investigated for interaction of [Fe(dapsox)(H₂O)₂] with uridine.     

Unwinding DNA and RNA with Synthetic Complexes: On the Way to Artificial Helicases

Synthetic helicases can be designed on the basis of ligands that bind more strongly to single‐stranded nucleic acids than to double‐stranded nucleic acids. This can be achieved with ligands containing phenyl groups, which intercalate into single strands, but due to their small size not into double strands. Moreover, two phenyl rings are combined with a distance that allows bis‐intercalation with only single strands and not double strands. In this respect, such ligands also mimic single‐strand binding (SSB) proteins. Exploration with more than 23 ligands, mostly newly synthesised, shows that the distance between the phenyl rings and between those and the linker influence the DNA unwinding efficiency, which can reach a melting point decrease of almost ΔT_m=50 °C at much lower concentrations than that with any other known artificial helicases. Conformational pre‐organisation of the ligand plays a decisive role in optimal efficiency. Substituents at the phenyl rings have a large effect, and increase, for example, in the order of H<F<Cl<Br, which illustrates the strong role of dispersive interactions in intercalation. Studies with homopolymers revealed significant selectivity: for example, with a ligand concentration of 40 μM at 35 °C, only GC double strands melt (ΔT_m=48 °C), whereas the AT strand remains untouched, and with poly(rA)–poly(rU) as an RNA model one observes unfolding at 29 °C with a concentration of only 30 μM .     

Luminescence Investigations on Eu(III) Thenoyltrifluoroacetonate Complexes with Amide Ligands

The influence of amide ligands on the photoluminescent behavior of tris(thenoyltrifluoroacetonate)- europium(III) in the solid state is reported. Elemental analysis showed that these compounds have the following formulas [Eu(TTA)₃·(ANL)₂] and [Eu(TTA)₃·PZA], where ANL = acetanilide and PZA = pyrazinamide. The photoluminescence spectra of the complexes recorded in the range 420-720 nm at 77 K show narrow bands arising from the ⁵D₀ → ⁷F _J transitions (where J = 0-4), under excitation at 394 nm. Based on the emission spectra and luminescence decay curves the intensity parameters (Ω_λ), lifetime (τ) and emission quantum efficiency (η) were determined. The Ω₂ values indicate that the Eu³⁺ion in these complexes is in a highly polarizable chemical environment. The higher value of η (60%) obtained for the complex with the ANL ligand, in comparison with the complex with the PZA ligand (30%), indicates a more efficient deactivation of the Eu³⁺ion in the [Eu(TTA)₃·PZA] complex.     

Synthesis and Structures of Homoleptic Monomeric Potassium Aryloxolanthanoidate(III) Complexes

Reaction of lanthanoid tris(2, 6‐diphenylphenolates) [Ln(Odpp)₃] with KOdpp in 1, 2, 4, 5‐tetramethylbenzene (durene) at 200‐250 °C affords [K{Ln(OC₆H₃Ph₂‐2, 6)₄}], (Ln = La ( 1 ) or Nd ( 2 )) and 2 has also been obtained from the reaction of [Nd(Odpp)₃] with potassium hydride. In the solid state, 1 and 2 are monomeric bimetallics in which Ln is surrounded by a distorted tetrahedral array of oxygen atoms. Two Odpp ligands are oxygen bridged between K and Ln and also are η⁴‐Ph linked to potassium. One Odpp ligand bridges the metals in an O(Ln): η⁶‐Ph(K) manner that is new for lanthanoid complexes of this ligand, with no close K‐O contact, and the remaining Odpp is terminal on the Ln.     

Metallosurfactants of Chromium(III) Coordination Complexes. Synthesis, Characterization and Determination of CMC Values

A number of mixed ligand chromium(III)–surfactant coordination complexes, of the type cis-[Cr(en)₂(A)X]²⁺ and cis-α-[Cr(trien)(A)X]²⁺ (A = Dodecyl or Cetylamine; X = F⁻, Cl⁻, Br⁻) were synthesized from the corresponding dihalogeno complexes by ligand substitution. These compounds form foam in aqueous solution when shaken. The critical micelle concentration (CMC) values of these surfactant metal complexes in aqueous solution were obtained from conductance measurements. Specific conductivity data (at 303, 308 and 313 K) served for evaluation of the temperature-dependent critical micelle concentration (cmc) and the thermodynamics of micellization (Δ G_m⁰, Δ H_m⁰ and Δ S_m⁰).     

