(.mu.-Nitrido)((tetraphenylporphyrinato)iron)((phthalocyaninato)iron) and Its Fe-Ru Analog: Redox Behavior and Characterization of New Fe(IV)-Containing Species. X-ray Crystal Structure of [(THF)(TPP)Fe-N-FePc(H2O)](I5).cntdot.2THF

Porous Molecular Crystals Derived from Cofacial Porphyrin/Phthalocyanine Heterodimers

Porphyrin-based porous materials are of growing interest as heterogeneous catalysts especially for reactions that are of importance to sustainability. Here we demonstrate that porous molecular crystals can be prepared by the simple co-crystallisation of tetraphenylporphyrin (TPP) with octa(2',6'-di-iso-propylphenoxy)phthalocyanine or some of its metal complexes [(dipPhO)8PcM; M=H2, Al-OH, Ti=O, Mn-Cl, Fe-Cl, Co, Ni, Cu, Zn, Ga-Cl, Ag, In-Cl or Au-Cl]. This process is facilitated by the efficient formation of the supramolecular heterodimer between TPP and (dipPhO)8PcM, which is driven by the complementary shape and symmetry of the two macrocycles. The (dipPhO)8PcM component directs the crystal structure of the heterodimers to form Phthalocyanine Nanoporous Crystals (PNCs) of similar structure to those formed by (dipPhO)8PcM alone. The incorporation of TPP appears to partially stabilise the PNCs towards the removal of included solvent and for cocrystals containing (dipPhO)8PcCo stability can be enhanced further by the insitu addition of 4,4-bipyridyl to act as a "molecular wall tie". These stabilised PNC/TPP cocrystals have a Brunauer-Emmett-Teller surface area (SABET) of 454 m2 g-1 and a micropore volume (Vmp) of 0.22 mL g-1. The reactivity of both macrocycles within the PNC/TPP co-crystals is demonstrated by insitu metal insertion.

N-H Bond Formation at a Diiron Bridging Nitride

Despite their connection to ammonia synthesis, little is known about the ability of iron-bound, bridging nitrides to form N-H bonds. Herein we report a linear diiron bridging nitride complex supported by a redox-active macrocycle. The unique ability of the ligand scaffold to adapt to the geometric preference of the bridging species was found to facilitate the formation of N-H bonds via proton-coupled electron transfer to generate a μ-amide product. The structurally analogous μ-silyl- and μ-borylamide complexes were shown to form from the net insertion of the nitride into the E-H bonds (E=B, Si). Protonation of the parent bridging amide produced ammonia in high yield, and treatment of the nitride with PhSH was found to liberate NH3 in high yield through a reaction that engages the redox-activity of the ligand during PCET.

X-Ray structures, Mössbauer hyperfine parameters, and molecular orbital descriptions of the phthalocyaninato iron(II) azole complexes

The electronic structures of a set of PcFe(azole)2 complexes (azole = imidazole, [Formula: see text]-methylimidazole, pyrazole, isoxazole, thiazole, 1,2,4-triazole, 3-amino-1,2,4,-triazole, and 5-amino-1,2,3,4-tetrazole) were examined by Mössbauer spectroscopy and Density Functional Theory (DFT) calculations. In addition, the geometric distortions in these compounds were elucidated by X-ray crystallography for imidazole, pyrazole, and thiazole-containing compounds. Predicted by DFT calculations, Mössbauer hyperfine parameters for all compounds are in reasonable agreement with experimental results, and the influence of the [Formula: see text]-donor and [Formula: see text]-acceptor properties of the axial azoles on the electronic structure of the PcFe(azole)2 complexes is demonstrated by comparison with the reference PcFePy2 compound.

Controlled Incorporation of Nitrides into W-Fe-S Clusters

Incorporation of monatomic 2p ligands into the core of iron-sulfur clusters has been researched since the discovery of interstitial carbide in the FeMo cofactor of Mo-dependent nitrogenase, but has proven to be a synthetic challenge. Herein, two distinct synthetic pathways are rationalized to install nitride ligands into targeted positions of W-Fe-S clusters, generating unprecedented nitride-ligated iron-sulfur clusters, namely [(Tp*)₂ W₂ Fe₆ (μ₄ -N)₂ S₆ L₄ ]^2- (Tp*=tris(3,5-dimethyl-1-pyrazolyl)hydroborate(1-), L=Cl^- or Br^- ). ⁵⁷ Fe Mössbauer study discloses metal oxidation states of W^IV ₂ Fe^II ₄ Fe^III ₂ with localized electron distribution, which is analogous to the mid-valent iron centres of FeMo cofactor at resting state. Good agreement of Mössbauer data with the empirical linear relationship for Fe-S clusters indicates similar ligand behaviour of nitride and sulfide in such clusters, providing useful reference for reduced nitrogen in a nitrogenase-like environment.

