Trivalent‐Intermediate Valent Cerium Ordering in Ce2RuZn4

The new intermetallic cerium compound Ce₂RuZn₄ was synthesized from the elements in a sealed tantalum tube in a water‐cooled sample chamber of an induction furnace. Ce₂RuZn₄ crystallizes with a new structure type: P4/nmm, Z = 2, a = 719.6(1), c = 520.2(1) pm, wR2 = 0.0816, 273 F² values and 15 variables. The structure contains two crystallographically independent cerium atoms: Ce1 with CN 16 (12 Zn + 4 Ce) and Ce2 with CN 14 (2 Ru + 8 Zn + 4 Ce). Based on the interatomic distances the two sites can be assigned to trivalent Ce1 and intermediate valent Ce2. The trivalent‐intermediate valent cerium ordering is underlined by magnetic susceptibility measurements. Ce₂RuZn₄ shows modified Curie‐Weiss behaviour in the temperature range 10–290 K with an experimental magnetic moment of 2.57(1) μ_B per formula unit. Thus only half of the cerium atoms are trivalent in Ce₂RuZn₄. A remarkable feature of the Ce₂RuZn₄ structure are short Ce2–Ru distances of 260 pm. The crystal chemistry of Ce₂RuZn₄ is discussed.     

Syntheses and Crystal Structures of Hydrated Ternary Cerium Sulfates: Mixed‐valence K5Ce2(SO4)6·H2O and K2Ce(SO4)3·H2O

A new chemical and structural interpretation of K₅Ce₂(SO₄)₆·H₂O ( I ) and a redetermination of the structure of K₂Ce(SO₄)₃·H₂O ( II ) is presented. The mixed‐valent compound I crystallizes in the space group C2/c with a = 17.7321(3), b = 7.0599(1), c = 19.4628(4) Å, β = 112.373(1)° and Z = 4. Compound I has been discussed earlier with space group Cc. In the structure of I , there are pairs of edge sharing cerium polyhedra connected by sulfate oxygen atoms in the μ₃ bonding mode. These cerium dimers are linked through edge and corner sharing sulfate bridges, forming layers. The layers are joined by potassium ions which together with the water molecules are placed between the layers. No irregularity in the distribution of the Ce^III and Ce^IV to cause the lost of a crystallographic center of symmetry was detected. We suggest that the charge exerted by the extra f¹ electron for every cerium dimer is delocalized over the Ce1–O₂–Ce2 moiety in a non‐bonding mode. As a result, the oxidations state of each cerium ion is a mean value between III and IV at each atomic position. Compound II crystallizes in the space group C2 with a = 20.6149(2), b = 7.0742(1), c = 17.8570(1) Å, β = 122.720(1)° and Z = 8. The hydrogen atoms have been located and the absolute structure has been established. Neither hydrogen atom positions nor anisotropic displacement parameters were given in the previous reports. In compound II , the cerium polyhedra are connected by edge and corner sharing sulfate groups forming a three‐dimensional network. This network contains Z‐shaped channels hosting the charge compensating potassium ions.     

Rare‐Earth‐Rich Magnesium Compounds RE23Rh7Mg4 (RE = La,Ce, Pr,Nd, Sm,Gd) with Tetrahedral Mg4 Clusters

The rare earth‐rich compounds RE₂₃Rh₇Mg₄ (RE = La, Ce, Pr, Nd, Sm, Gd) were prepared by induction‐melting the elements in sealed tantalum tubes. The new compounds were characterized by X‐ray powder diffraction. They crystallize with the hexagonal Pr₂₃Ir₇Mg₄ type structure, space group P6₃mc. The structures of La₂₃Rh₇Mg₄ (a = 1019.1(1), c = 2303.7(4) pm, wR2 = 0.0827, 1979 F² values, 69 variables), Nd₂₃Rh₇Mg₄ (a = 995.4(2), c = 2242.3(5) pm, wR2 = 0.0592, 2555 F² values, 74 variables) and Gd₂₃Rh_6.86(5)Mg₄ (a = 980.5(2), c = 2205.9(5) pm, wR2 = 0.0390, 2083 F² values, 71 variables) were refined from single crystal X‐ray diffractometer data. The three crystallographically different rhodium atoms have trigonal prismatic rare earth coordination with short RE–Rh distances (283–300 pm in Nd₂₃Rh₇Mg₄). The prisms are condensed via common edges, leading to a rigid three‐dimensional network in which isolated Mg₄ tetrahedra (312–317 pm Mg–Mg in Nd₂₃Rh₇Mg₄) are embedded. Temperature dependent magnetic susceptibility data of Ce₂₃Rh₇Mg₄ indicate Curie‐Weiss behavior with an experimental magnetic moment of 2.52(1) μ_B/Ce atom, indicative for stable trivalent cerium. Antiferromagnetic ordering is evident at 2.9 K.     

