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Rational design of materials for energy storage systems relies on our ability to probe these materials at various length scales. Solid-state NMR spectroscopy is a powerful approach for gaining chemical and structural insights at the atomic/molecular level, but its low detection sensitivity often limits applicability. This limitation can be overcome by transferring the high polarization of electron spins to the sample of interest in a process called dynamic nuclear polarization (DNP). Here, we employ for the first time metal ion-based DNP to probe pristine and cycled composite battery electrodes. A new and efficient DNP agent, Fe­(III), is introduced, yielding lithium signal enhancement up to 180 when substituted in the anode material Li4Ti5O12. In addition for being DNP active, Fe­(III) improves the anode performance. Reduction of Fe­(III) to Fe­(II) upon cycling can be monitored in the loss of DNP activity. We show that the dopant can be reactivated (return to Fe­(III)) for DNP by increasing the cycling potential window. Furthermore, we demonstrate that the deleterious effect of carbon additives on the DNP process can be eliminated by using carbon free electrodes, doped with Fe­(III) and Mn­(II), which provide good electrochemical performance as well as sensitivity in DNP-NMR. We expect that the approach presented here will expand the applicability of DNP for studying materials for frontier challenges in materials chemistry associated with energy and sustainability.

We succeeded in the synthesis of an anionic stannaferrocene by the reaction of a dilithiostannole with a Fe(III) reagent, which cannot be achieved by the use of cyclopentadienyl (Cp) and its relate...

Temperature-dependent 57Fe Mossbauer effect (ME) spectroscopic studies were carried out on ferrocene (Fc), 1,10-dimethylferrocene (1,10'(CH3)(2)Fc) and ferrocenium hexafluorophosphate (FcPF(6)) guest species in cucurbit[n] uril (n = 7, 8) inclusion complexes. The solid inclusion complexes were isolated by freeze-drying of dilute aqueous solutions and/or microwave-assisted precipitation from concentrated mixtures. The presence of genuine 1 : 1 (host : guest) inclusion complexes in the isolated solids was supported by liquid-state H-1 and solid-state C-13{H-1} MAS NMR, elemental and thermogravimetric analyses, powder X-ray diffraction, FTIR spectroscopy, and diffuse reflectance UV-Vis spectroscopy. The ME spectra of the complexes CB7.Fc and CB7.11'(CH3)(2)Fc consist of well-resolved doublets with hyperfine parameters (isomer shift and quadrupole splitting at 90 K) and temperature-dependent recoil-free fraction data that are very similar to those for the neat parent compounds, Fc and 1,10(CH3)(2)Fc, suggesting that the organometallic guest molecules do not interact significantly with the host environment over the experimental temperature range. The ME spectra for CB7.FcPF(6) and CB8.FcPF(6) consist of a major broad line resonance attributed to a paramagnetic FeIII site. From the temperature-dependence of the recoil-free fraction it is evident that the charged guest species in these systems interact with the host environment significantly more strongly than was observed in the case of the neutral guest species, Fc and 1,10(CH3)(2)Fc. Moreover, the ME data indicate that the vibrational amplitude of the ferrocenium guest molecule is significantly larger in the CB8 host molecule than in the CB7 homologue, as expected on the basis of the different cavity sizes. Fundacao para a Ciencia e a Tecnologia (FCT) [ POCI-01-0145-FEDER-007679] Ministerio da Educacao e Ciencia (MEC) Fundo Europeu de Desenvolvimento Regional (FEDER) under the PT Partnership Agreement European Union [SFRH/BPD/108541/2015] Ministerio da Ciencia, Tecnologia e Ensino Superior (MCTES) European Social Fund through the program Programa Operacional Potencial Humano (POPH) of Quadro de Referencia Estrategica Nacional (QREN) FCT [SFRH/BPD/108541/2015] info:eu-repo/semantics/publishedVersion

A transition-metal-only MnFe0.5Ru0.5O3 polycrystalline oxide was prepared by a reaction of starting materials MnO, MnO2, Fe2O3, RuO2 at 6 GPa and 1873 K for 30 minutes. A combination of X-ray and neutron powder diffraction refinements indicated that MnFe0.5Ru0.5O3 adopts the corundum (alpha-Fe2O3) structure type with space group R (3) over barc, in which all metal ions are disordered. The centrosymmetric nature of the MnFe0.5Ru0.5O3 structure is corroborated by transmission electron microscopy, lack of optical second harmonic generation, X-ray absorption near edge spectroscopy, and Mossbauer spectroscopy. X-ray absorption near edge spectroscopy of MnFe0.5Ru0.5O3 showed the oxidation states of Mn, Fe, and Ru to be 2+/3+, 3+, and similar to 4+, respectively. Resistivity measurements revealed that MnFe0.5Ru0.5O3 is a semiconductor. Magnetic measurements and magnetic structure refinements indicated that MnFe0.5Ru0.5O3 orders antiferromagnetically around 400 K, with magnetic moments slightly canted away from the c axis. Fe-57 Mossbauer confirmed the magnetic ordering and Fe3+ (S = 5/2) magnetic hyperfine splitting. First principles calculations are provided to understand the electronic structure more thoroughly. A comparison of synthesis and properties of MnFe0.5Ru0.5O3 and related corundum Mn2BB'O-6 derivatives is discussed.