Site-Selective Supramolecular Complexation Activates Catalytic Ethane Oxidation by a Nitrido-Bridged Iron Porphyrinoid Dimer

Development of supramolecular methods to further activate a highly reactive intermediate is a fascinating strategy to create novel potent catalysts for activation of inert chemicals. Herein, a supramolecular approach to enhance the oxidizing ability of a high-valent oxo species of a nitrido-bridged iron porphyrinoid dimer that is a known potent molecular catalyst for light alkane oxidation is reported. For this purpose, a nitrido-bridged dinuclear iron complex of porphyrin-phthalocyanine heterodimer 3⁵⁺ , which is connected through a fourfold rotaxane, was prepared. Heterodimer 3⁵⁺ catalyzed ethane oxidation in the presence of H₂ O₂ at a relatively low temperature. The site-selective complexation of 3⁵⁺ with an additional anionic porphyrin (TPPS^4- ) through π-π stacking and electrostatic interactions afforded a stable 1:1 complex. It was demonstrated that the supramolecular post-synthetic modification of 3⁵⁺ enhances its catalytic activity efficiently. Moreover, supramolecular conjugates achieved higher catalytic ethane oxidation activity than nitrido-bridged iron phthalocyanine dimer, which is the most potent iron-oxo-based molecular catalyst for light-alkane oxidation reported so far. Electrochemical measurements proved that the electronic perturbation from TPPS^4- to 3⁵⁺ enhanced the catalytic activity.

A Nitrido-bridged Heterometallic Ruthenium(IV)/Iron(IV) Phthalocyanine Complex Supported by A Tripodal Oxygen Ligand, [Co(η5-C5H5){P(O)(OEt)2}3]-: Synthesis, Structure, and Its Oxidation to Give Phthalocyanine Cation Radical and Hydroxyphthalocyanine Complexes

Dinuclear iron nitrido phthalocyanine complexes are of interest owing to their applications in catalytic oxidation of hydrocarbons. While nitrido-bridged diiron phthalocyanine complexes are well documented, the oxidation chemistry of heterodinuclear iron(IV) phthalocyanine nitrides has not been well explored. In this paper we report on the synthesis of a heterometallic Fe^IV/Ru^IV phthalocyanine nitride and its oxidation to yield phthalocyanine cation radical and hydroxyphthalocyanine complexes. Treatment of [Fe^II(Pc)] (Pc^2- = phthalocyanine dianion) with [Ru^VI(L_OEt)(N)Cl₂] (L_OEt^- = [Co(η⁵-C₅H₅){P(O)(OEt)₂}₃]^-) (1) afforded the heterometallic μ-nitrido complex [Cl₂(L_OEt)Ru^IV(μ-N)Fe^IV(Pc)(H₂O)] (2) that contains an Ru^IV=N = Fe^IV linkage with the Ru-N and Fe-N distances of 1.689(6) and 1.677(6) Å, respectively, and Ru-N-Fe angle of 176.0(4)°. Substitution of 2 with 4- tert-butylpyridine (Bupy) gave [Cl₂(L_OEt)Ru^IV(μ-N)Fe^IV(Pc)(Bupy)]. The cyclic voltammogram of 2 displayed a reversible Pc-centered oxidation couple at +0.18 V versus Fc^+/0 (Fc = ferrocene). The oxidation of 2 with [N(4-BrC₆H₄)₃]SbCl₆ led to isolation of the cationic complex [Cl₂(L_OEt)Ru^IV(μ-N)Fe^IV(Pc^·+)(H₂O)][SbCl₆]_0.85[SbCl₅(OH)]_0.15 (2[SbCl₆]_0.85[SbCl₅(OH)]_0.15), whereas that with PhICl₂ yielded the chloride complex [Cl₂(L_OEt)Ru^IV(μ-N)Fe^IV(Pc^·+)Cl] (3). Complexes 2[SbCl₆]_0.85[SbCl₅(OH)]_0.15 and 3 have been characterized by X-ray crystallography. The UV/visible spectra of 2⁺ (λ_max = 515 and 747 nm) and 3 (λ_max = 506 and 748 nm) displayed absorption bands that are characteristic of Pc cation radical. The EPR spectrum of 3 showed a signal with the g value of 2.0012 (width = 5 G) that is consistent with an organic radical. The spectroscopic data support the formulation of 2⁺ and 3 as Ru^IV-Fe^IV Pc cation radical complexes. The reaction of 2 with PhI(CF₃CO₂)₂ in dried CH₂Cl₂ afforded a mixture of [Cl₂(L_OEt)Ru^IV(μ-N)Fe^IV(Pc^·+)(CF₃CO₂)] (4) and a hydroxyphthalocyanine complex, [Cl₂(L_OEt)Ru^IV(μ-N)Fe^IV(Pc-OH)(H₂O)](CF₃CO₂) (5), whereas that in wet CH₂Cl₂ (containing ca. 0.5% water) led to isolation of 5 as the sole product. Complex 4 was independently prepared by salt metathesis of 3 with AgCF₃CO₂.

