F-block Element Research Articles

Crystal structure of [Th3(Cp*)3(O)(OH)3]2Cl2(N3)6: a discrete mol-ecular capsule built from multinuclear organothorium cluster cations.

An unusually large and structurally complex charge-neutral polynuclear cluster, hexa-μ2-azido-di-μ3-chlorido-hexa-μ2-hydroxido-di-μ3-oxido-hexa-kis-(penta-methyl-cyclo-penta-dien-yl)hexa-thorium-diethyl ether-tetra-hydro-furan (1/0.56/1.44), [Th3(C10H15)6Cl3(N3)6(OH)6O2]·0.56C4H10O·1.44C4H8O or [Th3(Cp*)3(O)(OH)3]2Cl2(N3)6·0.56C4H10O·1.44C4H8O (Cp* = [penta-methyl-cyclo-penta-dien-yl])-, has been crystallized as a mixed tetra-hydro-furan/diethyl ether solvate and structurally characterized. The mol-ecule contains a number of unusual features, the most notable being a finite yet exceptionally long cyclic metal-azido chain. These rare features are the consequence of both sterically protecting Cp* ligands and highly bridging oxide and hydroxide ligands in the same system and illustrate the inter-esting new possibilities that can arise from combining organometallic and solvothermal f-block element chemistry.

Coordination and extraction properties of 1,2-bis(diphenylphosphoryl)-benzene toward f-block element nitrates: Structural, spectroscopic and DFT characterization of the complexes

Reaction of 1,2-bis(diphenylpsphoryl)benzene 1,2-[Ph2(O)P]2C6H4 (L) with f-element nitrates resulted in 1:1 and 1:2 complexes. The isolated complexes, namely, [UO2(L)(NO3)2]·MeCN (1), [UO2(L)2(NO3)](NO3)·MeCN (2), [Th(L)2(NO3)3](NO3)·MeCN·H2O (3), [La(L)2(NO3)3]·0.5MeCN·1.5H2O (4), and [Lu(L)2(NO3)2](NO3)·2MeCN (5) have been characterized by elemental analysis and IR spectroscopy. The structures of complexes 1, 2, and 5 have been determined by single-crystal X-ray crystallography. Intraligand π-stacking and interligand CH… π interaction have been observed in the crystalline complexes. The π-stacking and CH… π interaction energy in two uranyl complexes 1 and 2 have been estimated from Bader’s AIM theory calculations performed at the DFT level. Solution structure of all complexes has been investigated by IR and multinuclear (1H, 13C, and 31P) NMR spectroscopy. The formation of 1:3 complexes with lanthanum nitrate (IR, 31P NMR) has been examined. Preliminary extraction study of U(VI), Th(IV), and Ln(III) from 2 M HNO3 into 1,2-dichloroethane have shown that ligand L recovers U(VI), Th(IV), and La(III) in the same extent as its tetraphosphoryl analog 1,2,4,5-[Ph2(O)P]4C6H2 (L') but it recovers Eu(III), and Lu(III) by several times better than L'. Furthermore, an improved modified method for the synthesis of ligand L has been suggested.

Porphyrinoid f-Element Complexes.

Porphyrin and related pyrrole-containing macrocycles, collectively porphyrinoids, are versatile ligands that allow access to a multitude of coordination modes. Judicious modification of the porphyrin core as well as the pendant substituents has extended the coordination chemistry of porphyrinoids to include systems that are able to stabilize f-block element complexes with possible utility. This review focuses on our group's efforts to prepare expanded porphyrin and porphyrinogen ligands that can serve as tools to study and apply f-element metal coordination chemistry: it covers the background of the topic, selected syntheses, and application of these species in the chemical and medical sciences.