Temperature-dependent 119Sn Mossbauer effect (ME) spectroscopy has been used to elucidate the hyperfine parameters (isomer shift and quadrupole splitting) as well as the dynamics of the motion of tin in three triphenyltin phosphide complexes, namely P(SnPh3)3 (C54H45PSn3, 1), P7(SnPh3)3 (C54H45P7Sn3, 2), and [Na(benzo-15-crown-5)][P(SnPh3)2] (C50H50NaO5PSn2, 3), as well as in triphenyltin chloride (4). Although the isomer shifts are very similar for all four compounds, the quadrupole splitting is dependent upon their detailed structures. The metal atom vibrations are essentially isotropic with respect to the principal symmetry axis passing through the tin atom and the triphenyltin moiety. The crystal structure of triphenyltin chloride has been re-determined at four different temperatures, and the root-mean-square amplitudes-of-vibration of the metal atom have been evaluated from the crystallographic Ui,j values and compared with the corresponding data derived from the Mossbauer measurements. These metal atom dynamics have been compared with those of the stannyl phosphide complexes derived from ME data and related to their structural details. The sensitivity of the ME technique with respect to elucidating the metal atom dynamics is demonstrated in detail.

Three new triple-decker complexes were synthesized by the reaction of nonamethylferrocene, Cp′FeCp* (Cp′ = C5Me4H, Cp* = C5Me5), with coordinatively unsaturated transition-metal complexes. The reaction of ruthenium cations [(C5R5)Ru]+ (R = H, Me) with Cp′FeCp* afforded the purple heterometallic triple-decker complexes [(C5R5)Ru(μ-Cp′)FeCp*]+ by electrophilic addition of ruthenium to the Cp′ ring of nonamethylferrocene. The analogous reaction with the manganese cation [Mn(CO)3]+ produced the blue homometallic triple-decker complex [Cp*Fe(μ-Cp′)FeCp*]+ by abstraction of the Cp′ ring from Cp′FeCp* and subsequent addition of the newly generated cation [Cp*Fe]+ to 1 equiv of Cp′FeCp*. These experiments demonstrate that the asymmetry of Cp′FeCp* gives rise to a remarkable degree of regioselectivity such that ruthenium electrophiles add only to the Cp′ ring and never to the Cp* ring. In a similar way, [Mn(CO)3]+ abstracts only the Cp′ ring from Cp′FeCp* to produce [Cp*Fe]+, which in turn adds only to the Cp′ rin...

The synthesis and characterization of a series of heavier group 14 element (Ge, Sn, and Pb) carbene homologues based on the electronically modified, 2,6-dimesityl substituted terphenyl ligands Ar#-3,5-iPr2, Ar#-4-SiMe3, and Ar#-4-Cl (Ar#-3,5-iPr2 = C6H2-2,6-Mes2-3,5-iPr2; Ar#-4-Cl = C6H2-2,6-Mes2-4-Cl; Ar#-4-SiMe3 = C6H2-2,6-Mes2-4-SiMe3; Mes = C6H2-2,4,6-Me3) are presented. The consequences of introducing electron withdrawing and -releasing substituents on the solid state structures of the newly synthesized germylenes, stannylenes, and plumbylenes as well as their Mossbauer, NMR and UV–vis spectroscopic properties are presented and discussed in the context of a second order Jahn–Teller type mixing of frontier orbitals with appropriate symmetry. Experimental findings were supported by DFT calculations. More electron withdrawing ligands lead to a bonding situation with higher contribution of p-orbitals from the central heavier group 14 element in σ-bonding toward the ligands and thus increased s-electron c...

High-oxidation-state metal complexes with multiply bonded ligands are of great interest for both their reactivity as well as their fundamental bonding properties. This paper reports a combined spectroscopic and theoretical investigation into the effect of the apical multiply bonded ligand on the spin-state preferences of threefold symmetric iron(IV) complexes with tris(carbene) donor ligands. Specifically, singlet (S = 0) nitrido [{PhB(ImR)3}FeN], R = tBu (1), Mes (mesityl, 2) and the related triplet (S = 1) imido complexes, [{PhB(ImR)3}Fe(NR′)]+, R = Mes, R′ = 1-adamantyl (3), tBu (4), were investigated by electronic absorption and Mossbauer effect spectroscopies. For comparison, two other Fe(IV) nitrido complexes, [(TIMENAr)FeN]+ (TIMENAr = tris[2-(3-aryl-imidazol-2-ylidene)ethyl]amine; Ar = Xyl (xylyl), Mes), were investigated by 57Fe Mossbauer spectroscopy, including applied-field measurements. The paramagnetic imido complexes 3 and 4 were also studied by magnetic susceptibility measurements (for 3) a...

Three structurally related bimetallic triple-decker complexes of iron and ruthenium have been studied by temperature-dependent 57 Fe Mossbauer Effect (ME) spectroscopy and their redox-behavior has been elucidated. The triple-decker compounds are [Cp′FeCp′FeCp′]BF 4 , [CpRuCp′FeCp′]PF 6 and [Cp*RuCp′FeCp′]PF 6 where Cp = C 5 H 5 , Cp′ = C 5 Me 4 H and Cp* = C 5 Me 5 . The metal atom (Fe) root-mean-square-vibrational-amplitude has been determined over the temperature range ∼90 T 4 is similar to the spectra for the two Ru–Fe compounds indicating that the substitution of Ru for Fe has only a minor effect on the hyperfine and associated parameters. Similarly, analysis of the metal atom dynamics for [CpRuCp′FeCp′]PF 6 and [Cp*RuCp′FeCp′]PF 6 shows that ring substitution has a negligible effect on the bonding parameters. A comparison of the three triple-decker compounds with the mono-iron diamagnetic compound Cp*FeCp* and the paramagnetic [Cp′FeCp′]BF 4 compound is also detailed.