Heteroleptic μ-nitrido diiron complex supported by phthalocyanine and octapropylporphyrazine ligands: Formation of oxo species and their reactivity with fluorinated compounds

The synthesis and reactivity of [Formula: see text]-bridged diiron macrocyclic complexes have been a topic of increasing interest in recent years since the observation of particular catalytic properties of these complexes. Herein, we report a preparation of a novel heteroleptic μ-nitrido diiron complex with unsubstituted phthalocyanine and octapropylporphyrazine macrocycles. This complex reacts with [Formula: see text]-chloroperbenzoic acid to form high-valent diiron oxo species showing strong oxidizing properties. The formation and structure of the transient oxo species was investigated by cryospray collision induced dissociation MS/MS technique. Analysis of fragmentation pattern showed that the attachment of oxo moiety occurred at either iron phthalocyanine or at iron porphyrazine site with slight preference for the phthalocyanine iron site. The catalytic properties of the heteroleptic μ-nitrido diiron complex were evaluated in the oxidative transformation of hexafluorobenzene and perfluoro(allylbenzene).

Heterobimetallic Nitrido Complexes of Group 8 Metalloporphyrins

Heterobimetallic nitrido porphyrin complexes with the [(L)(por)M-N-M'(L_OEt)Cl₂] formula {por^2- = 5,10,15,20-tetraphenylporphyrin (TPP^2-) or 5,10,15,20-tetra(p-tolyl)porphyrin (TTP^2-) dianion; L_OEt^- = [Co(η⁵-C₅H₅){P(O)(OEt)₂}₃]^-; M = Fe, Ru, or Os; M' = Ru or Os; L = H₂O or pyridine} have been synthesized, and their electrochemistry has been studied. Treatment of trans-[Fe(TPP)(py)₂] (py = pyridine) with Ru(VI) nitride [Ru(L_OEt)(N)Cl₂] (1) afforded Fe/Ru μ-nitrido complex [(py)(TPP)Fe(μ-N)Ru(L_OEt)Cl₂] (2). Similarly, Fe/Os analogue [(py)(TPP)Fe(μ-N)Os(L_OEt)Cl₂] (3) was obtained from trans-[Fe(TPP)(py)₂] and [Os(L_OEt)(N)Cl₂]. However, no reaction was found between trans-[Fe(TPP)(py)₂] and [Re(L_OEt)(N)Cl(PPh₃)]. Treatment of trans-[M(TPP)(CO)(EtOH)] with 1 afforded μ-nitrido complexes [(H₂O)(TPP)M(μ-N)Ru(L_OEt)Cl₂] [M = Ru (4a) or Os (5)]. TTP analogue [(H₂O)(TTP)Ru(μ-N)Ru(L_OEt)Cl₂] (4b) was prepared similarly from trans-[Ru(TTP)(CO)(EtOH)] and 1. Reaction of [(H₂O)(por)M(μ-N)M(L_OEt)Cl₂] with pyridine gave adducts [(py)(por)M(μ-N)Ru(L_OEt)Cl₂] [por = TTP, and M = Ru (6); por = TPP, and M = Os (7)]. The diamagnetism and short (por)M-N(nitride) distances in 2 [Fe-N, 1.683(3) Å] and 4b [Ru-N, 1.743(3) Å] are indicative of the M^IV═N═M'^IV bonding description. The cyclic voltammograms of the Fe/Ru (2) and Ru/Ru (4b) complexes in CH₂Cl₂ displayed oxidation couples at approximately +0.29 and +0.35 V versus Fc^+/0 (Fc = ferrocene) that are tentatively ascribed to the oxidation of the {L_OEtRu} and {Ru(TTP)} moieties, respectively, whereas the Fe/Os (3) and Os/Ru (5) complexes exhibited Os-centered oxidation at approximately -0.06 and +0.05 V versus Fc^+/0, respectively. The crystal structures of 2 and 4b have been determined.

