Sodium-coupled electron transfer reactivity of metal-organic frameworks containing titanium clusters: the importance of cations in redox chemistry.

Stoichiometric reduction reactions of two metal-organic frameworks (MOFs) by the solution reagents (M = Cr, Co) are described. The two MOFs contain clusters with TiO rings: TiO(OH)(bdc); bdc = terephthalate (MIL-125) and TiO(OH)(bdc-NH); bdc-NH = 2-aminoterephthalate (NH-MIL-125). The stoichiometry of the redox reactions was probed using solution NMR methods.

A Flexible Photoactive Titanium Metal-Organic Framework Based on a [Ti(IV)3(μ3-O)(O)2(COO)6] Cluster.

The synthesis of titanium-carboxylate metal-organic frameworks (MOFs) is hampered by the high reactivity of the commonly employed alkoxide precursors. Herein, we present an innovative approach to titanium-based MOFs by the use of titanocene dichloride to synthesize COK-69, the first breathing Ti MOF, which is built up from trans-1,4-cyclohexanedicarboxylate linkers and an unprecedented [Ti(IV)3(μ3-O)(O)2(COO)6] cluster. The photoactive properties of COK-69 were investigated in depth by proton-coupled electron-transfer experiments, which revealed that up to one Ti(IV) center per cluster can be photoreduced to Ti(III) while preserving the structural integrity of the framework.

Chelate-Thiolate-Coordinate Ligands Modulating the Configuration and Electrochemical Property of Dinitrosyliron Complexes (DNICs).

As opposed to the reversible redox reaction ({Fe(NO)2 }(10) reduced-form DNIC [(NO)2 Fe(S(CH2 )3 S)](2-) (1)⇌{Fe(NO)2 }(9) oxidized-form [(NO)2 Fe(S(CH2 )3 S)](-) ), the chemical oxidation of the {Fe(NO)2 }(10) DNIC [(NO)2 Fe(S(CH2 )2 S)](2-) (2) generates the dinuclear {Fe(NO)2 }(9) -{Fe(NO)2 }(9) complex [(NO)2 Fe(μ-SC2 H4 S)2 Fe(NO)2 ](2-) (3) bridged by two terminal [SC2 H4 S](2-) ligands. On the basis of the Fe K-edge pre-edge energy and S K-edge XAS, the oxidation of complex 1 yielding [(NO)2 Fe(S(CH2 )3 S)](-) is predominantly a metal-based oxidation. The smaller S1-Fe1-S2 bond angle of 94.

Dinitrosyl iron complexes (DNICs): from biomimetic synthesis and spectroscopic characterization toward unveiling the biological and catalytic roles of DNICs.

Dinitrosyl iron complexes (DNICs) have been recognized as storage and transport agents of nitric oxide capable of selectively modifying crucial biological targets via its distinct redox forms (NO(+), NO(•) and NO(-)) to initiate the signaling transduction pathways associated with versatile physiological and pathological responses. For decades, the molecular geometry and spectroscopic identification of {Fe(NO)2}(9) DNICs ({Fe(NO)x}(n) where n is the sum of electrons in the Fe 3d orbitals and NO π* orbitals based on Enemark-Feltham notation) in biology were limited to tetrahedral (CN = 4) and EPR g-value ∼2.03, respectively, due to the inadequacy of structurally well-defined biomimetic DNICs as well as the corresponding spectroscopic library accessible in biological environments.

Iron(III) bound by hydrosulfide anion ligands: NO-promoted stabilization of the [Fe(III)-SH] motif.