Dilithiostannoles, which are aromatic tin-containing ring compounds, were proposed to have stannylene character, as judged from their NMR analysis. We herein report on the synthesis of silyl-substituted dilithiostannoles, which were characterized by NMR spectroscopy and X-ray diffraction analysis. The silyl-substituted derivatives also exhibit features characteristic of aromatic dilithiostannoles such as 7Li NMR signals at high-field area and no C–C bond alternation in the stannole rings. Theoretical calculations and the 119Sn NMR chemical shifts revealed that the stannylene character in the silyl-substituted dilithiostannoles is enhanced due to greater interaction between 5p (Sn) and LUMO (butadiene) in comparison to those in alkyl and aryl derivatives. The 119Sn Mossbauer spectra of dilithiostannoles were measured for the first time, indicating that each of the tin atoms in dilithiostannoles can be characterized as having Sn(II) character.

(Cp2Sn)-Sn-BIG (Cp-BIG = (4-n-Bu-C6H4)(5)cyclopentadienyl), prepared by reaction of 2 equiv of (CpNa)-Na-BIG with SnCl2, crystallized isomorphous to other known metallocenes with this ligand (Ca, Sr, Ba, Sm, Eu, Yb). Similarly, it shows perfect linearity, C-H center dot center dot center dot C(pi) bonding between the Cp-BIG rings and out-of-plane bending of the aryl substituents toward the metal. Whereas all other (Cp2M)-M-BIG complexes show large disorder in the metal position, the Sn atom in (Cp2Sn)-Sn-BIG is perfectly ordered. In contrast, Sn-119 and Eu-151 Mossbauer investigations on the corresponding (Cp2M)-M-BIG metallocenes show that Sn(II) is more dynamic and loosely bound than Eu(II). The large displacement factors in the group 2 and especially in the lanthanide(II) metallocenes (Cp2M)-M-BIG can be explained by static metal disorder in a plane parallel to the Cp-BIG rings. Despite parallel Cp-BIG rings, these metallocenes have a nonlinear CDcenter-M-CPcenter geometry. This is explained by an ionic model in which metal atoms are polarized by the negatively charged Cp rings. The extent of nonlinearity is in line with trends found in M2+ ion polarizabilities. The range of known calculated dipole polarizabilities at the Douglas-Kroll CCSD(T) level was extended with values (atomic units) for Sn2+ 15.35, Sm2+(4f(67)F) 9.82, Eu2+(4f(7) S-8) 8.99, and Yb2+(4f(14) S-1)) 6.55. This polarizability model cannot be applied to predominantly covalently bound (Cp2Sn)-Sn-BIG, which shows a perfectly ordered structure. The bent geometry of Cp*Sn-2 should therefore not be explained by metal polarizability but is due to van der Waals Cp*center dot center dot center dot Cp* attraction and (to some extent) to a small p-character component in the Sn lone pair.

Using temperature-dependent Mossbauer effect spectroscopy, the hyperfine interactions and metal atom dynamics of three structurally related 1,1′ bis tert. butyl ferrocenes have been examined in detail over the temperature range 90 tert. butyl groups for the Cp ring protons lowers the melting point close to RT. Further ring substitution again raises the melting point above RT. As noted previously, the substitution of a tert. butyl group for a ring proton has little effect on the IS and QS parameters at 90° K. In contrast, the temperature-dependence of the IS reflects the covalency of the metal atom-ring interaction. The evaluation of the k 2 2 > parameter, and its comparison to its value in the parent ferrocene shows that the vibrational amplitude of the metal atom is significantly smaller in the butyl compounds than in ferrocene. The metal atom motions are isotropic in the phenyl phosphine and bromine complexes, indicative of the absence of a Goldanskii-Karayagin effect in these two molecular solids.

The compound {o-(Ph2P)C6H4}2Sn(CH3)2 was rigorously purified and examined by single crystal X-ray diffraction (XRD) studies at three different temperatures and by temperature-dependent Mossbauer effect (ME) determination at 8 temperatures in the interval 87

The hyperfine interactions and lattice dynamics of the two Fe atoms in the title compounds have been elucidated using temperature-dependent 57 Fe Mossbauer effect spectroscopy (MES). The two Fe atoms are distinct both with respect to the isomeric shift (IS) and quadrupole (QS) hyperfine interactions. The vibrational amplitudes of the metal atoms have been determined by MES and are compared to the corresponding values deduced from single crystal X-ray data at 150 K. The motional anisotropy of the Fe atom ligated to the four CO groups has been determined over the range 90 T ∗ group is effectively isotropic.

High purity samples of SnPc and SnPc2 (Pc = phthalocyanin, C32H16N82−) have been examined by temperature-dependent 119Sn Mossbauer effect (ME) spectroscopy in order to elucidate the metal atom dynamics over the temperature range 94

The synthesis and spectroscopic and structural characterization of an extensive series of acyclic, monomeric tetrylene dichalcogenolates of formula M(ChAr)2 (M = Si, Ge, Sn, Pb; Ch = O, S, or Se; Ar = bulky m-terphenyl ligand, including two new acyclic silylenes) are described. They were found to possess several unusual features-the most notable of which is their strong tendency to display acute interligand, Ch-M-Ch, bond angles that are often well below 90°. Furthermore, and contrary to normal steric expectations, the interligand angles were found to become narrower as the size of the ligand was increased. Experimental and structural data in conjunction with high-level DFT calculations, including corrections for dispersion effects, led to the conclusion that dispersion forces play an important role in stabilizing their acute interligand angles.

