Octanuclear Ni4Ln4 Coordination Aggregates from Schiff Base Anion Supports and Connecting of Two Ni2Ln2 Cubes: Syntheses,Structures, and Magnetic Properties

A family of 3d–4f aggregates have been reported through guiding the dual coordination modes of ligand anion (HL^?) and in situ generated ancillary bridge driven self‐assembly coordination responses toward two different types of metal ions. Reactions of lanthanide(III) nitrate (Ln=Gd, Tb, Dy, Ho and Yb), nickel(II) acetate and phenol‐based ditopic ligand anion of 2‐[{(2‐hydroxypropyl)imino}methyl]‐6‐methoxyphenol (H₂L) in MeCN‐MeOH (3 : 1) mixture and LiOH provided five new octanuclear Ni‐4f coordination aggregates from two Ni₂Ln₂ cubanes. Single‐crystal X‐ray diffraction analysis reveals that all the members of the family are isostructural, with the central core formed from the coupling of two distorted [Ni₂Ln₂O₄] heterometallic cubanes [Ni₂Ln₂(HL)₂(μ₃‐OH)₂(OH)(OAc)₄]⁺ (Ln=Gd ( 1 ), Tb ( 2 ), Dy ( 3 ), Ho ( 4 ) and Yb ( 5 )). Higher coordination demand of 4f ions induced the coupling of the two cubes by (OH)(OAc)₂ bridges. Variable temperature magnetic study reveals weak coupling between the Ni²⁺ and Ln³⁺ ions. For the Tb ( 2 ) and Dy ( 3 ) analogs, the compounds are SMMs without an applied dc field, whereas the Gd ( 1 ) analogue is not an SMM. The observation revealed thus that the anisotropy of the Ln³⁺ ions is central to display the SMM behavior within this structurally intriguing family of compounds.     

Heterotrimetallic Coordination Polymers: {CuIILnIIIFeIII} Chains and {NiIILnIIIFeIII} Layers: Synthesis,Crystal Structures,and Magnetic Properties

The use of the [Fe^III(AA)(CN)₄]^? complex anion as metalloligand towards the preformed [Cu^II(valpn)Ln^III]³⁺ or [Ni^II(valpn)Ln^III]³⁺ heterometallic complex cations (AA=2,2′‐bipyridine (bipy) and 1,10‐phenathroline (phen); H₂valpn=1,3‐propanediyl‐bis(2‐iminomethylene‐6‐methoxyphenol)) allowed the preparation of two families of heterotrimetallic complexes: three isostructural 1D coordination polymers of general formula {[Cu^II(valpn)Ln^III(H₂O)₃(μ‐NC)₂Fe^III(phen)(CN)₂ {(μ‐NC)Fe^III(phen)(CN)₃}]NO₃ ? 7 H₂O}_n (Ln=Gd ( 1 ), Tb ( 2 ), and Dy ( 3 )) and the trinuclear complex [Cu^II(valpn)La^III(OH₂)₃(O₂NO)(μ‐NC)Fe^III(phen)(CN)₃] ? NO₃ ? H₂O ? CH₃CN ( 4 ) were obtained with the [Cu^II(valpn)Ln^III]³⁺ assembling unit, whereas three isostructural heterotrimetallic 2D networks, {[Ni^II(valpn)Ln^III(ONO₂)₂(H₂O)(μ‐NC)₃Fe^III(bipy)(CN)] ? 2 H₂O ? 2 CH₃CN}_n (Ln=Gd ( 5 ), Tb ( 6 ), and Dy ( 7 )) resulted with the related [Ni^II(valpn)Ln^III]³⁺ precursor. The crystal structure of compound 4 consists of discrete heterotrimetallic complex cations, [Cu^II(valpn)La^III(OH₂)₃(O₂NO)(μ‐NC)Fe^III(phen)(CN)₃]⁺, nitrate counterions, and non‐coordinate water and acetonitrile molecules. The heteroleptic {Fe^III(bipy)(CN)₄} moiety in 5 – 7 acts as a tris‐monodentate ligand towards three {Ni^II(valpn)Ln^III} binuclear nodes leading to heterotrimetallic 2D networks. The ferromagnetic interaction through the diphenoxo bridge in the Cu^II?Ln^III ( 1 – 3 ) and Ni^II?Ln^III ( 5 – 7 ) units, as well as through the single cyanide bridge between the Fe^III and either Ni^II ( 5 – 7 ) or Cu^II ( 4 ) account for the overall ferromagnetic behavior observed in 1 – 7 . DFT‐type calculations were performed to substantiate the magnetic interactions in 1 , 4 , and 5 . Interestingly, compound 6 exhibits slow relaxation of the magnetization with maxima of the out‐of‐phase ac signals below 4.0 K in the lack of a dc field, the values of the pre‐exponential factor (τ_o) and energy barrier (E_a) through the Arrhenius equation being 2.0×10^?12 s and 29.1 cm^?1, respectively. In the case of 7 , the ferromagnetic interactions through the double phenoxo (Ni^II–Dy^III) and single cyanide (Fe^III–Ni^II) pathways are masked by the depopulation of the Stark levels of the Dy^III ion, this feature most likely accounting for the continuous decrease of χ_M T upon cooling observed for this last compound.     

