Cadmium-Inspired Self-Polymerization of {LnIIICd2} Units: Structure,Magnetic and Photoluminescent Properties of Novel Trimethylacetate 1D-Polymers (Ln = Sm,Eu, Tb,Dy, Ho,Er, Yb)

A series of heterometallic carboxylate 1D polymers of the general formula [Ln^IIICd₂(piv)₇(H₂O)₂]_n·nMeCN (Ln^III = Sm (1), Eu (2), Tb (3), Dy (4), Ho (5), Er (6), Yb (7); piv = anion of trimethylacetic acid) was synthesized and structurally characterized. The use of Cd^II instead of Zn^II under similar synthetic conditions resulted in the formation of 1D polymers, in contrast to molecular trinuclear complexes with Ln^IIIZn₂ cores. All complexes 1–7 are isostructural. The luminescent emission and excitation spectra for 2–4 have been studied, the luminescence decay kinetics for 2 and 3 was measured. Magnetic properties of the complexes 3–5 and 7 have been studied; 4 and 7 exhibited the properties of field-induced single-molecule magnets in an applied external magnetic field. Magnetic properties of 4 and 7 were modelled using results of SA-CASSCF/SO-RASSI calculations and SINGLE_ANISO procedure. Based on the analysis of the magnetization relaxation and the results of ab initio calculations, it was found that relaxation in 4 predominantly occurred by the sum of the Raman and QTM mechanisms, and by the sum of the direct and Raman mechanisms in the case of 7.     

CoLn dinuclear complexes (Ln = Gd,Tb, Dy,Ho and Er) as platforms for 1,5-dicyanamide-bridged tetranuclear Co2Ln2 complexes: A magneto-structural and theoretical study

Five acetate-diphenoxo triply-bridged Co^II-Ln^III complexes (Ln^III = Gd, Tb, Dy, Ho, Er) of formula [Co(μ-L)(μ-Ac)Ln(NO₃)₂] and two diphenoxo doubly-bridged Co^II-Ln^III complexes (Ln^III = Gd, Tb) of formula [Co(H₂O)(μ-L)Ln(NO₃)₃]·S (S = H₂O or MeOH), were prepared in one pot reaction from the compartmental ligand N,N′,N′′-trimethyl-N,N′′-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylene triamine (H₂L). The diphenoxo doubly-bridged Co^II-Ln^III complexes were used as platforms to obtain 1,5-dicyanamide-bridged tetranuclear Co^II-Ln^III complexes (Ln^III = Gd, Tb, Dy, Ho, Er). All exhibit ferromagnetic interactions between the Co^II and Ln^III ions and in the case of the Gd^III complexes, the J_CoGd were estimated to be ∼+0.7 cm⁻¹. Compound 3 exhibits slow relaxation of the magnetization.     

Systematic Investigation of Reaction‐Time Dependence of Three Series of Copper–Lanthanide/Lanthanide Coordination Polymers: Syntheses,Structures, Photoluminescence,and Magnetism

Three series of copper–lanthanide/lanthanide coordination polymers (CPs) Ln^IIICu^IICu^I(bct)₃(H₂O)₂ [Ln=La ( 1 ), Ce ( 2 ), Pr ( 3 ), Nd ( 4 ), Sm ( 5 ), Eu ( 6 ), Gd ( 7 ), Tb ( 8 ), Dy ( 9 ), Er ( 10 ), Yb ( 11 ), and Lu ( 12 ), H₂bct=2,5‐bis(carboxymethylmercapto)‐1,3,4‐thiadiazole acid], Ln^IIICu^I(bct)₂ [Ln=Ce ( 2 a ), Pr ( 3 a ), Nd ( 4 a ), Sm ( 5 a ), Eu ( 6 a ), Gd ( 7 a ), Tb ( 8 a ), Dy ( 9 a ), Er ( 10 a ), Yb ( 11 a ), and Lu ( 12 a )], and Ln^III₂(bct)₃(H₂O)₅ [Ln=La ( 1 b ), Ce ( 2 b ), Pr ( 3 b ), Nd ( 4 b ), Sm ( 5 b ), Eu ( 6 b ), Gd ( 7 b ), Tb ( 8 b ), and Dy ( 9 b )] have been successfully constructed under hydrothermal conditions by modulating the reaction time. Structural characterization has revealed that CPs 1 – 12 possess a unique one‐dimensional (1D) strip‐shaped structure containing two types of double‐helical chains and a double‐helical channel. CPs 2 a – 12 a show a three‐dimensional (3D) framework formed by Cu^I linking two types of homochiral layers with double‐helical channels. CPs 1 b – 9 b exhibit a 3D framework with single‐helical channels. CPs 6 b and 8 b display visible red and green luminescence of the Eu^III and Tb^III ions, respectively, sensitized by the bct ligand, and microsecond‐level lifetimes. CP 8 b shows a rare magnetic transition between short‐range ferromagnetic ordering at 110 K and long‐range ferromagnetic ordering below 10 K. CPs 9 a and 9 b display field‐induced single‐chain magnet (SCM) and/or single‐molecule magnet (SMM) behaviors, with U_eff values of 51.7 and 36.5 K, respectively.     

