Discrimination of mononuclear and dinuclear dinitrosyl iron complexes (DNICs) by S K-edge X-ray absorption spectroscopy: insight into the electronic structure and reactivity of DNICs

In addition to probing the formation of dinitrosyl iron complexes (DNICs) by the characteristic Fe K-edge pre-edge absorption energy ranging from 7113.4 to 7113.8 eV, the distinct S K-edge pre-edge absorption energy and pattern can serve as an efficient tool to unambiguously characterize and discriminate mononuclear DNICs and dinuclear DNICs containing bridged-thiolate and bridged-sulfide ligands. The higher Fe-S bond covalency modulated by the stronger electron-donating thiolates promotes the Fe → NO π-electron back-donation to strengthen the Fe-NO bond and weaken the NO-release ability of the mononuclear DNICs, which is supported by the Raman ν(Fe-NO) stretching frequency. The Fe-S bond covalency of DNICs further rationalizes the binding preference of the {Fe(NO)(2)} motif toward thiolates following the trend of [SEt](-) > [SPh](-) > [SC(7)H(4)SN](-). The relative d-manifold energy derived from S K-edge XAS as well as the Fe K-edge pre-edge energy reveals that the electronic structure of the {Fe(NO)(2)}(9) core of the mononuclear DNICs [(NO)(2)Fe(SR)(2)](-) is best described as {Fe(III)(NO(-))(2)}(9) compared to [{Fe(III)(NO(-))(2)}(9)-{Fe(III)(NO(-))(2)}(9)] for the dinuclear DNICs [Fe(2)(μ-SEt)(μ-S)(NO)(4)](-) and [Fe(2)(μ-S)(2)(NO)(4)](2-).     

Tuning the electronic structure of octahedral iron complexes [FeL(X)] (L = 1-alkyl-4,7-bis(4-tert-butyl-2-mercaptobenzyl)-1,4,7-triazacyclononane,X = Cl,CH(3)O,CN, NO). The S = 1/2 <==>3/2 Spin equilibrium of [FeL(Pr)(NO)

Two new pentadentate, pendent arm macrocyclic ligands of the type 1-alkyl-4,7-bis(4-tert-butyl-2-mercaptobenzyl)-1,4,7-triazacyclononane where alkyl represents an isopropyl, (L(Pr))(2-), or an ethyl group, (L(Et))(2-), have been synthesized. It is shown that they bind strongly to ferric ions generating six-coordinate species of the type [Fe(L(alk))X]. The ground state of these complexes is governed by the nature of the sixth ligand, X: [Fe(III)(L(Et))Cl] (2) possesses an S = 5/2 ground state as do [Fe(III)(L(Et))(OCH(3))] (3) and [Fe(III)(L(Pr))(OCH(3))] (4). In contrast, the cyano complexes [Fe(III)(L(Et))(CN)] (5) and [Fe(III)(L(Pr))(CN)] (6) are low spin ferric species (S = 1/2). The octahedral [FeNO](7) nitrosyl complex [Fe(L(Pr))(NO)] (7) displays spin equilibrium behavior S = 1/2<==>S = (3)/(2) in the solid state. Complexes [Zn(L(Pr))] (1), 4.CH(3)OH, 5.0.5toluene.CH(2)Cl(2), and 7.2.5CH(2)Cl(2) have been structurally characterized by low-temperature (100 K) X-ray crystallography. All iron complexes have been carefully studied by zero- and applied-field M?ssbauer spectroscopy. In addition, Sellmann's complexes [Fe(pyS(4))(NO)](0/1+) and [Fe(pyS(4))X] (X = PR(3), CO, SR(2)) have been studied by EPR and M?ssbauer spectroscopies and DFT calculations (pyS(4) = 2,6-bis(2-mercaptophenylthiomethyl)pyridine(2-)). It is concluded that the electronic structure of 7 with an S = 1/2 ground state is low spin ferrous (S(Fe) = 0) with a coordinated neutral NO radical (Fe(II)-NO) whereas the S = 3/2 state corresponds to a high spin ferric (S(Fe) = 5/2) antiferromagnetically coupled to an NO(-) anion (S = 1). The S = 1/2<==>S = 3/2 equilibrium is then that of valence tautomers rather than that of a simple high spin<==>low spin crossover.     

Influence of thiolate ligands on reductive N-O bond activation. Probing the O2(-) binding site of a biomimetic superoxide reductase analogue and examining the proton-dependent reduction of nitrite

