High-spin Nature Research Articles

Unrivaled single atom catalytic efficiency of Fe@Mg12O12 toward N2 reduction reaction (NRR) for NH3 generation

The quest for efficient and sustainable catalytic processes for ammonia synthesis has led to the exploration of transition metal (TM) doped single-atom catalysts (SACs) due to their exceptional catalytic properties and potential for overcoming the limitations of conventional catalysts. This study investigates the application of iron-doped Mg12O12 nanocage (Fe@Mg12O12) as a novel SAC for the nitrogen reduction reaction (NRR), employing density functional theory (DFT) calculations. The optimum reaction mechanism pathway of the NRR has been investigated and obtained by considering the stability of the different possible intermediates. Our analysis reveals that the high spin nature of Fe in Fe@Mg12O12 can stabilize the NRR intermediates by facilitating different total spin-states of the intermediates. Moreover, the importance of the role of support is highlighted as it stabilizes the adsorbed moiety by binding to it is crucial. This study promotes the use SACs for the realization of a sustainable and active electrocatalyst for the NRR, offering new avenues for addressing global energy and environmental challenges through the advancement of sustainable catalytic technologies.

An Air-Stable Carbon-Centered Triradical with a Well-Addressable Quartet Ground State.

Organic polyradicals with a high-spin ground state and quantum magnetic properties suitable for spin manipulation are valuable materials for diverse innovative technologies, including quantum devices. However, the typically high reactivity and low stability of conventional polyradicals present a major obstacle to such applications. In this study, a highly stable carbon-centered triradical TR with a quartet ground state and excellent stability (τ1/2 of ∼90 days in air-saturated toluene at room temperature) is achieved, which shows apposite magnetic anisotropy and Zeeman splitting partition with favorable addressability. By virtue of the optimal stability, thorough structural and magnetic characterizations are realized. With X-ray crystallography unambiguously proving the molecular structure, the quartet ground state (ΔED-Q = 0.78 kcal/mol) is confirmed by the SQUID measurements, while the cw- and pulsed EPR techniques offer additional supportive evidence for the high-spin nature. Remarkably, owing to the easily attained magnetic anisotropy, selective excitations between different Zeeman splitting levels are successfully demonstrated with TR in its frozen toluene solution without the requirement for special alignment, which is unprecedented for organic polyradicals. Along with the millisecond spin-lattice relaxation and microsecond coherence time manifested by TR, this triradical is promising for potential coherent spin manipulation applications as a multienergy-level quantum information carrier.

Phenoxide coordination to Fe(III) tetraphenylporphyrin: Exploring antibacterial and electrocatalytic HER activity

Herein, we report synthesis, solid and solution state structure as well as properties of three five coordinate (unsubstituted, 4-NO2 substituted and 2,4,6 trinitro substituted) phenoxide axially ligated to Fe(III)-tetraphenyl porphyrins. Spectroscopic characterization revealed high-spin (S = 5/2) nature of the phenoxide bound Fe(III) porphyrins (Fe1 and Fe2). However, the 2,4,6 trinitro substituted phenoxide axially ligated Fe(III) porphyrin (Fe3) demonstrate spin admixed nature (S = 5/2, 3/2) with predominate high spin contribution. (Phenolato)(porphinato)iron(III) complexes merit attention owing to structural analogy with the catalase enzyme. In this study we investigated their antibacterial as well as electrocatalytic hydrogen evolution reaction (HER) activity. Fe1 demonstrate potent antibacterial activity against gram-negative E. coli (MTCC 443) and gram-positive Staphylococcus aureus (MTCC 3160) human pathogenic bacteria. It also produce catalytic current for electrocatalytic HER activities upon gradual addition of PTSA (para-tolunesulphonic acid) as proton source. Compounds Fe2 and Fe3 also produce enhanced catalytic wave which originate possibly from reduction of proton coupled with reduction of –NO2 group.

