Halo Complexes Research Articles

Widening the Scope of Structural Correlations by Means of the van der Waals Crust Penetration Indices: The Dimerization of Groups 11 and 12 L–M–X Halo Complexes

Widening the Scope of Structural Correlations by Means of the van der Waals Crust Penetration Indices: The Dimerization of Groups 11 and 12 L–M–X Halo Complexes

Halo complexes of gold(I) containing glycoconjugate carbene ligands: synthesis, characterization, cytotoxicity and interaction with proteins and DNA model systems.

New neutral carbene complexes of gold(I) [Au(Im-Me)X] (X = Cl, Au1; X = Br, Au2; X = I, Au3) have been synthesized and fully characterized by different techniques, including NMR and UV-vis absorption spectroscopy and single crystal X-ray diffraction. The carbene ligand Im-Me is decorated with a glucoside fragment via a triazole linker, obtainable through a click chemistry reaction. The compounds retain the Au-NHC fragment in aqueous solvents, and an equilibrium between the neutral halo- and the cationic di-carbene form [Au(Im-Me)2]+ is observed, whose extent follows the trend Au1 < Au2 < Au3. Cytotoxicity studies on two cancer and two non-tumorigenic cell lines reflect the solution behavior, as a certain difference among the complexes was disclosed, with the iodo complex Au3 being more active and selective. The compounds interact with both DNA and protein model systems. The X-ray structure of the adduct formed upon the reaction of Au1 with bovine pancreatic ribonuclease (RNase A) reveals Au binding at the side chain of His105 of both protein molecules A and B of the asymmetric unit. The binding of gold atoms at both the nitrogen atoms of the imidazole ring of His15 and at the N-terminal tail has been found in the adduct formed with hen egg white lysozyme.

Syntheses and X-ray structure characterization of dimeric copper(I) halo(X)complexes (X = Br, I) of (diisopropylamino)(morpholino)(phenyl)phosphine

On continuing the investigation with the reaction between aminophosphines and Cu(I) halides, the reaction of aminophosphine, viz (Diisopropylamino)(morpholino)(phenyl)phosphine with CuX (X = Br, I) was studied in acetonitrile solvent. Dimeric bromo and iodo Cu(I) complexes were obtained at room temperature. In bromo and iodo complexes, copper(I) was found to be tri-coordinate and tetra-coordinate, respectively. In iodo complex solvent, acetonitrile coordinates to copper through nitrogen atom. The Cu–P bond distances in bromo complex was ∼2.19 Å. Cu–P bond distance for iodo complex was slightly longer, 2.249(4) Å. 31P NMR coordination chemical shifts of the complexes were negative.

Synthesis and Characterization of Palladium(II) Complexes with Substituted Dihydrobenzoimidazo Quinazoline Derivatives

A series of palladium(II) halo complexes of the types [PdX 2 L 2 ].nH 2 O {n = 0, X = Cl, L = L 2 , L 4 and L 5 ; X = Br, L = L 2 ; n = 1, X = Cl, L = L 1 and L 3 } and Pd 2 X 4 L 3 [X = Br, L = L 1 , L 3 , L 4 and L 5 ] were prepared where L is 6-R-5,6- dihydrobenzoimidazo quinazoline (R-Diq; where R = ethyl: L 1 / n or i-propyl: L 2 , L 3 / n or i-butyl: L 4 , L 5 ) and characterized by elemental analyses, conductivity measurements, TGA, infrared, electronic, NMR and mass spectral techniques. Based on these studies monomeric/dimeric structure with a square planar geometry around the metal ion was proposed for all the complexes. Some of the complexes were investigated for anti-microbial activity.