The organometallic compound ferrocenium hexafluorophosphate, [Fe(C5H5)2] PF6, has been studied by Mossbauer spectroscopy in the past, mainly to determine the crystal structure at high temperatures. Here we present studies at 95 K to 305 K and analyze the spectra in terms of spin relaxation theory which yields accurately the hyperfine interaction parameters and the spin-spin and spin-lattice relaxation rates in this paramagnetic compound. The spectral area under the resonance curve yields the recoil free fraction and thus the mean square of the vibration amplitude . One observes a large discontinuity in the slope of versus T at ˜210 K, indicative of a phase transition. The analysis of the spectra proves that the quadrupole interaction is small but certainly negative, ½e2qQ = -0.12(2) mm/s, and causes the asymmetry observed in the spectra. The detailed analysis yields also, for the first time, the fluctuating effective magnetic hyperfine field, H eff = 180(50) kOe.

International audience; Pyramidane and its derivatives are among the most desirable synthetic chemistry targets, whose appealing square-pyramidal design, fascinating nonclassical structure, and unusual bonding features have attracted the permanently growing interest of organic chemists for decades. Although they have been comprehensively approached on theoretical grounds, no member of the pyramidane family was experimentally realized until very recently, thus remaining one of the biggest synthetic challenges for experimental pursuits. In this paper, we report on a series of stable hybrid pyramidanes of group 14 elements, featuring germanium, tin, or lead at the apex of the square pyramid, capping the four-membered-ring base made of carbon, silicon, or germanium atoms. On the basis of the experimental results (X-ray diffraction and NMR and Mossbauer spectroscopy) and computational studies at the B3LYP/Def2TZVP level of theory (MO, NBO, NRT, and AIM), an extraordinarily high degree of ionicity of the pyramidal apex-to-base bonds was attributed to the overall structure of these nonclassical covalent compounds.

A series of perovskites Sr 4− x La x Fe 3 ReO 12 ( x =0.0, 1.0, 2.0) has been prepared by wet chemistry methods. The structure analyses by powder X-ray and neutron diffraction and electron microscopy show that these compounds adopt simple perovskite structures without cation ordering over the B sites: tetragonal ( I 4 /mcm ) for x =0.0 and 1.0 and orthorhombic ( Pbmn ) for x =2.0. The oxidation states of the cations in the compound with x =0.0 appear to be Fe 3+/4+ and Re 7+ and decrease for both with La substitution as evidenced by X-ray absorption spectroscopy. All the compounds are antiferromagnetically ordered above room temperature, as demonstrated by Mossbauer spectroscopy and the magnetic structures, which were determined by powder neutron diffraction. The substitution of Sr by La strongly affects the magnetic properties with an increase of T N up to ∼750 K.

Iron atom dynamics of CH 3 CpFe ligated to a concave face in π-bowl sumanene was investigated using temperature-dependent Mossbauer effect (ME) spectroscopy.

Temperature-dependent Mossbauer effect spectroscopy has been used to elucidate the dynamics of the metal atom in a number of tin organometallics. The vibrational amplitudes so obtained have been compared to those extracted from single crystal X-ray diffraction data, and the differences between these two sets are rationalized. GRAPHICAL ABSTRACT

We present a detailed study of the ferromagnetism in nano- Ni -doped SnO 2 and ZnO . It is shown that the ferromagnetic behavior is not an intrinsic property of the systems but rather associated with the presence of n Ni particles in both matrices. The ferromagnetic transition of all Ni -doped samples is at 631(2) K, the same as the TC value for bulk Ni and nano- Ni powder. The saturation moments of the nano- Ni -doped samples scale with the Ni concentration and are much lower than that of pure Ni . This is due to the large surface area of nano- Ni particles which are partially oxidized due to nano- NiO . 119 Sn Mössbauer spectroscopy studies on Sn 0.96 Ni 0.04 O 2 do not show any transferred hyperfine field on the Sn nuclei, confirming that the magnetic properties stem from a different phase.

Three structurally related bis phosphino ferrocene complexes have been examined by 57Fe Mossbauer effect (ME) spectroscopy in order to evaluate the hyperfine interaction parameters (IS and QS), their temperature dependencies, as well as the dynamics of the metal atom over a temperature range. For two of the compounds (1 and 2), for which single crystal X-ray diffraction data have been reported, a direct comparison can be effected between the Ui,j values derived from the X-ray study and that extracted from the ME data, and are found to be in good agreement. For complex 3, which is a waxy material at room temperature, no X-ray data can be obtained, but the ME data permit an evaluation of the metal atom vibrational amplitudes even in the high (>180 K) temperature regime. In addition, data are presented relating to the anisotropy of the metal atom motion in these ferrocene complexes.

Six structurally related cyano ferrocenes have been examined by temperature-dependent Mossbauer effect spectroscopy (MES) to yield information concerning the isomeric shift (IS), quadrupole splitting (QS), and related parameters characterizing the iron atom in these compounds. The IS is related to the s-electron density at the Fe nucleus, while the QS is related to the symmetry and magnitude of the electrostatic field. In addition, these data can yield information related to the dynamics of the metal atom and are in excellent agreement with X-ray crystal data. Density functional theory (DFT) calculations have been used to obtain values for the three principal components of the electric field gradient tensor as well as the electron density at the metal atom site. The results of the DFT calculations and the MES data are found to be in exceptionally good agreement in these compounds.