Symmetry and Electronic Properties of Metallic Nanoclusters

Spherical nanoclusters with countable member atoms and delocalized valence orbitals are superatoms with properties analogous to those of simple atoms. This is reflected, in particular, in their optical spectra and magnetic properties, in a similar sense to transition metal ions and complexes. Clusters can be of low-spin or high-spin with considerable contributions to magnetism by the large cluster orbital magnetic moment. Due to the large radius of the clusters, they can be diamagnetic with an unusually high diamagnetic susceptibility. Gold and platinum, which in the bulk are non-magnetic, show pronounced superparamagnetism associated with their high-spin nature, and the magnetic moment can be trapped in symmetry-breaking environments so that hysteresis pertains far beyond room temperature. A significant deviation from hydrogen-like orbitals results from the shape of the confining potential, which has the effect that the orbital quantum number ℓ is not limited to values less than the principal quantum number n.

Solution‐Phase Synthesis and Isolation of An Aza‐Triangulene and Its Cation in Crystalline Form

AbstractSynthesis of triangulene and its derivatives is challenging due to their intrinsic high spin nature. Herein, we report solution‐phase synthesis and isolation of a nitrogen‐doped triangulene (i.e., aza‐triangulene) (NT) and its cation (NT+) in single‐crystal form. Notably, the cationNT+can be regarded as an isoelectronic structure of the corresponding all‐carbon triangulene. BothNTandNT+show reasonable stability due to kinetic blocking by bulky and electron‐withdrawing aryl substituents, and intramolecular donor‐acceptor interaction. Bond length analysis, magnetic measurements and theoretical calculations reveal that the neutralNThas a doublet ground state with a zwitterionic character, while the cationNT+exhibits a triplet ground state with a singlet‐triplet energy gap of +0.84 kcal mol−1. This study provides a rational strategy to access high‐spin systems by heteroatom doping of pure π‐conjugated polycyclic hydrocarbons.

Solution-Phase Synthesis and Isolation of An Aza-Triangulene and Its Cation in Crystalline Form.

Synthesis of triangulene and its derivatives is challenging due to their intrinsic high spin nature. Herein, we report solution-phase synthesis and isolation of a nitrogen-doped triangulene (i.e., aza-triangulene) (NT) and its cation (NT+ ) in single-crystal form. Notably, the cation NT+ can be regarded as an isoelectronic structure of the corresponding all-carbon triangulene. Both NT and NT+ show reasonable stability due to kinetic blocking by bulky and electron-withdrawing aryl substituents, and intramolecular donor-acceptor interaction. Bond length analysis, magnetic measurements and theoretical calculations reveal that the neutral NT has a doublet ground state with a zwitterionic character, while the cation NT+ exhibits a triplet ground state with a singlet-triplet energy gap of +0.84 kcal mol-1 . This study provides a rational strategy to access high-spin systems by heteroatom doping of pure π-conjugated polycyclic hydrocarbons.

Importance of non-covalent interactions in a nitrile anion metal-complex based on pyridine ligands: A theoretical and experimental approach

The solvothermal synthesis and crystal structure of [bis(thiocyanato-κN)bis(tris(pyridin-2-yl-κN)amine)iron(II)] (1) are described. The structure obtained was i subjected to theoretical analysis of interaction energies and intra- and intermolecular bonding. This comprehensive study illustrates the richness of non-covalent interactions that are exhibited by nitrile anionmetal complexes. The neutral complex lies on a crystallographic two-fold axis. The iron atom is octahedrally coordinated, with two thiocyanato ligands in cis positions, and the two trispyridine ligands coordinated via the nitrogen atoms of just two of the three pyridine rings. Energy analysis of five significant dimers, supplemented by a detailed analysis of the Hirshfeld surfaces, indicates attractive interaction energies of up to 101 kJ, with the strongest dimer stabilized by bifurcated CH⋯S hydrogen bonds and additional π⋯π interactions. Solid-state and molecular quantum mechanical calculations confirm the high-spin nature of the complex, which is also reflected in the FeN bond lengths, and highlights the relevance of intramolecular ligand-ligand interactions. From a combined analysis using the Quantum Theory of Atoms in Molecules and the Non-Covalent Interaction index it was possible to identify further specific intermolecular interactions contributing the stability of the crystal structure, such as the H⋯H bonds, as well as the presence of several delocalized van der Waals forces, which are mainly of dispersive origin.