Gradual Cerium Valence Change in the Solid Solution CeRu1–xPdxAl (x = 0.1–0.9)

The solid solution CeRu_1–xPd_xAl was synthesized for x = 0.1–0.9 from the elements by arc‐melting and subsequent annealing and characterized by powder X‐ray diffraction. All members crystallize in the orthorhombic LaNiAl type structure, space group Pnma. The lattice parameters range from a = 718–722, b = 412–426, and c = 1588–1620 pm, but no linear change of the lattice parameters was found. Magnetic measurements reveal intermediate cerium valences, which change to more trivalent cerium with increasing Pd content. The susceptibility data was interpreted by either the Inter‐Configuration Fluctuation (ICF) model or the Curie‐Weiss law.     

Quaternary Germanides RE3TRh4Ge4 (RE = Ce,Pr, Nd; T = Nb,Ta) – A New Coloring Variant of the Aristotype AlB2

The quaternary germanides RE₃TRh₄Ge₄ (RE = Ce, Pr, Nd; T = Nb, Ta) were synthesized from the elements by arc‐melting and subsequent annealing in a muffle furnace. The structure of Ce₃TaRh₄Ge₄ was refined from single‐crystal X‐ray diffractometer data: new type, Pbam, a = 719.9(2), b = 1495.0(3), c = 431.61(8), wR₂ = 0.0678, 1004 F² values, and 40 variables. Isotypy of the remaining phases was evident from X‐ray powder patterns. Ce₃TaRh₄Ge₄ is a new superstructure variant of the aristotype AlB₂ with an ordering of cerium and tantalum on the aluminum site, whereas the honey‐comb network is built up by a 1:1 ordering of rhodium and germanium. This crystal‐chemical relationship is discussed based on a group‐subgroup scheme. The distinctly different size of tantalum and cerium leads to a pronounced puckering of the [Rh₄Ge₄] network, which shows the shortest interatomic distances (253–271 pm Rh–Ge) within the Ce₃TaRh₄Ge₄ structure. Another remarkable structural feature concerns the tantalum coordination with six shorter Ta–Rh bonds (265–266 pm) and six longer Ta–Ge bonds (294–295 pm). The [Rh₄Ge₄] network fully separates the tantalum and cerium atoms (Ce–Ce > 387 pm, Ta–Ta > 431 pm, and Ce–Ta > 359 pm). The electronic density of states DOS from DFT calculations show metallic behavior with large contributions of localized Ce 4f as well as itinerant ones from all constituents at the Fermi level but no significant magnetic polarization on Ce could be identified. The bonding characteristics described based on overlap populations illustrate further the crystal chemistry observations of the different coordination of Ce1 and Ce2 in Ce₃TaRh₄Ge₄. The Rh–Ge interactions within the network are highlighted as dominant. The bonding magnitudes follow the interatomic distances and identify differences of Ta bonding vs. Ce1/Ce2 bonding with the Rh and Ge substructures.     

Controlled Redox Chemistry at Cerium within a Tripodal Nitroxide Ligand Framework

Ligand reorganization has been shown to have a profound effect on the outcome of cerium redox chemistry. Through the use of a tethered, tripodal, trianionic nitroxide ligand, [((2‐tBuNOH)C₆H₄CH₂)₃N]^3? (TriNO_x^3?), controlled redox chemistry at cerium was accomplished, and typically reactive complexes of tetravalent cerium were isolated. These included rare cationic complexes [Ce(TriNO_x)thf][BAr^F₄], in which Ar^F=3,5‐(CF₃)₂‐C₆H₃, and [Ce(TriNO_x)py][OTf]. A rare complete Ce–halide series, Ce(TriNO_x)X, in which X=F^?, Cl^?, Br^?, I^?, was also synthesized. The solution chemistry of these complexes was explored through detailed solution‐phase electrochemistry and ¹H NMR experiments and showed a unique shift in the ratio of species with inner‐ and outer‐sphere anions with size of the anionic X^? group. DFT calculations on the series of calculations corroborated the experimental findings.     

