Lanthanide(II) Complexes Supported by N,O‐Donor Tripodal Ligands: Synthesis,Structure, and Ligand‐Dependent Redox Behavior

The preparation and characterization of a series of complexes of the Yb and Eu cations in the oxidation state II and III with the tetradentate N,O‐donor tripodal ligands (tris(2‐pyridylmethyl)amine (TPA), BPA^? (HBPA=bis(2‐pyridylmethyl)(2‐hydroxybenzyl)amine), BPPA^? (HBPPA=bis(2‐pyridylmethyl)(3.5‐di‐tert‐butyl‐2‐hydroxybenzyl)amine), and MPA^2? (H₂MPA=(2‐pyridylmethyl)bis(3.5‐di‐tert‐butyl‐2‐hydroxybenzyl)amine) is reported. The X‐ray crystal structures of the heteroleptic Ln²⁺ complexes [Ln(TPA)I₂] (Ln=Eu, Yb) and [Yb(BPA)I(CH₃CN)]₂, of the Ln²⁺ homoleptic [Ln(TPA)₂]I₂ (Ln=Sm, Eu, Yb) and [Eu(BPA)₂] complexes, and of the Ln³⁺ [Eu(BPPA)₂]OTf and [Yb(MPA)₂K(dme)₂] (dme=dimethoxyethane) complexes have been determined. Cyclic voltammetry studies carried out on the bis‐ligand complexes of Eu³⁺ and Yb³⁺ show that the metal center reduction occurs at significantly lower potentials for the BPA^? ligand as compared with the TPA ligand. This suggests that the more electron‐rich character of the BPA^? ligand results in a higher reducing character of the lanthanide complexes of BPA^? compared with those of TPA. The important differences in the stability and reactivity of the investigated complexes are probably due to the observed difference in redox potential. Preliminary reactivity studies show that whereas the bis‐TPA complexes of Eu²⁺ and Yb²⁺ do not show any reactivity with heteroallenes, the [Eu(BPA)₂] complex reduces CS₂ to afford the first example of a lanthanide trithiocarbonate complex.     

Nucleophilic Reactivity of a Nitride‐Bridged Diuranium(IV) Complex: CO2 and CS2 Functionalization

Thermolysis of the nitride‐bridged diuranium(IV) complex Cs{(μ‐N)[U(OSi(O^tBu)₃)₃]₂} ( 1 ) showed that the bridging nitride behaves as a strong nucleophile, promoting N?C bond formation by siloxide ligand fragmentation to yield an imido‐bridged siloxide/silanediolate diuranium(IV) complex, Cs{(μ‐N^tBu)(μ‐O₂Si(O^tBu)₂)U₂(OSi(O^tBu)₃)₅}. Complex 1 displayed reactivity towards CS₂ and CO₂ at room temperature that is unprecedented in f‐element chemistry, affording diverse N‐functionalized products depending on the reaction stoichiometry. The reaction of 1 with two equivalents of CS₂ yielded the thiocyanate/thiocarbonate complex Cs{(μ‐NCS)(μ‐CS₃)[U(OSi(O^tBu)₃)₃]₂} via a putative NCS^?/S^2? intermediate. The reaction of 1 with one equivalent of CO₂ resulted in deoxygenation and N?C bond formation, yielding the cyanate/oxo complex Cs{(μ‐NCO)(μ‐O)[U(OSi(O^tBu)₃)₃]₂}. Addition of excess CO₂ to 1 led to the unprecedented dicarbamate product Cs{(μ‐NC₂O₄)[U(OSi(O^tBu)₃)₃]₂}.     