Synthesis and Characterization of Palladium(II) Complexes with Substituted Dihydrobenzoimidazoquinazoline Derivatives

A series of palladium(II) halo complexes of the types[PdX2L2].nH2O {n = 0, X = Cl, L = L4and L6; X = Br, L = L3,L4, L5 and L6; n = 2, X = Cl, L = L3and L7, X = Br, L = L1};Pd2X4L2 {X = Cl, Br, L = L2 and L8} and Pd2X4L3 [X = Cl, L= L1; X = Br, L = L7] were prepared where L is 6-R-5,6-dihydrobenzoimidazo quinazoline (R-Diq; where R =phenyl: L1/furyl: L2/thiophenyl: L3/o- or phydroxyphenyl: L4, L5/o- or p-chlorophenyl: L6,L7/dimethylaminophenyl: L8and characterized byelemental analyses, molar conductivity measurements,TGA, infrared, electronic, NMR and mass spectraltechniques. Based on these studies, monomeric/dimericstructure with a square planar geometry around the metalion was proposed for these complexes. Anti-microbialactivity for some of the synthesized complexes wereinvestigated.Keywords: dihydrobenzoimidazoquinazoline, palladium(II),thermal analysis, mass spectra, biological activity.

Kinetic Studies of the Chirality Inversion of Salicylaldiminato–Ruthenium Using Racemic η6‐p‐Cymene Complexes as a Mechanistic Probe

Kinetic studies of the chirality inversion of a series of mono‐ and bimetallic (p‐cymene)(salicylaldiminato)RuII complexes with halo ligands (1 and 2) in solution have been performed by means of the line‐shape method, using 1H NMR spectroscopy to evaluate the signal exchange rates between diastereotopic protons in the p‐cymene ligand. The activation parameters (ΔH‡ and ΔS‡) associated with the flipping molecular mobility were determined from variable‐temperature NMR analyses, and it was found that the neutral halo complexes 1 and 2 exhibit much lower enthalpies and entropies than the corresponding cationic pyridine analogues 3.

Near-infrared luminescent Sn(IV) complexes of N-confused tetraphenylporphyrin: Effect of axial anion coordination

Novel tin(IV) halo complexes of an N-confused tetraphenylporphyrin with different axial ligands have been synthesized and characterized by various spectroscopic methods including X-ray crystallographic analysis. The molecular structures of the dichloro and dibromo derivatives possess perfect octahedral geometries, which are nearly comparable to the corresponding regular porphyrin complexes. In contrast, the iodide/triiodide complex obtained by a same reaction manner, demonstrated that the tin(IV) cation is slightly displaced towards axially coordinated iodide anion, giving rise to the different electronic structure due to the tautomeric form of N-confused porphyrin ligand. These structural differences reflected to the distinct photophysical and electrochemical properties. The Sn(IV) complexes are near IR luminescent, however the unsymmetrical axial coordination of iodide and triiodide anions in the tin(IV) N-confused porphyrin complex allows, in particular, the longer emission lifetimes and a smaller singlet-triplet energy gap, which were investigated by steady-state and time-resolved spectroscopies as well as theoretical calculations.

Synthesis, characterization, and biological activities of zinc, cadmium, copper, and nickel complexes containingmeta-aminophenyl benzimidazole

ZnX2, CdX2, CuX2, and NiX2 (X = Cl−, Br−, , or ) react with meta-aminophenyl benzimidazole in 1 : 2 mole ratio at reflux in methanol to give Zn2Cl4L3 · 2H2O, ZnBr2L2(OH2), [Zn(OClO3)L3]ClO4 · 3H2O, CdCl2L(OH2), Cd2Br4L3 · 2H2O, Cd(ONO2)2L2 · 2H2O, [Cu2Cl4L3] · 2H2O, Cu2Br4L3, [Cu(OClO3)L2]2(ClO4)2, [NiCl2L(OH2)] · 2H2O, [NiBrL3]Br · 3H2O, and [Ni(OClO3)L3]ClO4 · H2O. These complexes were characterized by elemental analysis, melting point, TGA, conductivity, magnetic moment measurements, IR, far-IR, NMR, electronic, and mass spectral studies. Based on these studies, Zn2Cl4L3 · 2H2O and Cd2Br4L3 · 2H2O were assigned binuclear structures while [Zn(OClO3)L3]ClO4 · 3H2O, CdCl2L(OH2), Cd(ONO2)2L2 · 2H2O, [NiCl2L(OH2)] · 2H2O, and [NiBrL3]Br · 3H2O were mononuclear with tetrahedral geometry. The copper complexes were binuclear and exhibit strong antiferromagnetic coupling at room temperature. Square pyramidal geometry was proposed for halo complexes of copper and ZnBr2L2(OH2) and square-planar geometry for perchlorato complexes of copper and nickel. All the synthesized compounds were screened for antimicrobial activities.