Cerium(III/IV) Formamidinate Chemistry,and a Stable Cerium(IV) Diolate

Four new cerium(III) formamidinate complexes comprising [Ce(p‐TolForm)₃], [Ce(DFForm)₃(thf)₂], [Ce(DFForm)₃], and [Ce(EtForm)₃] were synthesized by protonolysis reactions using [Ce{N(SiMe₃)₂}₃] and formamidines of varying functionality, namely N,N′‐bis(4‐methylphenyl)formamidine (p‐TolFormH), N,N′‐bis(2,6‐difluorophenyl)formamidine (DFFormH), and the sterically more demanding N,N′‐bis(2,6‐diethylphenyl)formamidine (EtFormH). The bimetallic cerium lithium complex [LiCe(DFForm)₄] was synthesized by treating a mixture of [Ce{N(SiHMe₂)₂}₃(thf)₂] and [Li{N(SiHMe₂)₂}] with four equivalents of DFFormH in toluene. Oxidation of the trivalent cerium(III) formamidinate complexes by trityl chloride (Ph₃CCl) caused dramatic color changes, although the cerium(IV) species appeared transient and reformed cerium(III) complexes and N′‐trityl‐N,N′‐diarylformamidines shortly after oxidation. The first structurally characterized homoleptic cerium(IV) formamidinate complex [Ce(p‐TolForm)₄] was obtained through a protonolysis reaction between [Ce{N(SiHMe₂)₂}₄] and four equivalents of p‐TolFormH. [Ce{N(SiHMe₂)₂}₄] was also treated with DFFormH and EtFormH, but the resulting cerium(IV) complexes decomposed before isolation was possible. The new cerium(IV) silylamide complex [Ce{N(SiMe₃)₂}₃(bda)_0.5]₂ (bda=1,4‐benzenediolato) was synthesized by treatment of [Ce{N(SiMe₃)₂}₃] with half an equivalent of 1,4‐benzoquinone, and showed remarkable resistance towards protonolysis or reduction.     

New Ternary Alkaline Earth Metal Cerium(IV) Nitrides: CaCeN2 and SrCeN2

CaCeN₂ and SrCeN₂ were prepared by reactions of Li₂CeN₂ with Ca₃N₂ or Sr₂N in a nitrogen atmosphere at 1020 K. According to measurements of the magnetic susceptibilities both compounds contain Ce^IV. The crystal structures were determined by full‐profile Rietveld refinements of the X‐ray powder diffraction patterns. CaCeN₂ crystallizes in a rocksalt‐type structure with disordered Ca and Ce (space group Fm3¯m, a = 499.21(1) pm, R_profile = 0.061, R_Bragg = 0.034). The low temperature modification of SrCeN₂ crystallizes in the α‐NaFeO₂ type structure (space group R3¯m, a = 362.18(4) pm, c = 1795.8(2) pm, R_profile = 0.085, R_Bragg = 0.031). At elevated temperatures an order‐disorder phase transition leads to HT‐SrCeN₂ (space group Fm3¯m, a = 515.01(2) pm, quenched from 1273 K) with a cubic unit cell and complete disorder of Sr and Ce.     

Complex Borides RERu4B4 (RE = Ce,Pr, Nd,Sm) – Bonding Peculiarities and Magnetic Properties

The rare earth borides RERu₄B₄ (RE = Ce, Pr, Nd, Sm) were synthesized from the elements by arc‐melting and their crystal structures were studied on the basis of X‐ray powder and single‐crystal diffraction: LuRu₄B₄ type, I4₁/acd, a = 747.47(8), c = 1506.4(3) pm, wR₂ = 0.0579, 362 F² values for CeRu₄B₄, a = 751.3(2), c = 1507.1(5) pm, wR₂ = 0.0724, 471 F² values for PrRu₄B₄, a = 751.0(2), c = 1506.9(6) pm, wR₂ = 0.0598, 384 F² values for NdRu₄B₄, and a = 749.1(1), c = 1506.0(3) pm, wR₂ = 0.0759, 413 F² values for SmRu₄B₄, with 18 variables per refinement. Striking structural motifs of the RERu₄B₄ structures are Ru₄ tetrahedra and B₂ dumbbells with Ru–Ru and B–B distances of 271 and 180 pm in CeRu₄B₄. The intermediate valence of cerium leads to shorter Ce–Ru distances of 292 pm. CeRu₄B₄ behaves like a Pauli paramagnet with a small room temperature susceptibility of 1.5 × 10^–4 emu · mol^–1. Chemical bonding analyses shows substantial Ru–B and B–B bonding within the [Ru₄B₄] substructure.     