Reduction of a Cerium(III) Siloxide Complex To Afford a Quadruple‐Decker Arene‐Bridged Cerium(II) Sandwich

Organometallic multi‐decker sandwich complexes containing f‐elements remain rare, despite their attractive magnetic and electronic properties. The reduction of the Ce^III siloxide complex, [KCeL₄] ( 1 ; L=OSi(OtBu)₃), with excess potassium in a THF/toluene mixture afforded a quadruple‐decker arene‐bridged complex, [K(2.2.2‐crypt)]₂[{(KL₃Ce)(μ‐η⁶:η⁶‐C₇H₈)}₂Ce] ( 3 ). The structure of 3 features a [Ce(C₇H₈)₂] sandwich capped by [KL₃Ce] moieties with a linear arrangement of the Ce ions. Structural parameters, UV/Vis/NIR data, and DFT studies indicate the presence of Ce^II ions involved in δ bonding between the Ce cations and toluene dianions. Complex 3 is a rare lanthanide multi‐decker complex and the first containing non‐classical divalent lanthanide ions. Moreover, oxidation of 1 by AgOTf (OTf=O₃SCF₃) yielded the Ce^IV complex, [CeL₄] ( 2 ), showing that siloxide ligands can stabilize Ce in three oxidation states.     

Abbau von Koordinationspolymeren bis zum Monomer und Konkurrenz von Polymerisation und Chemischer Schere an Carbazolaten von Yb und Eu mit N‐Phenylpiperazin

Degradation of Coordination Polymers to the Monomer and Competition of Polymerization and Chemical Scissors on Carbazolates of Yb and Eu with N‐Phenylpiperazine The coordination polymers , Ln = Yb, Eu, Cbz⁻ = carbazolate anion, C₁₂H₈N⁻, can be degraded by the use of strong N‐donor ligands like N‐phenylpiperazine (Phpip = (C₆H₅)C₄H₈NNH) as chemical scissors. The degradation process for the ytterbium containing polymer ends in the monomeric compound [Yb(Cbz)₃(Phpip)₂]·1/2Phpip and includes an oxidation step Yb^II → Yb^III. Thus the circle of reactions of Yb metal with carbazole (CbzH) starting in liquid NH₃ to the coordination polymer and ending with its degradation by the use of chemical scissors is resolved. Transformation on europium has been started on the base of both metals leading to coordination polymers of the same chemical formula. However already the prelude of reactions differs for Eu as the electride induced reaction of Eu metal with CbzH in liquid ammonia followed by Phpip treatment gives single crystalline [Eu₂(Cbz)₄(NH₃)₂(Phpip)₄]·2Phpip. This dimeric molecule contains Eu^II and ligands of all reaction steps, NH₃, Cbz⁻, Phpip, and is thereby an interesting starting point for the resolution of polymer formation and degradation as well as a competition of these counter reactions.     

Synthesis,Structures, and Luminescent Properties of Chloride and Nitrate LnIII Complexes Coordinated by tris(Pyrazolyl)methane

We report the synthesis of Ln³⁺ nitrate [Ln(Tpm)(NO₃)₃] ⋅ MeCN (Ln=Yb ( 1Yb ), Eu ( 1Eu )) and chloride [Yb(Tpm)Cl₃] ⋅ 2MeCN ( 2Yb ), [Eu(Tpm)Cl₂(μ-Cl)]₂ ( 2Eu ) complexes coordinated by neutral tripodal tris(3,5-dimethylpyrazolyl)methane (Tpm). The crystal structures of 1Ln and 2Ln were established by single crystal X-ray diffraction, while for 1Yb high resolution experiment was performed. Nitrate complexes 1Ln are isomorphous and both adopt mononuclear structure. Chloride 2Yb is monomeric, while Eu³⁺ analogue 2Eu adopts a binuclear structure due to two μ²-bridging chloride ligands. The typical lanthanide luminescence was observed for europium complexes ( 1Eu and 2Eu ) as well as for terbium and dysprosium analogues ([Ln(Tpm)(NO₃)₃] ⋅ MeCN, Ln=Tb ( 1Tb ), Dy ( 1Dy ); [Ln(Tpm)Cl₃] ⋅ 2MeCN, Ln=Tb ( 2Tb ), Dy ( 2Dy )).     

