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Russell JB, Jafari MG, Kim JH, Pudasaini B, Ozarowski A, Telser J, Baik MH, Mindiola DJ. Ynamide and Azaalleneyl. Acid-Base Promoted Chelotropic and Spin-State Rearrangements in a Versatile Heterocumulene [(Ad)NCC( tBu)] . Angew Chem Int Ed Engl 2024; 63:e202401433. [PMID: 38433099 DOI: 10.1002/anie.202401433] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2024] [Revised: 02/22/2024] [Accepted: 02/23/2024] [Indexed: 03/05/2024]
Abstract
We introduce the heterocumulene ligand [(Ad)NCC(tBu)]- (Ad=1-adamantyl (C10H15), tBu=tert-butyl, (C4H9)), which can adopt two forms, the azaalleneyl and ynamide. This ligand platform can undergo a reversible chelotropic shift using Brønsted acid-base chemistry, which promotes an unprecedented spin-state change of the [VIII] ion. These unique scaffolds are prepared via addition of 1-adamantyl isonitrile (C≡NAd) across the alkylidyne in complexes [(BDI)V≡CtBu(OTf)] (A) (BDI-=ArNC(CH3)CHC(CH3)NAr), Ar=2,6-iPr2C6H3) and [(dBDI)V≡CtBu(OEt2)] (B) (dBDI2-=ArNC(CH3)CHC(CH2)NAr). Complex A reacts with C≡NAd, to generate the high-spin [VIII] complex with a κ1-N-ynamide ligand, [(BDI)V{κ1-N-(Ad)NCC(tBu)}(OTf)] (1). Conversely, B reacts with C≡NAd to generate a low-spin [VIII] diamagnetic complex having a chelated κ2-C,N-azaalleneyl ligand, [(dBDI)V{κ2-N,C-(Ad)NCC(tBu)}] (2). Theoretical studies have been applied to better understand the mechanism of formation of 2 and the electronic reconfiguration upon structural rearrangement by the alteration of ligand denticity between 1 and 2.
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2
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Bhunia M, Sandoval-Pauker C, Fehn D, Grant LN, Senthil S, Gau MR, Ozarowski A, Krzystek J, Telser J, Pinter B, Meyer K, Mindiola DJ. Divalent Titanium via Reductive N-C Coupling of a Ti IV Nitrido with π-Acids. Angew Chem Int Ed Engl 2024:e202404601. [PMID: 38619509 DOI: 10.1002/anie.202404601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2024] [Revised: 04/09/2024] [Accepted: 04/10/2024] [Indexed: 04/16/2024]
Abstract
The nitrido-ate complex [(PN)2Ti(N){μ2-K(OEt2)}]2 (1) (PN-=(N-(2-PiPr2-4-methylphenyl)-2,4,6-Me3C6H2) reductively couples CO and isocyanides in the presence of DME or cryptand (Kryptofix222), to form rare, five-coordinate TiII complexes having a linear cumulene motif, [K(L)][(PN)2Ti(NCE)] (E=O, L=Kryptofix222, (2); E=NAd, L=3 DME, (3); E=NtBu, L=3 DME, (4); E=NAd, L=Kryptofix222, (5)). Oxidation of 2-5 with [Fc][OTf] afforded an isostructural TiIII center containing a neutral cumulene, [(PN)2Ti(NCE)] (E=O, (6); E=NAd (7), NtBu (8)) and characterization by CW X-band EPR spectroscopy, revealed unpaired electron to be metal centric. Moreover, 1e- reduction of 6 and 7 in the presence of Kryptofix222cleanly reformed corresponding discrete TiII complexes 2 and 5, which were further characterized by solution magnetization measurements and high-frequency and -field EPR (HFEPR) spectroscopy. Furthermore, oxidation of 7 with [Fc*][B(C6F5)4] resulted in a ligand disproportionated TiIV complex having transoid carbodiimides, [(PN)2Ti(NCNAd)2] (9). Comparison of spectroscopic, structural, and computational data for the divalent, trivalent, and tetravalent systems, including their 15N enriched isotopomers demonstrate these cumulenes to decrease in order of backbonding as TiII→TiIII→TiIV and increasing order of π-donation as TiII→TiIII→TiIV, thus displaying more covalency in TiIII species. Lastly, we show a synthetic cycle whereby complex 1 can deliver an N-atom to CO and CNAd.
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Bhunia M, Mohar JS, Sandoval-Pauker C, Fehn D, Yang ES, Gau M, Goicoechea J, Ozarowski A, Krzystek J, Telser J, Meyer K, Mindiola DJ. Softer Is Better for Titanium: Molecular Titanium Arsenido Anions Featuring Ti≡As Bonding and a Terminal Parent Arsinidene. J Am Chem Soc 2024; 146:3609-3614. [PMID: 38290427 DOI: 10.1021/jacs.3c12939] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2024]
Abstract
We introduce the arsenido ligand onto the TiIV ion, yielding a remarkably covalent Ti≡As bond and the parent arsinidene Ti═AsH moiety. An anionic arsenido ligand is assembled via reductive decarbonylation involving the discrete TiII salt [K(cryptand)][(PN)2TiCl] (1) (cryptand = 222-Kryptofix) and Na(OCAs)(dioxane)1.5 in thf/toluene to produce the mixed alkali ate-complex [(PN)2Ti(As)]2(μ2-KNa(thf)2) (2) and the discrete salt [K(cryptand)][(PN)2Ti≡As] (3) featuring a terminal Ti≡As ligand. Protonation of 2 or 3 with various weak acids cleanly forms the parent arsinidene [(PN)2Ti═AsH] (4), which upon deprotonation with KCH2Ph in thf generates the more symmetric anionic arsenido [(PN)2Ti(As){μ2-K(thf)2}]2 (5). Experimental and computational studies suggest the pKa of 4 to be ∼23, and the bond orders in 2, 3, and 5 are all in the range of a Ti≡As triple bond, with decreasing bond order in 4.
