161Dy Time‐Domain Synchrotron Mössbauer Spectroscopy for Investigating Single‐Molecule Magnets Incorporating Dy Ions

Time‐domain synchrotron Mössbauer spectroscopy (SMS) based on the Mössbauer effect of ¹⁶¹Dy has been used to investigate the magnetic properties of a Dy^III‐based single‐molecule magnet (SMM). The magnetic hyperfine field of [Dy(Cy₃PO)₂(H₂O)₅]Br₃?2 (Cy₃PO)?2 H₂O?2 EtOH is with B₀=582.3(5) T significantly larger than that of the free‐ion Dy^III with a ⁶H_15/2 ground state. This difference is attributed to the influence of the coordinating ligands on the Fermi contact interaction between the s and 4f electrons of the Dy^III ion. This study demonstrates that ¹⁶¹Dy SMS is an effective local probe of the influence of the coordinating ligands on the magnetic structure of Dy‐containing compounds.     

New magnetic material based on modified multi-walled carbon nanotubes and iron(III) derivatives

Magnetically active products of the interaction between the modified multi-walled carbon nanotubes, MWCNT-CO-L (L = 3-(NHCH₃)C₅H₄N), and compounds containing Fe^III ions, FeCl₃·6H₂O (including those with ⁵⁷Fe isotopes) and trinuclear pivalate Fe₂NiO(Piv)₆(HPiv)₃ (HPiv = HO₂CCMe₃), were obtained. The new substances were characterized by thermo-gravimetry combined with mass spectral analysis, Mössbauer spectroscopy, atomic absorption spectrophotometry, electron microscopy, and magnetic measurements. Based on the data of Mössbauer spectroscopy and magnetic studies, it was suggested that in the synthesized {Fe}-MWCNT-CO-L the surface of the carbon nanotubes contains nanoparticles of the polynuclear iron(III) derivatives.     

Crystal structure and the magnetic properties of tris(2-chloromethyl-4-oxo-4H-pyran-5-olato-κ2O5,O4)iron(III)

The tris(2-chloromethyl-4-oxo-4H-pyran-5-olato-κ²O⁵,O⁴)iron(III), [Fe(kaCl)₃], has been synthesized and characterized by the crystal structure analysis, magnetic susceptibility measurements, Mössbauer, and EPR spectroscopic methods. The X-ray single crystal analysis of [Fe(kaCl)₃] revealed a mer isomer. The magnetic susceptibility measurements indicated the paramagnetic character in the temperature range of 2 K–298 K. The EPR and Mössbauer spectroscopy confirmed the presence of an iron center in a high-spin state. Additionally, the temperature-independent Mössbauer magnetic hyperfine interactions were observed down to 77 K. These interactions may result from spin–spin relaxation due to the interionic Fe³⁺ distances of 7.386 Å.     

Mössbauer 237Np and crystallographic studies of MIINpF6·3H2O (MII = Mn,Fe, Co) compounds

The compounds M^IINpF₆3H₂O with M^II = Mn, Fe, Co were prepared as single crystals by hydrothermal synthesis (T = 400°C, P = 2000 bars). CoNpF₆3H₂O crystallises in a monoclinic system with C2 space group. Cell parameters are a = 12.143(9) ā; b = 6.922(5) ā; c = 7.942(5) ā; β = 92.84°.The Mössbauer measurements were performed in a conventional He Cryostat. The Mössbauer source used in the experiments was a 500 mCi ²⁴¹Am metal with a conventional sine mode drive system.A microbalance magnetometer attached to a varying temperature Cryostat was used for the susceptibility measurements. The maximum applied magnetic field was 14KG.The Mössbauer spectroscopy of ²³⁷Np shows a magnetically split hyperfine spectrum at 4.2K for all those compounds.The spectra can be fitted with a magnetic hyperfine field associated to a quadrupole splitting using the linear correlation between B_eff and e²qQ. From isomer shift measurements, we confirm the IV charge state of Np in these 3 compounds.The magnetic susceptibility shows antiferromagnetic type transition. 1/ξ = f(T) follows a Curie-Weiss law above T_N.     