Spontaneous transformation of the thermally stable [HS](-)-bound {Fe(NO)2}(9) dinitrosyl iron complex (DNIC) [(HS)2Fe(NO)2](-) (1) into [(NO)2Fe(μ-S)]2(2-) (Roussin's red salt (RRS)) along with release of H2S, probed by NBD-SCN (NBD = nitrobenzofurazan), was observed when DNIC 1 was dissolved in water at ambient temperature. The reversible transformation of RRS into DNIC 1 (RRS → DNIC 1) in the presence of H2S was demonstrated. In contrast, the thermally unstable hydrosulfide-containing mononitrosyl iron complex (MNIC) [(HS)3Fe(III)(NO)](-) (3) and [Fe(III)(SH)4](-) (5) in THF/DMF spontaneously dimerized into the first structurally characterized Fe(III)-hydrosulfide complexes [(NO)(SH)Fe(μ-S)]2(2-) (4) with two {Fe(NO)}(7) motifs antiferromagnetically coupled and [(SH)2Fe(μ-S)]2(2-) (6) resulting from two Fe(III) (S = 5/2) centers antiferromagnetically coupled to yield an S = 0 ground state with thermal occupancy of higher spin states, respectively.

The dinitrosyliron complex [Fe₄(μ₃-S)₂(μ₂-NO)₂(NO)₆]²⁻ containing bridging nitroxyls: ¹⁵N (NO) NMR analysis of the bridging and terminal NO-coordinate ligands.

The fluxional terminal and semibridging NO-coordinate ligands of DNIC [Fe4(μ3-S)2(μ2-NO)2(NO)6](2-), a precursor of Roussin's black salt (RBS), are characterized by IR ν(NO), (15)N (NO) NMR and single-crystal X-ray diffraction.

Nitrite activation to nitric oxide via one-fold protonation of iron(II)-O,O-nitrito complex: relevance to the nitrite reductase activity of deoxyhemoglobin and deoxyhemerythrin.

The reversible transformations [(Bim)3Fe(κ(2)-O2N)][BF4] (3) <-> [(Bim)3Fe(NO)(κ(1)-ONO)][BF4]2 (4) were demonstrated and characterized. Transformation of O,O-nitrito-containing complex 3 into [(Bim)3Fe(μ-O)(μ-OAc)Fe(Bim)3](3+) (5) along with the release of NO and H2O triggered by 1 equiv of AcOH implicates that nitrite-to-nitric oxide conversion occurs, in contrast to two protons needed to trigger nitrite reduction producing NO observed in the protonation of [Fe(II)-nitro] complexes.

Insight into one-electron oxidation of the {Fe(NO)2}9 dinitrosyl iron complex (DNIC): aminyl radical stabilized by [Fe(NO)2] motif.

A reversible redox reaction ({Fe(NO)(2)}(9) DNIC [(NO)(2)Fe(N(Mes)(TMS))(2)](-) (4) ⇄ oxidized-form DNIC [(NO)(2)Fe(N(Mes)(TMS))(2)] (5) (Mes = mesityl, TMS = trimethylsilane)), characterized by IR, UV-vis, (1)H/(15)N NMR, SQUID, XAS, single-crystal X-ray structure, and DFT calculation, was demonstrated. The electronic structure of the oxidized-form DNIC 5 (S(total) = 0) may be best described as the delocalized aminyl radical [(N(Mes)(TMS))(2)](2)(-•) stabilized by the electron-deficient {Fe(III)(NO(-))(2)}(9) motif, that is, substantial spin is delocalized onto the [(N(Mes)(TMS))(2)](2)(-•) such that the highly covalent dinitrosyl iron core (DNIC) is preserved. In addition to IR, EPR (g ≈ 2.

Transformation of the {Fe(NO)2}9 dinitrosyl iron complexes (DNICs) into S-nitrosothiols (RSNOs) triggered by acid-base pairs.

S-nitrosation of the coordinated thiolate of dinitrosyl iron complexes (DNICs) to generate S-nitrosothiols (RSNOs) was demonstrated. Transformation of [{(NO)(2)Fe(μ-StBu)}(2)] (1-tBuS) into the {Fe(NO)(2)}(9) DNIC [(NO)(2)Fe(StBu)(MeIm)] (2-MeIm) occurs under addition of 20 equiv of 1-methylimidazole (MeIm) into a solution of 1-tBuS in THF. The dynamic interconversion between {Fe(NO)(2)}(9) [(NO)(2)Fe(S-NAP)(dmso)] (2-dmso) (NAP = N-acetyl-D-penicillamine) and [{(NO)(2)Fe(μ-S-NAP)}(2)] (1-NAP) was also observed in a solution of complex 1-NAP in DMSO.