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Toubiana LA, Valaydon-Pillay A, Elinburg JK, Bacon JW, Ozarowski A, Doerrer LH, Stoian SA. Spectroscopic and Theoretical Investigation of High-Spin Square-Planar and Trigonal Fe(II) Complexes Supported by Fluorinated Alkoxides. Inorg Chem 2024; 63:2370-2387. [PMID: 38259134 DOI: 10.1021/acs.inorgchem.3c03236] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2024]
Abstract
The electronic structures and spectroscopic behavior of three high-spin FeII complexes of fluorinated alkoxides were studied: square-planar {K(DME)2}2[Fe(pinF)2] (S) and quasi square-planar {K(C222)}2[Fe(pinF)2] (S') and trigonal-planar {K(18C6)}[Fe(OC4F9)3] (T) where pinF = perfluoropinacolate and OC4F9 = tris-perfluoro-t-butoxide. The zero-field splitting (ZFS) and hyperfine structure parameters of the S = 2 ground states were determined using field-dependent 57Fe Mössbauer and high-field and -frequency electron paramagnetic resonance (HFEPR) spectroscopies. The spin Hamiltonian parameters were analyzed with crystal field theory and corroborated by density functional theory (DFT) and ab initio complete active space self-consistent field (CASSCF) calculations. Whereas the ZFS tensor of S has a small rhombicity, E/D = 0.082, and a positive D = 15.17 cm-1, T exhibits a negative D = -9.16 cm-1 and a large rhombicity, E/D = 0.246. Computational investigation of the structural factors suggests that the ground-state electronic configuration and geometry of T's Fe site are determined by the interaction of [Fe(OC4F9)3]- with {K(18C6)}+. In contrast, two distinct countercations of S/S' have a negligible influence on their [Fe(pinF)2]2- moieties. Instead, the distortions in S' are likely induced by the chelate ring conformation change from δλ, observed for S, to the δδ conformation, determined for S'.
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Wojnar MK, Kundu K, Kairalapova A, Wang X, Ozarowski A, Berkelbach TC, Hill S, Freedman DE. Ligand field design enables quantum manipulation of spins in Ni 2+ complexes. Chem Sci 2024; 15:1374-1383. [PMID: 38274078 PMCID: PMC10806831 DOI: 10.1039/d3sc04919a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2023] [Accepted: 12/02/2023] [Indexed: 01/27/2024] Open
Abstract
Creating the next generation of quantum systems requires control and tunability, which are key features of molecules. To design these systems, one must consider the ground-state and excited-state manifolds. One class of systems with promise for quantum sensing applications, which require water solubility, are d8 Ni2+ ions in octahedral symmetry. Yet, most Ni2+ complexes feature large zero-field splitting, precluding manipulation by commercial microwave sources due to the relatively large spin-orbit coupling constant of Ni2+ (630 cm-1). Since low lying excited states also influence axial zero-field splitting, D, a combination of strong field ligands and rigidly held octahedral symmetry can ameliorate these challenges. Towards these ends, we performed a theoretical and computational analysis of the electronic and magnetic structure of a molecular qubit, focusing on the impact of ligand field strength on D. Based on those results, we synthesized 1, [Ni(ttcn)2](BF4)2 (ttcn = 1,4,7-trithiacyclononane), which we computationally predict will have a small D (Dcalc = +1.15 cm-1). High-field high-frequency electron paramagnetic resonance (EPR) data yield spin Hamiltonian parameters: gx = 2.1018(15), gx = 2.1079(15), gx = 2.0964(14), D = +0.555(8) cm-1 and E = +0.072(5) cm-1, which confirm the expected weak zero-field splitting. Dilution of 1 in the diamagnetic Zn analogue, [Ni0.01Zn0.99(ttcn)2](BF4)2 (1') led to a slight increase in D to ∼0.9 cm-1. The design criteria in minimizing D in 1via combined computational and experimental methods demonstrates a path forward for EPR and optical addressability of a general class of S = 1 spins.