Complexes of Bifunctional DO3A-N-(α-amino)propinate Ligands with Mg(II), Ca(II), Cu(II), Zn(II), and Lanthanide(III) Ions: Thermodynamic Stability,Formation and Dissociation Kinetics,and Solution Dynamic NMR Studies

The thermodynamic, kinetic, and structural properties of Ln³⁺ complexes with the bifunctional DO3A-ACE⁴⁻ ligand and its amide derivative DO3A-BACE⁴⁻ (modelling the case where DO3A-ACE⁴⁻ ligand binds to vector molecules) have been studied in order to confirm the usefulness of the corresponding Gd³⁺ complexes as relaxation labels of targeted MRI contrast agents. The stability constants of the Mg²⁺ and Ca²⁺ complexes of DO3A-ACE⁴⁻ and DO3A-BACE⁴⁻ complexes are lower than for DOTA⁴⁻ and DO3A³⁻, while the Zn²⁺ and Cu²⁺ complexes have similar and higher stability than for DOTA⁴⁻ and DO3A³⁻ complexes. The stability constants of the Ln(DO3A-BACE)⁻ complexes increase from Ce³⁺ to Gd³⁺ but remain practically constant for the late Ln³⁺ ions (represented by Yb³⁺). The stability constants of the Ln(DO3A-ACE)⁴⁻ and Ln(DO3A-BACE)⁴⁻ complexes are several orders of magnitude lower than those of the corresponding DOTA⁴⁻ and DO3A³⁻ complexes. The formation rate of Eu(DO3A-ACE)⁻ is one order of magnitude slower than for Eu(DOTA)⁻, due to the presence of the protonated amine group, which destabilizes the protonated intermediate complex. This protonated group causes the Ln(DO3A-ACE)⁻ complexes to dissociate several orders of magnitude faster than Ln(DOTA)⁻ and its absence in the Ln(DO3A-BACE)⁻ complexes results in inertness similar to Ln(DOTA)⁻ (as judged by the rate constants of acid assisted dissociation). The ¹H NMR spectra of the diamagnetic Y(DO3A-ACE)⁻ and Y(DO3A-BACE)⁻ reflect the slow dynamics at low temperatures of the intramolecular isomerization process between the SA pair of enantiomers, R-Λ(λλλλ) and S-Δ(δδδδ). The conformation of the C_α-substituted pendant arm is different in the two complexes, where the bulky substituent is further away from the macrocyclic ring in Y(DO3A-BACE)⁻ than the amino group in Y(DO3A-ACE)⁻ to minimize steric hindrance. The temperature dependence of the spectra reflects slower ring motions than pendant arms rearrangements in both complexes. Although losing some thermodynamic stability relative to Gd(DOTA)⁻, Gd(DO3A-BACE)⁻ is still quite inert, indicating the usefulness of the bifunctional DO3A-ACE⁴⁻ in the design of GBCAs and Ln³⁺-based tags for protein structural NMR analysis.     

Triangular Ni2Ln and Ni2Y complexes derived from di-2-pyridyl ketone: Synthesis, structures and magnetic properties