A Series of High‐nuclear 3d‐4f (FeIII8LnIII2) Complexes: Syntheses,Structures, and Magnetic Properties

Six novel decanuclear clusters with formula of {[Fe₈Ln₂(O)₄(OH)₄(EtO)₂(dhbp)₄(dhbpH)₂(piv)₆]·4EtOH} (Ln = Y ( 1 ), Gd ( 2 ), Tb ( 3 ), Dy ( 4 ), Ho ( 5 ), Er ( 6 ), dhbpH₂ = 6,6′‐dihydroxyl‐2,2′‐bipyridine, Hpiv = pivalic acid, EtOH = ethanol) have been synthesized and characterized. Single‐crystal and powder X‐ray diffraction analyses reveal that complexes 1 – 6 are isostructural and show a sandwich‐like Fe^III₈Ln^III₂ structure, in which the [Ln₂] unit is sandwiched by two planar [Fe₄] units. Magnetic properties of complexes 1 – 6 have been investigated and display dominant antiferromagnetic interactions, thereinto, complexes 4 and 6 display weak ferromagnetic behaviors associated with Ln^III ions, while others are antiferromagnetic‐like features. Furthermore, complex 4 (Fe^III₈Dy^III₂) shows temperature/frequency‐dependent ac signals with an energy barrier of 4.1 K, indicating that complex 4 should be a single‐molecule magnet (SMM)     

Syntheses,Structures, and Magnetism of Trinuclear Zn2Ln Complexes with 2,6‐Dipicolinoylbis(N,N‐diethylthiourea)

The bifunctional ligand 2,6‐dipicolinoylbis(N,N‐diethylthiourea) (H₂L) readily reacts with mixtures of Zn(CH₃COO)₂ and LnCl₃ in MeOH at ambient temperature with formation of trinuclear heterobimetallic complexes [Zn₂Ln(L)₂(OAc)₃] ( 1a – 1f ) (Ln = Ce, Nd, Sm, Gd, Dy, Er). The X‐ray single‐crystal diffraction and structural studies of the complexes revealed their isostructural nature, in which two doubly‐charged ligands {L^2–} bind two Zn²⁺ ions with the terminal acylthiourea sites and one Ln³⁺ ion with the central 2,6‐pyridinedicarboxamide site. In the complexes, the coordination numbers of Ln^III and Zn^II ions are 9 and 5, respectively. Magnetic properties of the complexes were studied by temperature‐dependent dc magnetic measurements. The observed μ_eff values at room temperature are all closed to the calculated values. Fitting χ_M and M data of [Zn₂Gd(L)₂(OAc)₃] ( 1d ) shows a g_iso value of 1.94.     