Nitric oxide (NO) is frequently used to probe the substrate-binding site of "spectroscopically silent" non-heme Fe(2+) sites of metalloenzymes, such as superoxide reductase (SOR). Herein we use NO to probe the superoxide binding site of our thiolate-ligated biomimetic SOR model [Fe(II)(S(Me(2))N(4)(tren))](+) (1). Like NO-bound trans-cysteinate-ligated SOR (SOR-NO), the rhombic S = 3/2 EPR signal of NO-bound cis-thiolate-ligated [Fe(S(Me(2))N(4)(tren)(NO)](+) (2; g = 4.44, 3.54, 1.97), the isotopically sensitive ν(NO)(ν((15)NO)) stretching frequency (1685(1640) cm(-1)), and the 0.05 ? decrease in Fe-S bond length are shown to be consistent with the oxidative addition of NO to Fe(II) to afford an Fe(III)-NO(-) {FeNO}(7) species containing high-spin (S = 5/2) Fe(III) antiferromagnetically coupled to NO(-) (S = 1). The cis versus trans positioning of the thiolate does not appear to influence these properties. Although it has yet to be crystallographically characterized, SOR-NO is presumed to possess a bent Fe-NO similar to that of 2 (Fe-N-O = 151.7(4)°). The N-O bond is shown to be more activated in 2 relative to N- and O-ligated {FeNO}(7) complexes, and this is attributed to the electron-donating properties of the thiolate ligand. Hydrogen-bonding to the cysteinate sulfur attenuates N-O bond activation in SOR, as shown by its higher ν(NO) frequency (1721 cm(-1)). In contrast, the ν(O-O) frequency of the SOR peroxo intermediate and its analogues is not affected by H-bonds to the cysteinate sulfur or other factors influencing the Fe-SR bond strength; these only influence the ν(Fe-O) frequency. Reactions between 1 and NO(2)(-) are shown to result in the proton-dependent heterolytic cleavage of an N-O bond. The mechanism of this reaction is proposed to involve both Fe(II)-NO(2)(-) and {FeNO}(6) intermediates similar to those implicated in the mechanism of NiR-promoted NO(2)(-) reduction.     

Fe2 and Fe4 clusters encapsulated in vacant polyoxotungstates: hydrothermal synthesis, magnetic and electrochemical properties, and DFT calculations

While the reaction of [PW(11)O(39)](7-) with first row transition-metal ions M(n+) under usual bench conditions only leads to monosubstituted {PW(11)O(39)M(H(2)O)} anions, we have shown that the use of this precursor under hydrothermal conditions allows the isolation of a family of novel polynuclear discrete magnetic polyoxometalates (POMs). The hybrid asymmetric [Fe(II)(bpy)(3)][PW(11)O(39)Fe(2) (III)(OH)(bpy)(2)]12 H(2)O (bpy=bipyridine) complex (1) contains the dinuclear {Fe(micro-O(W))(micro-OH)Fe} core in which one iron atom is coordinated to a monovacant POM, while the other is coordinated to two bipyridine ligands. Magnetic measurements indicate that the Fe(III) centers in complex 1 are weakly antiferromagnetically coupled (J=-11.2 cm(-1), H=-JS(1)S(2)) compared to other {Fe(micro-O)(micro-OH)Fe} systems. This is due to the long distances between the iron center embedded in the POM and the oxygen atom of the POM bridging the two magnetic centers, but also, as shown by DFT calculations, to the important mixing of bridging oxygen orbitals with orbitals of the POM tungsten atoms. The complexes [Hdmbpy](2)[Fe(II)(dmbpy)(3)](2)[(PW(11)O(39))(2)Fe(4) (III)O(2)(dmbpy)(4)]14 H(2)O (2) (dmbpy=5,5'-dimethyl-2,2'-bipyridine) and H(2)[Fe(II)(dmbpy)(3)](2)[(PW(11)O(39))(2)Fe(4) (III)O(2)(dmbpy)(4)]10 H(2)O (3) represent the first butterfly-like POM complexes. In these species, a tetranuclear Fe(III) complex is sandwiched between two lacunary polyoxotungstates that are pentacoordinated to two Fe(III) cations, the remaining paramagnetic centers each being coordinated to two dmbpy ligands. The best fit of the chi(M)T=f(T) curve leads to J(wb)=-59.6 cm(-1) and J(bb)=-10.2 cm(-1) (H=-J(wb)(S(1)S(2)+S(1)S(2*)+S(1*)S(2)+S(1*)S(2*))-J(bb)(S(2)S(2*))). While the J(bb) value is within the range of related exchange parameters previously reported for non-POM butterfly systems, the J(wb) constant is significantly lower. As for complex 1, this can be justified considering Fe(w)--O distances. Finally, in the absence of a coordinating ligand, the dimeric complex [N(CH(3))(4)](10)[(PW(11)O(39)Fe(III))(2)O]12 H(2)O (4) has been isolated. In this complex, the two single oxo-bridged Fe(III) centers are very strongly antiferromagnetically coupled (J=-211.7 cm(-1), H=-JS(1)S(2)). The electrochemical behavior of compound 1 both in dimethyl sulfoxide (DMSO) and in the solid state is also presented, while the electrochemical properties of complex 2, which is insoluble in common solvents, have been studied in the solid state.     