Transformation of dinitrosyl iron complexes [(NO)2Fe(SR)2]- (R = Et, Ph) into [4Fe-4S] Clusters [Fe4S4(SPh)4]2-: relevance to the repair of the nitric oxide-modified ferredoxin [4Fe-4S] clusters.

Transformation of dinitrosyl iron complexes (DNICs) [(NO)(2)Fe(SR)(2)](-) (R = Et, Ph) into [4Fe-4S] clusters [Fe(4)S(4)(SPh)(4)](2-) in the presence of [Fe(SPh)(4)](2-/1-) and S-donor species S(8) via the reassembling process ([(NO)(2)Fe(SR)(2)](-) --> [Fe(4)S(3)(NO)(7)](-) (1)/[Fe(4)S(3)(NO)(7)](2-) (2) --> [Fe(4)S(4)(NO)(4)](2-) (3) --> [Fe(4)S(4)(SPh)(4)](2-) (5)) was demonstrated. Reaction of [(NO)(2)Fe(SR)(2)](-) (R = Et, Ph) with S(8) in THF, followed by the addition of HBF(4) into the mixture solution, yielded complex [Fe(4)S(3)(NO)(7)](-) (1). Complex [Fe(4)S(3)(NO)(7)](2-) (2), obtained from reduction of complex 1 by [Na][biphenyl], was converted into complex [Fe(4)S(4)(NO)(4)](2-) (3) along with byproduct [(NO)(2)Fe(SR)(2)](-) via the proposed [Fe(4)S(3)(SPh)(NO)(4)](2-) intermediate upon treating complex 2 with 1.

Anionic Roussin's red esters (RREs) syn-/anti-[Fe(mu-SEt)(NO)2]2(-): the critical role of thiolate ligands in regulating the transformation of RREs into dinitrosyl iron complexes and the anionic RREs.

The anionic syn-/ anti-[Fe(mu-SEt)(NO) 2] 2 (-) ( 2a) were synthesized and characterized by IR, UV-vis, EPR, and X-ray diffraction. The geometry of the [Fe(mu-S) 2Fe] core is rearranged in going from [{Fe(NO) 2} (9)-{Fe(NO) 2} (9)] Roussin's red ester [Fe(mu-SEt)(NO) 2] 2 ( 1a) (Fe..

New members of a class of dinitrosyliron complexes (DNICs): interconversion and spectroscopic discrimination of the anionic {Fe(NO)2}9 [(NO)2Fe(C3H3N2)2]- and [(NO)2Fe(C3H3N2)(SR)]- (C3H3N2 = deprotonated imidazole; R = tBu, Et, Ph).

The anionic {Fe(NO)2}(9) DNIC[(NO)2Fe(C3H3N2)2](-) (2) (C3H3N2 = deprotonated imidazole) containing the deprotonated imidazole-coordinated ligands and DNICs [(NO)2Fe(C3H3N2)(SR)](-) (R = (t)Bu(3), Et(4), Ph(5)) containing the mixed deprotonated imidazole-thiolate coordinated ligands, respectively, were synthesized by thiol protonation or thiolate(s) ligand-exchange reaction. The anionic {Fe(NO)2}(9) DNICs 2- 5 were characterized by IR, UV-vis, EPR, and single-crystal X-ray diffraction. The facile transformation among the anionic {Fe(NO)2}(9) DNICs 2- 5 and [(NO)2Fe(S(t)Bu)2](-)/[(NO)2Fe(SEt)2](-)/[(NO)2Fe(SPh)2](-) was demonstrated in this systematic study.