Pseudohalide Ions Research Articles

Impact of Coordinated Pseudohalide Ions and Picolinamide on Supramolecular Synthons in Selected Zinc and Cadmium Complexes.

Four new Zn(II) and Cd(II) picolinamide (pia) complexes with cyanate and azide, e.g. [Zn(OCN)2(pia)2] (1), [Cd(OCN)2(pia)2]n (2), [Zn(N3)2(pia)2] (3) and [Cd(N3)2(pia)2]n·nH2O (4), have been prepared and characterized by IR and NMR spectroscopy, and thermal (TG/DTA) methods. For the compounds 1 and 3 X-ray analysis revealed mononuclear molecular structure with octahedral N4O2 environment around the zinc(II) center with cis-arrangement of ligands. Only in 1 the amide head-to-head supramolecular motifs, represented by an R2(2) (8) designator, are observed, while in 3 none of the typical amide motifs were found. While the IR data suggests the polymeric structures for 2 and 4 in the solid state, all the NMR spectra agree with the monomeric structure of the compounds in the solution.

A Combined SNIFTIRS and XANES Study of Electrically Polarized Copper Electrodes in DMSO and DMF Solutions of Cyanate (NCO−), Thiocyanate (NCS−) and Selenocyanate (NCSe−) Ions

A SNIFTIRS (subtractively normalized interfacial Fourier transform infrared spectroscopy) and X-ray absorption spectroscopy (XAS) study of electrically polarized copper electrodes in six polar aprotic solvent-based systems is presented. In the systems investigated, i.e. dimethyl formamide (DMF) and dimethyl sulfoxide (DMSO) solutions containing pseudohalide species of cyanate (NCO−), thiocyanate (NCS−) and selenocyanate (NCSe−) codissolved with tetrabutylammonium perchlorate (TBAP), Cu was found to dissolve over a wide range of potentials to produce the corresponding Cu(I) pseudohalide and/or Cu(II) pseudohalide complex ion species. Insoluble deposited films were also observed at higher anodic applied potentials, thought to be CuSCN in the Cu/NCS−/DMSO or DMF systems, and solid K(SeCN)3 in the Cu/NCSe−/DMSO or DMF systems respectively. The presence of the Cu(II) and/or Cu(I) oxidation states in complexes formed by polarization in Cu/pseudohalide ion systems in DMSO was clearly proven using XAS of cell solutions sampled after SNIFTIRS/electrical polarization experiments. In addition, Fourier transform infrared (FTIR) and X-ray absorption near edge spectroscopy (XANES) data obtained from model solutions prepared from mixing Cu(I) and/or Cu(II) salts with the respective pseudohalide ions in DMF and DMSO confirmed the speciation observed in the electrochemical experiments.

Pseudohalide manganese(II) complexes of 2-hydroxymethylbenzimidazole – Synthesis, spectroscopy, X-ray structure and magnetic properties

Three new manganese(II) complexes of 2-hydroxymethylbenzimidazole [Mn(hmbzim)2(NCS)2] (1), [Mn2(hmbzim)4(μ1,1-N3)2](NO3)2 (2) and [Mn(hmbzim)2(dca)2]n (3) were synthesized and characterised. On the basis of structural data, the influence of pseudohalide ions on a final complex structure and role of weak intermolecular interactions in creation of molecular architecture have been discussed. The structure 1 consists of the mononuclear molecules [Mn(hmbzim)2(NCS)2] assembled via O–H⋯S and N–H⋯S hydrogen bonds into three dimensional supramolecular network The reaction with using of sodium azide resulted in formation of 0D dimeric structure of 2, whereas the complex 3 incorporating dicyanamide ions displays two-dimensional coordination framework. Magnetic measurements revealed ferromagnetic coupling (J=0.82(1)cm−1) inside the dimer of 2 and weak antiferromagnetic coupling (J=−0.37(1) cm−1) in 2D lattice of 3. The complex 1 indicated a very small antiferromagnetic interaction between MnII ions transmitted in the crystal lattice.