Modeling Metal Influence on the Gate Opening in ZIF-8 Materials

Zeolitic imidazolate frameworks (ZIFs) undergo pressure-induced phase transitions that are peculiar to each ZIF. The phase transition is associated with the rotation of the imidazolate, and it is accompanied by an increase of their pore openings, affecting ZIFs performance in separation processes. This phenomenon is known as the gate opening or the swing effect. Here we report the metal dependence of the ambient pressure and high pressure (HP) phases of ZIF-8(M) with M = Mg, Fe, and Zn, determined by using periodic Kohn–Sham density functional models. We show that the substitution of Zn with Mg or Fe has a big influence on the gate opening energy, which significantly decreases, an opposite trend than what was previously reported upon functionalization of the linker. The lowest energy phase of ZIF-8(Fe) is different than for ZIF-8(Mg) and ZIF-8(Zn), and its structure is significantly closer to the HP phase. Multireference wave function methods have been used to study the electronic structure of ZIF-8(Fe), confirming the metal center to be high spin (S = 2) divalent iron in antiferromagnetic coupling. The high-spin nature of the iron species coupled with a band gap in the visible light range makes ZIF-8(Fe) an interesting material for catalysis and photocatalysis.

Testing Evolution of LFQPOs with Mass Accretion Rate in GRS 1915+105 with Insight-HXMT

Abstract Using the Insight-HXMT observations of GRS 1915+105 when it exhibits low-frequency quasiperiodic oscillations (QPOs), we measure the evolution of the QPO frequency along with disk inner radius and mass accretion rate. We find a tight positive correlation between the QPO frequency and mass accretion rate. Our results extend the finding of previous work with AstroSat to a larger range of accretion rates with independent instruments and observations. Treating the QPO frequency of GRS 1915+105 as the relativistic dynamic frequency of a truncated disk, we are able to confirm the high spin nature of the black hole in GRS 1915+105. We also address the potential of our finding to test general relativity in the future.

Influences of electronic spin structures on the magnetic properties of Fe, Co and Ni ions and the adsorption of collectors

The electronic spin properties of Fe, Co and Ni metal ions in the octahedral field formed by S and O ligands were studied by density functional theory (DFT). It is found that in MO octahedral field, the metal exhibits a high spin nature, whereas in MS octahedral field, the metal exhibits a low spin nature. This suggests that O atom is a weak-field ligand and S atom is a strong-field ligand. It is found that MO atoms are mainly ionicly bonded, whereas MS atoms are mainly covalently bonded. This result is consistent with the MO and MS bonds in the real metal oxide and sulfide minerals. Hence, MO and MS coordination compound models can be used to simulate the crystals of the real oxide and sulfide minerals. Then the adsorption of O- and S-containing flotation collectors on these two mineral models was studied. It is indicated that S-containing collectors could not effectively collect oxide minerals, but O-containing collectors have strong collecting ability to oxide minerals. In addition, the collecting ability of S- and O-containing collectors to sulfide minerals is nearly the same. These are consistent with the flotation practice that O-containing collectors have no selective collecting capacity on oxide and sulfide minerals but S-containing collectors have strongly selectively collecting capacity to sulfide minerals.

Topological Crystalline Materials of J=3/2 Electrons: Antiperovskites, Dirac Points, and High Winding Topological Superconductivity

We present a theory of the high-spin generalization of topological insulators and their doped superconducting states. The higher-spin topological insulators involve a pair of $J=3/2$ bands with opposite parity, and are characterized by their band inversion. The low-energy effective theory reveals that the topological insulators host four different phases characterized by mirror Chern numbers, at which boundaries two different patterns of bulk Dirac points appear. For the carrier-doped case, it is shown that the system may host unique unconventional superconductivity because of its high-spin nature and additional orbital degrees of freedom intrinsic to topological insulators. The superconducting critical temperature is evaluated by using density-density pairing interactions, and odd-parity Cooper pairs are shown to be naturally realized in the presence of interorbital pairing interaction. It is observed that even the simplest spin 0 odd-parity pairing state exhibits a novel class of topological superconductivity---high winding topological superconductivity. We also discuss the experimental signals of high winding topological superconductivity in the case of the antiperovskite superconductor Sr$_{3-x}$SnO.