Two C3‐Symmetric Dy3III Complexes with Triple Di‐μ‐methoxo‐μ‐phenoxo Bridges,Magnetic Ground State,and Single‐Molecule Magnetic Behavior

Two series of isostructural C₃‐symmetric Ln₃ complexes Ln₃ ? [BPh₄] and Ln₃ ? 0.33[Ln(NO₃)₆] (in which Ln^III=Gd and Dy) have been prepared from an amino‐bis(phenol) ligand. X‐ray studies reveal that Ln^III ions are connected by one μ₂‐phenoxo and two μ₃‐methoxo bridges, thus leading to a hexagonal bipyramidal Ln₃O₅ bridging core in which Ln^III ions exhibit a biaugmented trigonal‐prismatic geometry. Magnetic susceptibility studies and ab initio complete active space self‐consistent field (CASSCF) calculations indicate that the magnetic coupling between the Dy^III ions, which possess a high axial anisotropy in the ground state, is very weakly antiferromagnetic and mainly dipolar in nature. To reduce the electronic repulsion from the coordinating oxygen atom with the shortest Dy?O distance, the local magnetic moments are oriented almost perpendicular to the Dy₃ plane, thus leading to a paramagnetic ground state. CASSCF plus restricted active space state interaction (RASSI) calculations also show that the ground and first excited state of the Dy^III ions are separated by approximately 150 and 177 cm^?1, for Dy₃ ? [BPh₄] and Dy₃ ? 0.33[Dy(NO₃)₆], respectively. As expected for these large energy gaps, Dy₃ ? [BPh₄] and Dy₃ ? 0.33[Dy(NO₃)₆] exhibit, under zero direct‐current (dc) field, thermally activated slow relaxation of the magnetization, which overlap with a quantum tunneling relaxation process. Under an applied H_dc field of 1000 Oe, Dy₃ ? [BPh₄] exhibits two thermally activated processes with U_eff values of 34.7 and 19.5 cm^?1, whereas Dy₃ ? 0.33[Dy(NO₃)₆] shows only one activated process with U_eff=19.5 cm^?1.     

Trinuclear [CoIII2–LnIII] (Ln=Tb,Dy) Single‐Ion Magnets with Mixed 6‐Chloro‐2‐Hydroxypyridine and Schiff Base Ligands

The Schiff base ligand N1,N3‐bis(3‐methoxysalicylidene)diethylenetriamine (H₂valdien) and the co‐ligand 6‐chloro‐2‐hydroxypyridine (Hchp) were used to construct two 3d–4f heterometallic single‐ion magnets [Co₂Dy(valdien)₂(OCH₃)₂(chp)₂] ? ClO₄ ? 5 H₂O ( 1 ) and [Co₂Tb(valdien)₂(OCH₃)₂(chp)₂] ? ClO₄ ? 2 H₂O ? CH₃OH ( 2 ). The two trinuclear [Co^III₂Ln^III] complexes behave as a mononuclear Ln^III magnetic system because of the presence of two diamagnetic cobalt(III) ions. Complex 1 has a molecular symmetry center, and it crystallizes in the C2/c space group, whereas complex 2 shows a lower molecular symmetry and crystallizes in the P2₁/c space group. Magnetic investigations indicated that both complexes are field‐induced single‐ion magnets, and the Co^III₂–Dy^III complex possesses a larger energy barrier [74.1(4.2) K] than the Co^III₂–Tb^III complex [32.3(2.6) K].     

Dinuclear Dysprosium and Ytterbium Complexes Incorporating N,N‐Bis(pyrrolyl‐α‐methyl)‐N‐methylamine Ligand: Syntheses and Structures

Reaction of DyCl₃ with two equivalents of NaN(SiMe₃)₂ in THF yielded {Dy(μ‐Cl)[N(SiMe₃)₂]₂(THF)}₂ ( 1 ). X‐ray crystal structure analysis revealed that 1 is a centrosymmetric dimer with asymmetrically bridging chloride ligands. The metal coordination arrangement can be best described as distorted trigonal bipyramid. The bond lengths of Ln–Cl and Ln–N showed a decreasing trend with the contraction of the size of Ln³⁺. Treatment of N,N‐bis(pyrrolyl‐α‐methyl)‐N‐methylamine (H₂dpma) with 1 and known compound {Yb(μ‐Cl)[N(SiMe₃)₂]₂(THF)}₂, respectively, led to the formations of [Dy(μ‐Cl)(dpma)(THF)₂]₂ ( 2 ) and {Yb(μ‐Cl)[N(SiMe₃)₂]₂(THF)}₂ ( 3 ). Compounds 2 and 3 were fully characterized by single‐crystal X‐ray crystallography, elemental analysis, and ¹H NMR spectroscopy. Structure determination indicated that 2 and 3 exhibit as centrosymmetric dimers with asymmetrically bridging chloride ligands. One pot reactions involving LnCl₃ (Ln = Dy and Yb), LiN(SiMe₃)₂, and H₂dpma were explored and desired products 2 and 3 were not yielded, which indicated that 1 and {Yb(μ‐Cl)[N(SiMe₃)₂]₂(THF)}₂ are the demanding precursors to synthesize Dysprosium and Ytterbium complexes supported by dpma^2– ligand. Compounds 2 and 3 are the first reported lanthanide complexes chelated by dpma^2– ligand.     