In Situ IR Study of the Anodic Polarization of Gold Electrodes in Polar Aprotic Solvents: DMSO and DMF Solutions of Cyanate, Thiocyanate and Selenocyanate Ions

Subtractively normalised Fourier transform infrared spectroscopic (SNIFTIRS) studies combined with volammetric and supporting model solution studies have conclusively shown that Au electrodes anodically polarized in DMSO and DMF solutions containing the pseudohalide ions: cyanate, thiocyanate and selenocyanate with tetrabutylammonium perchlorate as supporting electrolyte dissolve to form Au(I) pseudohalide complex ions (i.e. [Au(NCO)2]−, [Au(SCN)2]− and [Au(SeCN)2]−. This work has demonstrated the significance of the Au(I) oxidation state which occurs after applied voltages of +500 mV(AgCl/Ag) in the little characterized electrochemistry of this metal in polar aprotic solvents, DMSO and DMF The Au(I) species observed electrochemically by SNIFTIRS were confirmed by independent preparation in DMSO/DMF containing mixtures of KAuBr4 and the pseudohalide salt (KOCN/NaSCN/KSeCN) and exploiting fortuitous redox chemistry where Au(I) formed spontaneously. The model solutions examined by transmission FTIR and ESI-MS confirmed the existence of the Au(I) species posited in the SNIFTIRS experiments but additionally revealed other interesting side reactions occurring in the model solutions.

Anodically Polarized Nickel Electrodes in DMSO or DMF Solutions of Pseudohalide Ions: IR Spectroelectrochemical Studies

A novel subtractively normalized interfacial Fourier transform infrared spectroscopic (SNIFTIRS) investigation of anodically polarized nickel electrodes in pseudohalide-containing DMF or DMSO solutions (i.e. OCN−, SCN−, SeCN−), in supporting electrolyte, tetrabutylammonium perchlorate (TBAP), is presented. In general, the data showed that nickel demonstrated irreversible anodic dissolution in all solutions studied at very high values of the applied potential, > +500 mV (AgCl/Ag). The predominant speciation of nickel in these systems was as complex ions consisting of Ni2+ ion complexed to pseudohalide ions and solvent molecules. Insoluble films and dissolved CO2 were also detected, though mostly in the Ni/OCN− systems studied. Ni(II)/pseudohalide complex ion species detected were modeled using solutions containing Ni2+ ion mixed with pseudohalide ion in different mole ratios. In general, the Ni/OCN− electrochemical system behaved differently relative to those of Ni/SCN− and Ni/SeCN− due to the difference in colors observed in cell solutions after SNIFTIRS experiments which was mirrored in the model solutions. Ni(II)-cyanate species had a different, coordination geometry and gave a characteristic bright blue color due possibly to Ni(NCO)42− ion while Ni(II) thiocyanate and selenocyanate complex ion species had octahedral coordination geometries containing solvent and one coordinated pseudohalide ion and formed greeny yellow solutions.

A Triple-Stranded Ladder-Type Coordination Polymer

Stepwise synthesis and structural characterization of one-dimensional coordination polymers whose topologies depend on the anions are reported. A simple ladder-type precursor, {[Ag2(L)2](ClO4)2}n (1), was prepared by the reaction of bis(4-pyridylmethyl)sulfide (L) with AgClO4. Treatment of 1 with potassium thiocyanate and potassium cyanide afforded a twisted ribbon-type chain of type [Ag(L)SCN]n (2) and a triple-rail ladder of type [Ag3(L)2(CN)3]n (3), respectively. The result demonstrates that replacement of the noncoordinated perchlorate anions by pseudohalide ions in the coordination sphere of 1 plays a crucial role in determining the structures of the resulting species.

Pseudohalogenido complexes of iron-2,2′-bidipyrrins

The chlorido iron(III) complex of octaethyl-2,2′-bidipyrrin has been transformed to a series of pseudohalide complexes by ligand exchange reactions with azide, cyanate, thiocyanate and selenocyanate anions. All new complexes show the expected N-coordination of the axial ligand to the iron(III) center. In the solid state, all four species display an intermediate spin (S = 3/2) ground state, with a gradual increase of a high spin (S = 5/2) contribution at elevated temperatures for the members with the smallest ligand field strengths, i.e. the cyanato and the azido derivatives. In solution, proton NMR, and in particular IR spectroscopic studies support the interpretation of a high-spin state at ambient temperature throughout the series. The dependency of the spin state on the crystalline or dissolved state thus resembles that found for a similar series of halide derivatives before. In dichloromethane solution, the thiocyanato and selenocyanato complexes are very sensitive to aerial oxidation, forming oxacorrole and thiacorrole complexes as the only isolated products. These complexes show a S = 3/2 spin state in the solid as well as in solution, and their structural analyses prove the expected strong π-binding of the linear pseudohalide ion to the iron(III) central metal.