Variations in the molecularity of bis(formylpyrrolyl)cobalt(II) complexes

Abstract This work aims to extend the coordination chemistry of Co(II) with bis(2-formylpyrrolyl) ligands to different donor molecules. Treatment of a mixture of anhydrous CoCl2 and excess of pyridine in THF with two equivalents of sodium 2-formylpyrrolyl gives rise to complex [Co{κ2N,O-NC4H3-C(H) O}2(Py)2] (1) in good yields, after standard work-up procedures. By contrast, the reaction of two equivalents of sodium 2-formylpyrrolyl with anhydrous CoCl2 in neat THF or MeCN solutions systematically led, after standard work-up, to the identification of the tetrameric complex [Co{κ2N,O-NC4H3-C(H) O}2]4 (2) and other unknown contaminations. Analytically pure samples of complex 2 were only prepared when the synthesis reaction was performed in toluene at 90 °C. Complexes 1 and 2 are paramagnetic and were characterized by elemental analysis, magnetic susceptibility measurements (Evans method) and X-ray diffraction. Complex 1 is a hexacoordinated octahedral complex with a low-spin (S = 1/2) electronic configuration. On the other hand, the tetrameric complex 2 results from the self-assembling of the elusive and highly unsaturated complex “[Co{κ2N,O-NC4H3-C(H) O}2]” giving rise to a tetranuclear distorted cubane structure, comprising two hexacoordinated octahedral and two pentacoordinated trigonal bipyramidal Co(II) centers. Complex 2 revealed an overall high-spin (S = 3/2 per Co center) nature, as suggested in solution by the Evans method and in the solid state by SQUID magnetometry.

A Benzene-1,3,5-Triaminyl Radical Fused with ZnII -Porphyrins: Remarkable Stability and a High-Spin Quartet Ground State.

A benzene-1,3,5-triaminyl radical fused with three ZnII -porphyrins was synthesized through a three-fold oxidative fusion reaction of 1,3,5-tris(ZnII -porphyrinylamino)benzene followed by oxidation with PbO2 as key steps. This triaminyl radical has been shown to possess a quartet ground state with a doublet-quartet energy gap of 3.1 kJ mol-1 by superconducting quantum interference device (SQUID) studies. Despite its high-spin nature, this triradical is remarkably stable, which allows its separation and recrystallization under ambient conditions. Moreover, this triradical can be stored as a solid for more than one year without serious deterioration. The high stability of the triradical is attributed to effective spin delocalization over the porphyrin segments and steric protection at the nitrogen centers and the porphyrin meso positions.

Photoassociation spectroscopy of ultracold Yb173 atoms near the intercombination line

We report on photoassociation (PA) spectroscopy of a degenerate Fermi gas of $^{173}\mathrm{Yb}$ atoms near the dissociation limit of the spin-forbidden $^{1}S_{0}$--$^{3}P_{1}$ intercombination transition. An atom-loss spectrum is measured from a trapped sample for a spectral range down to $\ensuremath{-}1$ GHz with respect to the $f=5/2\ensuremath{\rightarrow}{f}^{\ensuremath{'}}=7/2$ atomic resonance. The spectrum shows 80 PA resonances, revealing the high nuclear spin nature of the system. To obtain additional information on the excited molecular states, we investigate the Zeeman effect on the spectrum near a detuning of $\ensuremath{-}0.8$ GHz and examine the quantum numbers of the Zeeman levels using various two-component spin mixture samples. Finally, we measure the atom-loss rate under PA light for several pronounced PA resonances.

A mononuclear non-heme-iron dioxygen-carrying protein?