Controlled Synthesis of Heterotrimetallic Single‐Chain Magnets from Anisotropic High‐Spin 3 d–4 f Nodes and Paramagnetic Spacers

By using the node‐and‐spacer approach in suitable solvents, four new heterotrimetallic 1D chain‐like compounds (that is, containing 3d–3d′–4f metal ions), {[Ni(L)Ln(NO₃)₂(H₂O)Fe(Tp*)(CN)₃] ? 2 CH₃CN ? CH₃OH}_n (H₂L=N,N′‐bis(3‐methoxysalicylidene)‐1,3‐diaminopropane, Tp*=hydridotris(3,5‐dimethylpyrazol‐1‐yl)borate; Ln=Gd ( 1 ), Dy ( 2 ), Tb ( 3 ), Nd ( 4 )), have been synthesized and structurally characterized. All of these compounds are made up of a neutral cyanide‐ and phenolate‐bridged heterotrimetallic chain, with a {? Fe? C?N? Ni(? O? Ln)? N?C? }_n repeat unit. Within these chains, each [(Tp*)Fe(CN)₃]^? entity binds to the Ni^II ion of the [Ni(L)Ln(NO₃)₂(H₂O)]⁺ motif through two of its three cyanide groups in a cis mode, whereas each [Ni(L)Ln(NO₃)₂(H₂O)]⁺ unit is linked to two [(Tp*)Fe(CN)₃]^? ions through the Ni^II ion in a trans mode. In the [Ni(L)Ln(NO₃)₂(H₂O)]⁺ unit, the Ni^II and Ln^III ions are bridged to one other through two phenolic oxygen atoms of the ligand (L). Compounds 1 – 4 are rare examples of 1D cyanide‐ and phenolate‐bridged 3d–3d′–4f helical chain compounds. As expected, strong ferromagnetic interactions are observed between neighboring Fe^III and Ni^II ions through a cyanide bridge and between neighboring Ni^II and Ln^III (except for Nd^III) ions through two phenolate bridges. Further magnetic studies show that all of these compounds exhibit single‐chain magnetic behavior. Compound 2 exhibits the highest effective energy barrier (58.2 K) for the reversal of magnetization in 3d/4d/5d–4f heterotrimetallic single‐chain magnets.     

The Building Block [FeIII(pzphen)(CN)4]– and its Lanthanide Complexes: Synthesis,Crystal Structure,and Magnetic Properties

The cyanide building block [Fe^III(pzphen)(CN)₄]^– and its four lanthanide complexes [{Fe^III(pzphen)(CN)₄}₂Ln^III(H₂O)₅(DMF)₃] · (NO₃) · 2(H₂O) · (CH₃CN) [Ln = Nd ( 1 ), Sm ( 2 ), DMF = dimethyl formamide] and [{Fe^III(pzphen)(CN)₄}₂Ln^III(NO₃)(H₂O)₂(DMF)₂](CH₃CN) [Ln = Gd ( 3 ), Dy ( 4 )] were synthesized and structurally characterized by single‐crystal X‐ray diffraction. Compounds 1 and 2 are ionic salts with two [Fe^III(pzphen)(CN)₄]^– cations and one Ln^III ion, but compounds 3 and 4 are cyano‐bridged Fe^III‐Ln^III heterometallic 3d‐4f complexes exhibiting a trinuclear structure in the same conditions. Magnetic studies show that compound 3 is antiferromagnetic between the central Fe^III and Gd^III atoms. Furthermore, the trinuclear cyano‐bridged Fe^III₂Dy^III compound 4 displays no single‐molecular magnets (SMMs) behavior by the alternating current magnetic susceptibility measurements.     