Cation‐Mediated Conversion of the State of Charge in Uranium Arene Inverted‐Sandwich Complexes

Two new arene inverted‐sandwich complexes of uranium supported by siloxide ancillary ligands [K{U(OSi(OtBu)₃)₃}₂(μ‐η⁶:η⁶‐C₇H₈)] ( 3 ) and [K₂{U(OSi(OtBu)₃)₃}₂(μ‐η⁶:η⁶‐C₇H₈)] ( 4 ) were synthesized by the reduction of the parent arene‐bridged complex [{U(OSi(OtBu)₃)₃}₂(μ‐η⁶:η⁶‐C₇H₈)] ( 2 ) with stoichiometric amounts of KC₈ yielding a rare family of inverted‐sandwich complexes in three states of charge. The structural data and computational studies of the electronic structure are in agreement with the presence of high‐valent uranium centers bridged by a reduced tetra‐anionic toluene with the best formulation being U^V–(arene^4?)–U^V, KU^IV–(arene^4?)–U^V, and K₂U^IV–(arene^4?)–U^IV for complexes 2 , 3 , and 4 respectively. The potassium cations in complexes 3 and 4 are coordinated to the siloxide ligands both in the solid state and in solution. The addition of KOTf (OTf=triflate) to the neutral compound 2 promotes its disproportionation to yield complexes 3 and 4 (depending on the stoichiometry) and the U^IV mononuclear complex [U(OSi(OtBu)₃)₃(OTf)(thf)₂] ( 5 ). This unprecedented reactivity demonstrates the key role of potassium for the stability of these complexes.     

Anionic bipyridyl complexes of lanthanides. Structure of [Yb(bipy)3][Li(THF)4]

Reactions of Sm^II, Tb^III, Tm^II, Yb^II, and Lu^III iodides with 2,2′-bipyridyllithium in THF afford [Li(THF)₄][Ln(bipy) _n ] complexes (n=3 or 4) containing trivalent lanthanides. X-ray structural analysis demonstrated that in the crystalline state, the Yb derivative has the ionic structure, [Li(THF)₄]⁺[Yb(bipy)₃]^?. In THF solutions, the reversible ligand exchange between metal atoms occurs to yield neutral compounds [Ln(bipy) _n?1(THF) _x ] and [Li(bipy)(THF) _y ]. A decrease in the temperature shifts the equilibrium to ionic pairs.     

Anion‐Dependence of Ytterbium Complexes and Their NIR Luminescence

The reaction of 2‐aldehyde‐8‐hydroxyquinoline, histamine, and YbX₃ · 6H₂O (X = NO₃^–, ClO₄^–) affords two ytterbium complexes [Yb(nma)₂] · ClO₄ · 2CH₂Cl₂ ( 1 ) and [Yb(nma)(NO₃)₂(DMSO)] · CH₃OH ( 2 ) (Hnma = N‐(2‐(8‐hydroxylquinolinyl)methane(2‐(4‐imidazolyl)ethanamine))). The crystal structures were determined by X‐ray diffraction and it has been revealed that the anions have played important role in the assembly. In the case of 1 , the Yb³⁺ ions are completely encapsulated by two nma ligands with uncoordinated perchlorate anion balancing the positive charge. In the case of 2 , the Yb³⁺ ions are ligated by the ligand, oxygen atoms of the nitrate ion, and DMSO. Both complexes exhibit essential NIR luminescence of Yb³⁺ ions.     

Physical Properties of Superbulky Lanthanide Metallocenes: Synthesis and Extraordinary Luminescence of [EuII(CpBIG)2] (CpBIG=(4‐nBu‐C6H4)5‐Cyclopentadienyl)