Oxidorhenium(V) and Rhenium(III) Complexes with m-Terphenyl Isocyanides

Reactions of the sterically encumbered m-terphenyl isocyanides CNAr^Dipp2 (Dipp = 2,6-diisopropylphenyl) and CNAr^Mes2 (Mes = 2,4,6-trimethylphenyl) with (NBu₄)[ReOCl₄] in CH₂Cl₂ form stable complexes of the composition (NBu₄)[ReOCl₃(CNAr^R)] or [ReOCl₃(CNAr^R)₂] depending on the amount of isocyanide added. In the [ReOCl₃(CNAr^R)₂] complexes, cis coordination of the two isocyanides is observed for CNAr^Mes2, while the sterically more demanding CNAr^DIPP2 ligands are found in trans positions. The rhenium(III) species [ReCl₃(PPh₃)(CNAr^Mes2)₂] was obtained from the reaction of [ReOCl₃(PPh₃)₂] and CNAr^Mes2. The ν(CN) IR frequencies measured for the Re^V complexes appear at higher wavenumbers than for the uncoordinated isocyanides, which suggests a low degree of backdonation into anti-bonding orbitals of these ligands.     

Redox‐Driven Symmetry Change for Terbium(III) Bis(porphyrinato) Double‐Decker Complexes by the Azimuthal Rotation of the Porphyrin Macrocycles

Molecular structures for three oxidation forms (anion, radical, and cation) of terbium(III) bis(porphyrinato) double‐decker complexes have been systematically studied. We found that the redox state controls the azimuthal rotation angle (φ) between the two porphyrin macrocycles. For [Tb^III(tpp)₂]ⁿ (tpp: tetraphenylporphyrinato, n=?1, 0, and +1), φ decreases at each stage of the oxidation process. The decrease in φ is due to the higher steric repulsion between the phenyl rings on the porphyrin macrocycle and the β hydrogen atoms on the other porphyrin macrocycle, which results from the shorter interfacial distance between the two porphyrin macrocycles. Conversely, φ=45° for both [Tb^III(oep)₂]^?1 and [Tb^III(oep)₂]⁰ (oep: octaethylporphyrinato), but φ=36° for [Tb^III(oep)₂]⁺¹. Theoretical calculations suggest that the smaller azimuthal rotation angle of the cation form is due to the electronic interaction in the doubly oxidized ligand system.     

The First Calcium(II) Complex with the Saccharinate Ligand: Synthesis,Crystal Structure,Spectral and Thermal Characterization of Trans—diaquabis[(2—hydroxyethyl)pyridinium]bis(saccharinato)calcium(II) Disaccharinate, [Ca(sac)2(H2O)2(Hpyet)2](sac)2

A new calcium(II) complex of the saccharinate ligand (sac) with 2—hydroxyethylpyridinium (Hpyet) was synthesized and characterized by elemental analysis, FT—IR spectroscopy, thermal analysis and single crystal X—ray diffractometry. The [Ca(sac)₂(H₂O)₂(Hpyet)₂](sac)₂ complex crystallizes in the triclinic space group (P1¯) with the cell dimensions a = 7.4360(7)Å, b = 12.5263(12)Å, c = 12.8329(13)Å, α = 82.534(8)°, β = 75.202(8)° and γ = 89.662(8)° (293 K). The title complex consists of a complex cation and two sac anions. In the complex cation, the calcium(II) ion is six—coordinate, bonding to two aqua ligands, two Hpyet ligands andtwo sac ligands located in the trans positions. Two of the sac ions are coordinated to the calcium(II) ion through the carbonyl O atom, while the other two remain outside the coordination sphere as the counter—ions. Thermal decomposition of the complex in air results in elimination of aqua, Hpyet, and sac ions, respectively.     

