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The process of oxygen evolution reaction (OER) is crucial for energy storage and conversion, and the spin electronic structure of catalyst significantly influences its catalytic activity. Precisely regulating the spin electronic structures of metal active centers with intermediate spin (IS) states is challenging but important. This study presents a general method for achieving spin‐state precise modulation by altering the secondary coordination sphere (SCS) in Fe‐substituted LaCo1‐xFexO3 perovskites, denoted as Co6‐y−[Co]−Fey (y = 0–6). The concentration‐dependent SCSs can precisely regulate the spin state of Co3+ from high‐spin (HS) to IS and low‐spin (LS) state by tuning the Co─O binding energy of primary coordination sphere (PCS) to ≈567 KJ mol−1. The binding energy demonstrates a strong negative correlation with the spin state of Co3+, serving as a quantitative descriptor for precise spin‐state modulation. Furthermore, a universal optimal doping concentration is proposed for generating IS‐state Co3+ with the best OER activity, ranging from 1/(m+1) to 2/(m+1) in M‐doped ACo1‐xMxOy system with the coordination number of m. As a proof‐of‐concept, the LaCo7/9Fe2/9O3 with IS Co3+ exhibits significantly enhanced OER activity, almost six times higher than the control samples (without IS Co3+). These findings provide new insights into spin‐state modulation for effective OER catalysts. [ABSTRACT FROM AUTHOR]

The synthesis, X-ray structure and properties of saddle distorted six-coordinated iron(III) porphyrins having weak axial coordination such as THF and dioxane have been reported which stabilize pure intermediate spin state of iron. The work also highlights the possible spin state switching of iron through external perturbations such as H-bonding interactions, weak axial coordination etc which are indeed important steps in the functioning of various heme proteins. Hemoproteins serve many diverse biological functions through the nearly identical heme prosthetic group. The elucidation of the electronic structures of synthetic hemes is quite important in understanding the function and catalytic processes of naturally occurring heme proteins. For example, an important step in cytochrome P450 catalysis has been the spin-state crossover upon substrate binding which thereby facilitates the reduction of the iron centre. Iron(III) porphyrins having intermediate-spin state have attained much of attention since Maltempo's discovery of its crucial contributions in several bacterial heme proteins such as Cytochromes c ′. We have analyzed here various factors responsible for stabilizing such intermediate-spin states of iron using the same iron(III)porphyrinato platform. We report the synthesis, X-ray structure and spectroscopic characterizations of saddle distorted six-coordinated iron(III) porphyrins having weak axial coordination such as THF and dioxane. Through combined solid as well as solution phase studies, it has been found that the complexes demonstrate iron(III) in pure intermediate-spin state. A brief comprehensive personal account for stabilizing intermediate-spin state of iron using the same iron(III) porphyrins has also been presented. Our work highlights the possible spin state switching of iron through external perturbations such as H-bonding interactions, weak axial coordination etc which are indeed important steps in the functioning of various heme proteins. [ABSTRACT FROM AUTHOR]

To investigate the influence of chemical pressure on the eg orbital occupation and the spin state of Co3+ ions, which are closely related to electrochemical reaction of catalysts for energy storage applications, we have prepared a new material Sr1.7Ca0.3CoO3F, which was previously predicted to possess an intermediate‐spin (IS) state with eg1 configuration. Our experimental Co‐L2,3 X‐ray absorption spectrum of Sr1.7Ca0.3CoO3F was very similar to those of the high‐spin (HS) Co3+ references Sr2CoO3F and Sr2CoO3Cl indicating an HS Co3+ ground state. The HS‐Co3+ ground state in Sr1.7Ca0.3CoO3F was further confirmed by using O‐K XAS spectra and theoretical simulation of the Co‐L2,3 XAS spectra with configuration‐interaction cluster calculations. We present theoretical energy diagrams of three spin states for Co3+ ions in Sr2CoO3F as a function of external pressure based on the crystal structures observed in a previous high‐pressure study. We have also investigated the structural conditions that are required to stabilize the IS state in this effective local pyramidal structure theoretically, and found that the in‐plane Co–O distance (<1.88 Å) and the out‐of‐plane Co displacement (<0.18 Å) are critical conditions for obtaining the IS‐Co3+ ground state. [ABSTRACT FROM AUTHOR]

Abstract: The complexes [FeLN2S2X] [in which LN2S2=2,2′‐(2,2′‐bipryridine‐6,6′‐diyl)bis(1,1′‐diphenylethanethiolate) and X=Cl, Br and I], characterized crystallographically earlier and here (Fe(L)Br), reveal a square pyramidal coordinated FeIII ion. Unusually, all three complexes have intermediate spin ground states. Susceptibility measurements, powder cw X‐ and Q‐band EPR spectra, and zero‐field powder Mössbauer spectra show that all complexes display distinct magnetic anisotropy, which has been rationalized by DFT calculations. [ABSTRACT FROM AUTHOR]

Abstract: Neutron scattering experiments were performed on the single crystals of layered-perovskite cobaltate La2− x Sr x CoO4. For a commensurate value of x=0.5, magnetic reflections due to high-spin (HS) state of Co2+ are observed in (H, 0, L) plane. Further, in (H, H, L) plane, we found super-lattice reflections with wave vector q m=(1/4, 1/4, 1). The latter magnetic peaks cannot be understood by the Co2+ spin configurations, indicating that these peaks are originated from Co3+ spin ordering. From the hole-doping dependence, short ranged charge and spin orderings were observed below x=0.5, while those of peaks were suppressed at x=0.6. Our results suggest that double exchange interaction between the HS state of Co2+ and the intermediate spin (IS) state of Co3+ mediate the IS state in this system. [Copyright &y& Elsevier]