Dinitrosyl iron complexes (DNICs) [L(2)Fe(NO)2]- (L = thiolate): interconversion among {Fe(NO)2}9 DNICs, {Fe(NO)2}10 DNICs, and [2Fe-2S] clusters, and the critical role of the thiolate ligands in regulating NO release of DNICs

Dinitrosyl iron complex [(-SC(7)H(4)SN)(2)Fe(NO)(2)](-) (1) was prepared by reaction of [S(5)Fe(NO)(2)](-) and bis(2-benzothiozolyl) disulfide. In synthesis of the analogous dinitrosyl iron compounds (DNICs), the stronger electron-donating thiolates [RS](-) (R = C(6)H(4)-o-NHCOCH(3), C(4)H(3)S, C(6)H(4)NH(2), Ph), compared to [-SC(7)H(4)SN](-) of complex 1, trigger thiolate-ligand substitution to yield [(-SC(6)H(4)-o-NHCOCH(3))(2)Fe(NO)(2)](-) (2), [(-SC(4)H(3)S)(2)Fe(NO)(2)](-) (3), and [(SPh)(2)Fe(NO)(2)](-) (4), respectively. At 298 K, complexes 2 and 3 exhibit a well-resolved five-line EPR signal at g = 2.038 and 2.027, respectively, the characteristic g value of DNICs. The magnetic susceptibility fit indicates that the resonance hybrid of {Fe(+)((*)NO)(2)}(9) and {Fe(-)((+)NO)(2)}(9) in 2 is dynamic by temperature. The IR nu(NO) stretching frequencies (ranging from (1766, 1716) to (1737, 1693) cm(-)(1) (THF)) of complexes 1-4 signal the entire window of possible electronic configurations for such stable and isolable {Fe(NO)(2)}(9) [(RS)(2)Fe(NO)(2)](-). The NO-releasing ability of {Fe(NO)(2)}(9) [(RS)(2)Fe(NO)(2)](-) is finely tuned by the coordinated thiolate ligands. The less electron-donating thiolate ligands coordinated to {Fe(NO)(2)}(9) motif act as better NO-donor DNICs in the presence of NO-trapping agent [Fe(S,S-C(6)H(4))(2)](2)(2-). Interconversion between {Fe(NO)(2)}(9) [(RS)(2)Fe(NO)(2)](-) and {Fe(NO)(2)}(10) [(Ph(3)P)(2)Fe(NO)(2)] was verified in the reaction of (a) [(RS)(2)Fe(NO)(2)](-), 10 equiv of PPh(3) and sodium-biphenyl, and (b) 2 equiv of thiol, [RS](-), and [(Ph(3)P)(2)Fe(NO)(2)], respectively. The biomimetic reaction cycle, transformation between {Fe(NO)(2)}(9) [(RS)(2)Fe(NO)(2)](-) and {Fe(NO)(2)}(9) [(R'S)(2)Fe(NO)(2)](-), reversible interconversion of {Fe(NO)(2)}(9) and {Fe(NO)(2)}(10) DNICs, and degradation/reassembly of [2Fe-2S] clusters may decipher and predict the biological cycle of interconversion of {Fe(NO)(2)}(9) DNICs, {Fe(NO)(2)}(10) DNICs, and the [Fe-S] clusters in proteins.     

Acetate-Bridged Platinum(III) Complexes Derived from Cisplatin

Oxidation of the acetate-bridged half-lantern platinum(II) complex cis-[Pt(II)(NH(3))(2)(μ-OAc)(2)Pt(II)(NH(3))(2)](NO(3))(2), [1](NO(3))(2), with iodobenzene dichloride or bromine generates the halide-capped platinum(III) species cis-[XPt(III)(NH(3))(2)(μ-OAc)(2)Pt(III)(NH(3))(2)X](NO(3))(2), where X is Cl in [2](NO(3))(2) or Br in [3](NO(3))(2), respectively. These three complexes, characterized structurally by X-ray crystallography, feature short (≈2.6 ?) Pt-Pt separations, consistent with formation of a formal metal-metal bond upon oxidation. Elongated axial Pt-X distances occur, reflecting the strong trans influence of the metal-metal bond. The three structures are compared to those of other known dinuclear platinum complexes. A combination of (1)H, (13)C, (14)N, and (195)Pt NMR spectroscopy was used to characterize [1](2+)-[3](2+) in solution. All resonances shift downfield upon oxidation of [1](2+) to [2](2+) and [3](2+). For the platinum(III) complexes, the (14)N and (195)Pt resonances exhibit decreased line widths by comparison to those of [1](2+). Density functional theory calculations suggest that the decrease in the (14)N line width arises from a diminished electric field gradient at the (14)N nuclei in the higher valent compounds. The oxidation of [1](NO(3))(2) with the alternative oxidizing agent bis(trifluoroacetoxy)iodobenzene affords the novel tetranuclear complex cis-[(O(2)CCF(3))Pt(III)(NH(3))(2)(μ-OAc)(2)Pt(III)(NH(3))(μ-NH(2))](2)(NO(3))(4), [4](NO(3))(4), also characterized structurally by X-ray crystallography. In solution, this complex exists as a mixture of species, the identities of which are proposed.     