Five Rare μ4‐O‐Centered Ln6 Clusters with Single‐Molecule Magnet Behavior for Dy6

Five hexanuclear lanthanide clusters of composition [Ln₆(μ₄‐O)₂(HCOO)₂L₄(HL′)₂(dmf)₂] [Ln=Dy ( 1 ), Er ( 2 ), Ho ( 3 ), Tb ( 4 ), Gd ( 5 ); H₂L=2‐{[2‐(hydroxymethyl)phenylimino]methyl}‐6‐methoxyphenol; H₃L′=3‐{[2‐(hydroxymethyl)phenylimino]methyl}benzene‐1,2‐diol; H₃L′ was derived in situ from the H₂L ligand] were prepared under solvothermal conditions. The [Ln₆] cores of 1 – 5 possess an unprecedented motif, namely, two tetrahedron Ln₄ units sharing an edge and two vertices. The six Ln^III ions of 1 – 5 are connected through two μ₄‐O anions. Magnetic susceptibility studies reveal that complex 1 exhibits frequency dependence of the alternating current susceptibility typical of single‐molecule magnets. Complex 1 possesses a relatively large energy barrier of 85 K among all of the reported Dy₆ single‐molecule magnets.     

Photoluminescence Properties of Lanthanide‐Organic Frameworks (LnOFs) with Thiophene‐2,5‐Dicarboxylate and Acetate

S‐heterocyclic dicarboxylic acid, thiophene‐2,5‐dicarboxylic acid (H₂TDC), was employed to construct a series of lanthanide‐organic frameworks (LnOFs) with coligand acetate, formulated as [Ln(TDC)(OAc)(H₂O)]_n [Ln = Eu ( 1 ), Tb ( 2 ), Gd ( 3 ), Dy ( 4 ), Sm ( 5 )] under hydrothermal conditions. Structure analysis reveals that 1 – 5 have dinuclear 3D metal organic frameworks (MOFs), in which TDC^2– and OAc^– display (κ¹‐κ¹)‐(κ¹–κ¹)‐μ₄ and (κ²‐κ¹)‐μ₂ coordination fashions, respectively. The dehydrated products of all compounds show high thermal stability above 410 °C. As for 1 , 2 , 4 , and 5 , the photoluminescence analyses exhibit characteristic luminescence emission bands of the corresponding lanthanide ions in the visible region. In particular, compound 2 displays bright green luminescence in the solid state with ⁵D₄ lifetime of 0.510 ms and relative high overall quantum yield of 16 %, based on an ideal energy gap between the lowest triplet state energy level of H₂TDC ligand and the ⁵D₄ state energy level of Tb³⁺. The energy transfer mechanisms in compounds 1 and 2 were also discussed.     

Two Oxime‐Based {LnIII3NiII3} Clusters with Triangular {Ln3(μ3‐Ο2)}7+ Core: Solvothermal Syntheses,Crystal Structures,and Magnetic Properties

Two isostructural heterometallic complexes, {[Dy₃Ni₃(H₂O)₃(mpko)₉(O₂)(NO₃)₃](ClO₄) · 3CH₃OH · 3CH₃CN} ( 1 ) and {[Gd₃Ni₃(H₂O)₃(mpko)₉(O₂)(NO₃)₃](NO₃) · 10.75CH₃OH} ( 2 ) [mpkoH = 1‐(pyrazin‐2‐yl)ethanone oxime], were solvothermally synthesized by varying lanthanide ions with different magnetic anisotropy. Structural analyses revealed that both complexes contain a peroxide anion‐aggregated triangular {Ln₃(μ₃‐Ο₂)}⁷⁺ core, which is surrounded by three Ni^II octahedra through threefold oxime linkages into a heterometallic hexanuclear cluster. Apparent antiferromagnetic interactions are observed between the adjacent spin carriers of 1 and 2 with the coupling constant J_{Ln ··· Ni} ≈ 12J_{Ln ··· Ln}. Additionally, 1 with highly anisotropic Dy^III site shows slow magnetization relaxation under zero dc field and 2 constructed from isotropic Gd^III ion displays significant cryogenic magnetocaloric effect with a maximum entropy change of 24.8 J · kg^–1 · K^–1 at 3.0 K and 70 kOe.     