Einkristalle des Cer(III)‐Borosilicats Ce3[BSiO6][SiO4]

Single Crystals of the Cerium(III) Borosilicate Ce₃[BSiO₆][SiO₄] Colorless, lath‐shaped single crystals of Ce₃[BSiO₆]‐ [SiO₄] (orthorhombic, Pbca; a = 990.07(6), b = 720.36(4), c = 2329.2(2) pm, Z = 8) were obtained in attempts to synthesize fluoride borates with trivalent cerium in evacuated silica tubes by reaction of educt mixtures of elemental cerium, cerium dioxide, cerium trifluoride, and boron sesquioxide (Ce, CeO₂, CeF₃, B₂O₃; molar ratio 3 : 1 : 3 : 3) in fluxing CsCl (700 °C, 7 d) with the glass wall. The crystal structure contains eight‐ (Ce1) and ninefold coordinated Ce³⁺ cations (Ce2 and Ce3) surrounded by oxygen atoms. Charge balance is achieved by both discrete borosilicate ([BSiO₆]^5– ≡ [O₂BOSiO₃]^5–) and ortho‐silicate anions ([SiO₄]^4–). The former consists of a [BO₃] triangle linked to a [SiO₄] tetrahedron by a single vertex. The anions form layers in [001] direction alternatingly built up from [BSiO₆]^5– and [SiO₄]^4– groups while Ce³⁺ cations are located in between.     

Organometallic Cerium Complexes from Tetravalent Coordination Complexes

The use of tetravalent cerium alkoxides, nitrates, and triflates was studied as a direct route to [Ce^IV(carbene)] complexes. Protonolysis reactions between 1H‐imidazolium‐ or imidazoline (=4,5‐dihydro‐1H‐imidazole)‐containing alkoxide proligands HL (L=OCMe₂CH₂[1‐C(NCHCHNⁱPr)]) and HL^S (L^S=OCMe₂CH₂[1‐C(NCH₂CH₂NⁱPr)]) and Ce^IV tert‐butoxide, triflate, and nitrate compounds were studied to target [Ce^IV(N‐heterocyclic carbene)] complexes (of unsaturated and saturated carbenes, resp.). Instead, tetravalent cerium imidazolium [(O^tBu)₃Ce(μ‐O^tBu)₂(μ‐HL)Ce(O^tBu)₃], or imidazolinium adducts [(O^tBu)₃Ce(μ‐O^tBu)₂(μ‐HL^S)Ce(O^tBu)₃] were isolated. However, the salt metathesis of cerium triflate with KL provided a simple route to [CeL₄], which was significantly improved if an external oxidant, benzoquinone, was included in the mixture to maintain oxidation‐state integrity. Likewise, the salt metathesis of cerium triiodide with KL and added benzoquinone provided a straightforward route to [CeL₄].     

Rare Earth Ruthenium Gallides with the Ideal Composition Ln2Ru3Ga5 (Ln = La–Nd,Sm) crystallizing with U2Mn3Si5 (Sc2Fe3Si5) Type Structure

The rare earth ruthenium gallides Ln₂Ru₃Ga₅ (Ln = La, Ce, Pr, Nd, Sm) were prepared by arc‐melting of cold‐pressed pellets of the elemental components. They crystallize with a tetragonal structure (P4/mnc, Z = 4) first reported for U₂Mn₃Si₅. The crystal structures of the cerium and samarium compounds were refined from single‐crystal X‐ray data, resulting in significant deviations from the ideal compositions: Ce₂Ru_2.31(1)Ga_5.69(1), a = 1135.10(8) pm, c = 580.58(6) pm, R_F = 0.022 for 742 structure factors; Sm₂Ru_2.73(2)Ga_5.27(2), a = 1132.95(9) pm, c = 562.71(6) pm, R_F = 0.026 for 566 structure factors and 32 variable parameters each. The deviations from the ideal compositions 2:3:5 are discussed. A mixed Ru/Ga occupancy occurs only for one atomic site. The displacement parameters are relatively large for atoms with mixed occupancy within their coordination shell and small for atoms with no neighboring sites of mixed occupancy. Chemical bonding is analyzed on the basis of interatomic distances. Ln–Ga bonding is stronger than Ln–Ru bonding. Ru–Ga bonding is strong and Ru–Ru bonding is weak. The Ga–Ga interactions are of similar strength as in elemental gallium.     

