Equatorial Perturbation Driven Reaction Bifurcation in Non-Heme Iron Complexes for Chlorite Oxidation

Chlorine oxyanions have various applications, such as bleaching and oxidizers in rocket fuels. However, their high solubility in water and long environmental lifetimes have led to ecological concerns, especially regarding drinking water quality. This study focuses on the conversion of chlorite to chlorine dioxide, which is of significant interest as it exhibits superior antimicrobial activity and generates less harmful byproducts for water treatment. Two nonheme iron(II) complexes capable of producing chlorine dioxide from chlorite at room temperature and pH 5.0 are presented. These complexes oxidize chlorite through high-valent iron (IV)-oxo intermediates formed in-situ. The study establishes second-order rate constants for chlorite oxidation and investigates the effects and mechanisms involved by substituting a methyl group in the secondary coordination sphere of the Fe^IV(O)(N4Py) system. By employing kinetic analysis and spectroscopic investigations, the crucial elements for the reaction mechanism in chlorite oxidation are identified. These findings pave the way for future advancements in this field.     

Oxidation of toluidine blue by chlorite in acid and mechanisms of the uncatalyzed and Ru(III)-catalyzed reactions: a kinetic approach

The complex mechanism of the uncatalyzed and Ru(III)-catalyzed oxidation of toluidine blue [(7-amino-8-methylphenothiazin-3-ylidene)dimethyl ammonium chloride, TB(+)Cl(-)] (λ(max) = 626 nm) by acidic chlorite is elucidated by a kinetic approach. Both the uncatalyzed and catalyzed reactions had a first-order dependence on the initial ClO(2)(-) and H(+) concentrations ([ClO(2)(-)](0) and [H(+)](0), respectively). The catalyzed reaction had a first-order dependence on the initial Ru(III) concentration ([Ru(III)](0)). The overall reaction of toluidine blue and chlorite ion was as follows: TB(+) + 5ClO(2)(-) + H(+) = P + 2ClO(2) + 2HCOOH + 3Cl(-) + H(2)O, where P is (7-amino-8-methyl-5-sulfoxophenothiazin-3-ylidene)amine. Consistent with the experimental results, the pertinent reaction mechanisms are proposed.     

Oxyhalogen-sulfur chemistry: kinetics and mechanism of oxidation of N-acetylthiourea by chlorite and chlorine dioxide

The oxidation reactions of N-acetylthiourea (ACTU) by chlorite and chlorine dioxide were studied in slightly acidic media. The ACTU-ClO(2)(-) reaction has a complex dependence on acid with acid catalysis in pH > 2 followed by acid retardation in higher acid conditions. In excess chlorite conditions the reaction is characterized by a very short induction period followed by a sudden and rapid formation of chlorine dioxide and sulfate. In some ratios of oxidant to reductant mixtures, oligo-oscillatory formation of chlorine dioxide is observed. The stoichiometry of the reaction is 2:1, with a complete desulfurization of the ACTU thiocarbamide to produce the corresponding urea product: 2ClO(2)(-) + CH(3)CONH(NH(2))C=S + H(2)O --> CH(3)CONH(NH(2))C=O + SO(4)(2-) + 2Cl(-) + 2H(+) (A). The reaction of chlorine dioxide and ACTU is extremely rapid and autocatalytic. The stoichiometry of this reaction is 8ClO(2)(aq) + 5CH(3)CONH(NH(2))C=S + 9H(2)O --> 5CH(3)CONH(NH(2))C=O + 5SO(4)(2-) + 8Cl(-) + 18H(+) (B). The ACTU-ClO(2)(-) reaction shows a much stronger HOCl autocatalysis than that which has been observed with other oxychlorine-thiocarbamide reactions. The reaction of chlorine dioxide with ACTU involves the initial formation of an adduct which hydrolyses to eliminate an unstable oxychlorine intermediate HClO(2)(-) which then combines with another ClO(2) molecule to produce and accumulate ClO(2)(-). The oxidation of ACTU involves the successive oxidation of the sulfur center through the sulfenic and sulfinic acids. Oxidation of the sulfinic acid by chlorine dioxide proceeds directly to sulfate bypassing the sulfonic acid. Sulfonic acids are inert to further oxidation and are only oxidized to sulfate via an initial hydrolysis reaction to yield bisulfite, which is then rapidly oxidized. Chlorine dioxide production after the induction period is due to the reaction of the intermediate HOCl species with ClO(2)(-). Oligo-oscillatory behavior arises from the fact that reactions that form ClO(2) are comparable in magnitude to those that consume ClO(2), and hence the assertion of each set of reactions is based on availability of reagents that fuel them. A computer simulation study involving 30 elementary and composite reactions gave a good fit to the induction period observed in the formation of chlorine dioxide and in the autocatalytic consumption of ACTU in its oxidation by ClO(2).     