The bio-relevant metals of the periodic table of the elements

AbstractThe bio-relevant metals (and derived compounds) of thePeriodic Table of the Elements(PTE) are in the focus. The bulk elements sodium (Na), potassium (K), magnesium (Mg), and calcium (Ca) from thes-block, which are essential for all kingdoms of life, and some of their bio-activities are discussed. The trace elements of thed-block of thePTEas far as they are essential for humans (Mn, Fe, Co, Cu, Zn, Mo) are emphasized, but V, Ni, Cd, and W, which are essential only for some forms of life, are also considered. Chromium is no longer classified as being essential. From thep-block metals only the metalloid (half-metal) selenium (Se) is essential for all forms of life. Two other metalloids, silicon and arsenic, are briefly mentioned, but they have not been proven as being essential for humans. All metals of thePTEand a plethora of their compounds are used in industry and many of them are highly toxic, like lead (Pb), which is discussed as a prime example. Several metals of thePTE, that is, their ions and complexes, are employed in medicine and we discuss the role of lithium, gallium, strontium, technetium, silver, gadolinium (the onlyf-block element), platinum, and gold.

Controlling the Intermediate Structure of an Ionic Liquid for f-Block Element Separations.

Recent research has revealed molecular structure beyond the inner coordination sphere is essential in defining the performance of separation processes; nevertheless, such structure remains largely unexplored. Here we apply small-angle neutron scattering (SANS) and X-ray absorption fine structure (XAFS) spectroscopy to investigate the structure of an ionic liquid system studied for f-block element separations. SANS data reveal dramatic changes in the ionic liquid microstructure (∼150 Å) which we demonstrate can be controlled by judicious selection of counterion. Mesoscale structural features (>500 Å) are also observed as a function of metal concentration. XAFS analysis supports formation of extended aggregate structures, similar to those observed in traditional solvent extraction processes, and suggests additional parallels may be drawn from further study. Achieving precise tunability over the intermediate features is an important development in controlling mesoscale structure and realizing advanced new forms of soft matter.

Efficient Lanthanide Catalyzed Debromination and Oligomeric Length-Controlled Ullmann Coupling of Aryl Halides

Lanthanide elements play a vital role in a broad range of high-tech applications, and there is an increasing interest in their catalytic activity, particularly in organometallics. However, their catalytic role on surfaces remains unexplored. Here, we present a scanning tunneling microscopy and density functional theory study of the debromination, contacting, and coupling of dibromine terphenyl species with Dy (f-block element) and Ag (d-block element) adatoms, respectively. We show that Dy debrominates the targeted species more efficiently than Ag adatoms at room temperature, promoting the formation of unprecedented C–Dy–C organometallic supramolecules versus C–Ag–C parallel chains for the Ag case. DFT calculations corroborate our results showing an almost spontaneous debromination process with Dy compared to Ag. Upon annealing, for samples containing Dy, the formation of C–Ag–C organometallic bonds and concomitant C–C coupling is inhibited, giving rise to a self-assembly of debrominated monomers, showing...

Electronic Structure of Corrole Derivatives: Insights from Molecular Structures, Spectroscopy, Electrochemistry, and Quantum Chemical Calculations.

Presented herein is a comprehensive account of the electronic structure of corrole derivatives. Our knowledge in this area derives from a broad range of methods, including UV-vis-NIR absorption and MCD spectroscopies, single-crystal X-ray structure determination, vibrational spectroscopy, NMR and EPR spectroscopies, electrochemistry, X-ray absorption spectroscopy, and quantum chemical calculations, the latter including both density functional theory and ab initio multiconfigurational methods. The review is organized according to the Periodic Table, describing free-base and main-group element corrole derivatives, then transition-metal corroles, and finally f-block element corroles. Like porphyrins, corrole derivatives with a redox-inactive coordinated atom follow the Gouterman four-orbital model. A key difference from porphyrins is the much wider prevalence of noninnocent electronic structures as well as full-fledged corrole•2- radicals among corrole derivatives. The most common orbital pathways mediating ligand noninnocence in transition-metal corroles are the metal(dz2)-corrole("a2u") interaction (most commonly observed in Mn and Fe corroles) and the metal(dx2-y2)-corrole(a2u) interaction in coinage metal corroles. Less commonly encountered is the metal(dπ)-corrole("a1u") interaction, a unique feature of formal d5 metallocorroles. Corrole derivatives exhibit a rich array of optical properties, including substituent-sensitive Soret maxima indicative of ligand noninnocence, strong fluorescence in the case of lighter main-group element complexes, and room-temperature near-IR phosphorescence in the case of several 5d metal complexes. The review concludes with an attempt at identifying gaps in our current knowledge and potential future directions of electronic-structural research on corrole derivatives.