Site-selective formation of an iron(iv)-oxo species at the more electron-rich iron atom of heteroleptic μ-nitrido diiron phthalocyanines

A combination of MS and computation on μ-nitrido bridged diiron complexes reveals H₂O₂ binding to the complex and generates an oxidant capable of oxidizing methane.

Iron(iv)–oxo species have been identified as the active intermediates in key enzymatic processes, and their catalytic properties are strongly affected by the equatorial and axial ligands bound to the metal, but details of these effects are still unresolved. In our aim to create better and more efficient oxidants of H-atom abstraction reactions, we have investigated a unique heteroleptic diiron phthalocyanine complex. We propose a novel intramolecular approach to determine the structural features that govern the catalytic activity of iron(iv)–oxo sites. Heteroleptic μ-nitrido diiron phthalocyanine complexes having an unsubstituted phthalocyanine (Pc1) and a phthalocyanine ligand substituted with electron-withdrawing alkylsulfonyl groups (PcSO₂R) were prepared and characterized. A reaction with terminal oxidants gives two isomeric iron(iv)–oxo and iron(iii)–hydroperoxo species with abundances dependent on the equatorial ligand. Cryospray ionization mass spectrometry (CSI-MS) characterized both hydroperoxo and diiron oxo species in the presence of H₂O₂. When m-CPBA was used as the oxidant, the formation of diiron oxo species (PcSO₂R)FeNFe(Pc1) Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O was also evidenced. Sufficient amounts of these transient species were trapped in the quadrupole region of the mass-spectrometer and underwent a CID-MS/MS fragmentation. Analyses of fragmentation patterns indicated a preferential formation of hydroperoxo and oxo moieties at more electron-rich iron sites of both heteroleptic μ-nitrido complexes. DFT calculations show that both isomers are close in energy. However, the analysis of the iron(iii)–hydroperoxo bond strength reveals major differences for the (Pc1)FeN(PcSO₂R)Fe^IIIOOH system as compared to (PcSO₂R)FeN(Pc1)Fe^IIIOOH system, and, hence binding of a terminal oxidant will be preferentially on more electron-rich sides. Subsequent kinetics studies showed that these oxidants are able to even oxidize methane to formic acid efficiently.

Synthesis and characterization of μ-nitrido, μ-carbido and μ-oxo dimers of iron octapropylporphyrazine

The structural and electronic properties of single-atom bridged diiron macrocyclic complexes are determined by the nature of the bridge.

Oxidation of methane by an N-bridged high-valent diiron–oxo species: electronic structure implications on the reactivity

Methane activation by dinuclear high-valent iron–oxo species: do we need two metals to activate such inert bonds? Our theoretical study using DFT methods where electronic structure details and mechanistic aspects are established answers this intriguing question.

Structural characterization of the μ-Nitrido Complex {[Fe(OEP)]2N}

The molecular structure of the μ-nitrido dimer, μ-nitrido-bis(2,3,7,8,12,13, 17,18-octaethylporphyrinato)iron, is reported. The axial Fe-N distances average to 1.657 (11) Å and the equatorial distances average to 2.005(5) Å. Although not required by symmetry, the two iron centers appear equivalent and are consistent with an assignment of a low-spin state and a formal oxidation state of +3.5. A comparison of this structure with other nitrido-bridged species is given.

Stability and catalytic properties of μ-oxo and μ-nitrido dimeric iron tetrasulfophthalocyanines in the oxidation of Orange II by tert-butylhydroperoxide

A study of catalytic activity of μ-nitrido- and μ-oxo-dimeric iron tetrasulfophthalocyanines in the oxidation of Orange II by tert-butylhydroperoxide in aqueous solutions has been performed. It is shown that though in one catalytic cycle activity of μ-oxo-dimer is higher, stability of this complex in oxidative conditions is poor. μ-nitrido-dimer combines relatively good catalytic activity with very high stability in the presence of tert-butylhydroperoxide. The mechanisms of oxidative decomposition of dimers and catalytic oxidation of Orange II have been proposed on the base of kinetic results. The products of catalytic processes are shown to be bio-degradable non-toxic small organic compounds.