Bis(triphenylphosphin)iminium-bis(methoxo)phthalocyaninato(2–)ferrat(III) – Synthese und Kristallstruktur

Bis(triphenylphosphine)iminium Bis(methoxo)phthalocyaninato(2–)ferrate(III) – Synthesis and Crystal Structure Chlorophthalocyaninato(2–)ferrate(III) reacts with bis(triphenylphosphine)iminium hydroxide in methanol/acetone solution to yield blue crystals of bis(triphenylphosphine)iminium bis(methoxo)phthalocyaninato(2–)ferrate(III). The complex salt crystallizes as an acetone/methanol solvate (^bPNP)[Fe(OCH₃)₂pc^2–] · (CH₃)₂CO · 1.5 CH₃OH in the triclinic space group P 1 (no. 2) with the cell parameters a = 13.160(5) Å, b = 15.480(5) Å, c = 17.140(5) Å, α = 97.54(5)°, β = 91.79(5)°, γ = 95.44(5)°. The Fe atom is located in the centre of the pc^2– ligand coordinating four isoindole N atoms (N_iso) of the pc^2– ligand and two O atoms of the methoxo ligands in a mutual trans arrangement. The average Fe–O and Fe–N_iso distances are 1.887 and 1.943 Å, respectively. The cation adopts the bent conformation (< P–N–P = 140.4(2)°) with P–N distances of 1.579(3) and 1.575(3) Å.     

Comparative Study of Ruthenium(II) and Ruthenium(III) Complexes with the Ligand dmbpy (dmbpy = 4, 4′‐Dimethyl‐2, 2′‐bipyridine)

The complex cis‐[Ru^III(dmbpy)₂Cl₂](PF₆) ( 2 ) (dmbpy = 4, 4′‐dimethyl‐2, 2′‐bipyridine) was obtained from the reaction of cis‐[Ru^II(dmbpy)₂Cl₂] ( 1 ) with ammonium cerium(IV) nitrate followed by precipitation with saturated ammonium hexafluoridophosphate. The ¹H NMR spectrum of the Ru^III complex confirms the presence of paramagnetic metal atoms, whereas that of the Ru^II complex displays diamagnetism. The ³¹P NMR spectrum of the Ru^III complex shows one signal for the phosphorus atom of the PF₆^– ion. The perspective view of each [Ru^II/III(dmbpy)₂Cl₂]^0/+ unit manifests that the ruthenium atom is in hexacoordinate arrangement with two dmbpy ligands and two chlorido ligands in cis position. As the oxidation state of the central ruthenium metal atom becomes higher, the average Ru–Cl bond length decreases whereas the Ru–N (dmbpy) bond length increases. The cis‐positioned dichloro angle in Ru^III is 1.3° wider than that in the Ru^II. The dihedral angles between pair of planar six‐membered pyridyl ring in the dmbpy ligand for the Ru^II are 4.7(5)° and 5.7(4)°. The observed inter‐planar angle between two dmbpy ligands in the Ru^II is 89.08(15)°, whereas the value for the Ru^III is 85.46(20)°.     

Deep Red Emitting Heteroleptic Ir(III) Complexes that Incorporate Unsymmetrical 4-quinoline Carboxylic Acid Derived Ligands

Six disubstituted ligands based upon 2-(2′-pyridinyl/pyrazinyl)quinoline-4-carboxylic acids have been synthesised, solvent-free, in one step from a range of commercially available isatin derivatives. These species behave as ancillary chelating ligands for Ir(III) complexes of the form [Ir(C^N)₂(N^N)]PF₆ (where C^N=cyclometalating ligand; N^N=2-(2′-pyridinyl/pyrazinyl)quinoline-4-carboxylic acids). An X-ray crystallographic study on one complex shows a distorted octahedral geometry wherein a cis-C,C and trans-N,N coordination mode is observed for the cyclometalating ligands. DFT calculations predicted that variations in N^N ligand from 2,2′-bipyridine to L^{1 – 6} should localise the LUMO on to the Lⁿ ligand and that the complexes are predicted to display MLCT/LLCT character. All complexes displayed luminescence in the deep red part of the visible region (674–679 nm) and emit from triplet states, but with little apparent tuning as a function of L^{1 – 6} . Further time-resolved transient absorption spectroscopy supports the participation of these triplet states to the excited state character.     

