Molecular and Electronic Structure of the Square Planar Bis(o-amidobenzenethiolato)iron(III) Anion and Its Bis(o-quinoxalinedithiolato)iron(III) Analogue

Electron-Triggered Imine Coupling: Synthesis and Characterization of Three Redox States (0,-1,-2) of a Ni(N2 S2 ) Complex

Metal imine-thiolate complexes, M(NS)2 are known to undergo imine C-C bond formation to give M(N2 S2 ) complexes (M=Co, Ni) containing a redox-active ligand. Although these transfor-mations are not typically quantitative, we demonstrate here that the one-electron reduction of a related Ni bis(imine-thiolate) complex affords the corresponding paramagnetic [Ni(N2 S2 )]- anion (2⋅- ) exclusively; subsequent oxidation with [Cp2 Fe]BF4 then affords a high yield of neutral 2 (Cp=η5 -cyclopentadienyl). Moreover, electrochemical studies indicate that a second one-electron reduction affords the diamagnetic dianion. Both anionic products were isolated and characterized by SC-XRD and their electronic structures were investigated by UV-vis spectro-electrochemistry, EPR and NMR spectroscopy, and DFT studies. These studies show that reduction proceeds primarily on the ligand, with (N2 S2 )4- containing both thiolate and ring-delocalized anions.

Iron Complexes of a Proton-Responsive SCS Pincer Ligand with a Sensitive Electronic Structure

Sulfur/carbon/sulfur pincer ligands have an interesting combination of strong-field and weak-field donors, a coordination environment that is also present in the nitrogenase active site. Here, we explore the electronic structures of iron(II) and iron(III) complexes with such a pincer ligand, bearing a monodentate phosphine, thiolate S donor, amide N donor, ammonia, or CO. The ligand scaffold features a proton-responsive thioamide site, and the protonation state of the ligand greatly influences the reduction potential of iron in the phosphine complex. The N-H bond dissociation free energy, derived from the Bordwell equation, is 56 ± 2 kcal/mol. Electron paramagnetic resonance (EPR) spectroscopy and superconducting quantum interference device (SQUID) magnetometry measurements show that the iron(III) complexes with S and N as the fourth donors have an intermediate spin (S = 3/2) ground state with a large zero field splitting, and X-ray absorption spectra show a high Fe-S covalency. The Mössbauer spectrum changes drastically with the position of a nearby alkali metal cation in the iron(III) amido complex, and density functional theory calculations explain this phenomenon through a change between having the doubly occupied orbital as dz2 or dyz, as the former is more influenced by the nearby positive charge.

Proton-Coupled Electron-Transfer Reactivity Controls Iron versus Sulfur Oxidation in Nonheme Iron-Thiolate Complexes

Reaction of the five-coordinate Fe^II(N₄S) complexes, [Fe^II(iPr₃TACN)(abt^X)](OTf) (abt = aminobenzenethiolate, X = H, CF₃), with a one-electron oxidant and an appropriate base leads to net H atom loss, generating new Fe^III(iminobenzenethiolate) complexes that were characterized by single-crystal X-ray diffraction (XRD), as well as UV-vis, EPR, and Mössbauer spectroscopies. The spectroscopic data indicate that the iminobenzenethiolate complexes have S = 3/2 ground states. In the absence of a base, oxidation of the Fe^II(abt) complexes leads to disulfide formation instead of oxidation at the metal center. Bracketing studies with separated proton-coupled electron-transfer (PCET) reagents show that the Fe^II(aminobenzenethiolate) and Fe^III(iminobenzenethiolate) forms are readily interconvertible by H⁺/e^- transfer and provide a measure of the bond dissociation free energy (BDFE) for the coordinated N-H bond between 64 and 69 kcal mol^-1. This work shows that coordination to the iron center causes a dramatic weakening of the N-H bond and that Fe- versus S-oxidation in a nonheme iron complex can be controlled by the protonation state of an ancillary amino donor.

Rotational isomerism of the amide units in rotaxanes based on a cyclic tetraamide and secondary ammonium ions

We describe the synthesis of [2]rotaxanes consisting of a macrocyclic tetraamide and mono- and bis-ammonium ions and their conformational isomerism.

High-mobility band-like charge transport in a semiconducting two-dimensional metal-organic framework

Metal-organic frameworks (MOFs) are hybrid materials based on crystalline coordination polymers that consist of metal ions connected by organic ligands. In addition to the traditional applications in gas storage and separation or catalysis, the long-range crystalline order in MOFs, as well as the tunable coupling between the organic and inorganic constituents, has led to the recent development of electrically conductive MOFs as a new generation of electronic materials. However, to date, the nature of charge transport in the MOFs has remained elusive. Here we demonstrate, using high-frequency terahertz photoconductivity and Hall effect measurements, Drude-type band-like transport in a semiconducting, π-d conjugated porous Fe₃(THT)₂(NH₄)₃ (THT, 2,3,6,7,10,11-triphenylenehexathiol) two-dimensional MOF, with a room-temperature mobility up to ~ 220 cm² V^-1 s^-1. The temperature-dependent conductivity reveals that this mobility represents a lower limit for the material, as mobility is limited by impurity scattering. These results illustrate the potential for high-mobility semiconducting MOFs as active materials in thin-film optoelectronic devices.