Halide Ion Complexes of Decaborane (B10H14) and Their Derivatives: Noncovalent Charge Transfer Effect on Second-Order Nonlinear Optical Properties

Quantum molecular engineering has been performed to determine the second-order nonlinear optical (NLO) properties in different halo complexes of decaborane (B(10)H(14)) and their derivatives using the density functional theory (DFT) method. These decaborane halo complexes of X(-)@B(10)H(14) (X = F, Cl, Br, and I) are found to possess noncovalent charge transfer interactions. The static polarizability (α(0)) and first hyperpolarizability (β(0)) among these complexes increase by moving down the group from F to I, partly due to the increase in size of their anionic radii and the decrease in their electron affinities. A two-level approximation has been employed to investigate the origin of β(0) values in these halo complexes, which show very consistent results with those by the finite-field method. Furthermore, in the same line, two experimentally existing complexes, I(-)@B(10)H(14) and I(-)@2,4-I(2)B(10)H(12), are found to have considerably large β(0) values of 2859 and 3092 a.u., respectively, which are about three times larger than a prototypical second-order NLO molecule of p-nitroaniline, as reported by Soscun et al. [Int. J. Quantum Chem.2006, 106, 1130-1137]. Besides this, the special effects of solvent, counterion, and bottom substitutions have also been investigated. Interestingly, 2,4-alkali metal-substituted decaborane iodide complexes show remarkably large second-order NLO response with β(0) amplitude as large as 62436 a.u. for I(-)@2,4-K(2)B(10)H(12) complex, which are explained in terms of their transition energies, frontier molecular orbitals and electron density difference plots. Thus, the present investigation provides several new comparative insights into the second-order NLO properties of halo complexes of decaborane, which possess not only large first hyperpolarizabilities, but also high tunability to get a robustly large second-order NLO response by alkali metal substitution effects.

Molecular Assemblies Based on Cp*BiX2 Units (X = Cl, Br, I): An Experimental and Computational Study

A series of pentamethylcyclopentadienyl-substituted bismuth halo complexes were prepared by the reactions of bismuth(III) halides BiX3 (X = Cl, Br, I) with LiCp* (Cp* = C5Me5) in 1:1 ratio. The crystal structures of [Cp*5Bi6Cl12][(thf)2Bi2Cl7] (1), [Cp*BiBr2]∞ (2), [{Cp*5Bi5Br9}{BiBr4}]2 (3), and [Cp*BiI2]∞ (4) were determined by single-crystal X-ray diffraction analysis. 1–4 display different types of aggregation, polymeric association, and Cp*–BiX2 bond hapticity depending on the halogen atom at Bi. The cationic portion of 1 is a distorted octahedral Bi6 cage that shows no Bi–Bi bonding, is capped by halo ligands and Cp* rings in a η5-fashion, and contains an interstitial Cl atom. The main structural difference in the bismuth halide framework between cationic portions {Cp*5Bi5Br9}+ in 3 and [Cp*5Bi6Cl12]+ in 1 is a neutral BiX3 unit complexed to the [{Cp*5Bi5Cl9}]+ fragment of the latter. 2 and 4 are zigzag polymers with different types of intermolecular interaction in the crystals. More ionic Cp*–Bi bonding results in higher hapticity and appears to favor cage formation, while more covalent bonding favors lower hapticity. According to quantum chemical calculations on the simplified gas phase models Cp*BiX2 (X = F, Cl, Br, I), the Cp* ring is attached via a η1(π)-bonding mode. The structural diversity of the observed assemblies is driven by the nature of Cp*–Bi bonding, which was examined by NBO analysis.