Bridging nitrate groups in [Mn(4)O(3)(NO(3))(O(2)CMe)(3)(R(2)dbm)(3)] (R = H, Et) and [Mn(4)O(2)(NO(3))(O(2)CEt)(6)(bpy)(2)](ClO(4)): acidolysis routes to tetranuclear manganese carboxylate complexes

New synthesis procedures are described to tetranuclear manganese carboxylate complexes containing the [Mn(4)O(2)](8+) or [Mn(4)O(3)X](6+) (X(-) = MeCO(2)(-), F(-), Cl(-), Br(-), NO(3)(-)) core. These involve acidolysis reactions of [Mn(4)O(3)(O(2)CMe)(4)(dbm)(3)] (1; dbm is the anion of dibenzoylmethane) or [Mn(4)O(2)(O(2)CEt)(6)(dbm)(2)] (8) with HX (X(-) = F(-), Cl(-), Br(-), NO(3)(-)); high-yield routes to 1 and 8 are also described. The X(-) = NO(3)(-) complexes [Mn(4)O(3)(NO(3))(O(2)CR)(3)(R'(2)dbm)(3)] (R = Me, R' = H (6); R = Me, R' = Et (7); R = Et, R' = H (12)) represent the first synthesis of the [Mn(4)O(3)(NO(3))](6+) core, which contains an unusual eta(1):mu(3)-NO(3)(-) group. Treatment of known [Mn(4)O(2)(O(2)CEt)(7)(bpy)(2)](ClO(4)) with HNO(3) gives [Mn(4)O(2)(NO(3))(O(2)CEt)(6)(bpy)(2)](ClO(4)) (15) containing a eta(1):eta(1):mu-NO(3)(-) group bridging the two body Mn(III) ions of the [Mn(4)O(2)](8+) butterfly core. Complex 7 x 4CH(2)Cl(2) crystallizes in space group P2(1)2(1)2(1) with (at -168 degrees C) a = 21.110(3) A, b = 22.183(3) A, c = 15.958(2) A, Z = 4, and V = 7472.4(3) A(3). Complex 15 x (3)/(2)CH(2)Cl(2) crystallizes in space group P2(1)/c with (at -165 degrees C) a = 26.025(4) A, b = 13.488(2) A, c = 32.102(6) A, beta = 97.27(1) degrees, Z = 8, and V = 11178(5) A(3). Complex 7 contains a [Mn(4)(mu(3)-O)(3)(mu(3)-NO(3))](6+) core (3Mn(III), Mn(IV)) as seen for previous [Mn(4)O(3)X](6+) complexes. Complex 15 contains a butterfly [Mn(4)(mu(3)-O)(2)](8+) core. (1)H NMR spectra have been recorded for all complexes reported in this work and the various resonances assigned. All complexes retain their structural integrity on dissolution in chloroform and dichloromethane. Magnetic susceptibility (chi(M)) data were collected on 12 in the 5-300 K range in a 10.0 kG (1 T) field. Fitting of the data to the theoretical chi(M) vs T expression appropriate for a [Mn(4)O(3)X](6+) complex of C(3)(v)() symmetry gave J(34) = -23.9 cm(-)(1), J(33) = 4.9 cm(-)(1), and g = 1.98, where J(34) and J(33) refer to the Mn(III)Mn(IV) and Mn(III)Mn(III) pairwise exchange interactions, respectively. The ground state of the molecule is S = 9/2, as found previously for other [Mn(4)O(3)X](6+) complexes. This was confirmed by magnetization data collected at various fields and temperatures. Fitting of the data gave S = 9/2, D = -0.45 cm(-1), and g = 1.96, where D is the axial zero-field splitting parameter.     

Syntheses and structural characterization of dinuclear and tetranuclear iron(III) complexes with dinucleating ligands and their reactions with hydrogen peroxide

The iron(III) complexes [Fe(2)(HPTB)(mu-OH)(NO(3))(2)](NO(3))(2).CH(3)OH.2H(2)O (1), [Fe(2)(HPTB)(mu-OCH(3))(NO(3))(2)](NO(3))(2).4.5CH(3)OH (2), [Fe(2)(HPTB)(mu-OH)(OBz)(2)](ClO(4))(2).4.5H(2)O (3), [Fe(2)(N-EtOH-HPTB)(mu-OH)(NO(3))(2)](ClO(4))(NO(3)).3CH(3)OH.1.5H(2)O (4), [Fe(2)(5,6-Me(2)-HPTB)(mu-OH)(NO(3))(2)](ClO(4))(NO(3)).3.5CH(3)OH.C(2)H(5)OC(2)H(5).0.5H(2)O (5), and [Fe(4)(HPTB)(2)(mu-F)(2)(OH)(4)](ClO(4))(4).CH(3)CN.C(2)H(5)OC(2)H(5).H(2)O (6) were synthesized (HPTB = N,N,N',N'-tetrakis(2-benzimidazolylmethyl)-2-hydroxo-1,3-diaminopropane, N-EtOH-HPTB = N,N,N',N'-tetrakis(N' '-(2-hydroxoethyl)-2-benzimidazolylmethyl)-2-hydroxo-1,3-diaminopropane, 5,6-Me(2)-HPTB = N,N,N',N'-tetrakis(5,6-dimethyl-2-benzimidazolylmethyl)-2-hydroxo-1,3-diaminopropane). The molecular structures of 2-6 were established by single-crystal X-ray crystallography. Iron(II) complexes with ligands similar to the dinucleating ligands described herein have been used previously as model compounds for the dioxygen uptake at the active sites of non-heme iron enzymes. The same metastable (mu-peroxo)diiron(III) adducts were observed during these studies. They can be prepared by adding hydrogen peroxide to the iron(III) compounds 1-6. Using stopped-flow techniques these reactions were kinetically investigated in different solvents and a mechanism was postulated.     