The superbulky deca‐aryleuropocene [Eu(Cp^BIG)₂], Cp^BIG=(4‐nBu‐C₆H₄)₅‐cyclopentadienyl, was prepared by reaction of [Eu(dmat)₂(thf)₂], DMAT=2‐Me₂N‐α‐Me₃Si‐benzyl, with two equivalents of Cp^BIGH. Recrystallizyation from cold hexane gave the product with a surprisingly bright and efficient orange emission (45 % quantum yield). The crystal structure is isomorphic to those of [M(Cp^BIG)₂] (M=Sm, Yb, Ca, Ba) and shows the typical distortions that arise from Cp^BIG???Cp^BIG attraction as well as excessively large displacement parameter for the heavy Eu atom (U_eq=0.075). In order to gain information on the true oxidation state of the central metal in superbulky metallocenes [M(Cp^BIG)₂] (M=Sm, Eu, Yb), several physical analyses have been applied. Temperature‐dependent magnetic susceptibility data of [Yb(Cp^BIG)₂] show diamagnetism, indicating stable divalent ytterbium. Temperature‐dependent ¹⁵¹Eu Mössbauer effect spectroscopic examination of [Eu(Cp^BIG)₂] was examined over the temperature range 93–215 K and the hyperfine and dynamical properties of the Eu^II species are discussed in detail. The mean square amplitude of vibration of the Eu atom as a function of temperature was determined and compared to the value extracted from the single‐crystal X‐ray data at 203 K. The large difference in these two values was ascribed to the presence of static disorder and/or the presence of low‐frequency torsional and librational modes in [Eu(Cp^BIG)₂]. X‐ray absorbance near edge spectroscopy (XANES) showed that all three [Ln(Cp^BIG)₂] (Ln=Sm, Eu, Yb) compounds are divalent. The XANES white‐line spectra are at 8.3, 7.3, and 7.8 eV, for Sm, Eu, and Yb, respectively, lower than the Ln₂O₃ standards. No XANES temperature dependence was found from room temperature to 100 K. XANES also showed that the [Ln(Cp^BIG)₂] complexes had less trivalent impurity than a [EuI₂(thf)_x] standard. The complex [Eu(Cp^BIG)₂] shows already at room temperature strong orange photoluminescence (quantum yield: 45 %): excitation at 412 nm (24270 cm^?1) gives a symmetrical single band in the emission spectrum at 606 nm (ν_max=16495 cm^?1, FWHM: 2090 cm^?1, Stokes‐shift: 2140 cm^?1), which is assigned to a 4f⁶5d¹→4f⁷ transition of Eu^II. These remarkable values compare well to those for Eu^II‐doped ionic host lattices and are likely caused by the rigidity of the [Eu(Cp^BIG)₂] complex. Sharp emission signals, typical for Eu^III, are not visible.     

Discrete Divalent Rare‐Earth Cationic ROP Catalysts: Ligand‐Dependent Redox Behavior and Discrepancies with Alkaline‐Earth Analogues in a Ligand‐Assisted Activated Monomer Mechanism

The first solvent‐free cationic complexes of the divalent rare‐earth metals, [{RO}RE^II]⁺[A]^? (RE^II=Yb^II, 1 ; Eu^II, 2 ) and [{LO}RE^II]⁺[A]^? ([A]^?=[H₂N{B(C₆F₅)₃}₂]^?; RE^II=Yb^II, 3 ; Eu^II, 4 ), have been prepared by using highly chelating monoanionic aminoether‐fluoroalkoxide ({RO}^?) and aminoether‐phenolate ({LO}^?) ligands. Complexes 1 and 2 are structurally related to their alkaline‐earth analogues [{RO}AE]⁺[A]^? (AE=Ca, 5 ; Sr, 6 ). Yet, the two families behave very differently during catalysis of the ring‐opening polymerization (ROP) of L ‐lactide (L ‐LA) and trimethylene carbonate (TMC) performed under immortal conditions with excess BnOH as an exogenous chain‐transfer agent. The ligand was found to strongly influence the behavior of the RE^II complexes during ROP catalysis. The fluoroalkoxide RE^II catalysts 1 and 2 are not oxidized under ROP conditions, and compare very favorably with their Ca and Sr congeners 5 and 6 in terms of activity (turnover frequency (TOF) in the range 200–400 mol_L‐LA (mol_Eu h^?1)) and control over the parameters during the immortal ROP of L ‐LA (M_n,theor≈M_n,SEC, M_w/M_n<1.05). The Eu^II‐phenolate 4 provided one of the most effective ROP cationic systems known to date for L ‐LA polymerization, exhibiting high activity (TOF up to 1 880 mol_L‐LA?(mol_Eu h)^?1) and good control (M_w/M_n=1.05). By contrast, upon addition of L ‐LA the Yb^II‐phenolate 3 immediately oxidizes to inactive RE^III species. Yet, the cyclic carbonate TMC was rapidly polymerized by combinations of 3 (or even 1 ) and BnOH, revealing excellent activities (TOF=5000–7000 mol_TMC?(mol_Eu h)^?1) and unusually high control (M_n,theor≈M_n,SEC, M_w/M_n<1.09); under identical conditions, the calcium derivative 5 was entirely inert toward TMC. Based on experimental and kinetic data, a new ligand‐assisted activated monomer ROP mechanism is suggested, in which the so‐called ancillary ligand plays a crucial role in the catalytic cycle. A coherent reaction pathway computed by DFT, compatible with the experimental data, supports the proposed scenario.     