The ability of mononuclear non-heme iron complexes to function as molecular oxygen transporters is investigated by density functional theory. The factors governing the efficiency of the reversible binding of dioxygen at the active site of the dinuclear non-heme iron enzyme hemerythrin, including antiferromagnetic coupling and the conversion of dioxygen to hydroperoxo by a proton coupled 2-electron transfer mechanism, are revisited and considered as possible tools in mononuclear non-heme complexes. Several mononuclear non-heme model complexes, including active sites of enzymes already known to interact with dioxgenic ligands, are constructed and the molecular oxygen transportation capabilities of these complexes are examined computationally. The high-spin nature of the ground state of these complexes implies an intrinsic kinetic lability of the oxy structures, as also evident from potential energy surface calculations towards iron-dioxygen cleavage. Proton affinities as calibrated with reference compounds showed that these complexes are highly unlikely to undergo protonation to form hydroperoxo-like adducts. Mixed superoxo descriptions of the dissociated dioxygenic ligands in all complexes add to the overall conclusion that these model structures are significantly disadvantaged in any attempt to be employed for molecular oxygen transportation.

A Two-Coordinate Cobalt(II) Imido Complex with NHC Ligation: Synthesis, Structure, and Reactivity.

The synthesis, structural characterization, and reactivity of the first two-coordinate cobalt complex featuring a metal-element multiple bond [(IPr)Co(NDmp)] (4; IPr=1,3-bis(2',6'-diisopropylphenyl)imidazole-2-ylidene; Dmp=2,6-dimesitylphenyl) is reported. Complex 4 was prepared from the reaction of [(IPr)Co(η(2) -vtms)2 ] (vtms=vinyltrimethylsilane) with DmpN3 . An X-ray diffraction study revealed its linear C-Co-N core and a short Co-N distance (1.691(6) Å). Spectroscopic characterization and calculation studies indicated the high-spin nature of 4 and the multiple-bond character of the Co-N bond. Complex 4 effected group-transfer reactions to CO and ethylene to form isocyanide and imine, respectively. It also facilitated E-H (E=C, Si) σ-bond activation of terminal alkyne and hydrosilanes to produce the corresponding cobalt(II) alkynyl and cobalt(II) hydride complexes as 1,2-addition products.

Linear and T-Shaped Iron(I) Complexes Supported by N-Heterocyclic Carbene Ligands: Synthesis and Structure Characterization.

The use of the N-heterocyclic carbene (NHC) ligands 1,3-bis(2',6'-diethylphenyl)-4,5-(CH2)4-imidazol-2-ylidene (cyIDep), 1,3-bis(2',6'-diethylphenyl)-imidazolin-2-ylidene (sIDep), and its N-mesityl analogue sIMes enables the preparation of the two-coordinate homoleptic iron(I)-NHC complexes [(cyIDep)2Fe][BAr(F)4] (3, Ar(F) denoted for 3,5-di(trifluoromethyl)phenyl) and [(sIDep)2Fe][BAr(F)4] (4) and the T-shaped iron(I)-NHC complex [(sIMes)2Fe(THF)][BPh4] (5, THF = tetrahydrofuran). Complexes 3-5 were prepared via the sequential protocol of control reduction of iron(II) dihalides by KC8 in the presence of the corresponding NHC ligands followed by halide-abstraction with NaBAr4. Spectroscopic characterization, including single-crystal X-ray diffraction studies and (57)Fe Mössbauer spectroscopy, in combination with density functional theory calculations, suggest their high-spin nature. Solution property study (absorption spectroscopy and cyclic voltammetry) indicates that 3 and 5 keep their corresponding two- and three-coordinate nature in THF solution, and 4 might reversibly coordinate a THF molecule to form, presumably, the T-shaped species [(sIDep)2Fe(THF)][BAr(F)4]. The isolation of 3 and 4 demonstrates the accessibility of homoleptic two-coordinate iron(I)-NHC complexes.