A Strongly Spin‐Frustrated FeIII7 Complex with a Canted Intermediate Spin Ground State of S=7/2 or 9/2

A disk‐shaped [Fe^III₇(Cl)(MeOH)₆(μ₃‐O)₃(μ‐OMe)₆ (PhCO₂)₆]Cl₂ complex with C₃ symmetry has been synthesised and characterised. The central tetrahedral Fe^III is 0.733 Å above the almost co‐planar Fe^III₆ wheel, to which it is connected through three μ₃‐oxide bridges. For this iron‐oxo core, the magnetic susceptibility analysis proposed a Heisenberg–Dirac–van Vleck (HDvV) mechanism that leads to an intermediate spin ground state of S=7/2 or 9/2. Within either of these ground state manifolds it is reasonable to expect spin frustration effects. The ⁵⁷Fe Mössbauer (MS) analysis verifies that the central Fe^III ion easily aligns its magnetic moment antiparallel to the externally applied field direction, whereas the other six peripheral Fe^III ions keep their moments almost perpendicular to the field at stronger fields. This unusual canted spin structure reflects spin frustration. The small linewidths in the magnetic Mössbauer spectra of polycrystalline samples clearly suggest an isotropic exchange mechanism for realisation of this peculiar spin topology.     

From the {FeIII2Ln2} Butterfly's Perspective: the Magnetic Benefits and Challenges of Cooperativity within 3 d–4 f Based Coordination Clusters

In this Review we discuss the tuning handles which can be used to steer the magnetic properties of Fe^III-4 f “butterfly” compounds. The majority of presented compounds were produced in the context of project A3 “Di- to tetranuclear compounds incorporating highly anisotropic paramagnetic metal ions” within the SFB/TRR88 “3MET”. These contain {Fe^III₂Ln₂} cores encapsulated in ligand shells which are easy to tune in a “test-bed” system. We identify the following advantages and variables in such systems: (i) the complexes are structurally simple usually with one crystallographically independent Fe^III and Ln^III, respectively. This simplifies theory and anaylsis; (ii) choosing Fe allows ⁵⁷Fe Mössbauer spectroscopy to be used as an additional technique which can give information about oxidation levels and spin states, local moments at the iron nuclei and spin-relaxation and, more importantly, about the anisotropy not only of the studied isotope, but also of elements interacting with this isotope; (iii) isostructural analogues with all the available (i. e. not Pm) 4 f ions can be synthesised, enabling a systematic survey of the influence of the 4 f ion on the electronic structure; (iv) this cluster type is obtained by reacting [Fe^III₃O(O₂CR)₆(L)₃](X) (X=anion, L=solvent such as H₂O, py) with an ethanolamine-based ligand L′ and lanthanide salts. This allows to study analogues of [Fe^III₂Ln₂(μ₃-OH)₂(L′)₂(O₂CR)₆] using the appropriate iron trinuclear starting materials. (v) the organic main ligand can be readily functionalised, facilitating a systematic investigation of the effect of organic substituents on the ligands on the magnetic properties of the complexes. We describe and discuss 34 {M^III₂Ln₂} (M=Fe or in one case Al) butterfly compounds which have been reported up to 2020. The analysis of these gives perspectives for designing new SMM systems with specific electronic and magnetic signatures     

Preparation,Characterization, and Reactions of Dinuclear Tris(2,2,2-trichloroethoxy) Iron(III), Fe(OCH2CCl3)3

The preparation, electrical conductivity, magnetic moments, infrared, reflectance, and ⁵⁷Fe Mössbauer spectra of tris(2,2,2-trichloroethoxy) iron(III) and its adducts with some oxygen and nitrogen donor ligands are reported. Cryoscopic data of the parent compound and its complex with ethylacetate suggest these compounds to be dimeric in nitrobenzene and benzene respectively. All the compounds are covalent with Fe^III having distorted octahedral arrangement which is achieved through alkoxy bridging. The magnetic moments are lesser than those required for the spin only value indicating antiferromagnetic interactions in Fe^III atoms. The Mössbauer spectra are explained in terms of two Fe^III high spin sites corresponding to trans- and cis-positions in the structure.     