Mono‐, Di‐, Tri‐ and Tetranuclear Rare Earth Complexes Obtained Using a Moderately Bulky Aryloxide Ligand

Redox transmetallation ligand exchange reactions involving a rare earth metal, 2,4,6‐trimethylphenol (HOmes), and a diarylmercurial afford rare earth aryloxo complexes, which are structurally characterized. Both the lanthanoid contraction and the identity of the reaction solvent are found to influence the outcome of the reactions. Using THF in the reaction affords a dinuclear species [Ln₂(Omes)₆(thf)₄]?2THF (Ln=La 1 , Nd 2 ) for the lighter rare earth metals, while a mononuclear species [Ln(Omes)₃(thf)₃] (Ln=Sm 3 , Tb 5 , Er 6 , Yb 7 , Y 8 ) is obtained for the heavier rare earth elements. Surprisingly, there is no change in metal coordination number between the two structural motifs. A divalent trinuclear linear complex [Eu₃(Omes)₆(thf)₆] 4 is obtained for Eu, and features solely bridging aryloxide ligands. Using DME as the reaction solvent affords [La(Omes)₃(dme)₂] 9 from the reaction mixture, and [Ln₂(Omes)₆(dme)₂]?PhMe (La 10 , Nd 11 ) and [Y(Omes)₃(dme)₂] 14 following crystallization of the crude product from toluene. The dinuclear species [Eu₂(Omes)₄(dme)₄] 12 contains two unidentate and two chelating DME ligands, and contrasts the linear structure of 4 . Treatment of HOmes and HgPh₂ with Yb metal in DME affords the mixed valent Yb^II/III complex [Yb₂(Omes)₅(dme)₂] 13 , which is stabilized by an intramolecular π‐Ph–Yb interaction, and is a rare example of a mixed valent rare earth aryloxide. Treatment of Er metal with HOmes at elevated temperature (solvent free) affords the homoleptic [Er₄(Omes)₁₂] 15 , which consists of a tetranuclear array of Er atoms arranged in a ‘herringbone’ fashion; the structure is stabilized by intramolecular π‐Ph–Er interactions. Reaction of La metal with HOmes under similar conditions yields toluene insoluble “La(Omes)₃”, which affords 1 following extraction with THF.     

Light Lanthanide Metallocenium Cations Exhibiting Weak Equatorial Anion Interactions

As the dysprosocenium complex [Dy(Cp^ttt)₂][B(C₆F₅)₄] (Cp^ttt=C₅H₂tBu₃-1,2,4, 1-Dy ) exhibits magnetic hysteresis at 60 K, similar lanthanide (Ln) complexes have been targeted to provide insights into this remarkable property. We recently reported homologous [Ln(Cp^ttt)₂][B(C₆F₅)₄] ( 1-Ln ) for all the heavier Ln from Gd–Lu; herein, we extend this motif to the early Ln. We find, for the largest Ln^III cations, that contact ion pairs [Ln(Cp^ttt)₂{(C₆F₅-κ¹-F)B(C₆F₅)₃}] ( 1-Ln ; La–Nd) are isolated from reactions of parent [Ln(Cp^ttt)₂(Cl)] ( 2-Ln ) with [H(SiEt₃)₂][B(C₆F₅)₄], where the anion binds weakly to the equatorial sites of [Ln(Cp^ttt)₂]⁺ through a single fluorine atom in the solid state. For smaller Sm^III, [Sm(Cp^ttt)₂][B(C₆F₅)₄] ( 1-Sm ) is isolated, which like heavier 1-Ln does not exhibit equatorial anion interactions, but the Eu^III analogue 1-Eu could not be synthesised due to the facile reduction of Eu^III precursors to Eu^II products. Thus with the exception of Eu and radioactive Pm this work constitutes a structurally similar family of Ln metallocenium complexes, over 50 years after the [M(Cp)₂]⁺ series was isolated for the 3d metals.     