Radical autoxidation and autogenous O2 evolution in manganese-porphyrin catalyzed alkane oxidations with chlorite

A manganese porphyrin catalyst employing chlorite (ClO(2)(-)) as a "shunt" oxidant displays remarkable activity in alkane oxidation, oxidizing cyclohexane to cyclohexanol and cyclohexanone with >800 turnover numbers. The ketone is apparently formed without the intermediacy of alcohol and accounts for an unusually large fraction of the product ( approximately 40%). Radical scavenging experiments indicate that the alkane oxidation mechanism involves both carbon-centered and oxygen-centered radicals. The carbon-radical trap CBrCl(3) completely suppresses cyclohexanone formation and reduces cyclohexanol turnovers, while the oxygen-radical trap Ph(2)NH inhibits all oxidation until it is consumed. These observations are indicative of an autoxidation mechanism, a scenario further supported by TEMPO inhibition and (18)O(2) incorporation into products. However, similar cyclohexane oxidation activity occurs when air is excluded. This is explained by mass spectrometric and volumetric measurements showing catalyst-dependent O(2) evolution from the reaction mixture. The catalytic disproportionation of ClO(2)(-) into Cl(-) and O(2) provides sufficient O(2) to support an autoxidation mechanism. A two-path oxidation scheme is proposed to explain all of the experimental observations. The first pathway involves manganese-porphyrin catalyzed decomposition of ClO(2)(-) into both O(2) and an unidentified radical initiator, leading to classical autoxidation chemistry providing equal amounts of cyclohexanol and cyclohexanone. The second pathway is a "rebound" oxygenation involving a high-valent manganese-oxo intermediate, accounting for the excess of alcohol over ketone. This system highlights the importance of mechanistic studies in catalytic oxidations with highly reactive oxidants, and it is unusual in its ability to sustain autoxidation even under apparent exclusion of O(2).     

Kinetics and mechanism of catalytic decomposition and oxidation of chlorine dioxide by the hypochlorite ion

The oxidation of ClO(2) by OCl(-)is first order with respect to both reactants in the neutral to alkaline pH range: -d[ClO(2)]/dt = 2k(OCl)[ClO(2)][OCl(-)]. The rate constant (T = 298 K, mu = 1.0 M NaClO(4)) and activation parameters are k(OCl) = 0.91 +/- 0.02 M(-1) s(-1), DeltaH = 66.5 +/- 0.9 kJ/mol, and DeltaS(++) = -22.3 +/- 2.9 J/(mol K). In alkaline solution, pH > 9, the primary products of the reaction are the chlorite and chlorate ions and consumption of the hypochlorite ion is not observed. The hypochlorite ion is consumed in increasing amounts, and the production of the chlorite ion ceases when the pH is decreased. The stoichiometry is kinetically controlled, and the reactants/products ratios are determined by the relative rates of the production and consumption of the chlorite ion in the ClO(2)/OCl(-) and HOCl/ClO(2)(-) reactions, respectively.     