Disproportionation of O-methylhydroxylamine catalyzed by aquapentacyanoferrate(II)

The aquapentacyanoferrate(II) ion, [Fe(II)(CN)(5)H(2)O](3-), catalyzes the disproportionation reaction of O-methylhydroxylamine, NH(2)OCH(3), with stoichiometry 3NH(2)OCH(3) → NH(3) + N(2) + 3CH(3)OH. Kinetic and spectroscopic evidence support an initial N coordination of NH(2)OCH(3) to [Fe(II)(CN)(5)H(2)O](3-) followed by a homolytic scission leading to radicals [Fe(II)(CN)(5)(?)NH(2)](3-) (a precursor of Fe(III) centers and bound NH(3)) and free methoxyl, CH(3)O(?), thus establishing a radical path leading to N-methoxyamino ((?)NHOCH(3)) and 1,2-dimethoxyhydrazine, (NHOCH(3))(2). The latter species is moderately stable and proposed to be the precursor of N(2) and most of the generated CH(3)OH. Intermediate [Fe(III)(CN)(5)L](2-) complexes (L = NH(3), H(2)O) form dinuclear cyano-bridged mixed-valent species, affording a catalytic substitution of the L ligands promoted by [Fe(II)(CN)(5)L](3-). Free or bound NH(2)OCH(3) may act as reductants of [Fe(III)(CN)(5)L](2-), thus regenerating active sites. At increasing concentrations of NH(2)OCH(3) a coordinated diazene species emerges, [Fe(II)(CN)(5)N(2)H(2)](3-), which is consumed by the oxidizing CH(3)O(?), giving N(2) and CH(3)OH. Another side reaction forms [Fe(II)(CN)(5)N(O)CH(3)](3-), an intermediate containing the nitrosomethane ligand, which is further oxidized to the nitroprusside ion, [Fe(II)(CN)(5)NO](2-). The latter is a final oxidation product with a significant conversion of the initial [Fe(II)(CN)(5)H(2)O](3-) complex. The side reaction partially blocks the Fe(II)-aqua active site, though complete inhibition is not achieved because the radical path evolves faster than the formation rates of the Fe(II)-NO(+) bonds.     

Syntheses, structures and properties of a series of non-heme alkoxide-Fe(III) complexes of a benzimidazolyl-rich ligand as models for lipoxygenase

The treatment of Fe(ClO(4))(2)·6H(2)O or Fe(ClO(4))(3)·9H(2)O with a benzimidazolyl-rich ligand, N,N,N',N'-tetrakis[(1-methyl-2-benzimidazolyl)methyl]-1,2-ethanediamine (medtb) in alcohol/MeCN gives a mononuclear ferrous complex, [Fe(II)(medtb)](ClO(4))(2)·?CH(3)CN·?CH(3)OH (1), and four non-heme alkoxide-iron(III) complexes, [Fe(III)(OMe)(medtb)](ClO(4))(2)·H(2)O (2, alcohol = MeOH), [Fe(III)(OEt)(Hmedtb)](ClO(4))(3)·CH(3)CN (3, alcohol = EtOH), [Fe(III)(O(n)Pr)(Hmedtb)](ClO(4))(3)·(n)PrOH·2CH(3)CN (4, alcohol = n-PrOH), and [Fe(III)(O(n)Bu)(Hmedtb)](ClO(4))(3)·3CH(3)CN·H(2)O (5, alcohol = n-BuOH), respectively. The alkoxide-iron(III) complexes all show 1) a Fe(III)-OR center (R = Me, 2; Et, 3; (n)Pr, 4; (n)Bu, 5) with the Fe-O bond distances in the range of 1.781-1.816 ?, and 2) a yellow color and an intense electronic transition around 370 nm. The alkoxide-iron(III) complexes can be reduced by organic compounds with a cis,cis-1,4-diene moiety via the hydrogen atom abstraction reaction.     