CS2 Reductive Coupling to Acetylenedithiolate by a Dinuclear Ytterbium(II) Complex

The activation of CS₂ is of interest in a broad range of fields and, more particularly, in the context of creating new C−C bonds. The reaction of the dinuclear ytterbium(II) complex [Yb₂L₄], 1 , [L=(OtBu)₃SiO⁻] with carbon disulfide led to the isolation of unprecedented reduction products. In particular, the crystallographic characterization of complex [Yb₂L₄(μ-C₂S₂)], 2 , provided the first example of an acetylenedithiolate ligand formed from metal reduction of CS₂. Computational studies indicated that this unprecedented reactivity can be ascribed to the unusual binding mode of CS₂²⁻ in the isolated “key intermediate” [Yb₂L₄(μ-CS₂)], 3 , which results from the dinuclear nature of 1 .     

Unprecedented Sensitization of Visible and Near‐Infrared Lanthanide Luminescence by Using a Tetrathiafulvalene‐Based Chromophore

Ligand L was synthesized and then coordinated to [Ln(hfac)₃] ? 2 H₂O (Ln^III=Tb, Dy, Er; hfac^?=1,1,1,5,5,5‐hexafluoroacetylacetonate anion) and [Ln(tta)₃]?2 H₂O (Ln^III=Eu, Gd, Tb, Dy, Er, Yb; tta^?=2‐thenoyltrifluoroacetonate) to give two families of dinuclear complexes [Ln₂(hfac)₆( L )] ? C₆H₁₄ and [Ln₂(tta)₆( L )] ? 2 CH₂Cl₂. Irradiation of the ligand at 37 040 cm^?1 and 29 410 cm^?1 leads to tetrathiafulvalene‐centered and 2,6‐di(pyrazol‐1‐yl)‐4‐pyridine‐centered fluorescence, respectively. The ligand acts as an organic chromophore for the sensitization of the infrared Er^III (6535 cm^?1) and Yb^III (10 200 cm^?1) luminescence. The energies of the singlet and triplet states of L are high enough to guarantee an efficient sensitization of the visible Eu^III luminescence (17 300–14 100 cm^?1). The Eu^III luminescence decay can be nicely fitted by a monoexponential function that allows a lifetime estimation of (0.49±0.01) ms. Finally, the magnetic and luminescence properties of [Yb₂(hfac)₆( L )] ? C₆H₁₄ were correlated, which allowed the determination of the crystal field splitting of the ²F_7/2 multiplet state with M_J=±1/2 as ground states.     

Synthesis and properties of bis(indenyl) derivatives of ytterbium and lutetium. Molecular structures of the complexes (C9H7)2Ln(μ-Cl)2Li(Et2O)2 (Ln = Yb, Lu) and [(C9H7)2YbCl2][Li(DME)3]

The heterobimetallic bis(indenyl) chloride complexes of ytterbium and lutetium (C₉H₇)₂Ln(μ-Cl)₂Li(Et₂O)₂ (Ln = Yb or Lu) were synthesized by the metathesis reaction of LnCl₃ with two equivalents of indenyllithium in diethyl ether. In the case of ytterbium, the analogous reaction in 1,2-dimethoxyethane afforded the ionic complex [(C₉H₇)₂YbCl₂]⁻[Li(DME)₃]⁺. The reaction of YbCl₃ with indenylpotassium in a molar ratio of 1: 2 in THF is accompanied by reduction of the metal atom to give the bis(indenyl) derivative of Yb^II, (C₉H₇)₂Yb(THF)₂. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 39–44, January, 2008.     