The synthetic investigation of the Ni^II/M(NO₃)₃·6H₂O/di-2-pyridyl ketone [(py)₂CO] tertiary reaction system in EtOH has yielded triangular Ni₂M cationic complexes (M = lanthanide, Y). The reaction between Ln(NO₃)₃·6H₂O, Ni(ClO₄)₂·6H₂O, (py)₂CO and base (1:3:3:3) in EtOH under gentle heating gave the isostructural complexes [Ni₂Ln{(py)₂C(OEt)(O)}₃{(py)₂C(OH)(O)}(NO₃)(H₂O)](ClO₄)₂ (Ln = Gd, 2; Ln = Tb, 3) in high yields. The ligands (py)₂C(OEt)(O)⁻ and (py)₂C(OH)(O)⁻ are the monoanions of the hemiketal and gem-diol derivatives of (py)₂CO, respectively, formed in situ in the presence of the metal ions. The cations of 2 and 3 consist of one 8-coordinate Ln^III and two distorted octahedral Ni^II atoms in an essentially isosceles, triangular arrangement capped by a central μ₃-Ο⁻ atom of the unique 3.3011 (Harris notation) (py)₂C(OH)(O)⁻ ligand. Each metal-metal edge is bridged by the deprotonated O atom of one 2.2011 (py)₂C(OEt)(O)⁻ ligand. The isostructural complexes [Ni₂M{(py)₂C(OEt)(O)}₄(NO₃)(H₂O)]₂[M(NO₃)₅](ClO₄)₂ (M = Y, 4 ; M = Tb, 5 ; M = Dy, 6) were prepared by the 1:1 reaction of the mononuclear “metalloligand” [Ni(O₂CMe){(py)₂CO}{(py)₂C(OH)₂}](ClO₄) (1) and M(NO₃)₃·6H₂O in EtOH under mild heating in moderate to good yields. The structures of the dications of 4-6 are similar to those in 2 and 3, the only difference being the replacement of the unique 3.3011 (py)₂C(OH)(O)⁻ ligand of the latter by one 3.3011 (py)₂C(OEt)(O)⁻ group in the former. The Y^III, Tb^III and Dy^III atoms in [M(NO₃)₅]²⁻ are coordinated by five bidentate chelating nitrato groups. Characteristic IR bands of the complexes are discussed in terms of the known structures and the coordination modes of the ligands. Variable temperature, solid-state direct current magnetic susceptibility and magnetization studies were carried out on dried samples of 2-4. The data indicate ferromagnetic Ni?Ni and Ni?Gd exchange interactions, and an S_T = 11/2 ground state for 2. Complex 3 is characterized by a high-spin ground state while the ferromagnetic Ni?Ni interaction for 2 is independently supported by the study of 4. No out-of-phase, alternating current susceptibility signals have been detected for 3 that would be indicative of SMM behavior.     

Di- and tetranuclear heterometallic CuII-LnIII complexes (Ln = Gd and Dy): Synthesis, structure and magnetic properties

Four 3d-4f heterometallic complexes, [CuⅡ LnⅢ (bpt) 2 (NO 3 ) 3 (MeOH)] (Ln = Gd, 1; Dy, 2; bptH = 3,5-bis(pyrid-2-yl)-1,2,4- triazole), [CuⅡ 2 LnⅢ 2 (μ-OH) 2 (bpt) 4 Cl 4 (H 2 O) 2 ]·6H 2 O (Ln = Gd, 3; Dy, 4), have been synthesized under solvothermal conditions. X-ray structural analyses reveal that 1 and 2 are isostructural while 3 and 4 are isostructural. In each complex, the copper and gadolinium or dysprosium ions are linked by two triazolate bridges and form a CuⅡ -LnⅢ dinuclear unit. The intramolecular Cu-Ln distances are 4.542, 4.525, 4.545 and 4.538 for 1, 2, 3 and 4, respectively. Two dinuclear CuLn units are bridged by two OH- groups into the zig-zag tetranuclear {CuⅡ 2 LnⅢ 2 } structures with the Ln(Ⅲ) Ln(Ⅲ) distances of 3.742 and 3.684 for 3 and 4, respectively. Magnetic studies show that the antiferromagnetic CuⅡ-LnⅢ interactions occur in 1 (J CuGd = 0.21 cm-1 ) and 2. The antiferromagnetic interaction occurs in complex 3 with J CuGd = 0.82 cm-1 and J GdGd = 0.065 cm-1 , while dominant ferromagnetic interaction occurs in complex 4.     

A [Cyclentetrakis(methylene)]tetrakis[2‐hydroxybenzamide] Ligand That Complexes and Sensitizes Lanthanide(III) Ions

The synthesis of the cyclen derivative H₄ L ¹ ?2 HBr containing four 2‐hydroxybenzamide groups is described. The spectroscopic properties of the Ln^III conplexes of L ¹ (Ln=Gd, Tb, Yb, and Eu) reveal changes of the UV/VIS‐absorption, circular‐dichroism‐absorption, luminescence, and circularly polarized luminescence spectra. It is shown that at least two metal‐complex species are present in solution, whose relative amounts are pH dependent. At pH>8.0, an intense long‐lived emission is observed (for [Tb L ¹ ] and [Yb L ¹ ]), while at pH<8.0, a weaker, shorter‐lived species predominates. Unconventional Ln^III emitters (Pr, Nd, Sm, Dy, and Tm) were sensitized in basic solution, both in the VIS and in the near‐IR, to measure the emission of these ions.     