Synthesen und Kristallstrukturen der chalkogenidoverbrückten Nickelclusterverbindungen [Ni5Se4Cl2(PPhEt2)6], [Ni12Se12(PnPr3)6] und [Ni18S18(PiPr3)6]

Syntheses and Crystal Structures of Chalcogenido‐bridged Nickel Cluster Compounds [Ni₅Se₄Cl₂(PPhEt₂)₆], [Ni₁₂Se₁₂(PⁿPr₃)₆], and [Ni₁₈S₁₈(PⁱPr₃)₆] The reaction of (R)ESiMe₃ (R = SiMe₃, Mes = C₉H₁₁; E = S, Se) with [NiCl₂(PPhEt₂)₂] and [NiCl₂(PR₃)₂] (R = ⁿPr, ⁱPr) gives new chalcogenido‐bridged nickel cluster compounds [Ni₅Se₄Cl₂(PPhEt₂)₆]·2THF ( 1 ), [Ni₁₂Se₁₂(PⁿPr₃)₆]·2THF ( 2 ), and [Ni₁₈S₁₈(PⁱPr₃)₆]·2THF ( 3 ). The structures of these compounds were determined by single crystal X‐ray structural analyses.     

New 2p‐3d‐4f Chain Compounds [LnZn(hfac)5(NIT‐Pyrim)2] constructed from Pyrimidine based Nitronyl Nitroxides

The 1:1:2 mixture of Ln(hfac)₃, Zn(hfac)₂, and NIT‐Pyrim (hfac = hexafluoroacetylacetonate, NIT‐Pyrim = 2‐pyrimidine‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide) afforded a series of 2p‐3d‐4f magnetic chains [Ln(hfac)₃Zn(hfac)₂(NIT‐Pyrim)₂] [Ln^III = Gd ( 1 ), Ho ( 2 ), Yb ( 3 )], in which Zn(hfac)₂ and Ln(hfac)₃ units are bridged by pyrimidine substituted nitronyl nitroxides through their NO moieties and pyrimidine nitrogen atoms. These complexes represent the first examples of 2p‐3d‐4f complexes with Zn^II ions. Magnetic studies show that there exist ferromagnetic exchange couplings between the coordinated NO groups of radical ligands and the Gd^III ions.     

Studies on the nuclease activity and interactions of the mixed‐polypyridyl [Ni2(1,3‐tpbd)(diimine)2(H2O)2]4+ complexes with thioredoxin reductase

Three new nickel(II) complexes formulated as [Ni₂(1,3‐tpbd)(diimine)₂(H₂O)₂]⁴⁺ [1,3‐tpbd = N,N,N′,N′‐tetrakis(2‐pyridylmethyl)benzene‐1,3‐diamine, where diimine is an N,N‐donor heterocyclic base like 1,10‐phenanthroline (phen),2,2′‐bipyridine (bpy), 4,5‐diazafluoren‐9‐one (dafo)], have been synthesized and structurally characterized by X‐ray crystallography: [Ni₂(1,3‐tpbd)(phen)₂(H₂O)₂]⁴⁺ (1), [Ni₂(1,3‐tpbd)(bpy)₂(H₂O)₂]⁴⁺(2) and [Ni₂(1,3‐tpbd)(dafo)₂(H₂O)₂]⁴⁺ (3). Single‐crystal diffraction reveals that the metal atoms in the complexes are all in a distorted octahedral geometry and in a trans arrangement around 1,3‐tpbd ligand. The interactions of the three complexes with calf thymus DNA (CT‐DNA) have been investigated by UV absorption, fluorescence spectroscopy, circular dichroism and viscosity. The apparent binding constant (K_app) values are calculated to be 1.91 × 10⁵ m ^?1 for 1, 1.18 × 10⁵ m ^?1 for 2, and 1.35 × 10⁵ m ^?1 for 3, following the order 1 > 3 > 2. The higher DNA binding affinity of 1 is due to the involvement in partial insertion of the phen ring between the DNA base pairs. A decrease in relative viscosities of DNA upon binding to 1–3 is consistent with the DNA binding affinities. These complexes efficiently display oxidative cleavage of supercoiled DNA in the presence of H₂O₂ (250 µ m ), with 3 exhibiting the highest nuclease activity. The rate constants for the conversion of supercoiled to nicked DNA are 5.28 × 10^?5 s^?1 (for 1), 6.67 × 10^?5 s^?1 (for 2) and 1.39 × 10^?4 s^?1 (for 3), also indicating that complex 3 shows higher catalytic activity than 1 and 2. Here the nuclease activity is not readily correlated to binding affinity. The inhibitory effect of complexes 1–3 on thioredoxin reductase has also been examined. The IC₅₀ values are calculated to be 26.54 ± 0.57, 31.03 ± 3.33 and 8.69 ± 2.54 µ m , respectively, showing a more marked inhibitory effect on thioredoxin reductase by complex 3 than the other two complexes. Copyright © 2012 John Wiley & Sons, Ltd.     