Crystal structure and magnetic properties of tris(2-hydroxymethyl-4-oxo-4H-pyran- 5-olato-κ2O5,O4)iron(III)

Tris(2-hydroxymethyl-4-oxo-4H-pyran-5-olato-κ²O⁵,O⁴)iron(III) [Fe(ka)₃], has been characterised by magnetic susceptibility measurements Mössbauer and EPR spectroscopy. The crystal structure of [Fe(ka)₃] has been determined by powder X-ray diffraction analysis. Magnetic susceptibility and EPR measurements indicated a paramagnetic high-spin iron centre. Mössbauer spectra revealed the presence of magnetic hyperfine interactions that are temperature-independent down to 4.2?K. The interionic Fe³⁺ distance of 7.31?Å suggests spin-spin relaxation as the origin of these interactions.     

Spectroscopic and structural properties of homonuclear Fe(II) pyrazine-bridged polymeric complexes [Fe(pyrazine)2X2]n. (X = Cl,Br or I)

The reactions of FeX₂ (X = Cl, Br or I) with pyrazine (pyz) yield the Fe(pyz)₂X₂ compounds. Examination of IR and Raman spectra in the medium- and far-IR region as well as studies of electronic and Mössbauer spectra suggests that the complexes contain six-coordinate high-spin Fe(II) in the FeN₄X₂ chromophore. The complexes have a polymeric pseudo-octahedral pyz-bridged structure. The magnetic moments are independent of temperature and low-temperature magnetic measurements do not indicate any magnetic ordering above 4.2 K in these compounds. The π-acceptor properties of pyz are reflected both in the electronic spectra evaluated in terms of the angular overlap model and the Mössbauer parameters.     

Exploring the Vibrational Side of Spin‐Phonon Coupling in Single‐Molecule Magnets via 161Dy Nuclear Resonance Vibrational Spectroscopy

Synchrotron‐based nuclear resonance vibrational spectroscopy (NRVS) using the Mössbauer isotope ¹⁶¹Dy has been employed for the first time to study the vibrational properties of a single‐molecule magnet (SMM) incorporating Dy^III, namely [Dy(Cy₃PO)₂(H₂O)₅]Br₃?2 (Cy₃PO)?2 H₂O ?2 EtOH. The experimental partial phonon density of states (pDOS), which includes all vibrational modes involving a displacement of the Dy^III ion, was reproduced by means of simulations using density functional theory (DFT), enabling the assignment of all intramolecular vibrational modes. This study proves that ¹⁶¹Dy NRVS is a powerful experimental tool with significant potential to help to clarify the role of phonons in SMMs.     

A study of the new cubic,ordered perovskites BaLaMRuO6 (M = Mg,Fe, Co,Ni, or Zn) and the related phases La2MRuO6 (M = Mg,Co, Ni,or Zn) by 99Ru Mössbauer spectroscopy and other techniques

⁵⁷Fe and ⁹⁹Ru Mössbauer spectroscopy, coupled with magnetic susceptibility measurements down to 4.2 K, have been used to study the electronic and magnetic properties of the new cubic-ordered perovskites BaLaMRuO₆ (M = Mg, Fe, Co, Ni, or Zn). The ruthenium is present in the +5 oxidation state in all the compounds except BaLaFeRuO₆ which contains iron(III) and ruthenium(IV). All the compounds exhibit long-range antiferromagnetic order, with Néel temperatures in the range 20–40 K. Mössbauer spectra for the new compound La₂CoRuO₆ and the isostructural cubic perovskites La₂MRuO₆ (M = Mg, Ni, or Zn) confirm the presence of ruthenium(IV) in these phases and indicate that they are not ordered magnetically at 4.2 K.     