Acetaminophen (paracetamol) inhibits myeloperoxidase-catalyzed oxidant production and biological damage at therapeutically achievable concentrations

The heme peroxidase enzyme myeloperoxidase (MPO) is released by activated neutrophils and monocytes, where it uses hydrogen peroxide (H 2O 2) to catalyze the production of the potent oxidants hypochlorous acid (HOCl), hypobromous acid (HOBr) and hypothiocyanous acid (HOSCN) from halide and pseudohalide (SCN −) ions. These oxidants have been implicated as key mediators of tissue damage in many human inflammatory diseases including atherosclerosis, asthma, rheumatoid arthritis, cystic fibrosis and some cancers. It is shown here that acetaminophen (paracetamol), a phenol-based drug with analgesic and antipyretic actions, is an efficient inhibitor of HOCl and HOBr generation by isolated MPO–H 2O 2–halide systems. With physiological halide concentrations, acetaminophen concentrations required for 50% inhibition of oxidant formation (IC 50) were 77 ± 6 μM (100 mM Cl −) and 92 ± 2 μM (100 mM Cl − plus 100 μM Br −), as measured by trapping of oxidants with taurine. The IC 50 for inhibition of HOCl generation by human neutrophils was ca. 100 μM. These values are lower than the maximal therapeutic plasma concentrations of acetaminophen (≤150 μM) resulting from typical dosing regimes. Acetaminophen did not diminish superoxide generation by neutrophils, as measured by lucigenin-dependent chemiluminescence. Inhibition of HOCl production was associated with the generation of fluorescent acetaminophen oxidation products, consistent with acetaminophen acting as a competitive substrate of MPO. Inhibition by acetaminophen was maintained in the presence of heparan sulfate and extracellular matrix, materials implicated in the sequestration of MPO at sites of inflammation in vivo. Overall, these data indicate that acetaminophen may be an important modulator of MPO activity in vivo.

Structural characterisation of mononuclear zinc(ii) complexes of 4-methyl-3,5-di(2-pyridyl)-4H-1,2,4-triazole with three-atom co-ligands: [ZnII(medpt)2X]ClO4 (X = NCS−, N3 −, NO2 −)

The reaction of 4-methyl-3,5-di(2-pyridyl)-4H-1,2,4-triazole (medpt) with Zn(ClO4)2·6H2O and NaSCN, NaN3 or NaNO2 in a 2:1:1 molar ratio in MeOH/H2O (9:1) affords the mononuclear complexes [ZnII(medpt)2(NCS)]ClO4, [ZnII(medpt)2(N3)]ClO4 and [ZnII(medpt)2(NO2)]ClO4, respectively. All three complexes have been structurally characterised and found to feature unusual coordination polyhedra for 3,5-di(2-pyridyl)-4H-1,2,4-triazole complexes. In [ZnII(medpt)2(NCS)]ClO4 and [ZnII(medpt)2(N3)]ClO4, the zinc atom resides within a distorted square-pyramidal N5 coordination sphere [τ = 0.22 and 0.04, respectively] with two bidentate medpt ligands bound equatorially and the pseudohalide ion coordinating as a unidentate co-ligand in the apical position. In contrast, the NO2− ion in [ZnII(medpt)2(NO2)]ClO4 acts as a bidentate ligand, which leads to a strongly distorted N4O2 coordination environment about the metal centre.