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Choroba K, Palion-Gazda J, Machura B, Bieńko A, Wojtala D, Bieńko D, Rajnák C, Boča R, Ozarowski A, Ozerov M. Large Magnetic Anisotropy in Mono- and Binuclear cobalt(II) Complexes: The Role of the Distortion of the Coordination Sphere in Validity of the Spin-Hamiltonian Formalism. Inorg Chem 2024; 63:1068-1082. [PMID: 38166196 DOI: 10.1021/acs.inorgchem.3c03405] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2024]
Abstract
To get a better insight into understanding the factors affecting the enhancement of the magnetic anisotropy in single molecule (single ion) magnets, two cobalt(II) complexes based on a tridentate ligand 2,6-di(thiazol-2-yl)pyridine substituted at the 4-position with N-methyl-pyrrol-2-yl have been synthesized and studied by X-ray crystallography, AC and DC magnetic data, FIRMS and HFEPR spectra, and theoretical calculations. The change of the counteranion in starting Co(II) salts results in the formation of pentacoordinated mononuclear [Co(mpyr-dtpy)Cl2]·2MeCN (1) complex and binuclear [Co(mpyr-dtpy)2][Co(NCS)4] (2) compound. The observed marked distortion of trigonal bipyramid geometry in 1 and cationic octahedral and anionic tetrahedral units in 2 brings up a question about the validity of the spin-Hamiltonian formalism and the possibility of determining the value and sign of the zero-field splitting D parameter. Both complexes exhibit field-induced slow magnetic relaxation with two or three relaxation channels at BDC = 0.3 T. The high-frequency relaxation time in the reciprocal form τ(HF)-1 = CTn develops according to the Raman relaxation mechanism (for 2, n = 8.8) and the phonon-bottleneck-like mechanism (for 1, n = 2.3). The high-frequency relaxation time at T = 2.0 K and BDC = 0.30 T is τ(HF) = 96 and 47 μs for 1 and 2, respectively.
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Xiang L, Dhakal R, Ozerov M, Jiang Y, Mou BS, Ozarowski A, Huang Q, Zhou H, Fang J, Winter SM, Jiang Z, Smirnov D. Disorder-Enriched Magnetic Excitations in a Heisenberg-Kitaev Quantum Magnet Na_{2}Co_{2}TeO_{6}. PHYSICAL REVIEW LETTERS 2023; 131:076701. [PMID: 37656855 DOI: 10.1103/physrevlett.131.076701] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2023] [Revised: 07/31/2023] [Accepted: 08/03/2023] [Indexed: 09/03/2023]
Abstract
Using optical magnetospectroscopy, we investigate the magnetic excitations of Na_{2}Co_{2}TeO_{6} in a broad magnetic field range (0 T≤B≤17.5 T) at low temperature. Our measurements reveal rich spectra of in-plane magnetic excitations with a surprisingly large number of modes, even in the high-field spin-polarized state. Theoretical calculations find that the Na-occupation disorder in Na_{2}Co_{2}TeO_{6} plays a crucial role in generating these modes. Our Letter demonstrates the necessity to consider disorder in the spin environment in the search for Kitaev quantum spin liquid states in practicable materials.
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Khachatryan L, Barekati-Goudarzi M, Asatryan R, Ozarowski A, Boldor D, Lomnicki SM, Cormier SA. Metal-Free Biomass-Derived Environmentally Persistent Free Radicals (Bio-EPFRs) from Lignin Pyrolysis. ACS OMEGA 2022; 7:30241-30249. [PMID: 36061701 PMCID: PMC9434622 DOI: 10.1021/acsomega.2c03381] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/31/2022] [Accepted: 08/04/2022] [Indexed: 06/15/2023]
Abstract
To assess contribution of the radicals formed from biomass burning, our recent findings toward the formation of resonantly stabilized persistent radicals from hydrolytic lignin pyrolysis in a metal-free environment are presented in detail. Such radicals have particularly been identified during fast pyrolysis of lignin dispersed into the gas phase in a flow reactor. The trapped radicals were analyzed by X-band electron paramagnetic resonance (EPR) and high-frequency (HF) EPR spectroscopy. To conceptualize available data, the metal-free biogenic bulky stable radicals with extended conjugated backbones are suggested to categorize as a new type of metal-free environmentally persistent free radicals (EPFRs) (bio-EPFRs). They can be originated not only from lignin/biomass pyrolysis but also during various thermal processes in combustion reactors and media, including tobacco smoke, anthropogenic sources and wildfires (forest/bushfires), and so on. The persistency of bio-EPFRs from lignin gas-phase pyrolysis was outlined with the evaluated lifetime of two groups of radicals being 33 and 143 h, respectively. The experimental results from pyrolysis of coniferyl alcohol as a model compound of lignin in the same fast flow reactor, along with our detailed potential energy surface analyses using high-level DFT and ab initio methods toward decomposition of a few other model compounds reported earlier, provide a mechanistic view on the formation of C- and O-centered radicals during lignin gas-phase pyrolysis. The preliminary measurements using HF-EPR spectroscopy also support the existence of O-centered radicals in the radical mixtures from pyrolysis of lignin possessing a high g value (2.0048).