Actinide covalency measured by pulsed electron paramagnetic resonance spectroscopy.

Our knowledge of actinide chemical bonds lags far behind our understanding of the bonding regimes of any other series of elements. This is a major issue given the technological as well as fundamental importance of f-block elements. Some key chemical differences between actinides and lanthanides-and between different actinides-can be ascribed to minor differences in covalency, that is, the degree to which electrons are shared between the f-block element and coordinated ligands. Yet there are almost no direct measures of such covalency for actinides. Here we report the first pulsed electron paramagnetic resonance spectra of actinide compounds. We apply the hyperfine sublevel correlation technique to quantify the electron-spin density at ligand nuclei (via the weak hyperfine interactions) in molecular thorium(III) and uranium(III) species and therefore the extent of covalency. Such information will be important in developing our understanding of the chemical bonding, and therefore the reactivity, of actinides.

Open-shell lanthanide(II+) or -(III+) complexes bearing σ-silyl and silylene ligands: synthesis, structure, and bonding analysis.

Complexes featuring lanthanide (Ln)–Si bonds represent a highly neglected research area. Herein, we report a series of open-shell LnII+ and LnIII+ complexes bearing σ-bonded silyl and base-stabilized N-heterocyclic silylene (NHSi) ligands. The reactions of the LnIII+ complexes Cp3Ln (Ln = Tm, Ho, Tb, Gd; Cp = cyclopentadienide) with the 18-crown-6 (18-cr-6)-stabilized 1,4-oligosilanyl dianion [(18-cr-6)KSi(SiMe3)2SiMe2SiMe2Si(SiMe3)2K(18-cr-6)] (1) selectively afford the corresponding metallacyclopentasilane salts [Cp2Ln({Si(SiMe3)2SiMe2}2)]−[K2(18-cr-6)2Cp]+ [Ln = Tm (2a), Ho (2b), Tb (2c), Gd (2d)]. Complexes 2a–2d represent the first examples of structurally characterized Tm, Ho, Tb, and Gd complexes featuring Ln–Si bonds. Strikingly, the analogous reaction of 1 with the lighter element analogue Cp3Ce affords the acyclic product [Cp3CeSi(SiMe3)2SiMe2SiMe2Si(SiMe3)2-Cp3Ce]2–2[K(18-cr-6)]+ (3) as the first example of a complex featuring a Ce–Si bond. In an alternative synthetic approach, the aryloxy-functionalized benzamidinato NHSi ligand Si(OC6H4-2-tBu){(NtBu)2CPh} (4a) and the alkoxy analogue Si(OtBu){(NtBu)2CPh} (4b) were reacted with Cp*2Sm(OEt2), affording, by OEt2 elimination, the corresponding silylene complexes, both featuring SmII+ centers: Cp*2Sm ← :Si(O–C6H4-2-tBu){(NtBu)2CPh} (6) and Cp*2Sm ← :Si(OtBu){(NtBu)2CPh} (5). Complexes 5 and 6 are the first four-coordinate silylene complexes of any f-block element to date. All complexes were fully characterized by spectroscopic means and by single-crystal X-ray diffraction analysis. In the series 2a–2d, a linear correlation was observed between the Ln–Si bond lengths and the covalent radii of the corresponding Ln metals. Moreover, in complexes 5 and 6, notably long Sm–Si bonds are observed, in accordance with a donor–acceptor interaction between Si and Sm [5, 3.4396(15) Å; 6, 3.3142(18) Å]. Density functional theory calculations were carried out for complexes 2a–2d, 5, and 6 to elucidate the bonding situation between the LnII+ or LnIII+ centers and Si. In particular, a decrease in the Mayer bond order (MBO) of the Ln–Si bond is observed in the series 2a–2d in moving from the lighter to the heavier lanthanides (Tm = 0.53, Ho = 0.62, Tb = 0.65, and Gd = 0.75), which might indicate decreasing covalency in the Ln–Si bond. In accordance with the long bond lengths observed experimentally in complexes 5 and 6, comparatively low MBOs were determined for both silylene complexes (5, 0.24; 6, 0.25) .