The role of hypothiocyanous acid (HOSCN) in biological systems

Hypohalous acids (HOX), produced by peroxidase-catalysed reactions of halide and pseudohalide ions with H2O2, play an important role in the human immune system. However, there is compelling evidence that these oxidants also mediate host tissue damage and contribute to the progression of a number of inflammatory diseases. Although it is well established that significant amounts of hypothiocyanous acid (HOSCN) are formed under physiological conditions, the reactions of this oxidant with host biological systems are relatively poorly characterized. It is generally accepted that HOSCN is a mild oxidant that reacts selectively with thiols. However, it is becoming increasingly recognized that this selectivity can result in the induction of significant cellular damage, which may contribute to disease. This review will outline the formation and reactivity of HOSCN and the role of this oxidant in biological systems.

Tryptophan residues are targets in hypothiocyanous acid-mediated protein oxidation

Myeloperoxidase, released by activated phagocytes, forms reactive oxidants by catalysing the reaction of halide and pseudo-halide ions with H(2)O(2). These oxidants have been linked to tissue damage in a range of inflammatory diseases. With physiological levels of halide and pseudo-halide ions, similar amounts of HOCl (hypochlorous acid) and HOSCN (hypothiocyanous acid) are produced by myeloperoxidase. Although the importance of HOSCN in initiating cellular damage via thiol oxidation is becoming increasingly recognized, there are limited data on the reactions of HOSCN with other targets. In the present study, the products of the reaction of HOSCN with proteins has been studied. With albumin, thiols are oxidized preferentially forming unstable sulfenyl thiocyanate derivatives, as evidenced by the reversible incorporation of (14)C from HOS(14)CN. On consumption of the HSA (human serum albumin) free thiol group, the formation of stable (14)C-containing products and oxidation of tryptophan residues are observed. Oxidation of tryptophan residues is observed on reaction of HOSCN with other proteins (including myoglobin, lysozyme and trypsin inhibitor), but not free tryptophan, or tryptophan-containing peptides. Peptide mass mapping studies with HOSCN-treated myoglobin, showed the addition of two oxygen atoms on either Trp(7) or Trp(14) with equimolar or less oxidant, and the addition of a further two oxygen atoms to the other tryptophan with higher oxidant concentrations (> or = 2-fold). Tryptophan oxidation was observed on treating myoglobin with HOSCN in the presence of glutathione and ascorbate. Thus tryptophan residues are likely to be favourable targets for the reaction in biological systems, and the oxidation products formed may be useful biomarkers of HOSCN-mediated protein oxidation.

Precise Investigation of the Axial Ligand Substitution Mechanism on a Hydrogenphosphato-Bridged Lantern-Type Platinum(III) Binuclear Complex in Acidic Aqueous Solution

Detailed equilibrium and kinetic studies on axial water ligand substitution reactions of the "lantern-type" platinum(III) binuclear complex, [Pt(2)(mu-HPO(4))(4)(H(2)O)(2)](2)(-), with halide and pseudo-halide ions (X(-) = Cl(-), Br(-), and SCN(-)) were carried out in acidic aqueous solution at 25 degrees C with I = 1.0 M. The diaqua Pt(III) dimer complex is in acid dissociation equilibrium in aqueous solution with -log K(h1) = 2.69 +/- 0.04. The consecutive formation constants of the aquahalo complex () and the dihalo complex () were determined spectrophotometrically to be log = 2.36 +/- 0.01 and log = 1.47 +/- 0.01 for the reaction with Cl(-) and log = 2.90 +/- 0.04 and log = 2.28 +/- 0.01 for the reaction with Br(-), respectively. In the kinetic measurements carried out under the pseudo-first-order conditions with a large excess concentration of halide ion compared to that of Pt(III) dimer (C(X)()- >> C(Pt)), all of the reactions proceeded via a one-step first-order reaction, which is a contrast to the consecutive two-step reaction for the amidato-bridged platinum(III) binuclear complexes. The conditional first-order rate constant (k(obs)) depended on C(X)()- as well as the acidity of the solution. From kinetic analyses, the rate-limiting step was determined to be the first substitution process that forms the monohalo species, which is in rapid equilibrium with the dihalo complex. The reaction with 4-penten-1-ol was also kinetically investigated to examine the reactivity of the lantern complex with olefin compounds.

Molecular and electronic structures by design: tuning symmetrical and unsymmetrical linear trichromium chains.