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G Jafari M, Fehn D, Reinholdt A, Hernández-Prieto C, Patel P, Gau MR, Carroll PJ, Krzystek J, Liu C, Ozarowski A, Telser J, Delferro M, Meyer K, Mindiola DJ. Tale of Three Molecular Nitrides: Mononuclear Vanadium (V) and (IV) Nitrides As Well As a Mixed-Valence Trivanadium Nitride Having a V 3N 4 Double-Diamond Core. J Am Chem Soc 2022; 144:10201-10219. [PMID: 35652694 DOI: 10.1021/jacs.2c00276] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Transmetallation of [VCl3(THF)3] and [TlTptBu,Me] afforded [(TptBu,Me)VCl2] (1, TptBu,Me = hydro-tris(3-tert-butyl-5-methylpyrazol-1-yl)borate), which was reduced with KC8 to form a C3v symmetric VII complex, [(TptBu,Me)VCl] (2). Complex 1 has a high-spin (S = 1) ground state and displays rhombic high-frequency and -field electron paramagnetic resonance (HFEPR) spectra, while complex 2 has an S = 3/2 4A2 ground state observable by conventional EPR spectroscopy. Complex 1 reacts with NaN3 to form the VV nitride-azide complex [(TptBu,Me)V≡N(N3)] (3). A likely VIII azide intermediate en route to 3, [(TptBu,Me)VCl(N3)] (4), was isolated by reacting 1 with N3SiMe3. Complex 4 is thermally stable but reacts with NaN3 to form 3, implying a bis-azide intermediate, [(TptBu,Me)V(N3)2] (A), leading to 3. Reduction of 3 with KC8 furnishes a trinuclear and mixed-valent nitride, [{(TptBu,Me)V}2(μ4-VN4)] (5), conforming to a Robin-Day class I description. Complex 5 features a central vanadium ion supported only by bridging nitride ligands. Contrary to 1, complex 2 reacts with NaN3 to produce an azide-bridged dimer, [{(TptBu,Me)V}2(1,3-μ2-N3)2] (6), with two antiferromagnetically coupled high-spin VII ions. Complex 5 could be independently produced along with [(κ2-TptBu,Me)2V] upon photolysis of 6 in arene solvents. The putative {VIV≡N} intermediate, [(TptBu,Me)V≡N] (B), was intercepted by photolyzing 6 in a coordinating solvent, such as tetrahydrofuran (THF), yielding [(TptBu,Me)V≡N(THF)] (B-THF). In arene solvents, B-THF expels THF to afford 5 and [(κ2-TptBu,Me)2V]. A more stable adduct (B-OPPh3) was prepared by reacting B-THF with OPPh3. These adducts of B are the first neutral and mononuclear VIV nitride complexes to be isolated.
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Gamage EH, Ribeiro RA, Harmer CP, Canfield PC, Ozarowski A, Kovnir K. Tuning of Cr-Cr Magnetic Exchange through Chalcogenide Linkers in Cr 2 Molecular Dimers. Inorg Chem 2022; 61:6160-6174. [PMID: 35412816 DOI: 10.1021/acs.inorgchem.2c00298] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A set of three Cr-dimer compounds, Cr2Q2(en)4X2 (Q: S, Se; X: Br, Cl; en: ethylenediamine), with monoatomic chalcogenide bridges have been synthesized via a single-step solvothermal route. Chalcogenide linkers mediate magnetic exchange between Cr3+ centers, while bidentate ethylenediamine ligands complete the distorted octahedral coordination of Cr centers. Unlike the compounds previously reported, none of the chalcogenide atoms are connected to extra ligands. Magnetic susceptibility studies indicate antiferromagnetic coupling between Cr3+ centers, which are moderate in Cr2Se2(en)4X2 and stronger in Cr2S2(en)4Cl2. Fitting the magnetic data requires a biquadratic exchange term. High-frequency EPR spectra showing characteristic signals due to coupled S = 1 spin states could be interpreted in terms of the "giant spin" Hamiltonian. A fourth compound, Cr2Se8(en)4, has a single diatomic Se bridge connecting the two Cr3+ centers and shows weak ferromagnetic exchange interactions. This work demonstrates the tunability in strength and type of exchange interactions between metal centers by manipulating the interatomic distances and number of bridging chalcogenide linkers.
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Arh T, Sana B, Pregelj M, Khuntia P, Jagličić Z, Le MD, Biswas PK, Manuel P, Mangin-Thro L, Ozarowski A, Zorko A. The Ising triangular-lattice antiferromagnet neodymium heptatantalate as a quantum spin liquid candidate. NATURE MATERIALS 2022; 21:416-422. [PMID: 34969994 DOI: 10.1038/s41563-021-01169-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2020] [Accepted: 11/11/2021] [Indexed: 06/14/2023]
Abstract
Disordered magnetic states known as spin liquids are of paramount importance in both fundamental and applied science. A classical state of this kind was predicted for the Ising antiferromagnetic triangular model, while additional non-commuting exchange terms were proposed to induce its quantum version-a quantum spin liquid. However, these predictions have not yet been confirmed experimentally. Here, we report evidence for such a state in the triangular-lattice antiferromagnet NdTa7O19. We determine its magnetic ground state, which is characterized by effective spin-1/2 degrees of freedom with Ising-like nearest-neighbour correlations and gives rise to spin excitations persisting down to the lowest accessible temperature of 40 mK. Our study demonstrates the key role of strong spin-orbit coupling in stabilizing spin liquids that result from magnetic anisotropy and highlights the large family of rare-earth (RE) heptatantalates RETa7O19 as a framework for realization of these states, which represent a promising platform for quantum applications.