Synthesis and characterization of two new halo complexes of iodine: (C4H9)4N[I2Br]−and (C4H9)4N[I2Cl]−and theoretical calculations of their structures

Two new compounds of iodine: (C4 H9 )4 N[I2 Br], (C4 H9 )4 N[I2 Cl], were easily synthesized in a nearly quantitative yield using a direct reaction of I2 with tetrabutylammonium halide salts (chloride and bromide). The products were separated and cha

Studies of the reactions of platinum halo complexes with tin(II) halides

The reaction of a dichloromethane solution of a mixture of cis,trans-[PtCl2(SMe2)2] with a tetrahydrofuran solution of SnBr2 resulted in oxidation of platinum(II) with halogen exchange producing cis,trans-[PtBr4(SMe2)2]. Reaction of a mixture of cis,trans-[PtCl2(SEt2)2], potassium tetrachloroplatinate(II) or potassium hexachloroplatinate(IV) with SnBr2 in hydrochloric acid solution resulted in formation of predominantly anionic five-coordinate trichlorostannyl platinum(II) complexes. Reaction of potassium tetrabromoplatinate(II) with SnCl2 in hydrobromic acid in the presence of tetraphenylphosphonium bromide affords cis-[PPh4]2[PtBr2(SnBr3)2]. The insertion of SnCl2 into Pt–Cl bond of platinum(II) complexes cis-[PtCl2(L2)] {L2 = (PPh3)2; (PMe3)2; {P(OMe)3}2; dppm (bis(diphenylphosphino)methane); dppa (bis(diphenylphosphino)amine); and dppe (1,2-bis(diphenylphosphino)ethane)} is described.

Synthesis of alkynyl(tricarbonyl)rhenium complexes containing a lightly coordinated diamine ligand

Several alkynyl(tricarbonyl)diaminerhenium complexes were prepared from corresponding halo complexes and silver acetylides. With the diamine N, N′-dimethylpiperazine the compounds were found to be sufficiently stable to allow synthetic transformations on the acetylide ligand as well as purification by chromatography and subsequent substitution of the diamine ligand by stronger ligands such as phenanthrolines or isocyanides.

Selectivity of Thiolate Ligand and Preference of Substrate in Model Reactions of Dissimilatory Nitrate Reductase

Complexes analogous to the active site of dissimilatory nitrate reductase from Desulfovibrio desulfuricans are synthesized. The hexacoordinated complexes [PPh 4][Mo (IV)(PPh 3)(SR)(mnt) 2] (R = -CH 2CH 3 ( 1), -CH 2Ph ( 2)) released PPh 3 in solution to generate the active model cofactor, {Mo (IV)(SR)(mnt) 2} (1-), ready with a site for nitrate binding. Kinetics for nitrate reduction by the complexes 1 and 2 followed Michaelis-Menten saturation kinetics with a faster rate in the case of 1 ( V Max = 3.2 x 10 (-2) s (-1), K M = 2.3 x 10 (-4) M) than that reported earlier ( V Max = 4.2 x 10 (-3) s (-1), K M = 4.3 x 10 (-4) M) ( Majumdar, A. ; Pal, K. ; Sarkar, S. J. Am. Chem. Soc. 2006, 128, 4196- 4197 ). The oxidized molybdenum species may be reduced back by PPh 3 to the starting complex, and a catalytic cycle involving [Bu 4N][NO 3] and PPh 3 as the oxidizing and reducing substrates, respectively, is established with the complexes 1 and 2. Isostructural complexes, [Et 4N][Mo (IV)(PPh 3)(X)(mnt) 2] (X = -Br ( 3), -I ( 4)) did not show any reductive activity toward nitrate. The selectivity of the thiolate ligand for the functional activity and the cessation of such activity in isostructural halo complexes demonstrate the necessity of thiolate coordination. Electrochemical data of all these complexes correlate the ability of the thiolated species for such oxotransfer activity. Compounds 1 and 2 are capable of reducing substrates like TMANO or DMSO, but after the initial 15-20% conversion, the product trimethylamine or dimethylsulfide formed interacts with the active parent complexes 1 and 2 thereby slowing down further oxo-transfer reaction similar to feedback type reactions. From the functional nitrate reduction, the molybdenum species finally reacts with the nitrite formed leading to nitrosylation similar to the NO evolution reaction by periplasmic nitrate reductase from Pseudomonas dentrificans. All these complexes ( 1- 4) are characterized structurally by X-ray, elemental analysis, electrochemistry, electronic, FT-IR, mass and (31)P NMR spectroscopic measurements.