New complexes of lanthanide Ln(III), (Ln = La, Sm, Gd, Er) with Schiff bases derived from 2-furaldehyde and phenylenediamines

Some new Schiff bases derivates from 2-furaldehyde and phenylenediamines (L^1-3) and their complexes with lanthanum (La), samarium (Sm), gadolinium (Gd) and erbium (Er) have been synthesized. These complexes with general formula [Ln(L^1-3)₂(NO₃)₂]NO₃·nH₂O (Ln = La, Sm, Gd, Er) were characterized by elemental analysis, UV-Vis, FT-IR and fluorescence spectroscopy, molar conductivity and thermal analysis. The metallic ions were found to be eight coordinated. The emission spectra of these complexes indicate the typical luminescence characteristics of the Sm(III), La(III), Er(III) and Gd(III) ions.     

Decanuclear Ln10 Wheels and Vertex‐Shared Spirocyclic Ln5 Cores: Synthesis,Structure, SMM Behavior,and MCE Properties

The reaction of a Schiff base ligand (LH₃) with lanthanide salts, pivalic acid and triethylamine in 1:1:1:3 and 4:5:8:20 stoichiometric ratios results in the formation of decanuclear Ln₁₀ (Ln=Dy( 1 ), Tb( 2 ), and Gd ( 3 )) and pentanuclear Ln₅ complexes (Ln=Gd ( 4 ), Tb ( 5 ), and Dy ( 6 )), respectively. The formation of Ln₁₀ and Ln₅ complexes are fully governed by the stoichiometry of the reagents used. Detailed magnetic studies on these complexes ( 1 – 6 ) have been carried out. Complex 1 shows a SMM behavior with an effective energy barrier for the reversal of the magnetization (U_eff)=16.12(8) K and relaxation time (τ_o)=3.3×10^?5 s under 4000 Oe direct current (dc) field. Complex 6 shows the frequency dependent maxima in the out‐of‐phase signal under zero dc field, without achieving maxima above 2 K. Complexes 3 and 4 show a large magnetocaloric effect with the following characteristic values: ?ΔS_m=26.6 J kg^?1 K^?1 at T=2.2 K for 3 and ?ΔS_m=27.1 J kg^?1 K^?1 at T=2.4 K for 4 , both for an applied field change of 7 T.     

Mono and trinuclear lanthanide complexes of 13-membered tetraaza macrocycle: Synthesis and characterization

The reaction of 1,8-diamino-3,6-diazaoctane and diethyl malonate in dry methanol yielded a 13-membered macrocycle. Complexes of the type [Ln(tatd)Cl₂ (H₂O)₃]Cl [Ln^III=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy; tatd=1, 5, 8, 11-tetra-azacyclotridecane-2,4-dione] have been synthesized by template condensation. The complex [La(tatd)Cl₂ (H₂O)₃]Cl in methanol was reacted with lanthanide chlorides to yield the trinuclear complexes of type [2{La(tatd)Cl₂(H₂O)₃}LnCl₃]Cl₂ [Ln^III=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy]. The chemical compositions of mono and trinuclear complexes have been established on the basis of analytical, molar conductance, electrospray (ES) and fast atom bombardment (FAB) mass data. In mononuclear complexes the Ln³⁺ ion is encapsulated by four ring nitrogens and in trimetallic complexes the exo-carbonyl oxygens of two mononuclear units coordinate to the Ln³⁺ ions resulting in a polyhedron around the lanthanide ions. Thus the macrocycle is bonded in a tetradentate fashion in the former complexes and hexadentate in the latter. The coordination number nine around the encapsulated Ln³⁺ and seven around the exo-oxygen bonded Ln³⁺ ions are established. The symmetry of the ligand field around the metal ions is indicated from the emission spectra.     

The Series of Rare Earth Complexes [Ln2Cl6(μ‐4,4′‐bipy)(py)6], Ln=Y,Pr, Nd,Sm‐Yb: A Molecular Model System for Luminescence Properties in MOFs Based on LnCl3 and 4,4′‐Bipyridine