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Moseley IP, Ard CP, DiVerdi JA, Ozarowski A, Chen H, Zadrozny JM. Slowing magnetic relaxation with open-shell diluents. CELL REPORTS. PHYSICAL SCIENCE 2022; 3:100802. [PMID: 35425929 PMCID: PMC9007552 DOI: 10.1016/j.xcrp.2022.100802] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Strategies for slowing magnetic relaxation via local environmental design are vital for developing next-generation spin-based technologies (e.g., quantum information processing). Herein, we demonstrate a technique to do so via chemical design of a local magnetic environment. We show that embedding the open-shell complex (Ph4P)2[Co(SPh)4] in solid-state matrices of the isostructural, open-shell species (Ph4P)2[M(SPh)4] (M = Ni2+, S = 1; M = Fe2+, S = 2; M = Mn2+, S = 5 2 ) will slow magnetic relaxation for the embedded [Co(SPh)4]2- ion by three orders of magnitude. Magnetometry, electron paramagnetic resonance (EPR), and computational analyses reveal that integer spin and large, positive zero-field splitting (D) values for the diluent produce a quiet, local magnetic field that slows relaxation rates for the embedded Co molecules. These results will enable the investigation of magnetic systems for which strictly diamagnetic congeners are either synthetically inaccessible or are not isostructural.
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Kühne IA, Ozarowski A, Sultan A, Esien K, Carter AB, Wix P, Casey A, Heerah-Booluck M, Keene TD, Müller-Bunz H, Felton S, Hill S, Morgan GG. Homochiral Mn 3+ Spin-Crossover Complexes: A Structural and Spectroscopic Study. Inorg Chem 2022; 61:3458-3471. [PMID: 35175771 PMCID: PMC8889584 DOI: 10.1021/acs.inorgchem.1c03379] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
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Structural, magnetic,
and spectroscopic data on a Mn3+ spin-crossover complex
with Schiff base ligand 4-OMe-Sal2323, isolated in crystal
lattices with five different counteranions,
are reported. Complexes of [Mn(4-OMe-Sal2323)]X where X
= ClO4– (1), BF4– (2), NO3– (3), Br– (4), and I– (5) crystallize isotypically in the chiral
orthorhombic space group P21212 with a range of spin state preferences for the [Mn(4-OMe-Sal2323)]+ complex cation over the temperature range
5–300 K. Complexes 1 and 2 are high-spin,
complex 4 undergoes a gradual and complete thermal spin
crossover, while complexes 3 and 5 show
stepped crossovers with different ratios of spin triplet and quintet
forms in the intermediate temperature range. High-field electron paramagnetic
resonance was used to measure the zero-field splitting parameters
associated with the spin triplet and quintet states at temperatures
below 10 K for complexes 4 and 2 with respective
values: DS=1 = +23.38(1) cm–1, ES=1 = +2.79(1) cm–1,
and DS=2 =
+6.9(3) cm–1, with a distribution of E parameters for the S = 2 state. Solid-state circular
dichroism (CD) spectra on high-spin complex 1 at room
temperature reveal a 2:1 ratio of enantiomers in the chiral conglomerate,
and solution CD measurements on the same sample in methanol show that
it is stable toward racemization. Solid-state UV–vis absorption
spectra on high-spin complex 1 and mixed S = 1/S = 2 sample 5 reveal different
intensities at higher energies, in line with the different electronic
composition. The statistical prevalence of homochiral crystallization
of [Mn(4-OMe-Sal2323)]+ in five lattices with
different achiral counterions suggests that the chirality may be directed
by the 4-OMe-Sal2323 ligand. Zero-field
splitting parameters of the spin triplet and
quintet forms of a spin-crossover Mn3+ complex stabilized
in lattices with different counterions are measured by high-field
electron paramagnetic resonance at different frequencies. The homochiral
crystallization of the enantiopure Δ or Λ forms of the
chelate complex, despite the use of achiral anions, is attributed
to the steric influence of the ligand substituent.
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Ksiądzyna M, Kinzhybalo V, Bieńko A, Medycki W, Jakubas R, Rajnák C, Boca R, Ozarowski A, Ozerov M, Piecha-Bisiorek A. Symmetry-Breaking Phase Transitions, Dielectric and Magnetic properties of Pyrrolidinium-Tetrahalidocobaltates. Inorg Chem Front 2022. [DOI: 10.1039/d2qi00187j] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
We report the physicochemical characteristics of novel Co-based pyrrolidinium analogs: (C4H10N)2CoCl4 (PCC) and (C4H10N)2CoBr4 (PCB). Both compounds consist of the zero-dimensional (OD) anionic network and disordered pyrolidinium cations. The structural...
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Blackmore WJA, Curley SPM, Williams RC, Vaidya S, Singleton J, Birnbaum S, Ozarowski A, Schlueter JA, Chen YS, Gillon B, Goukassov A, Kibalin I, Villa DY, Villa JA, Manson JL, Goddard PA. Magneto-structural Correlations in Ni 2+-Halide···Halide-Ni 2+ Chains. Inorg Chem 2021; 61:141-153. [PMID: 34939800 PMCID: PMC8753652 DOI: 10.1021/acs.inorgchem.1c02483] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
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We present the magnetic
properties of a new family of S = 1 molecule-based
magnets, NiF2(3,5-lut)4·2H2O
and NiX2(3,5-lut)4, where
X = HF2, Cl, Br, or I (lut = lutidine C7H9N). Upon creation of isolated Ni–X···X–Ni
and Ni–F–H–F···F–H–F–Ni
chains separated by bulky and nonbridging lutidine ligands, the effect
that halogen substitution has on the magnetic properties of transition-metal-ion
complexes can be investigated directly and in isolation from competing
processes such as Jahn–Teller distortions. We find that substitution
of the larger halide ions turns on increasingly strong antiferromagnetic
interactions between adjacent Ni2+ ions via a novel through-space
two-halide exchange. In this process, the X···X bond
lengths in the Br and I materials are more than double the van der
Waals radius of X yet can still mediate significant magnetic interactions.