2-Aminophenolate ligands for phosphorus(v): a lithium salt featuring the chiral [P(OC6H4NR)3]- anion

Phosphoranes P(OC6H4NR)2(OC6H4NHR) [R = Me (2a), Ph (2b), C6F5 (2c)] were synthesized by treating PCl5 with the respective 2-aminophenol derivative (1a-c, 3.1 equiv.). In one instance, an intermediate species, P(OC6H4NR)2Cl [R = Me (3a)], was isolated and structurally characterized. Deprotonation of the amine moieties (-NH[combining low line]R) in phosphoranes 2a and 2b with a strong alkali-metal base (e.g. n-BuLi) in the presence of a strong-donor solvent (e.g. THF) afforded salts composed of the hexacoordinate P(v)-anions [P(OC6H4NR)3]- (R = Me, [4a]-; Ph, [4b]-). Employing precursor 2a, the salt Li(THF)3fac-[4a]- was isolated. The X-ray crystal of each enantiomer of [4a]- was determined and, to our knowledge, represents the first structurally characterized example of a salt containing a hexacoordinate P(v)N3O3 anion featuring P(v)-N bonds.

A coronene-based semiconducting two-dimensional metal-organic framework with ferromagnetic behavior

Metal-organic frameworks (MOFs) have so far been highlighted for their potential roles in catalysis, gas storage and separation. However, the realization of high electrical conductivity (>10-3 S cm-1) and magnetic ordering in MOFs will afford them new functions for spintronics, which remains relatively unexplored. Here, we demonstrate the synthesis of a two-dimensional MOF by solvothermal methods using perthiolated coronene as a ligand and planar iron-bis(dithiolene) as linkages enabling a full π-d conjugation. This 2D MOF exhibits a high electrical conductivity of ~10 S cm-1 at 300 K, which decreases upon cooling, suggesting a typical semiconductor nature. Magnetization and 57Fe Mössbauer experiments reveal the evolution of ferromagnetism within nanoscale magnetic clusters below 20 K, thus evidencing exchange interactions between the intermediate spin S = 3/2 iron(III) centers via the delocalized π electrons. Our results illustrate that conjugated 2D MOFs have potential as ferromagnetic semiconductors for application in spintronics.

Effective, transition metal free and selective C–F activation under mild conditions

A simple and effective aromatic nucleophilic monosubstitution reaction for the synthesis of aromatic amines via selective C–F bond cleavage of various fluoroarenes with primary and secondary aromatic amines is demonstrated.

Octahedral monodithiolene complexes of iron: characterization of S,S'-coordinated dithiolate(1-) pi radical monoanions: a spectroscopic and density functional theoretical investigation

The reaction of cis-[Fe(III)(cyclam)Cl(2)]Cl with 1 equiv of sodium N-diethyldithiocarbamate, toluene-3,4-dithiolate, and maleonitriledithiolate in methanol in the presence of triethylamine afforded the cations [Fe(III)(cyclam)(Et(2)dtc)](2+) (1), [Fe(III)(cyclam)(tdt)](+) (2), and [Fe(III)(cyclam)(mnt)](+) (3), which were isolated as triflate, hexafluorophosphate, and tetrafluoroborate salt, respectively, using sodium triflate, potassium hexafluorophosphate, or sodium tetrafluoroborate as the source for the counteranion. Complexes 1, 2, and 3 possess an S = (1)/(2) ground state (low-spin ferric d(5)). These salts were characterized by X-ray crystallography, UV-vis, Mössbauer, and electron paramagnetic resonance spectroscopies. Cyclic voltammetry revealed that 2 and 3 are reversibly one-electron-reduced, generating neutral 2(red) and 3(red), respectively, and one-electron-oxidized, generating dicationic 2(ox) and 3(ox), respectively. Fe and S K-edge X-ray absorption spectroscopy (XAS) revealed that 2 (S = (1)/(2)) and 2(ox) (S = 0) possess a low-spin ferric ion. Complexes 2 and 3 are S,S'-coordinated to a closed-shell dithiolate(2-) ligand, whereas 2(ox) and 3(ox) consist of a low-spin ferric ion antiferromagnetically coupled to a dithiolate(1-) pi radical ligand. They are singlet diradicals [Fe(III)(cyclam)(dithiolate(*))](2+). The analysis of the sulfur K pre-edge transitions reveals significant multiplet effects in the spectra of 2 and 2(ox), which provide rare experimental evidence for a singlet diradical description for 2(ox). Mössbauer spectroscopy on frozen solutions of 2(red) clearly show the presence of a high-spin ferrous ion (S = 2). The experimentally established electronic structures of the three members of the electron transfer series [Fe(cyclam)(dithiolate)](2+,+,0) have been verified by broken symmetry density functional theoretical calculations, which have been calibrated against the experiment by calculating XAS and Mössbauer spectra.

Density functional theory analyses of bis(bipyridine)ruthenium noninnocent quinonoid and thiolosulfinato complexes containing ligands formally in the semiquinone oxidation state

Density functional theory and the polarized continuum model are used to derive the electronic structures of some open-shell, bis(bipyridine)ruthenium complexes bound to noninnocent quinonoid or thiolosulfinato ligands formally in the semiquinone oxidation state. The noninnocent properties of the o-thiolosulfinato ligand are explored and compared with those of the more conventional o-semiquinones with nitrogen, oxygen, and sulfur donor atoms. Spin densities are shown to be fairly localized in the metallocycle ring. It is demonstrated that oxidation of the parent [RuII(bpy)2 (1,2-(S,SO2)–C6H4] species occurs primarily in the metallocycle ring and is localized in the Ru–S0 bond.