The assignment of the two substrate water sites tetra-manganese penta-oxygen calcium (Mn 4 O 5 Ca) cluster photosystem II is essential for elucidation mechanism biological O-O bond formation and subsequent design bio-inspired water-splitting catalysts. We recently demonstrated using pulsed EPR spectroscopy that one five oxygen bridges (μ-oxo) exchanges unusually rapidly with bulk thus a likely candidate substrates. Ammonia, analog, was previously shown to bind Mn Ca cluster, potentially...

The S2 state of the oxygen-evolving complex photosystem II, which consists a Mn4O5Ca cofactor, is EPR-active, typically displaying multiline signal, arises from ground spin total ST = 1/2. precise appearance signal varies amongst different photosynthetic species, preparation and solvent conditions/compositions. Over past five years, using model species Thermosynechococcus elongatus, we have examined modifications that induce changes in i.e. Ca2+/Sr2+-substitution binding ammonia, to...

Nature's water-splitting catalyst, an oxygen-bridged tetramanganese calcium (Mn4O5Ca) complex, sequentially activates two substrate water molecules generating molecular O2. Its reaction cycle is composed of five intermediate (Si) states, where the index i indicates number oxidizing equivalents stored by cofactor. After formation S4 state, product dioxygen released and cofactor returns to its lowest oxidation S0. Membrane-inlet mass spectrometry measurements suggest that at least one bound...

Controlled switching of the spin state transition metal ions, particularly FeII and FeIII, is a prerequisite to achieve selectivity, efficiency, catalysis in number metalloenzymes. Here we report on an iron(III) porphyrin with photochromic axial ligand which, upon irradiation two different wavelengths reversibly switches its between low-spin (S = 1/2) high-spin 5/2) solution (DMSO-acetone, 2:598). The efficiency 76% at room temperature. system neither oxygen nor water sensitive, no fatigue...

Abstract The cobalt(II) in [Co(NCS) 2 (4‐methoxypyridine) ] n are linked by pairs of thiocyanate anions into linear chains. In contrast to a previous structure determination, two crystallographically independent centers have been found be present. the antiferromagnetic state, below critical temperature ( T c =3.94 K) and field H =290 Oe), slow relaxations ferromagnetic chains observed. They originate mainly from defects magnetic structure, which has elucidated micromagnetic Monte Carlo...

Ca2+ is an integral component of the Mn4O5Ca cluster oxygen-evolving complex in photosystem II (PS II). Its removal leads to loss water oxidizing functionality. The S2′ state Ca2+-depleted from spinach examined by X- and Q-band EPR 55Mn electron nuclear double resonance (ENDOR) spectroscopy. Spectral simulations demonstrate that upon removal, its electronic structure remains essentially unaltered, i.e. a manganese tetramer. No redistribution valence states only minor perturbation exchange...

Iron terminal imido species are typically implicated as reaction intermediates in iron-catalyzed transformations. While a large body of work has been devoted to mid- and high-valent iron imidos, date the chemistry iron(II) imidos remained largely unexplored due difficulty accessing them. Herein, we present study on two-coordinate complex [(IPr)Fe(NArTrip)] (3; IPr = 1,3-bis(2′,6′-diisopropylphenyl)imidazol-2-ylidene; ArTrip 2,6-bis(2′,4′,6′-triisopropylphenyl)phenyl) prepared from an iron(0)...

Two different isomers of [Co(NCS)2(4-chloropyridine)2]n (3C and 3L) were synthesized from solution by thermal decomposition Co(NCS)2(4-chloropyridine)2(H2O)2 (2), which show a metal coordination leading to corrugated chains in 3C linear 3L. Solvent mediated conversion experiments prove that is thermodynamically stable at room temperature where 3L metastable. Magnetic measurements reveal the magnetic exchange comparable observed for previously reported related chain compounds, whereas with...

The fascinating magnetic and catalytic properties of coordinatively unsaturated 3d metal complexes are a manifestation their electronic structures, in particular nearly doubly or triply degenerate orbital ground levels. Here, we propose criterion to determine the degree degeneracy this class based on experimentally accessible anisotropy (parametrized by electron spin g- zero-field splitting (ZFS)-tensors). is derived from comprehensive spectroscopic theoretical study trigonal planar iron(0)...

The effect of a pendant neutral alcohol moiety in the N‐alkylated cyclam (1,4,8,11‐tetraazacyclotetradecane) ligand backbone is examined for non‐heme mononuclear oxoiron(IV) unit [FeIV(Osyn)(TMC‐HOR)(NCCH3)]2+ (1‐syn) (TMC‐HOR = 2‐(4,8,11‐trimethyl‐1,4,8,11‐tetraazacyclotetradecan1‐yl)ethan‐1‐ol). Unlike related [FeIV(Oanti)(TMC‐SR)]+ (3‐anti) (TMC‐SR 1‐mercaptoethyl‐4,8,11‐trimethyl‐1,4,8,11‐tetraazacyclotetradecane) complex, bearing an axial mono‐anionic thiolate trans to oxo unit, 1‐syn...

<title>Abstract</title> Manipulating the physical properties of solid matter using only photons is a major challenge in materials science. In this study, we present photochemistry occurring single crystal simple cyanide complex, K₄[Mo^III(CN)₇]·2H₂O. Upon exposure to visible light at different wavelengths, reversible breaking and reformation dative bonds triggered, resulting photoswitching Mo^III coordination geometry between 6-...