Divergent Stabilities of Tetravalent Cerium,Uranium, and Neptunium Imidophosphorane Complexes**

The study of the redox chemistry of mid-actinides (U−Pu) has historically relied on cerium as a model, due to the accessibility of trivalent and tetravalent oxidation states for these ions. Recently, dramatic shifts of lanthanide 4+/3+ non-aqueous redox couples have been established within a homoleptic imidophosphorane ligand framework. Herein we extend the chemistry of the imidophosphorane ligand (NPC=[N=P^tBu(pyrr)₂]⁻; pyrr=pyrrolidinyl) to tetrahomoleptic NPC complexes of neptunium and cerium ( 1-M , 2-M , M=Np, Ce) and present comparative structural, electrochemical, and theoretical studies of these complexes. Large cathodic shifts in the M^4+/3+ (M=Ce, U, Np) couples underpin the stabilization of higher metal oxidation states owing to the strongly donating nature of the NPC ligands, providing access to the U^5+/4+, U^6+/5+, and to an unprecedented, well-behaved Np^5+/4+ redox couple. The differences in the chemical redox properties of the U vs. Ce and Np complexes are rationalized based on their redox potentials, degree of structural rearrangement upon reduction/oxidation, relative molecular orbital energies, and orbital composition analyses employing density functional theory.     

Ketimido Metallophthalocyanines: An Approach to Phthalocyanine‐Supported Mononuclear High‐Valent Ruthenium Complexes

A “metal–ketimine+ArI(OR)₂” approach has been developed for preparing metal–ketimido complexes, and ketimido ligands are found to stabilize high‐valent metallophthalocyanine (M? Pc) complexes such as ruthenium(IV) phthalocyanines. Treatment of bis(ketimine) ruthenium(II) phthalocyanines [Ru^II(Pc)(HN?CPh₂)₂] ( 1a ) and [Ru^II(Pc)(HNQu)₂] ( 1b ; HNQu=N‐phenyl‐1,4‐benzoquinonediimine) with PhI(OAc)₂ affords bis(ketimido) ruthenium(IV) phthalocyanines [Ru^IV(Pc)(N?CPh₂)₂] ( 2a ) and [Ru^IV(Pc)(NQu)₂] ( 2b ), respectively. X‐ray crystal structures of 1b and [Ru^II(Pc)(PhN?CHPh)₂] ( 1c ) show Ru? N(ketimine) distances of 2.075(4) and 2.115(3) Å, respectively. Complexes 2a , 2b readily revert to 1a , 1b upon treatment with phenols. ¹H NMR spectroscopy reveals that 2a , 2b are diamagnetic and 2b exists as two isomers, consistent with a proposed eclipsed orientation of the ketimido ligands in these ruthenium(IV) complexes. The reaction of 1a , 1b with PhI(OAc)₂ to afford 2a , 2b suggests the utility of ArI(OR)₂ as an oxidative deprotonation agent for the generation of high‐valent metal complexes featuring M? N bonds with multiple bonding characters. DFT and time‐dependent (TD)‐DFT calculations have been performed on the electronic structures and the UV/Vis absorption spectra of 1b and 2b , which provide support for the diamagnetic nature of 2b and reveal a significant barrier for rotation of the ketimido group about the Ru? N(ketimido) bond.     

Stabilizing the LaCoAl4 Structure through Indium‐Magnesium Substitution in CeRhIn4−xMgx (x = 0.79 and 0.84) – An Indide with Magnesium Centered Indium Cubes

The intermetallic compounds CeRhIn_4?xMg_x (x = 0.79 and 0.84) were prepared from the elements in sealed tantalum ampoules in a high‐frequency furnace. The samples were investigated by X‐ray powder and single crystal diffraction: LaCoAl₄ type, Pmma, a = 829.5(2), b = 433.56(9), c = 740.2(2) pm, wR2 = 0.0458, 651 F² values, 25 variables for CeRhIn_3.21Mg_0.79 and a = 831.44(10), b = 433.49(10), c = 741.04(10) pm, wR2 = 0.0543, 915 F² values, 25 variables for CeRhIn_3.16Mg_0.84. The indium atoms build up two‐dimensional networks perpendicular to the b axis in an AA stacking sequence leaving slightly distorted trigonal, square and pentagonal prismatic voids for the rhodium, magnesium, and cerium atoms. Both square prismatic voids show small magnesium/indium mixing. The shortest interatomic distances occur for the Rh–Mg contacts (257 pm). Together, the rhodium, indium, and magnesium atoms build up three‐dimensional [RhIn_4?xMg_x] networks in which the cerium atoms fill distorted pentagonal channels.     