The preparation, properties, and crystal structures of 12 trichromium extended metal atom chain (EMAC) compounds of the type Cr(3)(L)(4)X(2) (L = equatorial ligands dipyridylamide (dpa) or di-4,4'-ethyl-2,2'-pyridylamide (depa), and X = axial ligands, e.g., halide or pseudohalide ions) with large variations in metal-metal distances are reported here. These complexes, which belong to a broad class of fundamentally interesting trinuclear molecules over which the electrons may or may not be delocalized, pose significant theoretical and experimental challenges which are dealt with in this report. Complexes with strongly donating axial or equatorial ligands tend to favor a symmetrical (D(4)) molecular structure, while more weakly donating ligands give rise to unsymmetrical (C(4)) structures; the physical properties of these two classes of compounds are discussed fully, and important comparisons with a reported DFT model of the electronic structures of the compounds are made.

Synthesis and crystal structure of two dimeric cadmium(II) complexes bonded with pseudohalides, 1.1 and 1.3 bonding

Abstract Two different complexes were obtained from (dmpp) and Cd(II) ions with the aid of pseudohalide ions in non-aqueous solvents. The dinuclear complex formed with thiocyanate ions show, using XRD, to posses two 1.3 bond μ bridges [CdL(SCN)2]2. The other dinuclear complex was also seen to form with cyanate ions but with the μ-bridge in a 1.1 position [CdL(OCN)2]. All Cd atoms are located in a distorted octahedral environment in 1 and 2 complexes. The Cd…Cda distances are 6.032(4) Å in 1 and 3.704(3) Å in 2, respectively. The N—C—S and O—C—N angles are approximately linear as 178.1(3) and 178.6(3)° in 1 and 177.2(5) and 176.9(7)° in 2, respectively. The Cd—(μ N,S-NCS)2—Cda bonds form a zig-zag structure in 1 and the Cd—(μ O,N-OCN)2—Cda bonds form a distorted square planar in 2.

Reorientation and vibrational energy relaxation of pseudohalide ions confined in reverse micelle water pools

Reorientation and vibrational energy relaxation times have been measured by ultrafast transient polarization IR spectroscopy for the antisymmetric stretching band in the 2000–2200 cm−1 region of pseudohalide ions, N3−, NCO−, and NCS−, confined in nanosize water pools of reverse micelles (RMs). The RMs are composed of nonionic nonylphenyl poly-oxyethylene surfactant in cyclohexane. Vibrational energy relaxation times (T1) of the NCO− and NCS− ions are about three times longer in small RMs compared to bulk water, similar to our earlier results on the N3− ion [J. Chem. Phys. 118, 7074 (2003)]. The longer T1 times are attributed to the reduced interaction between the ions and water molecules due to confinement effects and hydration of the surfactant headgroups by water molecules. Reorientation times (TR) of the N3− and NCS− ions are found to be more than one order of magnitude longer in small RMs than in bulk H2O. The observed longer TR times support the notion that water molecules inside RMs have very restricted mobility. As the water pool becomes larger with increasing water content, the interior water is less affected by the interface and bulk water properties reappear, leading to shorter T1 and TR times.

In situ infrared spectroelectrochemical studies of the corrosion of a nickel electrode as a function of applied potential in cyanate, thiocyanate, and selenocyanate solutions

This paper presents the first subtractively normalized interfacial Fourier transform infrared spectroscopic (SNIFTIRS) study of the corrosion system Ni/XCN − (X=O, S, Se), pH 11, [XCN −]=0.05 mol L −1, supporting electrolyte 0.1 mol L −1 KNO 3, for a nickel electrode as a function of applied potential. Cyclic voltammograms, in situ infrared spectra, and current–potential data (recorded while the infrared spectral acquisition was in progress) were recorded for a nickel electrode in a three-electrode thin-layer cell containing the pseudohalides OCN −, SCN −, or SeCN − ions at pH 11 in a supporting electrolyte of KNO 3. In general, the data showed that all of the pseudohalide ions studied caused corrosion of the nickel electrode by forming the respective nickel–pseudohalide complex ion species as the potential was stepped anodically. Two of the ions, SCN − and SeCN −, caused surface modifications to the electrode which influenced the electrochemical reactions with respect to CO 2 formation. The Ni/SeCN − system, for instance, exhibited signs of instability during the spectroelectrochemical experiment, red-brown coatings observed on the electrode caused by the decomposition of the selenocyanate ion to colloidally dispersed elemental selenium. The selenium coated the electrode, hence modifying the surface and consequently the electrochemistry, by causing the “early” appearance of CO 2-associated IR peaks in SNIFTIRS spectra recorded from the electrode system at potentials lower than those for the Ni/OCN − system. In contrast, CO 2 formation at the electrode surface was not observed in the Ni/SCN − system, which was likely to have been caused by nickel sulfide poisoning of the electrode surface. In the Ni/SCN − and Ni/SeCN − systems, IR spectra also indicated the buildup of Ni(SCN) 2 and Ni(SeCN) 2 salts in the thin layer by the appearance of a peak at ca. 2165 cm −1 at anodic values of the applied potential.

