[Fe(µ-OH)] Linked FeO Triads: Mössbauer Evidence for Trigonal µ-O or µ-OH Groups in Bridged versus Unbridged Complexes.

The syntheses, coordination chemistry, and Mössbauer spectroscopy of hepta-iron(III) complexes using derivatised salicylaldoxime ligands from two categories; namely, 'single-headed' (H) and 'double-headed' (H) salicylaldoximes are described. All compounds presented here share a [Fe-µ-O] core in which the iron(III) ions are µ-hydroxo-bridged in the complex and µ-oxo-bridged in and . Each compound consists of 2 × [Fe-µ-O] triads that are linked via a central [Fe(µ-OH)] ion.

Synthesis and Characterization of Symmetrically Unsymmetrically Proton-Bridged Hexa-Iron Clusters.

Syntheses and magnetic and structural characterization of hexa-iron complexes of derivatized salicylaldoximes are discussed. Complexation of Fe(BF)·6HO with each ligand (H and H ) in a methanolic-pyridine solution resulted in hexa-iron compounds ( and , respectively), which each contain two near-parallel metal triangles of [Fe-μ-O], linked by six fluoride bridges and stabilized by a hydrogen-bonded proton between the μ-O groups. Within each metal triangle of , Fe(III) ions are connected the amine "straps" of (H -2H).

New salicylaldoximato-borate ligands resulting from anion hydrolysis and their respective copper and iron complexes.

Anion hydrolysis reactions between salicylaldoximato ligands (L'-L''') and copper and iron BF metal salts, have resulted in the formation of new salicylaldoximato borate containing transition metal complexes: [Fe(L' + 2H)](BF)(MeOH) (C1), [Fe(L'' + 4H)(OH)(Py)](BF)(HO)(Py) (C2), and [Cu(L''' + H)Cl] (C3). Each of the complexes have been structurally characterised, revealing the indirect role boron plays in the formation of these complexes. For complexes C1 and C2, Mössbauer spectroscopy confirmed the existence of Fe(iii) oxidation states.

Substrate Specificity in Thiol Dioxygenases.

Thiol dioxygenases make up a class of ferrous iron-dependent enzymes that oxidize thiols to their corresponding sulfinates. X-ray diffraction structures of cysteine-bound cysteine dioxygenase show how cysteine is coordinated via its thiolate and amine to the iron and oriented correctly for O atom transfer. There are currently no structures with 3-mercaptopropionic acid or mercaptosuccinic acid bound to their respective enzymes, 3-mercaptopropionate dioxygenase or mercaptosuccinate dioxygenase.

Guest-Responsive Elastic Frustration "On-Off" Switching in Flexible, Two-Dimensional Spin Crossover Frameworks.

In this study we exploit the flexible nature of porous coordination polymers (PCPs) with integrated spin crossover (SCO) properties to manipulate the multistability of spin-state switching profiles. We previously reported the two-dimensional Hofmann-type framework [Fe(thtrz)Pd(CN)]·EtOH,HO (1·EtOH,HO), N-thiophenylidene-4 H-1,2,4-triazol-4-amine), displaying a distinctive two-step SCO profile driven by extreme elastic frustration. Here, we reveal a reversible release mechanism for this elastic frustration via stepwise guest removal from the parent phase (1·EtOH,HO → 1·HO → 1·Ø).

Self-assembly of a mixed-valence Fe-Fe tetranuclear star.

A unique self-assembled mixed-valence FeII-FeIII tetranuclear star has been comprehensively characterised showing a large magnetic anisotropy at the peripheral FeII centres, ferromagnetic coupling between the iron centres and field-induced SMM behaviour.

Observation of Radical Rebound in a Mononuclear Nonheme Iron Model Complex.

A nonheme iron(III) terminal methoxide complex, [Fe(N3PyO)(OCH)]ClO, was synthesized. Reaction of this complex with the triphenylmethyl radical (PhC) leads to formation of PhCOCH and the one-electron-reduced iron(II) center, as seen by UV-vis, EPR, H NMR, and Mössbauer spectroscopy. These results indicate that homolytic Fe-O bond cleavage occurs together with C-O bond formation, providing a direct observation of the "radical rebound" process proposed for both biological and synthetic nonheme iron centers.

Mixed Valency in a 3D Semiconducting Iron-Fluoranilate Coordination Polymer.

A pair of coordination polymers of composition (NBu)[M(fan)] (fan = fluoranilate; M = Fe and Zn) were synthesized and structurally characterized. In each case the compound consists of a pair of interpenetrating three-dimensional, (10,3)-a networks in which metal centers are linked by chelating/bridging fluoranilate ligands. Tetrabutylammonium cations are located in the spaces between the two networks.

Heteroleptic iron(iii) Schiff base spin crossover complexes: halogen substitution, solvent loss and crystallite size effects.