Synergistic Effect between Bifunctional Ionic Liquids and a Molecular Extractant for Lanthanide Separation

A novel form of synergistic extraction using both ionic liquid extractants and a molecular extractant is reported. The molecular extractant (TRPO, a mixture of four trialkylphosphine oxides) and anion precursors of the ionic liquid extractants (HDEHP and HEH[EHP]) are the most commonly used industrial extractants for f-block element separation. Development of acid–base coupling bifunctional ionic liquids (ABC-BILs) for rare earth elements (REEs) separation offers a promising strategy to reduce the millions of tons of industrial saponification wastewater that are produced annually. The synergistic effects of the ABC-BILs with TRPO contributed to increased extractabilities and selectivities of middle and heavy lanthanides, revealing theoretical importance and engineering potential in REEs separation.

Solid-state dynamics of uranyl polyoxometalates.

Understanding fundamental uranyl polyoxometalate (POM) chemistry in solution and the solid state is the first step to defining its future role in the development of new actinide materials and separation processes that are vital to every step of the nuclear fuel cycle. Many solid-state geometries of uranyl POMs have been described, but we are only beginning to understand their chemical behavior, which thus far includes the role of templates in their self-assembly, and the dynamics of encapsulated species in solution. This study provides unprecedented detail into the exchange dynamics of the encapsulated species in the solid state through Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) spectroscopy. Although it was previously recognized that capsule-like molybdate and uranyl POMs exchange encapsulated species when dissolved in water, analogous exchange in the solid state has not been documented, or even considered. Here, we observe the extremely high rate of transport of Li(+) and aqua species across the uranyl shell in the solid state, a process that is affected by both temperature and pore blocking by larger species. These results highlight the untapped potential of emergent f-block element materials and vesicle-like POMs.

Rare-Earth Research Meeting

The 27th Rare Earth Research Conference will take place at the Village at Squaw Valley in Olympic Valley, Calif.—the site of the 1960 Winter Olympic Games—on June 22–26, 2014. Rare-earth element research spans several disciplines and brings together chemists, engineers, physicists, and materials scientists. The Rare Earth Research Conference is the venue of choice in the North American continent for scientists from all over the world to present their work and discuss the latest in f-block element research. Symposia will include “Critical Materials, Catalysis, Industrial & Technological Applications,” “Solid-State Chemistry & Physics, Magnetism & Spectroscopy,” “Organometallics, Coordination Chemistry & Polymers,” “Bioanalysis & Medical Applications,” “Actinide Chemistry & Physics,” and “Theory of 4f Elements.” The conference will feature five plenary lectures, along with several oral and poster sessions. The Frank H. Spedding Award, which is conferred for outstanding contributions to rare-earth science an...

Li(i=1–3) sub-shell x-ray relative intensities for some compounds of 66Dy at 22.6 and 59.54 keV incident photon energies

The intensity ratios, ILk/ILα (k=l,β1,4,β3,6,β2,7,9,10,15,γ1,5,γ2,3,γ4,β,γ), have been measured for some compounds of 66Dy, namely, Dy2O3, Dy2(CO3)3, Dy2(SO4)3, DyI2 and Dy metal by creating the Li(i=1–3) sub-shell vacancies in widely different proportions at two incident photon energies of 22.6keV and 59.54keV, in order to check the predicted dependence of these ratios on the incident photon energy and also investigate the influence of chemical effects on these ratios for an f-block element. The measurements were performed using the EDXRF spectrometer involving disk type radioactive sources of Cd109 and Am241 and a Peltier cooled Si PIN x-ray detector arranged in the 90° reflection geometry. The measured intensity ratios have been compared with the theoretical ILk/ILα values and those calculated using the two sets of fluorescence and Coster–Kronig yields available in literature in order to check the reliability of the theoretical/calculated values. Further, the measured ratio, ILγ4/ILα, was found to depend on the oxidation state of 66Dy as well as nature of ligand attached to it in a given compound.