Chemistry in Cages: Dinucleating Azacryptand Hosts and Their Cation and Anion Cryptates

This experiment involves the synthesis of an iminocryptand ligand, the investigation of its fluxional NMR spectrum, and the generation of its aerobically stable dicopper(I) cryptate, whose NMR spectrum reflects the conformational change from divergent in the free cryptand to convergent in the cryptate. A μ-hydroxo dicopper(II) cryptate showing strong antiferromagnetic interaction can be made if the synthesis is carried out quickly enough to avert solvolytic ring-opening. Borohydride reduction of the ligand generates the aminocryptand host, which has the capacity to stabilize the +2 in preference to the +1 redox state of copper. The pseudohalide ion cyanate can be accommodated in cascade fashion between the Cu2+ ions in the aminocryptate. This markedly affects the infrared spectrum of the pseudohalide guest, but not the magnetic susceptibility of the Cu2+ paramagnets. Finally an anion cryptate is made. The cryptands and cryptates have been structurally characterized; their structures can be accessed online to assist understanding of their spectroscopic and magnetic properties. As an optional extension, an ion-selective electrode based on the aminocryptand can be made and tested for response to Cu2+ in the presence and absence of the competing cation Zn2+.

Polymeric octahedral and monomeric tetrahedral Group 12 pseudohalogeno (NCX −: X=O, S, Se) complexes of 4-( N, N-dimethylamino)pyridine

A series of new pseudohalogeno complexes of Zn(II), Cd(II) and Hg(II) with 4-( N, N-dimethylamino)pyridine (4-dmap) has been prepared. The compounds Zn(NCS) 2L 2 ( 1), Cd(NCS) 2L 2 ( 2a), Hg 1.5(NCS) 3L 2 ( 3), Zn(NCO) 2L 2 ( 4), Cd(NCO) 2L 2 ( 5), Hg(NCO) 2L ( 6), Zn(NCSe) 2L 2 ( 7) and Cd(NCSe) 2L 2 ( 8a) (L=4-dmap) were characterized by elemental analyses, mid and far IR, 1H and 13C NMR spectroscopy, and differential scanning calorimetry. The structures of 1, 2a, 4 and 8a have been confirmed by X-ray crystallography. In addition, molecular geometries of Cd(NCS) 2L 2·2DMSO ( 2b) and Cd(NCSe) 2L 2·2DMSO ( 8b) have been determined by X-ray crystallography. Compounds 1 and 4 consist of monomeric units in which the Zn(II) atoms are tetrahedrally surrounded by two N-donating pseudohalide ions and two 4-dmap moities, coordinating at the endocyclic nitrogen atom. Complexes 2a and 8a are isostructural polymers comprised of chains of the monomeric unit MX 2N 2, where X is NCS − or NCSe −. Within each monomeric unit one pseudohalide ligand is bound through the chalcogen atom; the other through the nitrogen atom. The polymer chain is a distorted octahedron sharing common edges through nearly linear bridging pseudohalide groups displaced trans to each other; the two 4-dmap ligands are also displaced trans to each other. Complexes 2b and 8b are isostructural monomeric units, in which the central Cd(II) atom exhibits an N 4O 2 octahedral geometry.