N₂reduction and hydrogenation to ammonia by a molecular iron-potassium complex

The most common catalyst in the Haber-Bosch process for the hydrogenation of dinitrogen (N(2)) to ammonia (NH(3)) is an iron surface promoted with potassium cations (K(+)), but soluble iron complexes have neither reduced the N-N bond of N(2) to nitride (N(3-)) nor produced large amounts of NH(3) from N(2). We report a molecular iron complex that reacts with N(2) and a potassium reductant to give a complex with two nitrides, which are bound to iron and potassium cations. The product has a Fe(3)N(2) core, implying that three iron atoms cooperate to break the N-N triple bond through a six-electron reduction. The nitride complex reacts with acid and with H(2) to give substantial yields of N(2)-derived ammonia. These reactions, although not yet catalytic, give structural and spectroscopic insight into N(2) cleavage and N-H bond-forming reactions of iron.

Crystallographic and Spectroscopic Studies of Peroxide-derived Myoglobin Compound II and Occurrence of Protonated FeIV–O

High resolution crystal structures of myoglobin in the pH range 5.2-8.7 have been used as models for the peroxide-derived compound II intermediates in heme peroxidases and oxygenases. The observed Fe-O bond length (1.86-1.90 A) is consistent with that of a single bond. The compound II state of myoglobin in crystals was controlled by single-crystal microspectrophotometry before and after synchrotron data collection. We observe some radiation-induced changes in both compound II (resulting in intermediate H) and in the resting ferric state of myoglobin. These radiation-induced states are quite unstable, and compound II and ferric myoglobin are immediately regenerated through a short heating above the glass transition temperature (<1 s) of the crystals. It is unclear how this influences our compound II structures compared with the unaffected compound II, but some crystallographic data suggest that the influence on the Fe-O bond distance is minimal. Based on our crystallographic and spectroscopic data we suggest that for myoglobin the compound II intermediate consists of an Fe(IV)-O species with a single bond. The presence of Fe(IV) is indicated by a small isomer shift of delta = 0.07 mm/s from Mössbauer spectroscopy. Earlier quantum refinements (crystallographic refinement where the molecular-mechanics potential is replaced by a quantum chemical calculation) and density functional theory calculations suggest that this intermediate H species is protonated.

A Rare μ-Hydroxo-Bridged Species. Synthesis, Structure, and Properties of μ-Hydroxo(tetraphenylporphyrinatomanganese(III))(phthalocyaninato(azido)chromium(III)), [(TPP)Mn−O(H)−CrPc(N3)]

A novel ditetrapyrrolic, heteroleptic, and heterometallic (Mn-Cr) mu-hydroxo-bridged complex has been prepared, and its structural and general properties have been studied. The species mu-hydroxo(tetraphenylporphyrinatomanganese(III))(phthalocyaninato(azido)chromium(III)), [(TPP)Mn-O(H)-CrPc(N3)], isolated as a chloronaphthalene (ClNP) solvate, has been structurally characterized by single-crystal X-ray work. The two (TPP)Mn and CrPc(N3) fragments are held together by the bridging mu-hydroxo ion with long Mn-O [1.993(5) A] and Cr-O [1.976(5) A] bond distances and a Mn-O(H)-Cr angle of 163.7(3) degrees . The five-coordinate Mn center in the (TPP)Mn fragment is displaced from the TPP rigorously planar central N4 core by 0.128 A, and the environment is typical of a Mn(III) high-spin site. The six-coordinate Cr(III) in the CrPc(N3) moiety lies practically in the plane of the phthalocyanine macrocycle (displacement toward the azido group: 0.054 A). The average Mn-N(pyr) and Cr-N(pyr) bond distances are 2.011(6) and 1.982(6) A, respectively, and the Mn-Cr bond distance is 3.929(2) A. The porphyrin and phthalocyanine rings are in an almost eclipsed position [5.16(2) degrees ], and the mean planes of the two macrocycles form a dihedral angle of 5.79(4) degrees. Crystal data for [(TPP)Mn-O(H)-CrPc(N3)].2ClNP, C76H45CrMnN15O.2C10H7Cl: a = 16.645(3) A, b = 17.692(4) A, c = 25.828(5) A, alpha = 90 degrees , beta = 98.79(3) degrees , gamma = 90 degrees , space group P2(1)/c (No. 14), V = 7517(3) A(3), Z = 4, R1 = 0.086, and wR2 = 0.267. IR and UV-vis-near-IR spectral and room temperature magnetic susceptibility data of the [Mn-Cr] species are also presented.

Mid- to high-valent imido and nitrido complexes of iron

This short review summarizes recent advances in the synthesis and reactivity of iron imides and nitrides. Both monometallic and multimetallic assemblies featuring these moieties are discussed. Recent synthetic approaches have led to the availability of new mid- to high-valent iron imides and nitrides, allowing us to begin assembling models to describe the factors influencing their relative stabilities and reactivity patterns.