A series of mixed-valent (MV) complexes [(FeCp) 2 (μ-C 10 H 6 -(BPh) 2 )] + X ([1 + ]X; X=I 5 , PF 6 , SbF 6 , B(C 6 F 5 ) 4 ) were prepared by oxidation of diboradiferrocene [(FeCp) 2 (μ-C 10 H 6 -(BPh) 2 )] (1) with I 2 , AgPF 6 , and AgSbF 6 , respectively, and through anion exchange of the I 5 - salt with [Li-(Et 2 O) x ][B(C 6 F 5 ) 4 ] in the case of X=B-(C 6 F 5 ) 4 . The MV state of the cation was investigated in solution by multi-nuclear NMR spectroscopy, CV, and UV/Vis-NIR absorption spectroscopy, and in the solid state by IR spectroscopy, single-crystal X-ray crystallography, and Mossbauer spectroscopy. The cyclic voltammogram of 1 shows two distinct redox waves with a large redox splitting of ΔE=510 mV in CH 2 Cl 2 and the NIR spectrum for the mono-oxidized species displays an intervalence charge-transfer band at around 1500 to 1700 nm depending on the specific counterion present. The X-ray crystal structures of [1 + ]X show inversion-symmetric cations with X=I 5 and B-(C 6 F 5 ) 4 and unsymmetric valence-trapped structures composed of one ferrocene and one ferrocenium moiety with X=PF 6 and SbF 6 . Mossbauer data for X=PF 6 are consistent with valence trapping at all temperatures between 90 and 343 K. In comparison, fast electron transfer is evident on the Mossbauer timescale for X=I 5 and temperature-dependent behavior is observed for X=B(C 6 F 5 ) 4 . The anion dependence of the X-ray structural and Mossbauer data is discussed in the context of crystal symmetry and the possibility of static and dynamic disorder effects is considered.

clarity, the structures of these compounds are collected in scheme 1. In the present study, these compounds have been investigated by temperature-dependent MES and the dynamical data concerning the iron atom(s) have been compared to the temperature factor Ui,j values determined by single crystal X-ray diffraction. A comparison between the MES and X-ray based data relating to the vibrational amplitudes of the metal atom in organometallics should consider the effect of lattice imperfections which play a more significant role in the magnitude of the Ui,j values extracted from X-ray diffraction data than in the mean-square-amplitude-of-vibration data contributing the the recoil-free fraction (MES) values. Inter-molecular motions will contribute more to the former than the latter, since the X-ray measurements sample all atomic positions over a lengthy period of time while the MES measurements involve only a single atom during the scattering event. It should also be noted that the presence of solvate molecules in the unit cell will influence the atomic positions sensed by the X-ray technique relative to the MES measurements. This point will be addressed again in the discussion to follow. Hence, in general the vibrational amplitudes calculated from the X-ray data are larger than those derived from the MES data at the same temperature, as will be discussed in greater detail, below. This observation has also been examined in detail in relation to protein dynamics by Parak et al. 8 The second point relates to the temperature dependence of the vibrational amplitudes. The frequency of such vibrations can be expressed as ω ∝ [k/M] 1/2 where k is the appropriate force constant and M is the vibrating mass. For intra-molecular motions, k is large and M is small (relatively), whereas for inter-molecular motions, k is small and M is large. Thus, at low temperatures where the phonon frequencies are low, the major contribution to the vibrational amplitude will be due to the inter-molecular motions, while with increasing temperature the intra-molecular motions become more appreciable. These considerations lead to the expectation that the tempera

Reaction of the phosphadicarbollide anion [7,8,9-PC2B8H10]– (4) with [CpFe(C6H6)]+ or [Cp*Fe(MeCN)3]+ gives the expected 12-vertex ferraphosphadicarbollides [1-C5R5-1,2,3,4-FePC2B8H10] [R = H (5a), Me (5b); the metal atom is assigned number 1] in around 35 % yield. Compounds 5a,b undergo selective polyhedral rearrangement at 150 °C to give the corresponding isomers [1-C5R5-1,2,4,5-FePC2B8H10] (6a,b). The structure of 5a has been determined by X-ray diffraction. An electrochemical investigation has revealed that all the compounds obtained display the FeII/FeIII oxidation process with features of chemical reversibility on the cyclic voltammetric timescale. However, only cation [6b]+ is reasonably stable on the long timescales of electrolysis. Ferraphospadicarbollides 5a and 6a are more difficult to oxidize than the related dicarbollide and tricarbollide derivatives [CpFe(C2B9H11)]–and [CpFe(C3B8H11)], respectively. Temperature-dependent Mossbauer effect studies show that the recoil-free fraction over the temperature interval 110–342 K for 5a is well accounted for by a linear regression, and a calculation of the root-mean-square-amplitude-of-vibration (rmsav) of the iron atom, based on the Mossbauer effect (ME) data, is in reasonable agreement with the value calculated from the single-crystal X-ray study at 120 K. Similarly, the ME and X-ray rmsav data for 6a at 293 K are in excellent agreement with each other, and the value at 120 K calculated for 6a is in good agreement with that observed for 5a. The metal atom motion is nearly isotropic with respect to the major symmetry axis running through the Cp ring and the Fe atom. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Depending on the ratio of the starting reagents, the interaction of [FcTeI] with Fe(CO)(5) gave complex (Fc(2)Te(2))Fe(CO)(3)I-2 (1) bearing an Fc(2)Te(2) ligand, or a dimeric complex [(CO)(3)IFe(mu-TeFc)](2) (2). An interaction of equimolar amounts of [CpFe(CO)(2)](2) and Fc(2)Te(2) under the thermal conditions in toluene afforded CpFe(CO)(2)TeFc (3). Complex 3 can be easily halogenated at the Te center by elemental bromine and iodine to give monomeric CpFe(CO)(2)TeX(2)Fc (X = Br (4), I (5)). Complex 5 can be prepared alternatively via formal insertion of [FcTeI] into Fc-I bond of CpFe(CO)(2)I. Complex 3 readily substitutes one carbonyl in Fe(CO)(4)I-2 to give the adduct CpFe(CO)(2)(mu-TeFc)Fe(CO)(3)I-2 (6). (C) 2014 Elsevier B.V. All rights reserved.