New Type of Neutral Binuclear Spin-Crossover Complex of Iron(III) with Twist of Two Disulfide Bridges as a Product of Electrochemical Oxidation of [FeIII(5Cl-thsa)2]− Anions

As a result of the electrochemical oxidation process, the [Fe^III(5Cl-thsa)₂]⁻ spin-crossover (SCO) anion with N₂S₂O₂ coordination sphere transforms into N₄O₂-coordinated Fe^III SCO neutral binuclear complex 2 with twist of two disulfide bridges. Each dimeric complex is a binuclear double-stranded helicate with similar chirality of both Fe centers. The crystal structure of the complex 2 ⋅ 3H₂O at 100 K has a monoclinic C2/c space group and contains large cavities (about 21.5 % of the unit cell volume) half-filled by 3 water molecules per one dimer. The N₄O₂ coordination of iron(III) with two oxygen atoms (−O⁻) of phenoxy groups, two imine-type (−N_im=) nitrogen atoms of azomethine groups, one amidrazone-type (=N_amidH) nitrogen atom and one ionized terminal group (−N_ionizH) of nitrogen has not been observed in CCDC so far. The oxidation state of the iron atoms in the dimeric complex was confirmed by ⁵⁷Fe Mössbauer spectroscopy on 90 % enriched ⁵⁷Fe sample. Mössbauer spectra and dc magnetic measurements demonstrated the partial HS-HS→LS-LS SCO in the 185–225 K temperature range. The details of the structure of complex 2 and the features of its magnetic properties were refined by theoretical analysis based on DFT calculations. The B3LYP* functional correctly predicting the energy of the spin-crossover process was revealed.     

Mössbauer and X-ray photoelectron spectroscopic studies of prussian blue and its related compounds

The ⁵⁷Fe Mössbauer spectra of three isomorphous compounds of the type Fe₄[M^B(CN)₆]₃ · xH₂O, where M^B is Fe, Ru or Os, have been measured in the temperature range between ?178 and 25°C. The spectral pattern of the ruthenium and osmium compounds is very similar to that of selectively enriched ⁵⁷Fe₄[Fe(CN)₆]₃ · xH₂O. The temperature dependence of the isomer shift and quadrupole splitting is interpreted in terms of lattice dynamics. The X-ray photoelectron spectra also support the conclusions drawn from the Mössbauer study.     

Structural investigation of the EuBa2Cu3O7-δ high TC superconductor by 151Eu, 119Sn, 57Fe and 57Co Mössbauer spectroscopy

By introducing ¹⁵¹Eu, ¹¹⁹Sn, ⁵⁷Fe and ⁵⁷Co into the orthorhombic perovskite lattice of YBa₂Cu₃O_7-δ high T_C superconductors, the localization and distribution of these probe nuclides were investigated by Mössbauer spectroscopy in order to get further information on the structure of high T_C superconductors. The Mössbauer spectra of superconductor samples were considered as superpositions of subspectra belonging to Mössbauer nuclides occupying different sites with various surroundings in the lattice. The ¹⁵¹Eu spectra were evaluated as singlets corresponding to Eu^III situated at the normal rare earth site. The ¹¹⁹Sn spectra were decomposed into a singlet and a doublet, which were associated with Sn^IV at the Cu(2) and the Cu(1) sites, respectively. The ⁵⁷Fe and ⁵⁷Co spectra could be fitted with three doublets representing Fe^III and Fe^IV at the Cu(1) site as well as Fe^III at the Cu(2) site. Comparing the relative area fractions of Mössbauer lines corresponding to different Cu sites it was suggested that iron and cobalt prefer the Cu(1) site, while tin prefers the Cu(2) site in these superconductors.     

A Heterometallic FeII–DyIII Single‐Molecule Magnet with a Record Anisotropy Barrier

A record anisotropy barrier (319 cm^?1) for all d‐f complexes was observed for a unique Fe^II‐Dy^III‐Fe^II single‐molecule magnet (SMM), which possesses two asymmetric and distorted Fe^II ions and one quasi‐D_5h Dy^III ion. The frozen magnetization of the Dy^III ion leads to the decreased Fe^II relaxation rates evident in the Mössbauer spectrum. Ab initio calculations suggest that tunneling is interrupted effectively thanks to the exchange doublets.     