Gold(i) and silver(i) complexes containing a tripodal tetraphosphine ligand: influence of the halogen and stoichiometry on the properties. The X-ray crystal structure of two gold(i) dimeric aggregates

Complexes of the type [Au2(micro-PP3)2]X2 [X=Cl (), Br (), I ()], [Ag2(micro-PP3)2](NO3)2 (), Ag(PP3)Cl (), M3(micro-PP3)X3 [M=Au, X=Cl (), Br (), I (); M=Ag, X=NO3 ()] and Au4(micro-PP3)X4 [X=Cl (), Br (), I ()] have been prepared by interaction between gold(I) or silver(I) salts and the ligand tris[2-(diphenylphosphino)ethyl]phosphine (PP3) in the appropriate molar ratio. Microanalysis, mass spectrometry, IR and NMR spectroscopies and conductivity measurements were used for characterization. and are ionic dinuclear species containing four-coordinate gold(i) and four/three coordinate silver(i), respectively. Solutions of behave as mixtures of complexes in a 2:1 [Au2(micro-PP3)X2; X=Cl(), Br(), I()] and 4:1 () metal to ligand ratio. and react with free PP(3) in solution to generate the ionic compounds and , respectively. Complexes and , with four linear PAuX fragments per molecule, were shown by X-ray diffraction to consist of dimeric aggregates via close intermolecular gold(I)gold(I) contacts of 3.270 A () and 3.184 A (). The resultant octanuclear systems have an inversion center with two symmetry-related gold(I) atoms being totally out of the aurophilic area and represent a new form of aggregation compared to that found in other halo complexes of gold(I) containing polyphosphines. The luminescence properties of the ligand and complexes, in the solid state, have been studied. Most of the gold systems display intense luminescent emission at room and low temperature. The influence of the halogen on the aurophilic contacts of compounds with a 4:1 metal to ligand ratio results in different photophysical properties, while and are luminescent complex is nonemissive. The luminescence increases with increasing the phosphine/metal ratio affording for complexes , without aurophilic contacts, the stronger emissions. Silver complexes and are nonemissive at room temperature and show weaker emissions than gold(I) species at 77 K.

Structural and Magnetic Properties of a Complete Halide Series of NiIIComplexes with a Pyridine-Containing 14-Membered Macrocycle

The complete halide series of Ni(II) complexes containing the tetradentate macrocyclic ligand 3,11-dithia-7,17-diazabicyclo[11.3.1]heptadeca-1(17),13,15-triene (L), was fully characterized by X-ray diffraction. The fluoro, chloro, and bromo complexes are dinuclear species with formula [{Ni(L)}2(mu-X)2]2+ (X = halide), whereas only mononuclear species with formula [Ni(Y)(solv)(L)]n+ (Y = halide or solvent molecule), were obtained with I. To date, the fluoro derivative is the first nonorganometallic coordination compound containing the Ni(mu-F)2Ni core. The magnetic properties of these halo complexes have been studied. Intramolecular interactions were observed in the three dinuclear complexes, being antiferromagnetic in the fluoro derivative and ferromagnetic in both the chloro and bromo ones. The two iodo derivatives are paramagnetic species, as would be expected for mononuclear octahedral Ni(II) complexes. Density functional theory calculations led us to relate the magnetic behaviors of these compounds to the values of the corresponding Ni-X-Ni(i) angle. The analysis of the singly occupied molecular orbitals gave a clear comprehension of the different magnetic exchange interactions found in these Ni(II) complexes.