A number of organometallic and related iron-containing compounds have been examined by transmission 57Fe Mossbauer spectroscopy in modest (0–2.4 T) magnetic fields in order to determine the sign of the quadrupole-splitting hyperfine parameter (QS) as well as the internal magnetic field in derived paramagnetic solids. A computer program has been developed to extract these parameters from the spectroscopic data. The sign of the QS is found to be positive in the neutral ferrocenoid solids and negative in the derived cationic complexes. The internal hyperfine field makes a positive contribution in the cationic ferrocenoids and a negative contribution in FeF2 and Fe(phen)2(SCN)2. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Two new bucky-ferrocene compounds, incorporating two η 5-CpFe ligands in the C60 framework, have been examined by temperature-dependent 57Fe Mossbauer spectroscopy over the temperature range 86

Recent experiments have shown that root-mean-square amplitudes-of-vibration (rmsav) for iron atoms in organometallic complexes at various temperatures can be extracted from temperature-dependent 57Fe Mossbauer spectroscopic data related to the recoil-free fraction of the metal atom. The applicability of this procedure has been validated by comparison with rmsav data extracted from Uij values obtained from single-crystal X-ray diffraction parameters at various temperatures. This analysis has been applied in detail to a study of decamethylferrocene (DMFc), for which the agreement between the rmsav values derived from the two experimental procedures is compared in the present study. A comparison of these rmsav values for a number of related structures is also reported over a similar temperature range. An improved method for the quantitative preparation of isotopically enriched DMFc is described. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Temperature-dependent 57Fe Mossbauer spectroscopy has been used to elucidate the hyperfine parameters and dynamical behavior of the metal atom in several organo-iron complexes which have one or more η 5 P5 ring structures as ligated groups. The spin-lattice relaxation of the (paramagnetic) one-electron oxidation products occurs on a time scale fast compared to τ 1/2 (ME) at temperatures in the range 85 < T < 320 K.

Mossbauer spectroscopic studies of BaFeO 4 and K 2 FeO 4 as prepared, then either sealed, or exposed to air, or exposed to moist air for a period up to more than one year, were performed at room temperature as a function of time. Some of the samples were studied as a function of temperature down to 4.2 K. K 2 FeO 4 and BaFeO 4 after preparation, exhibit a pure Fe 6+ spectrum. K 2 FeO 4 shows low stability. After a period of 14 months in a sealed sample holder, the spectrum exhibits 83% noncrystalline Fe 3+ , as Fe 2 O 3 nanoparticles, and only 17% of the original Fe 6+ . BaFeO 4 sealed, or exposed to dry air disintegrates slowly, exhibiting a spectrum composed of three subspectra. In addition to the original Fe 6+ and final Fe 3+ subspectra, a subspectrum, of an intermediate stage of a crystalline Fe 4+ system, is present. In the first month the increase of the Fe 3+ subspectrum is 15%, and that of the Fe 4+ is 8%. BaFeO 4 exposed to moist air, disintegrates at a very fast rate. The Fe 3+ subspectrum, due to Fe 2 O 3 nanoparticles, increases in the first days at the rapid rate of ∼13%/day, and there is no evidence for Fe 4+ in the spectrum. The Fe 6+ in BaFeO 4 , Fe 3+ and Fe 4+ in the disintegrated systems are all magnetically ordered at 4.2 K. Above 90 K the Fe 3+ subspectra exhibit a superposition of a paramagnetic doublet and a diffuse magnetic sextet, with relative intensities changing with temperature, and changing from sample to sample according to their blocking temperatures, which are determined by the distribution in size of the nanoparticles.