The concentration effects of s-, p-, d- and f-block element doping on the growth, crystalline perfection and properties of KDP crystals

The effect of dopants (over a wide concentration range from 0.5 to 10 mol%), namely s-, p-, d- and f-block elements (Mg, Sb, Pd and La) on the growth process, crystalline perfection, external morphology, vibrational patterns, XRD profile and second order nonlinear optical (NLO) properties of potassium dihydrogen phosphate (KH2PO4, KDP) crystals grown by the slow evaporation solution growth technique has been systematically investigated. Incorporation of the dopants into the crystalline matrix even at low concentrations was well confirmed by the inductively coupled plasma (ICP) technique. The change in intensity patterns in XRD profiles of doping specimens reveals lattice distortion, further supported by slight shifts in characteristic vibrational frequencies in FT-IR. The scanning electron microscope (SEM) micrographs exhibit the effectiveness of the impurity in varying the surface morphology. The high-resolution X-ray diffraction (HRXRD) studies used to evaluate the crystalline perfection reveal many interesting features on the ability of accommodating the dopants by the crystalline matrix. It appears that the crystalline perfection depends mostly on the concentration of the dopant. Multi-peaks appear for highly doped specimens indicating the inhomogeneous accommodation. The second harmonic generation (SHG) efficiency is enhanced considerably when the concentration of the dopant is low while depressed activity is observed with poor crystalline perfection at high concentrations irrespective of the nature of the dopants.

THORIUM ATTRACTS A CROWD

A MULTIDISCIPLINARY research team has reported the first example of a stable, crystallographically characterized 15-coordinate metal complex, an achievement that extends the boundaries of chemical bonding. The thorium aminodiboranate created by Gregory S. Girolami of the University of Illinois, Urbana-Champaign, and colleagues bests the prior record of 14 two-electron metal-ligand bonds in complexes such as U(BH 4 ) 4 . But for one errant hydrogen atom, the molecule’s metal could have had 16 bonds, the theoretical maximum based on the number of atomic orbitals thorium has available for bonding; some metallocenes can have more metal-ligand contacts but at most 12 two-electron metal-ligand bonds. The trick to reaching high coordination numbers is combining a large metal cation with small chelating ligands. Girolami and graduate student Scott R. Daly accomplished that by pairing thorium, an f-block element with a large covalent radius, and hydrogen, the smallest of ligands. They made the 15- coordinate Th[H ...

Interaction of trivalent f-element cations with iodide in methanol + water solvents

The stability constants (β1) of iodide ion-pairs of trivalent f-block element ions (lanthanoids Ce, Eu, Gd, Tb and Tm, and actinoid Am) were determined in the vicinity of pH 2.5 of mixed methanol/water solvent solutions of an ionic strength of 1.00 mol·dm−3 at 298±1 K. The values were less than 2. From the variation in distance between Eu3+ and I−, which was calculated using a Born-type equation for Gibbs’ free energy derived from β1(Eu), the Eu3+-I− interaction was shown to be solvent-shared ion-pair formation when the mole fraction of methanol (XMeOH)≤0.40. In contrast, it was suggested that the interaction of Am3+-I− changed from solvent-separated ion-pair to solvent-shared ion-pair with increasing XMeOH when XMeOH≤0.10, but remained as solvent-shared ion-pair in the range 0.16≤XMeOH≤0.40. Furthermore, β2(Am) was measured in the range 0.31≤XMeOH≤0.40. It was also shown that the β1 values of lanthanoids at XMeOH = 0.40, except for that of Gd(III), decreased with increasing atomic number.

Reductive disproportionation of carbon dioxide by a Sm(ii) complex: Unprecedented f-block element reactivity giving a carbonate complex

A macrocyclic organosamarium(II) complex has been shown to provide the first example of the reductive disproportionation of carbon dioxide, giving a bimetallic carbonate complex and carbon monoxide in a facile reaction under ambient conditions.

Solid-state structure and solution behavior of eight-coordinate Sm(III) poly(pyrazolyl)borate compounds.