Oxidative Addition of Aryl Halides to Palladium(0) Complexes: A Density-Functional Study Including Solvation

Using density-functional theory calculations in combination with an electrostatic continuum solvation model, we have investigated the oxidative addition of phenyl halides PhX to palladium(0) complexes of bidentate phosphanes [Pd(PP)], yielding aryl halo complexes [(PP)Pd(Ph)(X)], with X = Cl, Br, I and PP = 1,2-bis(dimethylphosphino)ethane or (P)-2,2‘-bis(dimethylphosphino)-1,1‘-biphenyl. We have considered the formation of the reactive 14-electron species from the saturated [Pd(PP)2] as well as different prereaction complexes [(PP)Pd(PhX)] with an intact phenyl halide. We find that ligand dissociation is the limiting reaction step, while the formation of the prereaction complex and the oxidative addition itself are energetically (very) favorable. The concerted transition state for oxidative addition known in the gas phase could not be found in solution. Instead, we propose a pathway involving the very facile dissociation of the halide from the prereaction complex, with subsequent collapse to the product.

Synthesis, reactivity and comparative structural studies on copper(I) and gold(I) halo complexes with tripodal polyphosphines in 1:1 metal to ligand ratio. The X-ray crystal structures of three mononuclear neutral compounds

Cu(I) and Au(I) halides interact with equimolecular amounts of tripodal polyphosphines as CH 3C(CH 2PPh 2) 3(CP 3) in CHCl 3, N(CH 2CH 2PPh 2) 3(NP 3) in CH 2Cl 2 or CH 2Cl 2–S (S=MeOH, Et 2O) and P(CH 2CH 2PPh 2) 3 (PP 3) in CH 2Cl 2 to form Cu(CP 3)X [X=Br ( 1), I ( 2)], [Au 3(CP 3) 2Cl 2]Cl ( 3), [Au 3(CP 3) 3X]X 2 [X=Br ( 4), I ( 5)], Cu(NP 3)X [X=Cl ( 6), Br ( 7), I ( 8)], [Au 2(NP 3) 2]X 2 [X=Cl ( 9), Br ( 10)], Au(NP 3)I ( 11), [Cu 2(PP 3) 2X]X [X=Cl ( 12), Br ( 13)] and [Au 2(PP 3) 2]X 2 [X=Br ( 14), I ( 15)]. Complexes 1, 7 and 11 were shown by X-ray diffraction to consist of neutral monomers with distorted tetrahedral geometry around the metal and the phosphine acting as tridentate chelating ligand. The mass spectra, conductivity measurements and 31P{ 1H} NMR studies for 9 and 10 are indicative of a coexistence with mononuclear forms. Complexes 3, 9 and 14 were also achieved in solution by addition of the appropriate polyphosphine to the compounds Au 3(CP 3)Cl 3 ( 3a), Au 3(NP 3)Cl 3 ( 9a) and Au 4(PP 3)Br 4 ( 14a), respectively, involving ring-closure reactions. Likewise, crystals of 1 were obtained both from solutions of this compound in CH 2Cl 2–EtOH and from solutions in CHCl 3 of ( 1a)·2.5Et 2O ( 1a=Cu 3(CP 3)Br 3). Further additions of the appropriate polyphosphine to 9 and 14 give complexes with new “MP 4” environments and dangling phosphorus that for 14 involve ring-opening processes. By reaction of 3 with CP 3 the complex [Au 3(CP 3) 3Cl]Cl 2, isostructural with 4 and 5, is afforded in solution. The reaction of Cu(CP 3)Cl ( I) with CP 3 followed by 31P{ 1H} NMR seems to occur with retention in part of the starting CuP 3 core and formation of other species containing linear arrangements for Cu(I). No reaction was observed between 6 or 13 and NP 3 or PP 3, respectively.