Oxidation of ammonia in osmium polypyridyl complexes

The oxidations of cis- and trans-[OsIII(tpy)(Cl)2(NH3)](PF6), cis-[OsII(bpy)2(Cl)(NH3)](PF6), and [OsII(typ)(bpy)(NH3)](PF6)2 have been studied by cyclic voltammetry and by controlled-potential electrolysis. In acetonitrile or in acidic, aqueous solution, oxidation is metal-based and reversible, but as the pH is increased, oxidation and proton loss from coordinated ammonia occurs. cis- and trans-[OsIII(tpy)(Cl)2(NH3)](PF6) are oxidized by four electrons to give the corresponding OsVI nitrido complexes, [OSVI(typ)(Cl)2(N)]+. Oxidation of [Os(typ)(bpy)(NH3)](PF6)2 occurs by six electrons to give [Os(tpy)(bpy)(NO)](PF6)3. Oxidation of cis-[OsII(bpy)2(Cl)(NH3)](PF6) at pH 9.0 gives cis-[OsII(bpy)2(Cl)(NO)](PF6)2 and the mixed-valence form of the mu-N2 dimer [cis-[Os(bpy)2(Cl)2[mu-N2)](PF6)3. With NH4+ added to the electrolyte, cis-[OsII(bpy)2(Cl)(N2)](PF6) is a coproduct. The results of pH-dependent cyclic voltammetry measurements suggest OsIV as a common intermediate in the oxidation of coordinated ammonia. For cis- and trans-[OsIII(tpy)(Cl)2(NH3)]+, OsIV is a discernible intermediate. It undergoes further pH-dependent oxidation to [OsVI(tpy)(Cl)2(N)]+. For [OsII(tpy)(bpy)(NH3)]2+, oxidation to OsIV is followed by hydration at the nitrogen atom and further oxidation to nitrosyl. For cis-[OsII(bpy)2(Cl)-(NH3)]+, oxidation to OsIV is followed by N-N coupling and further oxidation to [cis-[Os(bpy)2(Cl)2(mu-N2)]3+. At pH 9, N-N coupling is competitive with capture of OsIV by OH- and further oxidation, yielding cis-[OsII(bpy)2(Cl)(NO)]2+.     

S-oxygenation of thiocarbamides II: Oxidation of trimethylthiourea by chlorite and chlorine dioxide

The kinetics of the oxidation of a substituted thiourea, trimethylthiourea (TMTU), by chlorite have been studied in slightly acidic media. The reaction is much faster than the comparable oxidation of the unsubstituted thiourea by chlorite. The stoichiometry of the reaction was experimentally deduced to be 2ClO2- + Me2N(NHMe)C=S + H2O --> 2Cl- + Me2N(NHMe)C=O + SO4(2-) + 2H+. In excess chlorite conditions, chlorine dioxide is formed after a short induction period. The oxidation of TMTU occurs in two phases. It starts initially with S-oxygenation of the sulfur center to yield the sulfinic acid, which then reacts in the second phase predominantly through an initial hydrolysis to produce trimethylurea and the sulfoxylate anion. The sulfoxylate anion is a highly reducing species which is rapidly oxidized to sulfate. The sulfinic and sulfonic acids of TMTU exists in the form of zwitterionic species that are stable in acidic environments and rapidly decompose in basic environments. The rate of oxidation of the sulfonic acid is determined by its rate of hydrolysis, which is inhibited by acid. The direct reaction of chlorine dioxide and TMTU is autocatalytic and also inhibited by acid. It commences with the initial formation of an adduct of the radical chlorine dioxide species with the electron-rich sulfur center of the thiocarbamide followed by reaction of the adduct with another chlorine dioxide molecule and subsequent hydrolysis to yield chlorite and a sulfenic acid. The bimolecular rate constant for the reaction of chlorine dioxide and TMTU was experimentally determined as 16 +/- 3.0 M(-1) s(-1) at pH 1.00.     

Electronic structure of oxidized complexes derived from cis-[Ru(II)(bpy)2(H2O)2]2+ and its photoisomerization mechanism

The geometry and electronic structure of cis-[Ru(II)(bpy)(2)(H(2)O)(2)](2+) and its higher oxidation state species up formally to Ru(VI) have been studied by means of UV-vis, EPR, XAS, and DFT and CASSCF/CASPT2 calculations. DFT calculations of the molecular structures of these species show that, as the oxidation state increases, the Ru-O bond distance decreases, indicating increased degrees of Ru-O multiple bonding. In addition, the O-Ru-O valence bond angle increases as the oxidation state increases. EPR spectroscopy and quantum chemical calculations indicate that low-spin configurations are favored for all oxidation states. Thus, cis-[Ru(IV)(bpy)(2)(OH)(2)](2+) (d(4)) has a singlet ground state and is EPR-silent at low temperatures, while cis-[Ru(V)(bpy)(2)(O)(OH)](2+) (d(3)) has a doublet ground state. XAS spectroscopy of higher oxidation state species and DFT calculations further illuminate the electronic structures of these complexes, particularly with respect to the covalent character of the O-Ru-O fragment. In addition, the photochemical isomerization of cis-[Ru(II)(bpy)(2)(H(2)O)(2)](2+) to its trans-[Ru(II)(bpy)(2)(H(2)O)(2)](2+) isomer has been fully characterized through quantum chemical calculations. The excited-state process is predicted to involve decoordination of one aqua ligand, which leads to a coordinatively unsaturated complex that undergoes structural rearrangement followed by recoordination of water to yield the trans isomer.     