Synthesis and investigation of the metal–metal interactions in heterobimetallic Cr/Rh and Cr/Ir complexes

The chromium(III) tris(phosphinoamide) precursor Cr(iPrNPiPr2)3 (1) has been used to synthesize Cr/Rh and Cr/Ir heterobimetallic complexes. Treatment of [MCl(COD)]2 with 1 affords the open shell S=3/2 complexes ClCr(μ-iPrNPiPr2)2M(η2-iPrNPiPr2) (M=Rh (2), Ir (3)). Instead of simple coordination of the late transition metal fragment to the C3-symmetric tris(phosphinoamide) binding pocket, the preference of RhI and IrI for a square planar environment leads to a chloride/amide ligand exchange process. Complexes 1–3 have been structurally characterized using X-ray crystallography, revealing short Cr–Rh and Cr–Ir distances (2.6095(3)Å (2); 2.6064(4)Å (3)) indicative of metal–metal bonds. A computational investigation of the electronic structures of 2 and 3 reveals substantial metal–metal orbital overlap, but the high spin nature of the CrIII center leads to population of metal–metal antibonding orbitals and relatively weak metal–metal bonding. The effects of the metal–metal interaction on the redox properties of the CrIII center are investigated using cyclic voltammetry.

Iron(II) complexes of 2,6-di(1-alkylpyrazol-3-yl)pyridine derivatives – The influence of distal substituents on the spin state of the iron centre

2,6-Di(1-methyl-pyrazol-3-yl)pyridine (LMe), 2,6-di(1-allyl-pyrazol-3-yl)pyridine (LAll), 2,6-di(1-benzyl-pyrazol-3-yl)pyridine (LBz) and di(1-isopropyl-pyrazol-3-yl)pyridine (LiPr) have been synthesized by alkylation of deprotonated di{1H-pyrazol-3-yl}pyridine (3-bpp), and converted to salts of the corresponding [Fe(LR)2]2+ complexes (R=Me, All, Bz and iPr). Crystal structures of [Fe(LMe)2]X2 (X−=BF4−, ClO4− and PF6−), [Fe(LAll)2][BF4]2, [Fe(LBz)2][BF4]2 and [Fe(LiPr)2][PF6]2 have been determined at 150K. All of these contain high-spin iron centres except [Fe(LMe)2][BF4]2·xH2O, which is predominantly low-spin at that temperature. All the complexes are high-spin between 5 and 300K as solvent-free bulk powders, and are also high-spin in (CD3)2CO solution between 193 and 293K. This was unexpected, since the parent complex [Fe(3-bpp)2]2+ undergoes spin-crossover in the same solvent with T½=247K [40]. The high-spin nature of the [Fe(LR)2]2+ complexes in solution must reflect a subtle balance of steric and electronic factors involving the ligand ‘R’ substituents.

A Family of Three-Dimensional Molecular Framework Materials Containing the Three-Connecting Ligands 2,4,6-Tris(n'-pyridyl)-1,3,5-triazine: 3-tpt and 4-tpt

Three-dimensional (3D) framework materials containing the ligands 2,4,6-tris(4′-pyridyl)-1,3,5-triazine (4-tpt) and 2,4,6-tris(3′-pyridyl)-1,3,5-triazine (3-tpt) have been prepared and their structure and magnetic properties investigated. The [MII(NCS)2(py)4] (MII = Fe, Co, py = 3-tpt, and 4-tpt) coordination environments in these materials have been targeted in an effort to prepare high-dimensional coordination polymers which contain spin crossover (SCO) centres. Using FeII, two isotopological cubic 3D materials [Fe(NCS)2(4-tpt)4/3]·n(BzOH,ac) (1a(Bz,ac)) and [Fe(NCS)2(3-tpt)4/3]·n(BzOH,ac) (1b(Bz,ac)) were formed. However, with CoII a different 3D framework topology results, [Co(NCS)2(3-tpt)4/3]·(BzOH,ac) (2(Bz,ac)). Further synthetic variation leads to the isostructural 3D materials trans-[MII(NCS)2(4-tpt)4/3]cis-[MII(NCS)2(4-tpt)2]·n(tce, EtOH) (Fe: 3a(Tce,Et) and Co: 3b(Tce,Et)) which form 3D networks outside Wellsian classification – and for which uniquely both two- and three-connecting modes of 4-tpt are present in the one complex. Despite having the metal coordination environments for which SCO has previously been observed, magnetic susceptibilities of this family of materials reveal a high spin nature.