We also find that a simple model based on elongation/compression of
the Ni2+ octahedra cannot explain the observed single-ion
anisotropy in mixed-ligand compounds. We offer an alternative that
takes into account the difference in the electronegativity of axial
and equatorial ligands. The magnetic
properties of well-separated Ni2+ chains are highly dependent
on the bridging halide ligands. By increasing
the size of the halide ions, we can decrease the single-ion anisotropy
such that the system moves from easy plane to easy axis. Through-space
magnetic interactions between adjacent Ni2+ ions are also
turned on as the larger halides are substituted into the exchange
pathway.
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16
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Van Trieste GP, Reid KA, Hicks MH, Das A, Figgins MT, Bhuvanesh N, Ozarowski A, Telser J, Powers DC. Nitrene Photochemistry of Manganese
N
‐Haloamides**. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202108304] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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17
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Zolnhofer EM, Opalade AA, Jackson TA, Heinemann FW, Meyer K, Krzystek J, Ozarowski A, Telser J. Electronic Structure and Magnetic Properties of a Low-Spin Cr II Complex: trans-[CrCl 2(dmpe) 2] (dmpe = 1,2-Bis(dimethylphosphino)ethane). Inorg Chem 2021; 60:17865-17877. [PMID: 34719919 DOI: 10.1021/acs.inorgchem.1c02471] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Octahedral coordination complexes of the general formula trans-[MX2(R2ECH2CH2ER2)2] (MII = Ti, V, Cr, Mn; E = N, P; R = alkyl, aryl) are a cornerstone of both coordination and organometallic chemistry, and many of these complexes are known to have unique electronic structures that have been incompletely examined. The trans-[CrCl2(dmpe)2] complex (dmpe = Me2PCH2CH2PMe2), originally reported by Girolami and co-workers in 1985, is a rare example of a six-coordinate d4 system with an S = 1 (spin triplet) ground state, as opposed to the high-spin (S = 2, spin quintet) state. The ground-state properties of S = 1 systems are challenging to study using conventional spectroscopic methods, and consequently, the electronic structure of trans-[CrCl2(dmpe)2] has remained largely unexplored. In this present work, we have employed high-frequency and -field electron paramagnetic resonance (HFEPR) spectroscopy to characterize the ground-state electronic structure of trans-[CrCl2(dmpe)2]. This analysis yielded a complete set of spin Hamiltonian parameters for this S = 1 complex: D = +7.39(1) cm-1, E = +0.093(1) (E/D = 0.012), and g = [1.999(5), 2.00(1), 2.00(1)]. To develop a detailed electronic structure description for trans-[CrCl2(dmpe)2], we employed both classical ligand-field theory and quantum chemical theory (QCT) calculations, which considered all quintet, triplet, and singlet ligand-field states. While the high density of states suggests an unexpectedly complex electronic structure for this "simple" coordination complex, both the ligand-field and QCT methods were able to reproduce the experimental spin Hamiltonian parameters quite nicely. The QCT computations were also used as a basis for assigning the electronic absorption spectrum of trans-[CrCl2(dmpe)2] in toluene.
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18
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Shylin SI, Pogrebetsky JL, Husak AO, Bykov D, Mokhir A, Hampel F, Shova S, Ozarowski A, Gumienna-Kontecka E, Fritsky IO. Expanding manganese(IV) aqueous chemistry: unusually stable water-soluble hexahydrazide clathrochelate complexes. Chem Commun (Camb) 2021; 57:11060-11063. [PMID: 34610631 DOI: 10.1039/d1cc04870h] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Mn cage complexes are rare, and the ones successfully isolated in the solid state are not stable in water and organic solvents. Herein, we present the first report of mononuclear Mn clathrochelates, in which the encapsulated metal exists in the oxidation state +4. The complexes are extremely stable in the crystalline state and in solutions and show rich redox chemistry.
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19
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Van Trieste GP, Reid KA, Hicks MH, Das A, Figgins MT, Bhuvanesh N, Ozarowski A, Telser J, Powers DC. Nitrene Photochemistry of Manganese N-Haloamides*. Angew Chem Int Ed Engl 2021; 60:26647-26655. [PMID: 34662473 DOI: 10.1002/anie.202108304] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2021] [Indexed: 11/06/2022]
Abstract
Manganese complexes supported by macrocyclic tetrapyrrole ligands represent an important platform for nitrene transfer catalysis and have been applied to both C-H amination and olefin aziridination catalysis. The reactivity of the transient high-valent Mn nitrenoids that mediate these processes renders characterization of these species challenging. Here we report the synthesis and nitrene transfer photochemistry of a family of MnIII N-haloamide complexes. The S=2 N-haloamide complexes are characterized by 1 H NMR, UV-vis, IR, high-frequency and -field EPR (HFEPR) spectroscopies, and single-crystal X-ray diffraction. Photolysis of these complexes results in the formal transfer of a nitrene equivalent to both C-H bonds, such as the α-C-H bonds of tetrahydrofuran, and olefinic substrates, such as styrene, to afford aminated and aziridinated products, respectively. Low-temperature spectroscopy and analysis of kinetic isotope effects for C-H amination indicate halogen-dependent photoreactivity: Photolysis of N-chloroamides proceeds via initial cleavage of the Mn-N bond to generate MnII and amidyl radical intermediates; in contrast, photolysis of N-iodoamides proceeds via N-I cleavage to generate a MnIV nitrenoid (i.e., {MnNR}7 species). These results establish N-haloamide ligands as viable precursors in the photosynthesis of metal nitrenes and highlight the power of ligand design to provide access to reactive intermediates in group-transfer catalysis.