Mössbauer and infrared study of the thermal decomposition of iron and nickel compounds impregnated in alumina

In this work, studies of Fe₃(CO)₁₂ and a mixture of Fe₃(CO)₁₂ and Ni (acac)₂ impregnated in Al₂O₃ were undertaken using Mössbauer and i.r. spectroscopies. In freshly prepared samples, low oxidation species were shown to be present. After thermal decomposition, the data indicate the appearance of aluminum compounds of Fe^II and Fe^III plus superparamagnetic Fe^III. No Fe° species were detected, even under H₂ atmosphere.     

A Trinuclear Radical‐Bridged Lanthanide Single‐Molecule Magnet

Assembly of the triangular, organic radical‐bridged complexes Cp*₆Ln₃(μ₃‐HAN) (Cp*=pentamethylcyclopentadienyl; Ln=Gd, Tb, Dy; HAN=hexaazatrinaphthylene) proceeds through the reaction of Cp*₂Ln(BPh₄) with HAN under strongly reducing conditions. Significantly, magnetic susceptibility measurements of these complexes support effective magnetic coupling of all three Ln^III centers through the HAN^3−. radical ligand. Thorough investigation of the Dy^III congener through both ac susceptibility and dc magnetic relaxation measurements reveals slow relaxation of the magnetization, with an effective thermal relaxation barrier of U_eff=51 cm⁻¹. Magnetic coupling in the Dy^III complex enables a large remnant magnetization at temperatures up to 3.0 K in the magnetic hysteresis measurements and hysteresis loops that are open at zero‐field up to 3.5 K.     

Magnetic Properties of M3[Fe(Cn)6]2Xh2O (M = Co (II), Ni(II), Cu(II), Zn(II))

Compounds of the type M₃[Fe(CN)₆]₂XH₂O (M = Co(II), Ni(II), Cu(II), and Zn(II)) were prepared and magnetic properties of their powders were investigated by means of EPR spectra, Mössbauer effect and magnetic susceptibility measurements. The temperature dependence of the magnetization for the complexes Co₃[Fe(CN)₅]₂- 10H₂O, Ni₃[Fe(CN)₆]₂-10H₂O and Cu₃[Fe(CN)₆]₂-4H₂O revealed that below the critical temperatures 15, 22 and 20 K respectively, these complexes have zero-field magnetization. The magnetic hysteresis at 10 K for Co(II), Ni(II) and Cu(II) complexes was observed. Mössbauer spectra at 4.2 K for the compounds are discussed.     

Mössbauer spectra of bis-[π-(3)-1,2-dicarbollyl] cobaltate(III), tetrachlorogallate,and ferricinium molybdate

The Mössbauer spectra of the new salt-like complexes of the ferricinium ions [Fe^IIICp₂]⁺{Co^III[π-(3)-1,2-B₉C₂H₁₁]₂}^? (I) with π-sandwich aromatic anions and of the [FeCp₂]⁺[GaCl₄]^?(II) and [FeCp₂] ₂ ⁺ [MoO₄]^2? (III) compounds are compared. It is shown that the Mössbauer spectra of these compounds are broadened asymmetric lines whose broadening and asymmetry increase with decreasing temperature. The peculiarities of the spectra are associated with paramagnetic relaxation effects, in particular, with the Blume effect. In I–III, the sign of the electric field gradients on the iron nuclei is negative, while ferrocene exhibits a positive electric field gradient. It is noted that the nature of the anion affects the frequency of spin fluctuations, but has no effect on the electronic state of iron atoms, as well as on the symmetry of its local surrounding in FeCp ₂ ⁺ . Analysis of the probability of the Mössbauer effect suggests that in compound I the anion-cation interaction is stronger than that in compounds II and III.     

121Sb-Mössbauer-Spektren von Antimon(V)-Verbindungen. II

¹²¹Sb Mössbauer Spectra of Antimony (V) Compounds. II The Mössbauer resonance effect of ¹²¹Sb has been studied at 4.2 K in a series of 11 antimony(V) compounds which are in most cases bridged. Isomer shift and quadrupole splitting variations are considered in the light of results of X-ray and vibrational spectroscopy. Preparation and the vibrational spectra of [NMe₄][SbCl₄(n₃)₂] are described. Within the limitations of available structural data related tin compounds are compared with those of corresponding ¹¹⁹Sn Mössbauer spectra.