A comparison of the molecular structures of mono-, di- and tetraborylated ferrocenes [Fc{B(R(1))(R(2))}] (R(1)/R(2)=Br/Br, Br/Fc, Br/Me, Me/Me, Me/OH, OMe/OMe), 1,1'-[fc{B(R(1))(R(2))}(2)] (R(1)/R(2)=Br/Br, Br/Me, OMe/OMe), and 1,1',3,3'-[Fe{C(5)H(3)(BMe(2))(2)}(2)] revealed the boryl substituent(s) to be bent out of the Cp ring plane towards the iron center. The corresponding dip angle alpha* decreases with decreasing Lewis acidity of the boron atom and with increasing degree of borylation at the ferrocene core. This trend is well reproduced by DFT calculations (including [FcBH(2)], not yet accessible experimentally). A Bader analysis of the electron density topology of [FcBH(2)] (alpha*=26.5 degrees ; BP86/TZVP) clearly showed that there is no direct iron-boron bonding in this compound. Instead, strongly delocalized orbital interactions have been identified that involve the boron p orbital, C(ipso) of the adjacent Cp ring, d orbitals at iron, and a through-space interaction with the second Cp ring. A second important factor is attractive electrostatic interactions, which are enhanced upon ligand bending. Cyclic voltammetric measurements on the series [FcBMe(2)], 1,1'-[fc(BMe(2))(2)], and 1,1',3,3'-[Fe{C(5)H(3)(BMe(2))(2)}(2)] indicate a substantial anodic shift in the oxidation potential of the central iron atom upon introduction of BMe(2) substituents. Addition of 4-dimethylaminopyridine (DMAP) does not just counterbalance this effect, but leads to a cathodic shift of the Fe(II)/Fe(III) redox transition far beyond the half-wave potential of parent ferrocene. In the Mossbauer spectra, a continuous decrease in the quadrupole splitting (QS) is observed upon going from parent ferrocene to [FcBMe(2)], to 1,1'-[fc(BMe(2))(2)], and to 1,1',3,3'-[Fe{C(5)H(3)(BMe(2))(2)}(2)]. In contrast, no significant differences are found between the QS values of ferrocene, [Fc(BMe(2)-DMAP)], and 1,1'-[fc(BMe(2)-DMAP)(2)].

Two types of intermetallic lithium alloys, Li 21 Si 5 and Li 17 Sn 4 (previously Li 22 Si 5 and Li 22 Sn 5 ), were prepared for the first time using microwave-assisted solid-state reaction. The optimum oven power for their preparation is 80–60%, and the irradiation times are 5 min for Li 21 Si 5 or 10 min for Li 17 Sn 4 . A cheap alumina crucible was found to be the most suitable container in quick (less than 10 min) microwave reactions for Li-containing alloys. The synthesized compounds were characterized by PXRD. Mossbauer spectroscopy was used to characterize Li 17 Sn 4 under different conditions. The hyperfine interaction parameters of 119 Sn in Li 17 Sn 4 show a typical Li–Sn alloy Sn isomer shift (1.88 mm/s). The oxidization processes of the two intermetallic lithium alloys in air were investigated. The microwave method was found to be simple, fast and efficient, with high selectivity for the preparation of these compounds.

A number of structurally related sandwich compounds of iron, in which the central metal atom is ligated to rings containing one or five phosphorus atoms, have been investigated by temperature-dependent 57Fe Mossbauer spectroscopy, differential scanning calorimetry and single-crystal X-ray diffraction. The quadrupole hyperfine interaction at 90 K evidences a linear dependence on the number of ring phosphorus atoms, decreasing by about 0.35 mm·s−1 for each ring carbon atom replaced by P. This effect is directly related to the change in the overlap between metal atom d-orbitals and ligand 3s,3p or 2s,2p orbitals due to an increase in the respective bond lengths. Several one-electron oxidation products of these compounds, which are paramagnetic, have also been examined and show spin−lattice relaxation rates which are fast compared to the characteristic Mossbauer timescale of 98 ns at all temperatures above 90 K. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

(Octamethylferrocenylmethylene)malononitrile (dicyanoethenyl-octamethylferrocene) was synthesized by condensation of octamethylferrocene carbaldehyde with malononitrile. The visible positive solvatochromism of the new compound was studied in 33 solvents and discussed in terms of Kamlet-Taft's π* and a scales. Temperature-dependent Moessbauer spectroscopy using a 5 7 Fe-enriched sample suggests that the onset of ring rotation of the tetramethyl Cp ring was not accompanied by a significant librational motion of the ring. The quadrupole splitting parameter went through a maximum at ∼220 K suggesting a phase change in the solid. Differential scanning calorimetry showed two endotherms at 228 and 236 K. Single crystal X-ray structure determinations at different temperatures showed two kinds of disorder at 243 K, only one of which remained at 183 K. A reversible change of disorder was observed at 213 K.

High-pressure 57Fe Mossbauer measurements of octamethyl-ethynyl-ferrocene (OMFA) were performed using a diamond anvil cell (DAC) in order to clarify the pressure effects on the phase transition occurring at ~248 K. A sharp resonance can be seen at 300 K and 12.6 GPa, suggesting a pressure-induced recovery to a rather large Lamb-Mossbauer factor. The resonance effect gradually decreases with a decrease of the external pressure.

Temperature-dependent 57 Fe Mossbauer spectroscopy over the range 90≤ T ≤360 K has been used to elucidate the hyperfine interactions and dynamical behavior of the iron atom in two ferrocenyl substituted six-membered ring compounds. The root-mean-square amplitude of vibration (rmsav) of the iron atom in ferrocenyl boroxine I extracted from the Mossbauer measurements is in good agreement with the average U ij values observed in X-ray diffraction experiments, but is in less good agreement with the X-ray data reported for ferrocenyl borazine II . Moreover, the Mossbauer data lead to the conclusion that with respect to the iron atom motion, the boroxine compound I is a softer lattice than II . Significant motional anisotropy of the iron atom at 294 K is observed in I in agreement with the room temperature X-ray data reported earlier.