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20
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Witwicki M, Lewińska A, Ozarowski A. o-Semiquinone radical anion isolated as an amorphous porous solid. Phys Chem Chem Phys 2021; 23:17408-17419. [PMID: 34351330 DOI: 10.1039/d1cp01596f] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The use of metal cations is a commonly applied strategy to create S > 1/2 stable molecular systems containing semiquinone radicals. Persistent mono-semiquinonato complexes of diamagnetic metal ions (S = 1/2) have been hitherto less common and mostly limited to the complexes of heavy metal ions. In this work, a mono-semiquinonato complex of aluminum, derived from 1,2-dihydroxybenzene, is obtained using a surprisingly short and uncomplicated procedure. The isolated product is an amorphous and porous solid that exhibits very good stability under ambient conditions. To characterise its molecular and electronic structure, 9.7, 34 and 406 GHz EPR spectroscopy was used in concert with computational techniques (DFT and DLPNO-CCSD). It was revealed that the radical complex is composed of two chemically equivalent aluminum cations and two catechol-like ligands with the unpaired electron uniformly distributed between the two organic molecules. The good stability and porous structure make this complex applicable in heterogeneous aerobic reactions.
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21
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Gompa TP, Greer SM, Rice NT, Jiang N, Telser J, Ozarowski A, Stein BW, La Pierre HS. High-Frequency and -Field Electron Paramagnetic Resonance Spectroscopic Analysis of Metal-Ligand Covalency in a 4f 7 Valence Series (Eu 2+, Gd 3+, and Tb 4+). Inorg Chem 2021; 60:9064-9073. [PMID: 34106710 DOI: 10.1021/acs.inorgchem.1c01062] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The recent isolation of molecular tetravalent lanthanide complexes has enabled renewed exploration of the effect of oxidation state on the single-ion properties of the lanthanide ions. Despite the isotropic nature of the 8S ground state in a tetravalent terbium complex, [Tb(NP(1,2-bis-tBu-diamidoethane)(NEt2))4], preliminary X-band electron paramagnetic resonance (EPR) measurements on tetravalent terbium complexes show rich spectra with broad resonances. The complexity of these spectra highlights the limits of conventional X-band EPR for even qualitative determination of zero-field splitting (ZFS) in these complexes. Therefore, we report the synthesis and characterization of a novel valence series of 4f7 molecular complexes spanning three oxidation states (Eu2+, Gd3+, and Tb4+) featuring a weak-field imidophosphorane ligand system, and employ high-frequency and -field electron paramagnetic resonance (HFEPR) to obtain quantitative values for ZFS across this valence series. The series was designed to minimize deviation in the first coordination sphere from the pseudotetrahedral geometry in order to directly interrogate the role of metal identity and charge on the complexes' electronic structures. These HFEPR studies are supported by crystallographic analysis and quantum-chemical calculations to assess the relative covalent interactions in each member of this valence series and the effect of the oxidation state on the splitting of the ground state and first excited state.
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22
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Manson JL, Curley SPM, Williams RC, Walker D, Goddard PA, Ozarowski A, Johnson RD, Vibhakar AM, Villa DY, Rhodehouse ML, Birnbaum SM, Singleton J. Controlling Magnetic Anisotropy in a Zero-Dimensional S = 1 Magnet Using Isotropic Cation Substitution. J Am Chem Soc 2021; 143:4633-4638. [PMID: 33724822 PMCID: PMC8017523 DOI: 10.1021/jacs.0c12516] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
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The [Zn1–xNix(HF2)(pyz)2]SbF6 (x = 0.2; pyz = pyrazine)
solid solution exhibits a zero-field
splitting (D) that is 22% larger [D = 16.2(2) K (11.3(2) cm–1)] than that observed
in the x = 1 material [D = 13.3(1)
K (9.2(1) cm–1)]. The substantial change in D is accomplished by an anisotropic lattice expansion in
the MN4 (M = Zn or Ni) plane, wherein the increased concentration
of isotropic Zn(II) ions induces a nonlinear variation in M-F and
M-N bond lengths. In this, we exploit the relative donor atom hardness,
where M-F and M-N form strong ionic and weak coordinate covalent bonds,
respectively, the latter being more sensitive to substitution of Ni
by the slightly larger Zn(II) ion. In this way, we are able to tune
the single-ion anisotropy of a magnetic lattice site by Zn-substitution
on nearby sites. This effect has possible applications in the field
of single-ion magnets and the design of other molecule-based magnetic
systems.