3d-Metal derivatives of the [Cu(I)(SO3)4]7- ion: structure and magnetism

The Cu(SO(3))(4)(7-) anion, which consists of a tetrahedrally coordinated Cu(I) centre coordinated to four sulfur atoms, is able to act as a multidentate ligand in discrete and infinite supramolecular species. The slow oxidation of an aqueous solution of Na(7)Cu(SO(3))(4) yields a mixed oxidation state, 2D network of composition Na(5){[Cu(II)(H(2)O)][Cu(I)(SO(3))(4)]}·6H(2)O. The addition of Cu(II) and 2,2'-bipyridine to an aqueous Na(7)Cu(SO(3))(4) solution leads to the formation of a pentanuclear complex of composition {[Cu(II)(H(2)O)(bipy)](4)[Cu(I)(SO(3))(4)]}(+); a combination of hydrogen bonding and π-π stacking interactions leads to the generation of infinite parallel channels that are occupied by disordered nitrate anions and water molecules. A pair of Cu(SO(3))(4)(7-) anions each act as a tridentate ligand towards a single Mn(II) centre when Mn(II) ions are combined with an excess of Cu(SO(3))(4)(7-). An anionic pentanuclear complex of composition {[Cu(I)(SO(3))(4)](2)[Fe(III)(H(2)O)](3)(O)} is formed when Fe(II) is added to a Cu(+)/SO(3)(2-) solution. Hydrated ferrous [Fe(H(2)O)(6)(2+)] and sodium ions act as counterions for the complexes and are responsible for the formation of an extensive hydrogen bond network within the crystal. Magnetic susceptibility studies over the temperature range 2-300 K show that weak ferromagnetic coupling occurs within the Cu(II) containing chains of Na(5){[Cu(II)(H(2)O)][Cu(I)(SO(3))(4)]}·6H(2)O, while zero coupling exists in the pentanuclear cluster {[Cu(II)(H(2)O)(bipy)](4)[Cu(I)(SO(3))(4)]}(NO(3))·H(2)O. Weak Mn(II)-O-S-O-Mn(II) antiferromagnetic coupling occurs in Na(H(2)O)(6){[Cu(I)(SO(3))(4)][Mn(II)(H(2)O)(2)](3)}, the latter formed when Mn was in excess during synthesis. The compound, Na(3)(H(2)O)(6)[Fe(II)(H(2)O)(6)](2){[Cu(I)(SO(3))(4)](2)[Fe(III)(H(2)O)](3)(O)}·H(2)O, contained trace magnetic impurities that affected the expected magnetic behaviour.     

Proton control of oxidation and spin state in a series of iron tripodal imidazole complexes

Reaction of iron salts with three tripodal imidazole ligands, H(3)(1), H(3)(2), H(3)(3), formed from the condensation of tris(2-aminoethyl)amine (tren) with 3 equiv of an imidazole carboxaldehyde yielded eight new cationic iron(III) and iron(II), [FeH(3)L](3+or2+), and neutral iron(III), FeL, complexes. All complexes were characterized by EA(CHN), IR, UV, M?ssbauer, mass spectral techniques and cyclic voltammetry. Structures of three of the complexes, Fe(2).3H(2)O (C(18)H(27)FeN(10)O(3), a = b = c = 20.2707(5), cubic, I3d, Z = 16), Fe(3).4.5H(2)O (C(18)H(30)FeN(10)O(4.5), a = 20.9986(10), b = 11.7098(5), c = 19.9405(9), beta = 109.141(1), monoclinic, P2(1)/c), Z = 8), and [FeH(3)(3)](ClO(4))(2).H(2)O (C(18)H(26)Cl(2)FeN(10)O(9), a = 9.4848(4), b = 23.2354(9), c = 12.2048(5), beta = 111.147(1) degrees, monoclinic, P2(1)/n, Z = 4) were determined at 100 K. The structures are similar to one another and feature an octahedral iron with facial coordination of imidazoles and imine nitrogen atoms. The iron(III) complexes of the deprotonated ligands, Fe(1), Fe(2), and Fe(3), are low-spin while the protonated iron(III) cationic complexes, [FeH(3)(1)](ClO(4))(3) and [FeH(3)(2)](ClO(4))(3), are high-spin and spin-crossover, respectively. The iron(II) cationic complexes, [FeH(3)(1)]S(4)O(6), [FeH(3)(2)](ClO(4))(2), [FeH(3)(3)](ClO(4))(2), and [FeH(3)(3)][B(C(6)H(5))(4)](2) exhibit spin-crossover behavior. Cyclic voltammetric measurements on the series of complexes show that complete deprotonation of the ligands produces a negative shift in the Fe(III)/Fe(II) reduction potential of 981 mV on average. Deprotonation in air of either cationic iron(II) or iron(III) complexes, [FeH(3)L](3+or2+), yields the neutral iron(III) complex, FeL. The process is reversible for Fe(3), where protonation of Fe(3) yields [FeH(3)(3)](2+).     

The reaction of Li[Al(OR)4] R = OC(CF3)2Ph, OC(CF3)3 with NO/NO2 giving NO[Al(OR)4], Li[NO3] and N2O. The synthesis of NO[Al(OR)4] from Li[Al(OR)4] and NO[SbF6] in sulfur dioxide solution