Initial members of the family of molecular mid-valent high-nuclearity iron nitrides: [Fe4N2X10]4- and [Fe10N8X12]5- (X = Cl-, Br-)

Current theoretical and experimental evidence points toward X = N as the identity of the interstitial atom in the [MoFe7S9X] core of the iron-molybdenum cofactor cluster of nitrogenase. This atom functions with mu6 bridging multiplicity to six iron atoms and, if it is nitrogen as nitride, raises a question as to the existence of a family of molecular iron nitrides of higher nuclearity than known dinuclear Fe(III,IV) species with linear [Fe-N-Fe]5+,4+ bridges. This matter has been initially examined by variation of reactant stoichiometry in the self-assembly systems [FeX4]1-/(Me3Sn)3N (X = Cl-, Br-) in acetonitrile. A 2:1 mol ratio affords [Fe4N2Cl10]4- (1), isolated as the Et4N+ salt (72%). This cluster has idealized C2h symmetry with a planar antiferromagnetically coupled [Fe(III)4(mu3-N)2]6+ core containing an Fe2N2 rhombus to which are attached two FeCl3 units. DFT calculations have been performed to determine the dominant magnetic exchange pathway. An 11:8 mol ratio leads to [Fe10N8Cl12]5- (3) as the Et4N+ salt (37%). The cluster possesses idealized D2h symmetry and is built of 15 edge- and vertex-shared rhomboids involving two mu3-N and six mu4-N bridging atoms, and incorporates two of the core units of 1. Four FeN2Cl2 and four FeN3Cl sites are tetrahedral and two FeN5 sites are trigonal pyramidal. The cluster is mixed-valence (9Fe(III) + Fe(IV)); a discrete Fe(IV) site was not detected by crystallography or Mössbauer spectroscopy. The corresponding clusters [Fe4N2Br10]4- and [Fe10N8Br12]5- are isostructural with 1 and 3, respectively. Future research is directed toward defining the scope of the family of molecular iron nitrides.

Chalcogen-rich lanthanide clusters: compounds with Te(2-), (TeTe)(2-), TePh, TeTePh, (TeTeTe(Ph)TeTe)(5-), and [(TeTe)(4)TePh](9-) ligands; single source precursors to solid-state lanthanide tellurides

Lanthanide metals react with PhTeTePh and elemental Te in pyridine to give (py)(y)Ln(4)(Te)(TeTe)(2)(TeTeTe(Ph)TeTe)(Te(x)TePh) (Ln = Sm (y = 9; x = 0); Tb, Ho (y = 8, x = 0.1)), and (py)(7)Tm(4)(Te)[(TeTe)(4)TePh](Te(0.6)TePh) clusters. The Sm, Tb, and Ho compounds contain a square array of Ln(III) ions all connected to a central Te(2-) ligand. Two adjacent edges of the square are bridged by ditelluride ligands, with the Ln ion that is eta(2) bound to both of these TeTe ligands also coordinating to a terminal TePh ligand. The other two edges of the square are spanned by ditellurides that both coordinate a TePh ligand that has been displaced from the Ln ion by pyridine, to give the pentaanion (mu-eta(2)-eta(2)-Te(2)Te(Ph)Te(2)).(5-) In the Tm compound, the displaced TePh interacts with all four TeTe units. The compounds are air-, light-, and temperature-sensitive. Upon thermolysis, they decompose to give solid-state TbTe(2-x), HoTe, or TmTe, with elimination of Te and TePh(2).

Chalcogen-rich lanthanide clusters: cluster reactivity and the influence of ancillary ligands on structure