Characterization and Molecular Structure of Bis(Isopropyl Xanthate) Bis(1,10-Phenanthroline) Nickel(II): [Ni(phen)2(CH3)2CHOCSS](CH3)2CHOCSS

The crystal and molecular structure of the title compound, [Ni(phen)₂(CH₃)₂CHOCSS](CH₃)₂CHOCSS has been determined by X-ray diffraction. The brown crystal is triclinic of space group Pi, with parameters a = 11.790(2), b = 12.410(3), c = 12.680(3) Å, α = 92.49(3), β = 96.54(3), γ = 117.43(3)° and Z = 2. The compound contains a six-coordinate cation and an isopropyl xanthate anion (CH₃)₂CHOCSS^?, the central Ni atom is chelated by four nitrogen atoms of two phenanthroline ligands and two sulfur atoms of an isopropyl xanthate ligand. The TG data indicate that it decomposed completely at 734°C.     

Strongly Luminescent Cyclometalated Gold(III) Complexes Supported by Bidentate Ligands Displaying Intermolecular Interactions and Tunable Emission Energy

A series of charge‐neutral Au^III complexes, which comprise a dicarbanionic C‐deprotonated biphenyl ligand and bidentate ancillary ligands ([Au(C^C)(L^X)]; L^X=β‐diketonate and relatives (O^O), quinolinolate and relatives (N^O), and diphosphino (P^P) ligands), were prepared. All the complexes are emissive in degassed CH₂Cl₂ solutions and in thin‐film samples with Φ _em up to 18 and 35 %, respectively, except for 5 and 6 , which bear (N^O)‐type ancillary ligands. Variation of the electronic characteristics of the β‐diketonate ancillary ligand was demonstrated to be a viable route for tuning the emission color from blue‐green (peak λ _em at ca. 466 nm for 1 and 2 ; 501 nm for 4 a and 4 b ) to orange (peak λ _em at 585 nm for 3 ), in contrast to the common observations that the ancillary ligand has a negligible effect on the excited‐state energy of the Au^III complexes reported in the literature. DFT/time‐dependent (TD) DFT calculations revealed that the energies of the ³ππ*(C^C) and the ³ILCT(O^O) excited states (ILCT=intraligand charge transfer) switch in order on going from O^O=acetylacetonate (acac) to aryl‐substituted β‐diketonate ligands. Solution‐processed and vacuum‐deposited organic light‐emitting diode (OLED) devices of selected complexes were prepared. The vacuum‐deposited OLED fabricated with 2 displays a sky‐blue emission with a maximum external quantum efficiency (EQE) of 6.71 % and CIE coordinates of (0.22, 0.40). The crystal structures of 7 and 9 reveal short intermolecular Au^III⋅⋅⋅Au^III contacts, with intermetal distances of 3.408 and 3.453 Å, respectively. DFT/TDDFT calculations were performed on 7 and 9 to account for the noncovalent interactions. Solid samples of 1 , 3 , and 9 exhibit excimeric emission at room temperature, which is rarely reported in Au^III complexes.     

Synthesis and Evaluation of Conformationally Restricted N4-Tetradentate Ligands for Implementation in An(III)/Ln(III) Separations

The previous literature demonstrates that donor atoms softer than oxygen are effective for separating trivalent lanthanides (Ln(III)) from trivalent actinides (An(III)) (Nash, K.L., in: Gschneider, K.A. Jr., et al. (eds.) Handbook on the Physics and Chemistry of Rare Earths, vol. 18—Lanthanides/Actinides Chemistry, pp. 197–238. Elsevier Science, Amsterdam, 1994). It has also been shown that ligands that “restrict” their donor groups in a favorable geometry, appropriate to the steric demands of the cation, have an increased binding affinity. A series of tetradentate nitrogen containing ligands have been synthesized with increased steric “limits”. The pK _a values for these ligands have been determined using potentiometric titration methods and the formation of the colored copper(II) complex has been used as a method to determine ligand partitioning between the organic and aqueous phases. The results for the 2-methylpyridyl-substituted amine ligands are encouraging, but the results for the 2-methylpyridyl-substituted diimines indicate that these ligands are unsuitable for implementation in a solvent extraction system due to hydrolysis.