Bis(p-methoxyphenyl)carbene is the first carbene that at cryogenic temperatures can be isolated in both its lowest energy singlet and triplet states. At 3 K, states coexist indefinitely under these conditions. The investigated argon matrices by IR, UV-vis, X-band EPR spectroscopy MTHF glasses W-band Q-band ENDOR spectroscopy. UV (365 nm) irradiation of system results formation predominantly carbene, whereas visible (450 light shifts photostationary equilibrium toward state. Upon annealing...

Reaction of Co(NCS)2 with different coligands leads to the formation three compounds general composition [Co(NCS)2(L)2]n (L = aniline (1), morpholine (2), and ethylenethiourea (3)). In all these cobalt(II) cations are octahedrally coordinated by two trans thiocyanate N S atoms apical donor linked into linear chains pairs anionic ligands. The magnetic behavior was investigated a combination static dynamic susceptibility as well specific-heat measurements, computational studies, THz-EPR...

New cobalt(II)-based complexes with [N

Ca2+-depleted and Ca2+-reconstituted spinach photosystem II was studied using polarized X-ray absorption spectroscopy of oriented PS preparations to investigate the structural functional role Ca2+ ion in Mn4O5Ca cluster oxygen-evolving complex (OEC). Samples were prepared by low pH/citrate treatment as one-dimensionally ordered membrane layers poised S1 (S1′) S2 (S2′) states, S2′YZ• state, at which point catalytic cycle water oxidation is inhibited, state. Polarized Mn K-edge XANES EXAFS...

In many metalloenzymes, sulfur-containing ligands participate in catalytic processes, mainly via the involvement electron transfer reactions. a biomimetic approach, we now demonstrate implication of S-ligation cobalt mediated oxygen reduction reactions (ORR). A comparative study between ORR capabilities four-nitrogen bound [Co(cyclam)]2+ (1; cyclam=1,5,8,11-tetraaza-cyclotetradecane) and S-containing analog [Co(S2 N2 -cyclam)]2+ (2; S2 -cyclam=1,8-dithia-5,11-diaza-cyclotetradecane) reveals...

Abstract The methanol solvomorph 1 ⋅ 2MeOH of the cobalt(II) complex [Co(L Sal,2−Ph ) 2 ] ( with sterically demanding Schiff‐base ligand 2‐(([1,1′‐biphenyl]‐2‐ylimino)methyl)phenol (HL shows thus far largest dihedral twist distortion between two chelate planes compared to an ideal pseudotetrahedral arrangement. ion in exhibits easy‐axis anisotropy leading a spin‐reversal barrier 55.3 cm −1 , which corresponds increase about 17 % induced by larger solvent‐free . magnetic relaxation for is...

A mononuclear iron(III) porphyrin compound exhibiting unexpectedly slow magnetic relaxation, which is a characteristic of single-ion magnet behaviour, reported. This behaviour originates from the close proximity (≈550 cm-1 ) intermediate-spin S=3/2 excited states to high-spin S=5/2 ground state. More quantitatively, although state mostly S=5/2, spin-admixture model evidences sizable contribution (≈15 %) state, as consequence experiences large and positive axial anisotropy (D=+19.2 )....

A unique type of Cu2/O2 adduct with orthogonal (close to 90°) Cu-O-O-Cu arrangement has been proposed for initial stages O2 binding at biological III dicopper sites, and targeted ligand design now allowed us emulate such an in a pyrazolate-based μ-η1:η1-peroxodicopper(II) complex (2) torsion φ 87°, coined ⊥P intermediate. Full characterization 2, including X-ray diffraction (dO-O = 1.452 Å) Raman spectroscopy (ν̃O-O 807 cm-1), completes series closely related intermediates featuring cores...

Cytochrome c oxidase (CcO) is a heme−copper (HCO) that catalyzes the natural reduction of oxygen to water. A pro-found understanding some elementary steps leading intricate 4e−/4H+ O2 presently lacking. St = 1 FeIII−(O22−)−CuII (IP) intermediate proposed reduce overpotentials associated with reductive O−O bond rupture by allowing electron transfer from tyrosine moiety without necessity any spin-surface crossing. Direct evidence in-volvement IP in HCO catalytic cycle is, however, missing....

Cytochrome c oxidase (CcO) is a heme copper (HCO) that catalyzes the natural reduction of oxygen to water. A profound understanding some elementary steps leading intricate 4e–/4H+ O2 presently lacking. total spin St = 1 FeIII–(O22–)–CuII (IP) intermediate proposed reduce overpotentials associated with reductive O–O bond rupture by allowing electron transfer from tyrosine moiety without necessity any spin-surface crossing. Direct evidence involvement IP in CcO catalytic cycle is, however,...

The reaction of Co(NCS)2 with N-methylaniline leads to the formation [Co(NCS)2(N-methylaniline)2]n (1), in which cobalt(II) cations are octahedrally coordinated and linked into linear chains by pairs thiocyanate anions. In contrast [Co(NCS)2(aniline)2]n (2) reported recently, strong interchain N-H···S hydrogen bonding, such interactions absent 1. Computational studies reveal that ions compound 1 show an easy-axis anisotropy is lower than 2, but direction easy axis being similar both...