Three Phenoxo‐Bridged Dinuclear Lanthanide Complexes: Syntheses,Crystal Structures,and Magnetic Properties

Three dinuclear lanthanide complexes [Ln₂(H₂L)₂(NO₃)₄] [Ln = Dy ( 1 ), Tb ( 2 ), and Gd ( 3 )] [H₃L = 2‐hydroxyimino‐N′‐[(2‐hydroxy‐3‐methoxyphenyl)methylidene]‐propanohydrazone] were solvothermally synthesized by varying differently anisotropic rare earth ions. Single‐crystal structural analyses demonstrate that all the three complexes are crystallographically isostructural with two centrosymmetric Ln^III ions aggregated by a pair of monodeprotonated H₂L^– anions. Weak intramolecular antiferromagnetic interactions with different strength were mediated by a pair of phenoxo bridges due to superexchange and/or single‐ion anisotropy. Additionally, the Dy^III‐based entity shows the strongest anisotropy exhibits field‐induced single‐molecule magnetic behavior with two thermally activated relaxation processes. In contrast, 3 with isotropic Gd^III ion has a significant cryogenic magnetocaloric effect with the maximum entropy change of 25.7 J · kg^–1 · K^–1 at 2.0 K and 70.0 kOe.     

Triphenylphosphane Oxide Complexes of Lanthanide Nitrates: Polymorphs and Photophysics

A series of mer‐[Ln(NO₃)₃(Ph₃PO)₃] complexes were prepared from Ln(NO₃)₃ · xH₂O and Ph₃PO in chloroform (Ln = La, Nd, Sm, Eu, Gd, Tb, Dy, and Er). The La and Nd complexes were 0.25 CHCl₃ solvates, whereas the others were solvent‐free. The identical reaction using Yb(NO₃)₃ · xH₂O produced the unique salt trans‐[Yb(NO₃)₂(Ph₃PO)₄][Yb(NO₃)₄(Ph₃PO)] · Et₂O. All nitrate ions in all complexes are η²‐chelating. A comparison of the various [Ln(NO₃)₃(Ph₃PO)₃] structures, including those in the literature, reveals at least four common polymorphs, each of which is represented by isomorphic structures of multiple Ln ions. Luminescence of mer‐[Ln(NO₃)₃(Ph₃PO)₃] (Ln = Y, La, Nd, Sm, Eu, Gd, Tb, and Dy), trans‐[Yb(NO₃)₂(Ph₃PO)₄][Yb(NO₃)₄(Ph₃PO)] and Ph₃PO assignments are reported. Latva's empirical rule allows for the antenna effect, in which energy is transferred from the triplet state of the Ph₃PO ligand, to occur only for Tb³⁺. Excitation via Ph₃PO results in strong green luminescence for Tb³⁺ having twice the intensity as that which results from direct excitation of the f‐f transitions.     