Co-ordination of weak field ligands by N-acetylmicroperoxidase-8 (NAcMP8), a ferric haempeptide from cytochrome c, and the influence of the axial ligand on the reduction potential of complexes of NAcMP8 †

N-Acetylmicroperoxidase-8 (NAcMP8), a ferric haempeptide derived from cytochrome c, retains the His-18 ligand and, in addition, has a readily-displaced coordinated water molecule. The co-ordination of ligands which leave Fe(III) in a predominantly high spin state has been investigated by difference UV–visible spectrophotometry. The affinity for these ligands is low (K = 0.69, 0.45, 0.46 and 0.35 dm3 mol−1 for co-ordination of Cl−, Br−, I− and SCN−, respectively), and somewhat larger for N3− (K = 25 dm3 mol−1), where the metal is in an equilibrium between an admixed spin state (S = 3/2, 5/2) and a low spin state (S = 1/2). By contrast, previous work has shown that the affinity of Fe(III) for ligands that produce a low spin state is considerably larger (K = 102 to >106 dm3 mol−1). The effect of the axial ligand on the potential of the Fe(III)|Fe(II) couple in complexes of L–NAcMP8 (L = ligand trans to His-18) in aqueous solution at a glassy carbon electrode has been examined by cyclic voltammetry. The potentials of the quasi-reversible reduction of the halo complexes of NAcMP8 decrease in the order L = Cl− > Br− > I− and reflect the hardness of the coordinated anion. The reduction potentials of some low spin complexes investigated (L = imidazole, ethanolamine, glycine, propylamine, cyanide) span less than 50 mV (E½ = −0.203 ± 0.015 V vs. NHE), and are similar to complexes in which the metal is in a spin equilibrium (L = OH−, N3−; E½ = −0.209 ± 0.005 V), whereas high spin complexes (L = H2O, Cl−, Br−, I−, SCN−) have somewhat higher reduction potentials (E½ = −0.146 ± 0.023 V). Work with pyridine and primary amine ligands shows that an increase in ligand basicity stabilises the Fe(III) state relative to the Fe(II). The rate constants for heterogeneous electron transfer are relatively insensitive to the nature of the axial ligand. Thus, changing the axial ligand of an iron porphyrin modulates the reduction potential only by a relatively small amount. The implications of this observation for biological systems is discussed.

Partitioning of mercury in aqueous biphasic systems and on ABEC™ resins

Poly(ethylene glycol)-based aqueous biphasic systems (PEG-ABS) can be utilized to separate and recover metal ions in environmental and hydrometallurgical applications. A concurrent study was conducted comparing the partitioning of mercury between aqueous layers in an ABS [Me-PEG-5000/(NH 4) 2SO 4] and partitioning of mercury from aqueous solutions to aqueous biphasic extraction chromatographic (ABEC-5000) resins. In ammonium sulfate solutions, mercury partitions to the salt-rich phase in ABS, but by using halide ion extractants, mercury will partition to the PEG-rich phase after formation of a chloro, bromo or iodo complex. The efficacy of the extractant increases in the order Cl −<Br −<I −. This behavior is also observed using the ABEC resins where halo complexes of mercury will adsorb to the resin from (NH 4) 2SO 4 solutions with retention following the same order. The onset of mercury extraction or adsorption is different for the three extractants, occurring at the lowest extractant concentration for I −, followed by Br −, and then Cl −. Fluoride does not extract mercury. Extraction or adsorption of mercury is improved at the lowest halide concentrations in the presence of sulfuric acid. The addition of sulfuric acid to (NH 4) 2SO 4 solution results in ABEC retention of mercury even in the absence of halide extractant.