Syntheses of High‐Valent fac‐[99mTcO3]+ Complexes and [3+2] Cycloadditions with Alkenes in Water as a Direct Labelling Strategy

Reported herein is a new concept for the labelling of biomolecules with small [^{99 m}TcO₃]⁺ complexes through a [3+2] cycloaddition with alkenes for radiopharmaceutical applications. We developed convenient reactions for the synthesis of small, water stable fac‐[TcO₃(tacn‐R)]⁺ complexes (⁹⁹Tc and ^99mTc, tacn=1,4,7‐triazacyclononane, R=H, ‐CH₂‐C₆H₅, ‐CH₂‐C₆H₄COOH). With alkenes, these high valent [^99mTcO₃]⁺ complexes undergo [3+2] cycloaddition with formation of the corresponding Tc^V–glycolato complexes. The ^99mTc^V and ^99mTc^VII complexes are stable at 37 °C in water and in the presence of serum proteins. Therefore, new opportunities in technetium chemistry are enabled with a high potential for medicinal and biological applications. In contrast to classical labelling, the presented strategy is ligand and not metal‐centred.     

Semiconducting La2AuP3, the Metallic Conductor Ce2AuP3, and other Rare‐Earth Gold Phosphides Ln2AuP3 with Two Closely Related Crystal Structures

The compounds Ln₂AuP₃ were synthesized by reaction of the elemental components in evacuated silica tubes. Their crystal structures were determined from single‐crystal diffractometer data. The compounds with Ln = La, Ce, and Pr crystallize with an orthorhombic U₂NiC₃ type structure (Pnma, Z = 4). The structure refinement for Ce₂AuP₃ resulted in a = 774.14(6) pm, b = 421.11(4) pm, c = 1612.3(1) pm, R = 0.019 for 1410 structure factors and 38 variable parameters. For Pr₂AuP₃ a residual of R = 0.024 was obtained. Nd₂AuP₃ crystallizes with a monoclinic distortion of this structure: P2₁/c, Z = 4, a = 416.14(4) pm, b = 768.87(6) pm, c = 1647.1(2) pm, β = 104.06(1)°, R = 0.022 for 1361 F values and 56 variables. The near‐neighbor coordinations of the two structures are nearly the same. In both structures the gold and phosphorus atoms form two‐dimensionally infinite nets, where the gold atoms are tetrahedrally coordinated by phosphorus atoms with Au–P distances varying between 245.8 and 284.2 pm. Two thirds of the phosphorus atoms form pairs with single‐bond distances varying between 217.7 and 218.9 pm. Thus, using oxidation numbers the structures can be rationalized with the formulas (Ln⁺³)₂[AuP₃]^–6 and (Ln⁺³)₂Au⁺¹(P₂)^–4P^–3. Accordingly, La₂AuP₃ is a diamagnetic semiconductor. Pr₂AuP₃ is semiconducting with an antiferromagnetic ground state, showing metamagnetism with a critical field of B_c = 0.5(± 0.1) T. In contrast, the cerium compound is a metallic conductor, even though its cell volume indicates that the cerium atoms are essentially trivalent, as is also suggested by the ferro‐ or ferrimagnetic behavior of the compound.     