[Sm(Tp(Me2)(2)(kappa(2)-S(2)CNR(2))] compounds (R = Et (1), Me (2); Tp(Me2) = HB(3,5-Me2pz)(3)) have been isolated from reaction of (R(2)NC(S)S)(2) with 2 equiv of [Sm(Tp(Me2)(2)]. Reductive cleavage of 2,2'-dipyridyl disulfide or 2,2'-dipyridyl diselenide by [Sm(Tp(Me2)(2)] afforded good yields of [Sm(Tp(Me2)(2)(kappa(2)-Y)] compounds (Y = 2-SC(5)H(4)N (3), 2-SeC(5)H(4)N (4)). 4 is the first selenopyridine complex of an f-block element. Sm(Tp(Me2)(2)(2-OC(5)H(4)N) (5) has been synthesized by salt metathesis of [Sm(Tp(Me2)(2)Cl] with the sodium salt of the 2-hydroxypyridine. The solid-state structures of 1, 3, 4, and 5 were determined by single-crystal X-ray diffraction analysis and revealed that the compounds are all eight-coordinate with dodecahedral geometry. The samarium atoms are bound in tridentate fashion to two pyrazolylborate ligands and in bidentate fashion by the third ligand. The solution behavior of the compounds was studied by (1)H NMR techniques. (1)H-(1)H exchange spectroscopy experiments give evidence for two distinct dynamic regimes occurring in solution.

ChemInform Abstract: The First High Resolution Direct NMR Observation of an f‐Block Element.

ChemInformVolume 20, Issue 32 Physical Organic Chemistry ChemInform Abstract: The First High Resolution Direct NMR Observation of an f-Block Element. A. G. AVENT, A. G. AVENT Sch. Chem. Mol. Sci., Univ. Sussex, Brighton BN1 9QJ, UKSearch for more papers by this authorM. A. EDELMAN, M. A. EDELMAN Sch. Chem. Mol. Sci., Univ. Sussex, Brighton BN1 9QJ, UKSearch for more papers by this authorM. F. LAPPERT, M. F. LAPPERT Sch. Chem. Mol. Sci., Univ. Sussex, Brighton BN1 9QJ, UKSearch for more papers by this authorG. A. LAWLESS, G. A. LAWLESS Sch. Chem. Mol. Sci., Univ. Sussex, Brighton BN1 9QJ, UKSearch for more papers by this author A. G. AVENT, A. G. AVENT Sch. Chem. Mol. Sci., Univ. Sussex, Brighton BN1 9QJ, UKSearch for more papers by this authorM. A. EDELMAN, M. A. EDELMAN Sch. Chem. Mol. Sci., Univ. Sussex, Brighton BN1 9QJ, UKSearch for more papers by this authorM. F. LAPPERT, M. F. LAPPERT Sch. Chem. Mol. Sci., Univ. Sussex, Brighton BN1 9QJ, UKSearch for more papers by this authorG. A. LAWLESS, G. A. LAWLESS Sch. Chem. Mol. Sci., Univ. Sussex, Brighton BN1 9QJ, UKSearch for more papers by this author First published: August 8, 1989 https://doi.org/10.1002/chin.198932040Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume20, Issue32August 8, 1989 RelatedInformation

The first high resolution direct NMR observation of an f-block element

The last decade has seen a dramatic increase in the importance of the organometallic chemistry of the lanthanide elements. In particular, iodides, cyclopentadienyls, and bis(trimethylsilyl)amides of Sm(II), Eu(II), or Yb(II), due to their unique reactivity (e.g., as selective reducing agents), have attracted much attention. Yet high resolution, solution-state NMR, one of the organometallic chemists most informative tools, has not previously been applied to the direct observation of an f-block element, excluding complexes of the f{sup 0} La(III). The reason for this neglect is probably because the majority of complexes (except those of La(III), Yb(II), and Lu(III)) are paramagnetic, and many of the NMR-active f-block nuclei have large quadrupole moments. Yet for certain of these elements spin-{1/2} isotopes exist, and the range of diamagnetic compounds is rapidly increasing. As a case in point, {sup 171}Yb is a spin-{1/2}nucleus, with a natural abundance of 14.27% and a moderately sized, positive gyromagnetic ratio (4.4712 {times} 10{sup 7} rad T{sup {minus}1} s{sup {minus}1}); these features combine to give a receptivity four times greater than that of {sup 13}C. Three solid-state, wide-line studies of this nucleus have appeared. The authors now report {sup 171}Yb chemical shift solution NMR data for the series of Yb(II) complexes.