Sorption of selenite onto chlorite considering mineral dissolution

In this study we investigated the sorption of selenite (SeO₃ ^2?) onto chlorite as a function of Se(IV) concentration, pH, and ionic strength. The sorption isotherm of Se(IV) onto chlorite was successfully presented by both the Langmuir isotherm and Tempkin equation although the Langmuir isotherm is somewhat better than the Tempkin equation. The sorption of Se(IV) onto chlorite was maintained to be constant at an acidic pH region, while the sorption decreased with an increasing pH at neutral and alkaline pH regions. However, the Se(IV) sorption onto chlorite was independent of the ionic strength of NaClO₄ solution. The amount of Se(IV) sorbed onto chlorite was significantly low compared to those of iron oxides such as apatite, goethite, hematite, and magnetite because of the lower content of Fe. We also investigated the effect of Fe(II) ions dissolved from chlorite on the Se(IV) sorption as a function of contact time. The chemical oxidation states of selenium sorbed onto chlorite surface were identified using X-ray absorption near edge structure (XANES) at the Pohang synchrotron light source. The amount of Fe(II) dissolved was increased by the contact time of 28 days but decreased after 28–56 days although the amount of dissolved Fe(II) ions was significantly small. This decrease of the dissolved Fe(II) may be due to the formation of Fe-oxyhydroxides such as ferrihydrite. The results of XANES measurements also showed that the Se(IV) sorbed onto chlorite was not reduced into Se(0) or Se(-II) even in the presence of Fe(II) ions in the solution because of the low Fe content of the chlorite although the mechanism was not clearly understood.     

Oxidative verdoheme formation and stabilization by axial isocyanide ligation

The effect of isocyanides as axial ligands on the formation and stability of verdoheme by oxidation has been examined. The reaction of [Fe(III)(OEPO)]2 with t-butyl isocyanide under dioxygen-free conditions results in the formation of (t-BuNC)2Fe(II)(OEPO*) with an electron paramagnetic resonance at g=2.009 with a peak-to-peak separation of 23.5 G at 4 K. (OEPO is the trianion of octaethyloxophlorin and OEPO* is the radical dianion obtained from OEPO by one-electron oxidation.) Exposure of chloroform solutions of either (2,6-xylylNC)2Fe(II)(OEPO*) or (t-BuNC)2Fe(II)(OEPO*) to dioxygen followed by the addition of ammonium hexafluorophosphate results in their transformation into the diamagnetic verdohemes, [(2,6-xylylNC)2Fe(II)(OEOP)](PF6) and [(t-BuNC)2Fe(II)(OEOP)](PF6), yields 68 and 70%, respectively. (OEOP is the anion of octaethyl-5-oxaporphyrin.) The oxidation reactions of (2,6-xylylNC)2Fe(II)(OEPO*) and (t-BuNC)2Fe(II)(OEPO*) have also been monitored by 1H NMR spectroscopy. No resonances due to paramagnetic products could be detected, the reactions appear to result only in the formation of the diamagnetic verdohemes, and the products are not susceptible to further oxidation.     

Catalytic oxidative ring opening of THF promoted by a carboxylate-bridged diiron complex, triarylphosphines, and dioxygen