Ternary Complexation of Manganese(II) and Cadmium(II) with 1,10-Phenanthroline and Halide or Thiocyanato Ions in N,N-Dimethylformamide

Ternary complexation of manganese(II) and cadmium(II) with1,10-phenanthroline (phen), and halide (chloride, bromide) or pseudohalide (thiocyanate) ions asligands has been studied by precise titration calorimetry inN,N-dimethylformamide (DMF) at 25°C. Data obtained for the ternary system were analyzed onthe basis of thermodynamic parameters for the binary MII-phen and MII-X-(M= Mn or Cd, X = Cl, Br, or SCN) systems. In the binary MII-phen system,formation of a series of mono- to tris- 1,10-phenanthroline complexes isestablished and the formation constants and reaction enthalpies and entropies areobtained. Thermodynamic parameters of complexation for the MII-X- systemshave previously been obtained. All titration curves obtained in the ternary systemsare explained well in terms of formation of mononuclear complexes of the type[MX m (phen) N ](2−m)+. With manganese(II), formation of [MnX(phen)]+,[MnX2(phen)], [MnX3(phen)]−,[MnX(phen)2]+, and[MnX2(phen)] is establishedfor X = Cl and SCN, and [MnX(phen)]+, [MnX2(phen)], [MnX(phen)2]+, and[MnX2(phen)2] for X = Br. With cadmium(II), formation of [CdX(phen)]+,[CdX2(phen)], [CdX3(phen)]−, [CdX(phen)2]+, and [CdX2(phen)2], is establishedfor X = Cl and Br, and [CdX(phen)]+, [CdX2(phen)], [CdX(phen)2]+, and[CdX2(phen)2] for X = SCN. The formation constants, and reaction enthalpiesand entropies are obtained. The results are discussed in comparison with thosefor the corresponding 2,2′-bipyridine systems.

Substitution and Redox Chemistry of [Bu(4)N](2)[Ta(6)Cl(12)(OSO(2)CF(3))(6)

Two sequential electrochemical reductions occur for the cluster anion [Ta(6)Cl(12)(OSO(2)CF(3))(6)](2)(-) at 0.89 and 0.29 V vs Ag/AgCl, with the generation [Ta(6)Cl(12)(OSO(2)CF(3))(6)](3)(-) and [Ta(6)Cl(12)(OSO(2)CF(3))(6)](4)(-). Chemical reduction of [Ta(6)Cl(12)(OSO(2)CF(3))(6)](2)(-) by ferrocene produces [Ta(6)Cl(12)(OSO(2)CF(3))(6)](3)(-) with the concomitant shift of the nu(SO(2)) stretch from 1002 to 1018 cm(-)(1). Reaction of [Bu(4)N](2)[Ta(6)Cl(12)(OSO(2)CF(3))(6)] (1) with [Bu(4)N]X (X = Cl, Br, I, NCS) occurs by reduction and substitution, yielding [Bu(4)N](3)[Ta(6)Cl(12)X(6)], where the clusters with X = Br, I, and NCS are new. Spectroscopic (IR and UV-vis) evidence indicates that the reduced cluster core {Ta(6)Cl(12)}(2+) is produced in reaction mixtures of 1 with the halide and pseudohalide ions. Concomitant substitution of the triflate ligands of 1 by X(-) occurs and the rates for the overall reduction and substitution increase in the order X(-) = Cl(-) < Br(-) < NCS(-) < I(-) < CN(-). Reduction of 1 with ferrocene followed by addition of [Bu(4)N]O(2)CCH(3) produces the new cluster [Ta(6)Cl(12)(O(2)CCH(3))(6)](3)(-) isolated as the tetrabutylammonium salt. Cyclic voltammetry and UV-vis spectroscopy on the new clusters [Bu(4)N](3)[Ta(6)Cl(12)X(6)] (X = Br, I, NCS, and O(2)CCH(3)) are reported. Crystal data for [Bu(4)N](3)[Ta(6)Cl(12)(NCS)(6)].CH(2)Cl(2): monoclinic, space group, P2(1)/c (No. 14); a = 25.855(6) Å, b = 21.843(6) Å, c = 16.423(3) Å; beta = 100.03(2) degrees; V = 9133(3) Å(3); Z = 4.