Ytterbium metal reacts with PhEEPh (E = S, Se, Te) and elemental Se in pyridine to give (pyridine)(8)Yb(4)(SeSe)(2)(Se)(2)(mu(2)-SPh)(2)(SPh)(2), (py)(8)Yb(4)Se(SeSe)(3)(SeSeSePh)(Se(0.38)SePh), and (py)(8)Yb(4)Se(SeSe)(3)(SeSeTePh)(SeTePh), respectively. The SePh and TePh compounds contain a square array of Ln(III) ions all connected to a central Se(2)(-) ligand. Three edges of the square are bridged by diselenide ligands, with the fourth SeSe unit coordinating to an EPh ligand that has been displaced from an inner Yb coordination sphere. Differences in the two compounds have their origin in the relative strength of the Yb-E(Ph) bond. In the TePh compound, there is a complete insertion of Se into the remaining Yb-Te(Ph) bond to give a terminal SeTePh ligand, while in the SePh compound there is a compositional disorder in the structure comprised of a terminal SePh ligand and a minor component that has Se inserted into the Yb-Se(Ph) bond to give a terminal SeSePh ligand. The thiolate compound differs dramatically, crystallizing as a rhombohedral array of four Yb(III) ions connected by a pair of mu(3)-Se(2)(-) ligands, with the edges of the rhombus spanned by alternating diselenide and SPh. The SPh coordinate directly to Yb(III) ions in terminal or bridging modes. Cluster interconversion is facile: (py)(4)Yb(SePh)(2) reduces (py)(8)Yb(4)Se(SeSe)(3)(SeSeSePh)(Se(0.38)SePh) to give the cubane cluster [(py)(2)YbSe(SePh)](4), and the cubane reacts with elemental Se to give (py)(8)Yb(4)Se(SeSe)(3)(SeSeSePh)(Se(0.38)SePh). Upon thermolysis, these compounds give YbSe(x)().

Metal- and ligand-centered monoelectronic oxidation of mu-nitrido[((tetraphenylporphyrinato)manganese)phthalocyaninatoiron)], [(TPP)Mn-N-FePc]. X-ray crystal structure of the Fe(IV)-containing species [(THF)(TPP)Mn-N-FePc(H(2)O)](I(5))02THF

The reaction of mu-nitrido[((tetraphenylporphyrinato)manganese)(phthalocyaninatoiron)], [(TPP)Mn-N-FePc], with I(2) in THF develops with the formation of two different species, i.e., [(THF)(TPP)Mn-N-FePc(H(2)O)](I(5)).2THF (I) and [(TPP)Mn(IV)-N-Fe(III)Pc](I(3)) (II). On the basis of single-crystal X-ray work and Mössbauer, EPR, Raman, and magnetic susceptibility data, I, found to be isostructural with the corresponding Fe-Fe complex, is shown to contain a low-spin triatomic Mn(IV)=N=Fe(IV) system (metal-centered oxidation). Data at hand for II (Mössbauer, EPR, Raman) show, instead, that oxidation takes place at one of the two macrocycles, very likely TPP (ligand-centered oxidation). The same cationic fragment present in I, and containing the Mn(IV)=N=Fe(IV) bond system, is also obtained when (TPP)Mn-N-FePc is allowed to react in THF with (phen)SbCl(6) (molar ratio 1:1). There are indications that the use of (phen)SbCl(6) in excess (2:1 molar ratio), in benzene, probably determines further oxidation with the formation of a species showing the combined presence of the Mn(IV)-Fe(IV) couple and of a pi-cation radical.

The reduction of oxygen and hydrogen peroxide on dinuclear ruthenium phthalocyanine electrocatalytic surfaces

The electrochemical properties of both mononuclear L2RuIIPc and dinuclear [(THF)Rupc]2 species are described. The former is dominated by ring oxidation and reduction processes while the latter displays a series of metal localized processes. A Pourbaix diagram describes the various surfaces which can be generated by exposing a graphite electrode modified with [(THF)Rupc]2 to aqueous buffer at different polarization over a wide range of pH. The behavior of these various surfaces towards the electrocatalytic reduction of both oxygen and hydrogen peroxide is described. Most importantly, three different regimes of hydrogen peroxide reduction are observed dependent on the nature of the modified electrode surface. At high pH the four electron reduction of oxygen to water is observed via a 2 + 2 mechanism.Key words: phthalocyanine, ruthenium, ruthenium phthalocyanine, cyclic voltammetry, suface modified electrode, Pourbaix diagram, electrocatalysis, oxygen reduction, hydrogen peroxide reduction.

Hetero trinuclear oxo-bridged complexes of ruthenium porphyrin and iron phthalocyanine