Homoleptic rare-earth metal(III) tetramethylaluminates: structural chemistry, reactivity, and performance in isoprene polymerization

The complexes [Ln(AlMe4)3] (Ln=Y, La, Ce, Pr, Nd, Sm, Ho, Lu) have been synthesized by an amide elimination route and the structures of [Lu{(micro-Me)2AlMe2}3], [Sm{(micro-Me)2AlMe2}3], [Pr{(micro-Me)2AlMe2}3], and [La{(micro-Me)2AlMe2}2{(micro-Me)3AlMe}] determined by X-ray crystallography. These structures reveal a distinct Ln3+ cation size-dependency. A comprehensive insight into the intrinsic properties and solution coordination phenomena of [Ln(AlMe4)3] complexes has been gained from extended dynamic 1H and 13C NMR spectroscopic studies, as well as 1D 89Y, 2D 1H/89Y, and 27Al NMR spectroscopic investigations. [Ce(AlMe4)3] and [Pr(AlMe4)3] have been used as alkyl precursors for the synthesis of heterobimetallic alkylated rare-earth metal complexes. Both carboxylate and siloxide ligands can be introduced by methane elimination reactions that give the heterobimetallic complexes [Ln{(O2CAriPr)2(micro-AlMe2)}2(AlMe4)(C6H14)n] and [Ln{OSi(OtBu)3}(AlMe3)(AlMe4)2], respectively. [Pr{OSi(OtBu)3}(AlMe3)(AlMe4)2] has been characterized by X-ray structure analysis. All of the cerium and praseodymium complexes are used as precatalysts in the stereospecific polymerization of isoprene (1-3 equivalents of Et2AlCl as co-catalyst) and compared to the corresponding neodymium-based initiators reported previously. The superior catalytic performance of the homoleptic complexes leads to quantitative yields of high-cis-1,4-polyisoprene (>98%) in almost all of the polymerization experiments. In the case of the binary catalyst mixtures derived from carboxylate or siloxide precatalysts quantitative formation of polyisoprene is only observed for nLn:nCl=1:2. The influence of the metal size is illustrated for the heterobimetallic lanthanum, cerium, praseodymium, neodymium, and gadolinium carboxylate complexes, and the highest activities are observed for praseodymium as a metal center in the presence of one equivalent of Et2AlCl.     

Hetero‐tri‐spin [2p‐3d‐4f] Chain Compounds Based on Nitronyl Nitroxide Lanthanide Metallo‐Ligands: Synthesis,Structure, and Magnetic Properties

Employing nitronyl nitroxide lanthanide(III) complexes as metallo‐ligands allowed the efficient and highly selective preparation of three series of unprecedented hetero‐tri‐spin (Cu?Ln‐radical) one‐dimensional compounds. These 2p–3d–4f spin systems, namely [Ln₃Cu(hfac)₁₁(NitPhOAll)₄] (Ln^III=Gd 1_Gd , Tb 1_Tb , Dy 1_Dy ; NitPhOAll=2‐(4′‐allyloxyphenyl)‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide), [Ln₃Cu(hfac)₁₁(NitPhOPr)₄] (Ln^III=Gd 2_Gd , Tb 2_Tb , Dy 2_Dy , Ho 2_Ho , Yb 2_Yb ; NitPhOPr=2‐(4′‐propoxyphenyl)‐4,4,5,5‐tetramethyl‐imidazoline‐1‐oxyl‐3‐oxide) and [Ln₃Cu(hfac)₁₁(NitPhOBz)₄] (Ln^III=Gd 3_Gd , Tb 3_Tb , Dy 3_Dy ; NitPhOBz=2‐(4′‐benzyloxyphenyl)‐4,4,5,5‐tetramethyl‐imidazoline‐1‐oxyl‐3‐oxide) involve O‐bound nitronyl nitroxide radicals as bridging ligands in chain structures with a [Cu‐Nit‐Ln‐Nit‐Ln‐Nit‐Ln‐Nit] repeating unit. The dc magnetic studies show that ferromagnetic metal–radical interactions take place in these hetero‐tri‐spin chain complexes, these and the next‐neighbor interactions have been quantified for the Gd derivatives. Complexes 1_Tb and 2_Tb exhibit frequency dependence of ac magnetic susceptibilities, indicating single‐chain magnet behavior.     