Temperature dependent 5 7 Fe Mossbauer effect studies on nonamethyl ferrocene (NMF), have been carried out on isotopically enriched material over the temperature range 90 < T < 290 K. These measurements have led to the elucidation of the dynamical behaviour of the iron atom and reflect the onset of ring rotation and libration. These results are compared to corresponding data for ferrocene and related compounds. A convenient small scale synthesis suited for the preparation of 5 7 Fe-enriched nonamethylferrocene which allows its easy separation in pure form, is also presented. With the exception of nonamethylferrocene, which is unresolvable due to its lattice-neighbour related conformational ring disorders, X-ray structure determinations of all new compounds of the reaction sequence, and of the starting compound hydroxymethyloctamethylferrocene (octamethylferrocenyl methanol) have been performed.

Temperature-dependent 57 Fe Mossbauer effect spectroscopy has been used over the interval 4.2≤ T ≤300 K to determine the hyperfine interactions in [{(η 5 -C 5 (CH 3 ) 5 )Fe} 2 (μ-H) 4 ], and to elucidate the dynamical behavior of the two metal atoms in this solid. The isomer shift (IS) (at 90 K) is 0.27 mm s −1 smaller than that of ferrocene [(η 5 -C 5 H 5 )Fe] at the same temperature, diagnostic of a larger s-electron density at the Fe nucleus in the former, compared to the latter. The quadrupole splitting is nearly temperature independent over the above range. The iron atom motion is strongly anisotropic, even at low temperatures, and the temperature-dependent recoil-free fraction data and the corresponding intensity asymmetry data extracted from the Mossbauer spectra permit an evaluation of the difference in the mean-square-amplitude of vibration parallel and perpendicular to the molecular symmetry axis passing through the two Fe atoms and the two Cp rings.

Two structurally related diferrocenyl [10]annulenes have been examined over the range 90≤ T ≤370 K by temperature dependent 57 Fe Mossbauer effect (ME) spectroscopy. While the hyperfine interaction parameters [isomer shift (IS) and quadrupole splitting (QS)], and their temperature dependencies are very similar to those which have been reported earlier for similar ferrocenyl complexes, the vibrational anisotropy of the iron atom motion is diagnostic of a cofacial interaction of the two cyclopentadienyl rings in the 2,10-diferrocenyl compound, and absent in the 2,7-diferrocenyl homologue. These results are compared with the corresponding behavior of the 1,5- and 1,8-diferrocenylnaphthalene compounds reported earlier.

Octamethylferrocenecarbaldehyde reacts with excess nitromethane in the presence of potassium tert-butanoxide to give, after silylation and hydrolysis, 2-nitro-3-(octamethylferrocenyl)acrylonitrile in moderate yield. This compound exhibits visible positive solvatochromism. The molar transition energies ET in 26 different solvents are correlated with the dipolarity-polarizability parameter π* and the hydrogen bond donor acidity α. The results from temperature-dependent Mossbauer spectroscopy suggest that the cyclopentadienyl ring rotation and libration (‘gear wheel’ effect) is inhibited up to a temperature within a few degrees below the melting point, presumably due to the steric requirements of the side chain. The crystal structure has been determined.

Mossbauer studies of ferrocene [ η 5 (C 5 H 5 ) 2 Fe] have been carried out over the temperature range 90 to 370 K. The spectra display unequal intensity quadrupole doublets, with the asymmetry showing a pronounced temperature dependence. Least squares fits of the experimental spectra, using a transmission integral program yield, besides the conventional hyperfine interaction parameters, the average recoil-free fraction and the intensity ratio of the quadrupole doublet components. These in turn yield the temperature dependence of the mean-square displacement amplitudes parallel and perpendicular to the iron atom local electric field gradient symmetry axis. At room temperature, [〈 x 2 para 〉] 1/2 =0.226±0.008 A while [〈 x 2 perp 〉] 1/2 =0.179±0.010 A. These results are in good agreement with data extracted from X-ray diffraction studies at the same temperature.

Temperature-dependent Mossbauer spectroscopy has been used to study the details of the metal atom motion in a number of "face-to-face" ferrocenyl moiety containing solids. While the hyperfine parameters for the 1,8-bis(ferrocenyl)naphthalene complexes are very similar to those observed for other ferrocenyl-group-containing organometallics, the "face-to-face" complexes show an unusual Gol'danskii-Karyagin asymmetry, which is not observed for the 1,5-bis(ferrocenyl) homologue. High-temperature data show that the difference in the mean-square-amplitude of vibration parallel and perpendicular to the symmetry axis running through the Fe atom is ∼9.3 x 10 - 1 9 cm 2 at 378 K when the ferrocenyl group is bonded directly to the naphthalene backbone and ∼4.6 x 10 - 1 9 cm 2 when there is an intervening carbon-carbon triple bond. One-electron oxidation of the 1,8-bis(ferrocenyl)-naphthalene complex leads to a cation in which there is no electron exchange between the two iron atoms on the Mossbauer time scale. The oxidized metal atoms evidence spin-lattice relaxation phenomena with very fast relaxation rates above T ≥ ∼200 K. The nonoxidized iron atom clearly exhibits anisotropic vibrations at T ≥ ∼270 K.

Temperature dependent 57 Fe Mossbauer effect measurements of octamethylferrocenylmethanol, using 57 Fe enriched samples, have been carried out over the temperature range 90≤ T ≤320 K, and analyzed to elucidate the dynamics of the metal atom motion in this solid ( T mp =484 K). In consonance with earlier observation of related octamethylferrocenes (OMFcs), there is a significant drop in the recoil-free fraction at temperatures well below T mp . However, the almost complete disappearance of the resonance effect observed earlier at T ≪ T mp in OMFcs is absent, presumably due to a ring–ring interaction effected by hydrogen-bond coupling, consistent with room temperature infra-red data for this solid.