NO[Al(OC(CF(3))(2)Ph)(4)] 1 and NO[Al(OC(CF(3))(3))(4)] 2 were obtained by the metathesis reaction of NO[SbF(6)] and the corresponding Li[Al(OR)(4)] salts in liquid sulfur dioxide solution in ca 40% (1) and 85% (2) isolated yield. 1 and 2, as well as Li[NO(3)] and N(2)O, were also given by the reaction of an excess of mixture of (90 mol%) NO, (10 mol%) NO(2) with Li[Al(OR)(4)] followed by extraction with SO(2). The unfavourable disproportionation reaction of 2NO(2)(g) to [NO](+)(g) and [NO(3)](-)(g)[DeltaH degrees = +616.2 kJ mol(-1)] is more than compensated by the disproportionation energy of 3NO(g) to N(2)O(g) and NO(2)(g)[DeltaH degrees =-155.4 kJ mol(-1)] and the lattice energy of Li[NO(3)](s)[U(POT)= 862 kJ mol(-1)]. Evidence is presented that the reaction proceeds via a complex of [Li](+) with NO, NO(2)(or their dimers) and N(2)O. NO(2) and Li[Al(OC(CF(3))(3))(4)] gave [NO(3)(NO)(3)][Al(OC(CF(3))(3))(4)](2), NO[Al(OC(CF(3))(3))(4)] and (NO(2))[Al(OC(CF(3))(3))(4)] products. The aluminium complex [Li[AlF(OC(CF(3))(2)Ph)(3)]](2) 3 was prepared by the thermal decomposition of Li[Al(OC(CF(3))(2)Ph)(4)]. Compounds 1 and 3 were characterized by single crystal X-ray structural analyses, 1-3 by elemental analyses, NMR, IR, Raman and mass spectra. Solid 1 contains [Al(OC(CF(3))(2)Ph)(4)](-) and [NO](+) weakly linked via donor acceptor interactions, while in the SO(2) solution there is an equilibrium between the associated [NO](+)[Al(OC(CF(3))(2)Ph)(4)](-) and separated solvated ions. Solid 2 contains essentially ionic [NO](+) and [Al(OC(CF(3))(3))(4)](-). Complex 3 consists of two [Li[AlF(OC(CF(3))(2)Ph)(3)]] units linked via fluorine lithium contacts. Compound 1 is unstable in the SO(2) solution and decomposes to yield [AlF(OC(CF(3))(2)Ph)(3)](-), [(PhC(CF(3))(2)O)(3)Al(mu-F)Al(OC(CF(3))(2)Ph)(3)](-) anions as well as (NO)C(6)H(4)C(CF(3))(2)OH, while compound 2 is stable in liquid SO(2). The [small nu](NO(+)) in 1 and [NO](+)(toluene)[SbCl(6)] are similar, implying similar basicities of [Al(OC(CF(3))(2)Ph)(4)](-) and toluene.     

Structure and magnetic exchange in heterometallic 3d-3d transition metal triethanolamine clusters

Synthetic methods are described that have resulted in the formation of seven heterometallic complexes, all of which contain partially deprotonated forms of the ligand triethanolamine (teaH(3)). These compounds are [Mn(III)(4)Co(III)(2)Co(II)(2)O(2)(teaH(2))(2)(teaH)(0.82)(dea)(3.18)(O(2)CMe)(2)(OMe)(2)](BF(4))(2)(O(2)CMe)(2)·3.18MeOH·H(2)O (1), [Mn(II)(2)Mn(III)(2)Co(III)(2)(teaH)(4)(OMe)(2)(acac)(4)](NO(3))(2)·2MeOH (2), [Mn(III)(2)Ni(II)(4)(teaH)(4)(O(2)CMe)(6)]·2MeCN (3), [Mn(III)(2)Co(II)(2)(teaH)(2)(sal)(2)(acac)(2)(MeOH)(2)]·2MeOH (4), [Mn(II)(2)Fe(III)(2)(teaH)(2)(paa)(4)](NO(3))(2)·2MeOH·CH(2)Cl(2) (5), [Mn(II)Mn(III)(2)Co(III)(2)O(teaH)(2)(dea)(Iso)(OMe)(F)(2)(Phen)(2)](BF(4))(NO(3))·3MeOH (6) and [Mn(II)(2)Mn(III)Co(III)(2)(OH)(teaH)(3)(teaH(2))(acac)(3)](NO(3))(2)·3CH(2)Cl(2) (7). All of the compounds contain manganese, combined with 3d transition metal ions such as Fe, Co and Ni. The crystal structures are described and examples of 'rods', tetranuclear 'butterfly' and 'triangular' Mn(3) cluster motifs, flanked in some cases by diamagnetic cobalt(III) centres, are presented. Detailed DC and AC magnetic susceptibility and magnetization studies, combined with spin Hamiltonian analysis, have yielded J values and identified the spin ground states. In most cases, the energies of the low-lying excited states have also been obtained. The features of note include the 'inverse butterfly' spin arrangement in 2, 4 and 5. A S = 5/2 ground state occurs, for the first time, in the Mn(III)(2)Mn(II) triangular moiety within 6, the many other reported [Mn(3)O](6+) examples having S = ? or 3/2 ground states. Compound 7 provides the first example of a Mn(II)(2)Mn(III) triangle, here within a pentanuclear Mn(3)Co(2) cluster.     