The catalytic oxidation of triphenylphosphine in the presence of dioxygen by the diiron(II) complex [Fe(2)(micro-O(2)CAr(Tol))(2)(Me(3)TACN)(2)(MeCN)(2)](OTf)(2) (1), where (-)O(2)CAr(Tol) = 2,6-di(p-tolyl)benzoate and Me(3)TACN = 1,4,7-trimethyl-1,4,7-triazacyclononane, has been investigated. The corresponding diiron(III) complex, [Fe(2)(micro-O)(micro-O(2)CAr(Tol))(2)(Me(3)TACN)(2)](OTf)(2) (2), the only detectable iron-containing species during the course of the reaction, can itself promote the reaction. Phosphine oxidation is coupled to the catalytic oxidation of THF solvent to afford, selectively, the C-C bond-cleavage product 3-hydroxypropylformate, an unprecedented transformation. After consumption of the phosphine, solvent oxidation continues but results in the products 2-hydroperoxytetrahydrofuran, butyrolactone, and butyrolactol. The similarities of the reaction pathways observed in the presence and absence of catalyst, as well as (18)O labeling, solvent dependence, and radical probe experiments, provide evidence that the oxidation is initiated by a metal-centered H-atom abstraction from THF. A mechanism for catalysis is proposed that accounts for the coupled oxidation of the phosphine and the THF ring-opening reaction.     

Cd(2+) Complexation with P(CH(2)OH)(3), OP(CH(2)OH)(3), and (HOCH(2))(2)PO(2)(-): Coordination in Solution and Coordination Polymers

The coordination of Cd(2+) with P(CH(2)OH)(3) (THP) in methanol was followed by (31)P and (111)Cd NMR techniques. A cadmium-to-phosphine coordination ratio of 1:3 has been established, and effective kinetic parameters have been calculated. Air oxidation of THP in the presence of CdCl(2) at room temperature produces coordination polymer (3)(∞)[Cd(3)Cl(6)(OP(CH(2)OH)(3))(2)] (1). The same oxidation reaction at 70 °C gives another coordination polymer, (∞)[CdCl(2)(OP(CH(2)OH)(3))] (2). Complexes 1 and 2 are the first structurally characterized complexes featuring OP(CH(2)OH)(3) as a ligand that acts as a linker between Cd atoms. The addition of NaBPh(4) to the reaction mixture gives coordination polymer (∞)[Na(2)CdCl(2)(O(2)P(CH(2)OH)(2))(2)(H(2)O)(3)] (3) with (HOCH(2))(2)PO(2)(-) as the ligand. Coordination polymers 1-3 have been characterized by X-ray analysis, elemental analysis, and IR spectroscopy.     

FeCl3-activated oxidation of alkanes by [Os(N)O3]-

Although the ion [Os(VIII)(N)(O)(3)](-) is a stable species and is not known to act as an oxidant for organic substrates, it is readily activated by FeCl(3) in CH(2)Cl(2)/CH(3)CO(2)H to oxidize alkanes efficiently at room temperature. The oxidation can be made catalytic by using 2,6-dichloropyridine N-oxide as the terminal oxidant. The active intermediates in stoichiometric and catalytic oxidation are proposed to be [(O)(3)Os(VIII)N-Fe(III)] and [Cl(4)(O)Os(VIII)N-Fe(III)], respectively.     

亚氯酸盐-硫脲反应体系的非线性动力学

The reaction between chlorite and thiourea could display batch oligooscillation and CSTR oscillation of pH.Batch pH peak has the same character with pH oscillation in a CSTR.The oxidation of thiourea produced intermediates such as HOSC(NH)NH2,HO2SC(NH)NH2,HO3S(NH)NH2 and bisulfite.The valence change of sulfur has close relation with pH dynamics.Through the mechanistic analysis,a general model of sulfur(－ II) oxidation,which consists of negative hydrogen ion feedback(S(－ II) to S(0)),a transition process of S(0) to S(IV) and positive proton feedback from S(IV) to S(VI),could simulate batch oligooscillation and CSTR oscillation.This result is setting up a new channel to uncover the reaction mechanism and simulate the nonlinear phenomena in the reactions between chlorite and Sulfur(－ II).     

Water oxidation by mononuclear ruthenium complexes with TPA-based ligands

The synthesis, characterization, and water oxidation activity of mononuclear ruthenium complexes with tris(2-pyridylmethyl)amine (TPA), tris(6-methyl-2-pyridylmethyl)amine (Me(3)TPA), and a new pentadentate ligand N,N-bis(2-pyridinylmethyl)-2,2'-bipyridine-6-methanamine (DPA-Bpy) have been described. The electrochemical properties of these mononuclear Ru complexes have been investigated by both experimental and computational methods. Using Ce(IV) as oxidant, stoichiometric oxidation of water by [Ru(TPA)(H(2)O)(2)](2+) was observed, while Ru(Me(3)TPA)(H(2)O)(2)](2+) has much less activity for water oxidation. Compared to [Ru(TPA)(H(2)O)(2)](2+) and [Ru(Me(3)TPA)(H(2)O)(2)](2+), [Ru(DPA-Bpy)(H(2)O)](2+) exhibited 20 times higher activity for water oxidation. This study demonstrates a new type of ligand scaffold to support water oxidation by mononuclear Ru complexes.     