Solution Synthesis,Structure, and CO2 Reduction Reactivity of a Scandium(II) Complex, {Sc[N(SiMe3)2]3}−

The first crystallographically characterizable complex of Sc²⁺, [Sc(NR₂)₃]⁻ (R=SiMe₃), has been obtained by LnA₃/M reactions (Ln=rare earth metal; A=anionic ligand; M=alkali metal) involving reduction of Sc(NR₂)₃ with K in the presence of 2.2.2‐cryptand (crypt) and 18‐crown‐6 (18‐c‐6) and with Cs in the presence of crypt. Dark maroon [K(crypt)]⁺, [K(18‐c‐6)]⁺, and [Cs(crypt)]⁺ salts of the [Sc(NR₂)₃]⁻ anion are formed, respectively. The formation of this oxidation state of Sc is also indicated by the eight‐line EPR spectra arising from the I =7/2 ⁴⁵Sc nucleus. The Sc(NR₂)₃ reduction differs from Ln(NR₂)₃ reactions (Ln=Y and lanthanides) in that it occurs under N₂ without formation of isolable reduced dinitrogen species. [K(18‐c‐6)][Sc(NR₂)₃] reacts with CO₂ to produce an oxalate complex, {K₂(18‐c‐6)₃}{[(R₂N)₃Sc]₂(μ‐C₂O₄‐κ ¹O:κ ¹O′′)}, and a CO₂⁻ radical anion complex, [(R₂N)₃Sc(μ‐OCO‐κ ¹O:κ ¹O′)K(18‐c‐6)]_n .     

Eu5F[SiO4]3 und Yb5S[SiO4]3: Gemischtvalente Lanthanoid‐Silicate mit Apatit‐Struktur

Eu₅F[SiO₄]₃ and Yb₅S[SiO₄]₃: Mixed‐Valent Lanthanoid Silicates with Apatite‐Type of Structure By the reaction of Eu, EuF₃, Eu₂O₃ with SiO₂ in evacuated gold ampoules, using NaF as flux, at a temperature of 1000 °C for ten hours, dark‐red, platelet‐shaped single crystals of Eu₅F[SiO₄]₃ are obtained. Similarly dark‐red, but pillar‐shaped single crystals of Yb₅S[SiO₄]₃ are obtained by the reaction of Yb, Yb₂O₃ and S with SiO₂ in the presence CsBr as flux in evacuated silica ampoules at 850 °C and an annealing time of seven days. Both compounds crystallize hexagonally (P6₃/m, Z = 2; Eu₅F[SiO₄]₃: a = 954.79(9), c = 704.16(6) pm; Yb₅S[SiO₄]₃: a = 972.36(9), c = 648.49(6) pm) in the case of Eu₅F[SiO₄]₃ analogous to the mineral fluorapatite and for Yb₅S[SiO₄]₃ as a bromapatite—type variety. The crystal structure containing isolated [SiO₄]^4— tetrahedra distinguishes two rare‐earth cation positions with coordination numbers of nine (M1) and seven (M2), in which the position M1 of the europium fluoride silicate is almost exclusively occupied by Eu²⁺ cations, whereas in ytterbium sulfide silicate it contains di‐ and trivalent Yb cations in the ratio 1 : 1. In both cases, however, the M2 position is only populated with M³⁺.     

NIR‐to‐NIR Two‐Photon Scanning Laser Microscopy Imaging of Single Nanoparticles Doped by YbIII Complexes

The photophysical and nonlinear optical properties of water‐soluble chromophore‐functionalised tris‐dipicolinate complexes [LnL₃]^3? (Ln=Yb and Nd) are thoroughly studied, revealing that only the Yb^III luminescence can be sensitized by a two‐photon excitation process. The stability of the complex in water is strongly enhanced by embedding in dispersible organosilicate nanoparticles (NPs). Finally, the spectroscopic properties of [NBu₄]₃[YbL₃] are studied in solution and in the solid state. The high brightness of the NPs allows imaging them as single objects using a modified two‐photon microscopy setup in a NIR‐to‐NIR configuration.