New diamagnetic hetero bi- and trinuclear oxo-bridged metal complexes of formula (L)(Pc)Fe-O-Ru(TPP')(O) and (L)(Pc)Fe-O-Ru(TPP')-O-Fe(Pc)(L) have been prepared from Ru(TPP')(O)2 and Fe(Pc)(L)2 (TPP' = tetrakis(4-methoxyphenyl)porphyrinate, Pc = phthalocyanate ion, L = monodentate ligand). The trinuclear complex binds a variety of ligands (4,4'-bipy, 4-MePy, P(OEt)3, pip, NH3, 1-MeIm, P(Me)2Ph) trans to the oxo-bridge. 1H NMR spectra are characterized by large ring current shifts (rcs) due to the TPP' and Pc ions. The complexes show an unusually weak Pc Q band in their visible spectra at 700 nm and two CT bands in the near-IR region from 1000 to 1500 nm, which are sensitive to the trans ligand. The trinuclear complex can be reversibly oxidized to the +1 and +2 ions, formally Fe(IV)-O-Ru(IV)-O-Fe(III) and Fe(IV)-O-Ru(IV)-O-Fe(IV) at 0.4 and 0.76 V. The +1 ion is chemically obtained by reaction of the neutral species with (Cp)2Fe+ for L = 4-MePy and this reaction is reversed upon addition of L' = P(Me)2Ph. Reductive cleavage by hydroquinone, phosphines and phosphites are the slowest of all RuTPP[O(FeN4)]2 systems studied to date (t1/2 = 8 h at 40°C).Key words: ruthenium, iron, porphyrin, phthalocyanine, oxo.

1,2-bis(pyridine-2-carboxamido)benzenate(2-), (bpb)2-: a noninnocent ligand. Syntheses, structures, and mechanisms of formation of [(n-Bu)4N][FeIV2(mu-N)(bpb)2(X)2] (X = CN-, N3-) and the electronic structures of [MIII(bpbox1)(CN)2] (M = Co, Fe)

The well-known tetradentate ligand 1,2-bis(pyridine-2-carboxamido)benzenate(2-), (bpb)2-, and its 4,5-dichloro analogue, (bpc)2-, are shown to be "noninnocent" ligands in the sense that in coordination compounds they can exist in their radical one- and diamagnetic two-electron-oxidized forms (bpbox1)- and (bpbox2)0 (and (bpcox1)- and (bpcox2)0), respectively. Photolysis of high-spin [(n-Bu)4N][FeIII(bpb)(N3)2] and its (bpc)2- analogue in acetone solution at room temperature generates the diamagnetic dinuclear complex [(n-Bu)4N][FeIV2(mu-N)(bpb)2(N3)2] and its (bpc)2- analogue; the corresponding cyano complex [(n-Bu)4N][FeIV2(mu-N)(bpb)2(CN)2] has been prepared via N3- substitution by CN-. Photolysis in frozen acetonitrile solution produces a low-spin ferric species (S = 1/2) which presumably is [FeIII(bpbox2)(N)(N3)]-, as has been established by EPR and Mössbauer spectroscopy. The mononuclear complexes [(n-Bu)4N][FeIII(bpb)(CN2)] (low spin), [Et4N][CoIII(bpb)(CN)2] and Na[CoIII(bpc)-(CN)2].3CH3OH can be electrochemically or chemically one-electron-oxidized to give [FeIII(bpbox1)(CN)2]0 (S = 0), [CoIII(bpbox1)(CN)2]0 (S = 1/2), and [CoIII(bpcox1)(CN)2]0 (S = 1/2). All complexes have been characterized by UV-vis, EPR, and Mössbauer spectroscopy, and their electro- and magnetochemistries have been studied. The crystal structures of [(n-Bu)4N][FeIII(bpb)(N3)2].1/2C6H6CH3, Na[FeIII(bpb)(CN)2], Na[CoIII(bpc)(CN)2].3CH3OH, [(n-Bu)4N][FeIV2(mu-N)(bpb)2(CN)2], and [(n-Bu)4N][FeIV2(mu-N)(bpb)(N3)2] have been determined by single-crystal X-ray diffraction.

Molecular structure of an Fe(IV) species:

The molecular structure of the formal iron(IV) porphyrinate derivative, [[Fe(TTP)]2N]SbCl6 (TTP = tetratolylporphyrinate), is reported. The structural parameters are compared to the previously reported species [Fe(TPP)]2N, in which the iron oxidation state is +3.5. Both the equatorial and axial bond distances in [[Fe(TTP)]2N]SbCl6 are slightly shortened and consistent with an increased formal charge on iron. The value for the axial Fe-N distance is 1.6280(7) A, and the average value of the equatorial Fe-Np distances is 1.979(5) A. The Mössbauer isomer shift decreases upon oxidation, again consistent with an increase in formal charge. Values for the isomer shift at room temperature are -0.13 mm/s for [[Fe(TTP)]2N]SbCl6 and 0.04 mm/s for [Fe(TTP)]2N. Crystal data for [[Fe(TTP)]2N]SbCl6 are as follows: orthorhombic, space group Fddd, Z = 8, a = 23.689(2) A, b = 31.056(3) A, c = 22.7788(18) A.