A New Class of Homogeneous Visible‐Light Photocatalysts: Molecular Cerium Vanadium Oxide Clusters

The first systematic access to molecular cerium vanadium oxides is presented. A family of structurally related, di‐cerium‐functionalized vanadium oxide clusters and their use as visible‐light‐driven photooxidation catalysts is reported. Comparative analyses show that photocatalytic activity is controlled by the cluster architecture. Increased photoreactivity of the cerium vanadium oxides in the visible range compared with nonfunctionalized vanadates is observed. Based on the recent discovery of the first molecular cerium vanadate cluster, (nBu₄N)₂[(Ce(dmso)₃)₂V₁₂O₃₃Cl] ? 2 DMSO ( 1 ), two new di‐cerium‐containing vanadium oxide clusters [(Ce(dmso)₄)₂V₁₁O₃₀Cl] ? DMSO ( 2 ) and [(Ce(nmp)₄)₂V₁₂O₃₂Cl] ? NMP ? Me₂CO ( 3 ; NMP=N‐methyl‐2‐pyrrolidone) were obtained by using a novel fragmentation and reassembly route. Pentagonal building units {(V)M₅} (M=V, Ce) reminiscent of “Müller‐type” pentagons are observed in 2 and 3 . Compounds 1 – 3 feature high visible‐light photooxidative activity, and quantum efficiencies >10 % for indigo photooxidation are observed. Photocatalytic performance increases in the order 1 < 3 < 2 . Mechanistic studies show that the irradiation wavelength and the presence of oxygen strongly affect photoreactivity. Initial findings suggest that the photooxidation mechanism proceeds by intermediate formation of hydroxyl radicals. The findings open new avenues for the bottom‐up design of sunlight‐driven photocatalysts.     

Substituent and Solvent Effects on the Electrochemical Properties and Intervalence Transfer in Asymmetric Mixed‐Valent Complexes Consisting of Cyclometalated Ruthenium and Ferrocene

Four heterodimetallic complexes [Ru(Fcdpb)(L)](PF₆) (Fcdpb=2‐deprotonated form of 1,3‐di(2‐pyridyl)‐5‐ferrocenylbenzene; L=2,6‐bis‐(N‐methylbenzimidazolyl)‐pyridine (Mebip), 2,2′:6′,2′′‐terpyridine (tpy), 4‐nitro‐2,2′:6′,2′′‐terpyridine (NO₂tpy), and trimethyl‐4,4′,4′′‐tricarboxylate‐2,2′:6′,2′′‐terpyridine (Me₃tctpy)) have been prepared. The electrochemical and spectroelectrochemical properties of these complexes have been examined in CH₂Cl₂, CH₃NO₂, CH₃CN, and acetone. These complexes display two consecutive redox couples owing to the stepwise oxidation of the ferrocene (Fc) and ruthenium units, respectively. The potential difference, ΔE_1/2 (E_1/2(Ru^II/III)?E_1/2(Fc^0/+)), decreased slightly with increasing solvent donocity. The mixed‐valent states of these complexes have been generated by electrolysis and the resulting intervalence charge‐transfer (IVCT) bands have been analyzed by Hush theory. Good linear relationships exist between the energy of the IVCT band, E_op, and ΔE_1/2 of four mixed‐valent complexes in a given solvent.     

The Ternary Stannides MgRuSn4 and MgxRh3Sn7—x (x = 0.98—1.55)

The magnesium transition metal stannides MgRuSn₄ and Mg_xRh₃Sn_7—x (x = 0.98—1.55) were synthesized from the elements in glassy carbon crucibles in a water‐cooled sample chamber of a high‐frequency furnace. They were characterized by X‐ray diffraction on powders and single crystals. MgRuSn₄ adopts an ordered PdGa₅ type structure: I4/mcm, a = 674.7(1), c = 1118.1(2) pm, wR2 = 0.0506, 515 F² values and 12 variable parameters. The ruthenium atoms have a square‐antiprismatic tin coordination with Ru—Sn distances of 284 pm. These [RuSn_8/2] antiprisms are condensed via common faces forming two‐dimensional networks. The magnesium atoms fill square‐prismatic cavities between adjacent [RuSn₄] layers with Mg—Sn distances of 299 pm. The rhodium based stannides Mg_xRh₃Sn_7—x crystallize with the cubic Ir₃Ge₇ type structure, space groupe Im3m. The structures of four single crystals with x = 0.98, 1.17, 1.36, and 1.55 have been refined from X‐ray diffractometer data. With increasing tin substitution the a lattice parameter decreases from 932.3(1) pm for x = 0.98 to 929.49(6) pm for x = 1.55. The rhodium atoms have a square antiprismatic tin/magnesium coordination. Mixed Sn/Mg occupancies have been observed for both tin sites but to a larger extend for the 12d Sn2 site. Chemical bonding in MgRuSn₄ and Mg_xRh₃Sn_7—x is briefly discussed.