Reactivity of [Ni(cod)2][Al(ORF)4] towards Small Molecules and Elements

To provide a better understanding of the recently published pure metalorganic Ni^I species, [Ni(cod)₂][Al(OR^F)₄] ( 1 ) [cod = 1,5‐cyclooctadiene, R^F = C(CF₃)₃], further characterizations were performed and analyzed. Thus, the solvation of 1 in THF was examined by EPR, surprisingly disclosing the initiation of a disproportionation reaction to [Ni^II(THF)₆][Al(OR^F)₄]₂ ( 3 ) and Ni⁰. Further studies concerning the ability of 1 to activate small molecules exhibit the formation of a remarkable [Ni₃S₂(cod)₃]²⁺ cluster ( 5 ) in an oxidation reaction with S₈, while EPR measurements of the resulting product in a reaction with oxygen indicate a possible coordination of O₂. Single crystal X‐ray structures as well as spectroscopic analyses of 3 and 5 are described.     

Synthesis,Structure, and Magnetic Properties of a Series of Dinuclear Lanthanide Complexes Assembled by Acetate and a Schiff Base Ligand

Five dinuclear lanthanide complexes [Ln₂L₂(NO₃)₂(OAc)₄] · 2CH₃CN [Ln = Gd ( 1 ), Tb ( 2 ), Dy ( 3 ), Ho ( 4 ), and Er ( 5 )] [L = 2‐((2‐pyridinylmethylene)hydrazine)ethanol] were synthesized from the reactions of Ln(NO₃)₃ · 6H₂O with L and CH₃COOH in the presence of triethylamine. Their crystal structures were determined. They show similar dinuclear cores with the two lanthanide ions bridged by four acetate ligands in the μ₂‐η¹:η² and μ₂‐η¹:η¹ bridging modes. Each Ln^III ion in complexes 1 – 5 is further chelated by one L ligand and one nitrate ion, leading to the formation of a nine‐coordinated mono‐capped square antiprism arrangement. The dinuclear molecules in 1 – 5 are consolidated by hydrogen bonds and π ··· π stacking interactions to build a two‐dimensional sheet. Their magnetic properties were investigated. It revealed antiferromagnetic interactions between the Gd^III ions in 1 and ferromagnetic interactions between the Tb^III ions in 2 . The profiles of χ_mT vs. T curves of 3 – 5 reveal that the magnetic properties of 3 – 5 are probably dominated by the thermal depopulation of the Stark sublevels of Ln^III ions.     

Homoleptic Organoderivatives of High‐Valent Nickel(III)

Homoleptic perhalophenyl derivatives of divalent nickel complexes with the general formula [NBu₄]₂[Ni^II (C₆X₅)₄] [X=F ( 1 ), Cl ( 2 )] have been prepared by low‐temperature treatment of the halo‐complex precursor [NBu₄]₂[NiBr₄] with the corresponding organolithium reagent LiC₆X₅. Compounds 1 and 2 are electrochemically related by reversible one‐electron exchange processes with the corresponding organometallate(III) compounds [NBu₄][Ni^III (C₆X₅)₄] [X=F ( 3 ), Cl ( 4 )]. The potentials of the [Ni^III (C₆X₅)₄]^?/[Ni^II (C₆X₅)₄]^2? couples are +0.07 and ?0.11 V for X=F or Cl, respectively. Compounds 3 and 4 have also been prepared and isolated in good yield by chemical oxidation of 1 or 2 with bromine or the amminium salt [N(C₆H₄Br‐4)₃][SbCl₆]. The [Ni^III (C₆X₅)₄]^? species have SP‐4 structures in the salts 3 and 4 , as established by single‐crystal X‐ray diffraction methods. The [Ni^II (C₆F₅)₄]^2? ion in the parent compound 1 has also been found to exhibit a rather similar SP‐4 structure. According to their SP‐4 geometry, the Ni^III compounds (d⁷) behave as S=1/2 systems both at microscopic (EPR) and macroscopic levels (ac and dc magnetization measurements). The spin Hamiltonian parameters obtained from the analysis of the magnetic behavior of 3 and 4 within the framework of ligand field theory show that the unpaired electron is centered mainly on the metal atom, with >97 % estimated d contribution. Thermal decomposition of 3 and 4 proceeds with formation of the corresponding C₆X₅? C₆X₅ coupling compounds.