Coordinated hydrazone ligands as nucleophiles: reactions of Fe(papy)2

The diamagnetic iron(II) complexes of the hydrazone ligand pyridinecarboxaldehyde-2'-pyridylhydrazone (papyH) have been characterized by NMR, IR, UV-vis, and electrochemistry. The dication Fe(papyH)(2)(2+) undergoes reversible one-electron oxidation at 0.66 V vs internal ferrocene and shows a strong metal-ligand charge-transfer band in the visible region at 524 nm. Deprotonation with NaOH gives diamagnetic, neutral Fe(papy)(2) with an oxidation potential of -0.25 V vs internal ferrocene and a charge-transfer band at 603 nm. Fe(papy)(2) reacts with active alkylating agents to give dialkyl complexes Fe(papyR)(2)(2+) with spectroscopic properties similar to those of Fe(papyH)(2)(2+). Monitoring the alkylation by UV-vis reveals the intermediacy of a monoalkylated species.     

A manganese oxido complex bearing facially coordinating trispyridyl ligands--is coordination geometry crucial for water oxidation catalysis?

In this work the synthesis of the novel manganese complex [Mn(2)(III,III)(tpdm)(2)(μ-O)(μ-OAc)(2)](2+) (1) is reported, containing two manganese centres ligated to the unusual, facially coordinating, all-pyridine ligand tpdm (tris(2-pyridyl)methane). The geometric and electronic properties of complex 1 were characterised by X-ray crystallography, vibrational (IR and Raman) and optical spectroscopy (UV/Vis and MCD). Cyclic voltammograms of 1 showed a quasi-reversible oxidation event at 950 mV and an irreversible reduction wave at -250 mV vs. Ag/Ag(+). The redox behaviour of the compound was investigated in detail by UV/Vis- and X-band EPR-spectroelectrochemistry. Both electrochemical (+1200 mV) and chemical (tBuOOH) oxidations transform 1 into the singly oxidized di-μ-oxido species [Mn(2)(III,IV)(tpdm)(2)(μ-O)(2)(μ-OAc)](2+). Further electrochemical oxidation at the same potential results in the removal of a second electron to obtain a Mn(2)(IV,IV)-species. The ability of compound 1 to evolve O(2) was studied using different reaction agents. While reactions with both hydrogen peroxide and peroxomonosulfate yield O(2), homogeneous water-oxidation using Ce(IV) was not observed. Nevertheless, the oxidation reactions of 1 are very interesting model processes for oxidation state (S-state) transitions of the natural manganese water-oxidation catalyst in photosynthesis. However, despite its favourable coordination geometry and multielectron redox chemistry, complex 1 fails to be a catalytically active model for natural water-oxidation.     

Peroxydisulfate activation by [RuII(tpy)(pic)(H2O)]+. Kinetic, mechanistic and anti-microbial activity studies

The oxidation of [Ru(II)(tpy)(pic)H(2)O](+) (tpy = 2,2',6',2'-terpyridine; pic(-) = picolinate) by peroxidisulfate (S(2)O(8)(2-)) as precursor oxidant has been investigated kinetically by UV-VIS, IR and EPR spectroscopy. The overall oxidation of Ru(II)- to Ru(IV)-species takes place in a consecutive manner involving oxidation of [Ru(II)(tpy)(pic)H(2)O](+) to [Ru(III)(tpy)(pic)(OH)](+), and its further oxidation of to the ultimate product [Ru(IV)(tpy)(pic)(O)](+) complex. The time course of the reaction was followed as a function of [S(2)O(8)(2-)], ionic strength (I) and temperature. Kinetic data and activation parameters are interpreted in terms of an outer-sphere electron transfer mechanism. Anti-microbial activity of Ru(II)(tpy)(pic)H(2)O](+) complex by inhibiting the growth of Escherichia coli DH5α in presence of peroxydisulfate has been explored, and the results of the biological studies have been discussed in terms of the [Ru(IV)(tpy)(pic)(O)](+) mediated cleavage of chromosomal DNA of the bacteria.     