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23
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Vassilyeva OY, Buvaylo EA, Kokozay VN, Skelton BW, Sobolev AN, Bieńko A, Ozarowski A. Ferro- vs. antiferromagnetic exchange between two Ni(II) ions in a series of Schiff base heterometallic complexes: what makes the difference? Dalton Trans 2021; 50:2841-2853. [PMID: 33533773 DOI: 10.1039/d0dt03957h] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Three new NiII/ZnII heterometallics, [NiZnL'2(OMe)Cl]2 (1), [NiZnL''(Dea)Cl]2·2DMF (2) and [Ni2(H3L''')2(o-Van)(MeOH)2]Cl·[ZnCl2(H4L''')(MeOH)]·2MeOH (3), containing three-dentate Schiff bases as well as methanol or diethanolamine (H2Dea) or o-vanillin (o-VanH), all deprotonated, as bridging ligands were synthesized and structurally characterized. The Schiff base ligands were produced in situ from o-VanH and CH3NH2 (HL'), or NH2OH (HL"), or 2-amino-2-hydroxymethyl-propane-1,3-diol (H4L'''); a zerovalent metal (Ni and Zn in 1, Zn only in 2 and 3) was employed as a source of metal ions. The first two complexes are dimers with a Ni2Zn2O6 central core, while the third compound is a novel heterometallic cocrystal salt solvate built of a neutral zwitterionic ZnII Schiff base complex and of ionic salt containing dinuclear NiII complex cations. The crystal structures contain either centrosymmetric (1 and 2) or non-symmetric di-nickel fragment (3) with NiNi distances in the range 3.146-3.33 Å. The exchange coupling is antiferromagnetic for 1, J = 7.7 cm-1, and ferromagnetic for 2, J = -6.5 cm-1 (using the exchange Hamiltonian in a form Ĥ = Jŝ1ŝ2). The exchange interactions in 1 and 2 are comparable to the zero-field splitting (ZFS). High-field EPR revealed moderate magnetic anisotropy of opposite signs: D = 2.27 cm-1, E = 0.243 cm-1 (1) and D = -4.491 cm-1, E = -0.684 cm-1 (2). Compound 3 stands alone with very weak ferromagnetism (J = -0.6 cm-1) and much stronger magnetic anisotropy with D = -11.398 cm-1 and E = -1.151 cm-1. Attempts to calculate theoretically the exchange coupling (using the DFT "broken symmetry" method) and ZFS parameters (with the ab initio CASSCF method) were successful in predicting the trends of J and D among the three complexes, while the quantitative results were less good for 1 and 3.
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24
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Janas Z, Jezierska J, Ozarowski A, Bieńko A, Lis T, Jezierski A, Krawczyk M. Investigation of vanadium(III) and vanadium(IV) compounds supported by the linear diaminebis(phenolate) ligands: correlation between structures and magnetic properties. Dalton Trans 2021; 50:5184-5196. [PMID: 33881036 DOI: 10.1039/d0dt04302h] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
A family of oxidovanadium(iv) compounds containing linear diaminebis(phenolate (salans) L1-5 ligands (L1 = [MeNCH2CH2NMe(CH2-4-CMe2CH2CMe3-C6H3O)2]2-; L2 = [MeNCH2CH2NMe(CH2-4-CH3-C6H3O)2]2-; L3 = [MeNCH2CH2NMe(CH2-4-Cl-C6H3O)2]2-; L4 = {MeNCH2CH2NMe[CH2-4,6-(CH3)2-C6H2O]2}2-; and L5 = {MeNCH2CH2NMe[CH2-4,6-(Br)2-C6H2O]2}2-) and non-oxidovanadium(iii) with L2,4 and acac ligands has been prepared and characterized by chemical and physical techniques. Reactions of [VO(acac)2] with ligand precursors H2L2,4 in toluene or hexane afforded vanadium(iii) compounds [V(L-κ4ONNO)(acac)] (1, L2; 2, L4), while the use of acetonitrile or ethanol led to the formation of dimeric oxidovanadium(iv) [(VO)2(μ-L-κ4ONNO)2] (3, L1; 4, L2; 5, L3) and monomeric [VO(L-κ4ONNO)] (6, L4, 7, L5) compounds. As shown by X-ray crystallography, compounds 1 and 2 are monomeric, in which the chelating ligands afford octahedral cis-α geometry at the vanadium center. In the dimeric structures of 3-5, the six-coordinate vanadium centers are bridged via two oxygen atoms of the L1-3 ligands while the L4,5 ligands generate square pyramidal structures of the monomeric 6 and 7 compounds. HFEPR studies allowed the determination of the spin Hamiltonian parameters of the S = 1 spin state of the monomeric V(iii) and dimeric V(iv), and S = ½ in monomeric V(iv) compounds. Magnetic measurements of 3-5 indicated weak ferromagnetic metal-metal exchange interactions. A reaction course for the deoxygenation and reduction of vanadyl-salan compounds is proposed.
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25
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Świtlicka A, Machura B, Bieńko A, Kozieł S, Bieńko DC, Rajnák C, Boča R, Ozarowski A, Ozerov M. Non-traditional thermal behavior of Co( ii) coordination networks showing slow magnetic relaxation. Inorg Chem Front 2021. [DOI: 10.1039/d1qi00667c] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Three new Co(ii) coordination polymers show the DC magnetic data consistent with the S = 3/2 spin system with large zero-field splitting D > 0, which was confirmed by HF EPR and FIRMS measurements.
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