The influence of the halogen substituent on the qsal moiety of iron(iii) heteroleptic compounds with the formulae [Fe(qsal-X)(thsa)]·nMeCN, where qsal-X = X-substituted quinolylsalicylaldimine; thsa = thiosemicarbazone-salicylaldiminate; X = F; n = 2.5, 1·2.5MeCN and X = Cl 2, Br 3 and I 4, n = 1 (labelled 2·MeCN, 3·MeCN and 4·MeCN, respectively) has been systematically investigated.

Halogen Substitution Effects on N O Schiff Base Ligands in Unprecedented Abrupt Fe Spin Crossover Complexes.

A family of halogen-substituted Schiff base iron(II) complexes, [Fe (qsal-X) ], (qsal-X=5-X-N-(8-quinolyl)salicylaldimines)) in which X=F (1), Cl (2), Br (3) or I (4) has been investigated in detail. Compound 1 shows a temperature invariant high spin state, whereas the others all show abrupt spin transitions, at or above room temperature, namely, 295 K (X=I) up to 342 K (X=Br), these being some of the highest T values obtained, to date, for Fe N/O species. We have recently reported subtle symmetry breaking in [Fe (qsal-Cl) ] 2 with two spin transition steps occurring at 308 and 316 K.

Symmetry breaking above room temperature in an Fe(ii) spin crossover complex with an NO donor set.

[Fe(qsal-Cl)] is one of the few known Fe(ii) spin crossover compounds with an NO donor atom environment. It shows an abrupt two-step spin transition at 308 and 316 K and importantly, symmetry breaking at the highest temperature reported, to date, in spin crossover compounds.

Aromatic C-F Hydroxylation by Nonheme Iron(IV)-Oxo Complexes: Structural, Spectroscopic, and Mechanistic Investigations.

The synthesis and reactivity of a series of mononuclear nonheme iron complexes that carry out intramolecular aromatic C-F hydroxylation reactions is reported. The key intermediate prior to C-F hydroxylation, [Fe(O)(N4Py)](BF) (1-O, Ar = -2,6-difluorophenyl), was characterized by single-crystal X-ray diffraction. The crystal structure revealed a nonbonding C-H···O═Fe interaction with a CHCN molecule.

Spin Crossover, Polymorphism and Porosity to Liquid Solvent in Heteroleptic Iron(III) {Quinolylsalicylaldimine/Thiosemicarbazone-Salicylaldimine} Complexes.

Heteroleptic iron(III) complexes of formula [Fe(qsal)(thsa)]⋅solvent have been synthesized: [Fe(qsal)(thsa)]⋅0.4 BuOH (1), [Fe(qsal)(thsa)]⋅0.5 MeCN (2) and [Fe(qsal)(thsa)]⋅0.

Ligand effects in a heteroleptic bis-tridentate iron(iii) spin crossover complex showing a very high T1/2 value.

We describe the first example of a bis-tridentate heteroleptic iron(iii) spin crossover (SCO) complex, [Fe(3-OMe-SalEen)(thsa)]. Compared to the parent homoleptic compounds, the spin crossover features in the heteroleptic species are enhanced with a gradual-abrupt spin transition at 344 K. Clear correlations between π-π interactions and the T1/2 value have been revealed.

The Cys-Tyr cross-link of cysteine dioxygenase changes the optimal pH of the reaction without a structural change.

Cysteine dioxygenase (CDO) is a non-heme monoiron enzyme with an unusual posttranslational modification in the proximity of the ferrous iron active site. This modification, a cysteine to tyrosine thioether bond, cross-links two β-strands of the β-barrel. We have investigated its role in catalysis through a combined crystallographic and kinetic approach.

Direct observation of a nonheme iron(IV)-oxo complex that mediates aromatic C-F hydroxylation.

The synthesis of a pentadentate ligand with strategically designed fluorinated arene groups in the second coordination sphere of a nonheme iron center is reported. The oxidatively resistant fluorine substituents allow for the trapping and characterization of an Fe(IV)(O) complex at -20 °C. Upon warming of the Fe(IV)(O) complex, an unprecedented arene C-F hydroxylation reaction occurs.

Dramatically accelerated selective oxygen-atom transfer by a nonheme iron(IV)-oxo complex: tuning of the first and second coordination spheres.

The new ligand N3Py(amide)SR and its Fe(II) complex [Fe(II)(N3Py(amide)SR)](BF4)2 (1) are described. Reaction of 1 with PhIO at -40 °C gives metastable [Fe(IV)(O)(N3Py(amide)SR)](2+) (2), containing a sulfide ligand and a single amide H-bond donor in proximity to the terminal oxo group. Direct evidence for H-bonding is seen in a structural analogue, [Fe(II)(Cl)(N3Py(amide)SR)](BF4)2 (3).