Variable Nitric Oxide Reactivity of Tropocoronand Cobalt(III) Nitrite Complexes as a Function of the Polymethylene Linker Chain Length

The size-dependent reactivity of cobalt tropocoronands [TC-n,n](2-) is manifest in the NO chemistry of the cobalt(III) nitrite complexes [Co(η(2)-NO(2))(TC-n,n)] (n = 4-6), the synthesis and characterization of which are reported for the first time. Complete conversion of [Co(η(2)-NO(2))(TC-4,4)] to the cobalt mononitrosyl [Co(NO)(TC-4,4)] occurs upon exposure to NO(g). In contrast, addition of NO(g) to [Co(η(2)-NO(2))(TC-5,5)] generates both cobalt mono- and dinitrosyl adducts, and addition of nitric oxide to [Co(η(2)-NO(2))(TC-6,6)] converts this complex to the dicobalt tetranitrosyl species [Co(2)(NO)(4)(TC-6,6)]. In the latter complex, two tetrahedral cobalt dinitrosyl units are bound to the aminotroponeiminate poles of the [TC-6,6](2-) ligand. These results significantly broaden the chemistry of cobalt tropocoronands with nitric oxide and the nitrite anion.     

Self-assembly of [M8L4] and [M4L2] fluorescent metallomacrocycles with carbazole-based dipyrazole ligands

Fluorescent carbazole-based dipyrazole ligands (H(2)L(1-4)) were employed to coordinate with dipalladium corners ([(phen)(2)Pd(2)(NO(3))(2)](NO(3))(2), [(dmbpy)(2)Pd(2)(NO(3))(2)](NO(3))(2), or [(15-crown-5-phen)(2)Pd(2)(NO(3))(2)](NO(3))(2), where phen = 1,10-phenanthroline and dmbpy = 4,4'-dimethyl-2,2'-bipyridine, in aqueous solution to afford a series of positively charged [M(8)L(4)](8+) or [M(4)L(2)](4+) multimetallomacrocycles with remarkable water solubility. Their structures were characterized by (1)H NMR spectroscopy, electrospray ionization mass spectrometry, and elemental analysis and in the cases of 1·8BF(4)(-) ([(phen)(8)Pd(8)L(1)(4)](BF(4))(8)), and 3·4BF(4)(-) ([(phen)(4)Pd(4)L(2)(2)](BF(4))(4)) by single-crystal X-ray diffraction analysis. Complexes 3-8 are square-type hybrid metallomacrocycles, while complexes 1 and 2 exhibit folding cyclic structures. Interestingly, in single-crystal structures of 1·8BF(4)(-) and 3·4BF(4)(-), BF(4)(-) anions are trapped in the dipalladium clips through anion-π interaction. The luminescence properties and interaction toward anions of these metallomacrocycles were discussed.     

A quantum chemical survey of metalloporphyrin-nitrosyl linkage isomers: insights into the observation of multiple FeNO conformations in a recent crystallographic determination of nitrophorin 4

Using density functional theory-based geometry optimizations, we have searched for eta(1)-NO, eta(1)-ON (isonitrosyl), and eta(2)-NO (side-on bound NO) linkage isomers of a number of metalloporphyrin-NO complexes, M(Por)(NO)(L), where Por = porphinato dianion, M = Mn(II), Fe(II), Fe(III), Ru(II), Ru(III), Co(II), and Rh(II), and L = no ligand, SMe, Ph, and imidazole. The eta(1)-NO isomer had the lowest energy in all cases, and the isonitrosyl isomer was also located as a higher energy potential energy minimum in a number of cases. The eta(2)-NO isomer was only located as a minimum for Mn(II) (L = no ligand), Fe(III) (L = no ligand), and Ru(III) (L = Ph, imidazole, pyrdine), suggesting that an [MNO](6) electron count is important for stabilization of the eta(2) mode of ligation. However, in the presence of axial ligands L, the side-on isomers of [FeNO](6) complexes were not stable and opened up to an unusual geometry where the FeN(O) and NO vectors were tilted in opposite directions relative to the heme normal. Exactly such a geometry, as well as a "normal" upright geometry, has been observed in a recent crystallographic determination of nitrophorin 4 (Nature Struct. Biol. 2000, 7, 551), a salivary protein from the blood-sucking insect Rhodnius prolixus. Together, the calculated and experimental result illustrate the extreme softness of the FeNO potential energy surface toward various forms of tilting and bending deformations.     

Absorption, Circular Dichroism, and Luminescence Spectroscopy of Electrogenerated Delta-[Ru(bipy)(3)](+/0/)(-) and Delta-[Os(bipy)(3)](+/0/)(-) (bipy = 2,2'-Bipyridine)

The electronic absorption and circular dichroism (CD) spectra of the complexes produced by the one, two, and three electron reduction of Delta-[Ru(bipy)(3)](2+) and Delta-[Os(bipy)(3)](2+) are reported. The CD spectra give unequivocal proof that the added electrons are localized on individual bipiridine ligands and thus that the complexes are correctly formulated [M(bipy)(2)(bipy(-))](+), [M(bipy)(bipy(-))(2)](0), and [M(bipy(-))(3)](-). The absorption spectra of the triply reduced species [M(bipy(-))(3)](-) (M = Ru, Os) are compared to those of the Fe(II) and Ir(III) analogs. The luminescence spectra of the two triply reduced complexes [Ru(bipy(-))(3)](-) and [Os(bipy(-))(3)](-). are also presented. The MLCT luminescence found in the parent complexes is completely quenched and is replaced by a weak luminescence attributed to the pi(10) --> pi(7) transition of the (coordinated) [bipy](-) ion.