The extraordinary ability of guanidinate derivatives to stabilize higher oxidation numbers in dimetal units by modification of redox potentials: structures of Mo(2)(5+) and Mo(2)(6+) compounds

Full characterization of the first homologous series of dimolybdenum paddlewheel compounds having electronic configurations of the types sigma(2)pi(4)delta(x), x = 2, 1, 0, and Mo-Mo bond orders of 4, 3.5, and 3, respectively, has been accomplished with the guanidinate-type ligand hpp (hpp = the anion of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine). Essentially quantitative oxidation of Mo(2)(hpp)(4), 1, by CH(2)Cl(2) gives Mo(2)(hpp)(4)Cl, 2. The halide in 2 can be replaced by reaction with TlBF(4) to produce Mo(2)(hpp)(4)(BF(4)), 3. Further oxidation of 2 by AgBF(4) produces Mo(2)(hpp)(4)ClBF(4), 4. The change from bond order 4 (in 1) to 3.5 in Mo(2)(hpp)(4)Cl is accompanied by an increase in the Mo-Mo bond length of 0.061 to 2.1280(4) A. A further increase of 0.044 A in the Mo-Mo distance to 2.172(1) A is observed as the bond order decreases to 3 in 4. At the same time, the Mo-N distances decrease smoothly as the oxidation state of the Mo atoms increases. Electrochemical studies have shown two chemically reversible processes at very negative potentials, E(1)(1/2)= -0.444 V and E(2)(1/2)= -1.271 V versus Ag/AgCl. These correspond to the processes Mo(2)(6+/5+) and Mo(2)(5+/4+), respectively. The latter potential is displaced by over 1.5 V relative to those of the Mo(2)(formamidinate)(4) compounds and the first one has never been observed in such complexes. Thus, in surprising contrast to previously observed behavior of the dimolybdenum unit, when it is surrounded by the very basic guanidinate ligand hpp, there is an extraordinary stabilization of the higher oxidation numbers of the molybdenum atoms.     

Water exchange rates in the diruthenium mu-oxo ion cis,cis-[(bpy)(2)Ru(OH(2))](2)O(4+).

Addition of 2 equiv of Ce(4+) to the dimeric ruthenium mu-oxo ion cis,cis-[(bpy)(2)Ru(OH(2))](2)O(4+) (formal oxidation state III-III, subsequently denoted [3,3]) or addition of 1 equiv of Ce(4+) to the corresponding [3,4] ion gave near-quantitative conversion to the [4,4] ion, confirming our recent assignment of this oxidation state as an accumulating intermediate during water oxidation by the cis,cis-[(bpy)(2)Ru(O)](2)O(4+) ([5,5]) ion. The rates of water exchange at the cis-aqua positions in the [3,3] and [3,4] ions were investigated by incubating H(2)(18)O-enriched samples in normal water for predetermined times, then oxidizing them to the [5,5] state and measuring by resonance Raman (RR) spectroscopy changes in the magnitudes of the O-isotope sensitive bands at 780 and 818 cm(-1). These bands have been assigned to Ru=(18)O and Ru=(16)O stretching modes, respectively, for ruthenyl bonds formed by deprotonation of the aqua ligands upon oxidation to the [5,5] state. An intermediate accumulated during the course of the isotope exchange reaction that gave a [5,5] ion possessing both approximately 782 and approximately 812 cm(-1) bands; this spectrum was assigned to the mixed-isotope species, (bpy)(2)Ru((16)O)(16)ORu((18)O)(bpy)(2)(4+). Kinetic analysis of solutions at various levels of oxidation indicated that only the [3,3] ion underwent substitution; the exchange rate constant obtained in 0.5 M trifluoromethanesulfonic acid, 23 degrees C, was 7 x 10(-3) s(-1), which is (10(3)-10(5))-fold larger than rate constants measured for anation of monomeric (bpy)(2)Ru(III)X(H(2)O)(3+) ions bearing simple sigma-donor ligands (X).