A series of 12 dinuclear complexes [Ln₂Cl₆(μ‐4,4′‐bipy)(py)₆], Ln=Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, ( 1 – 12 , respectively) was synthesized by an anhydrous solvothermal reaction in pyridine. The complexes contain a 4,4′‐bipyridine bridge and exhibit a coordination sphere closely related to luminescent lanthanide MOFs based on LnCl₃ and 4,4‐bipyridine. The dinuclear complexes therefore function as a molecular model system to provide a better understanding of the luminescence mechanisms in the Ln‐N‐MOFs ${\hbox{}{{\hfill 2\atop \hfill \infty }}}$ [Ln₂Cl₆(4,4′‐bipy)₃] ? 2(4,4′‐bipy). Accordingly, the luminescence properties of the complexes with Ln=Y, Sm, Eu, Gd, Tb, Dy, ( 1 , 4 – 8 ) were determined, showing an antenna effect through a ligand–metal energy transfer. The highest efficiency of luminescence is observed for the terbium‐based compound 7 displaying a high quantum yield (QY of 86 %). Excitation with UV light reveals typical emission colors of lanthanide‐dependent intra 4f–4f‐transition emissions in the visible range (Tb^III: green, Eu^III: red, Sm^III: salmon red, Dy^III: yellow). For the Gd^III‐ and Y^III‐containing compounds 6 and 1 , blue emission based on triplet phosphorescence is observed. Furthermore, ligand‐to‐metal charge‐transfer (LMCT) states, based on the interaction of Cl^? with Eu^III, were observed for the Eu^III compound 5 including energy‐transfer processes to the Eu^III ion. Altogether, the model complexes give further insights into the luminescence of the related MOFs, for example, rationalization of Ln‐independent quantum yields in the related MOFs.     

Neue Ergebnisse auf dem Gebiet der Komplexchemie der Lanthanoiden Die Strukturen von [(C11H21N2)2LnBr] (Ln = Sm,Gd)

New Results in the Chemistry of Lanthanoide Complexes. The Crystal Structures of [(C₁₁H₂₁N₂)₂LnBr] (Ln = Sm, Gd) LnBr₃ leads with [(ⁱPr₂AIP)Li] (AIP = 2-ⁱPropylamino-4-ⁱPropylimino-2-Pentene) to the mononuclear complex [(ⁱPr₂AIP)₂LnBr] (Ln = Gd 1 , Sm = 2 ). The structures of 1 – 2 were characterized by X-ray single crystal structure analysis.

• 1: Space group Cc, Z = 4, a = 1283.3(7) pm, b = 1558.6(8) pm, c = 1330.1(7) pm, β = 90.24(4)°
• 2: Space group Cc, Z = 4, a = 1281.7(2) pm, b = 1562.3(3) pm, c = 1329.8(2) pm, β = 90.09(1)°.

The Ln-Ion is coordinated by a Brom-Atom and the four Nitrogen-Atoms of the chelate ligand.     

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.     

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.     

Assessing the exchange coupling in binuclear lanthanide(iii) complexes and the slow relaxation of the magnetization in the antiferromagnetically coupled Dy2 derivative

We report here the synthesis and the investigation of the magnetic properties of a series of binuclear lanthanide complexes belonging to the metallacrown family. The isostructural complexes have a core structure with the general formula [Ga₄Ln₂(shi^3–)₄(Hshi^2–)₂(H₂shi^–)₂(C₅H₅N)₄(CH₃OH)_x(H₂O)_x]·xC₅H₅N·xCH₃OH·xH₂O (where H₃shi = salicylhydroxamic acid and Ln = Gd^III1; Tb^III2; Dy^III3; Er^III4; Y^III5; Y^III_0.9Dy^III_0.16). Apart from the Er-containing complex, all complexes exhibit an antiferromagnetic exchange coupling leading to a diamagnetic ground state. Magnetic studies, below 2 K, on a single crystal of 3 using a micro-squid array reveal an opening of the magnetic hysteresis cycle at zero field. The dynamic susceptibility studies of 3 and of the diluted DyY 6 complexes reveal the presence of two relaxation processes for 3 that are due to the excited ferromagnetic state and to the uncoupled Dy^III ions. The antiferromagnetic coupling in 3 was shown to be mainly due to an exchange mechanism, which accounts for about 2/3 of the energy gap between the antiferro- and the ferromagnetic states. The overlap integrals between the Natural Spin Orbitals (NSOs) of the mononuclear fragments, which are related to the magnitude of the antiferromagnetic exchange, are one order of magnitude larger for the Dy₂ than for the Er₂ complex.     

The synthesis, structural characterization, magnetochemistry and Mössbauer spectroscopy of [Fe3LnO2(CCl3COO)8H2O(THF)3] (Ln = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Lu and Y)

The new tetranuclear complexes [Fe₃Ln(μ₃-O)₂(CCl₃COO)₈(H₂O)(THF)₃]·THF (Ln = Ce^III (1), Pr^III (2), Nd^III (3)) and [Fe₃Ln(μ₃-O)₂(CCl₃COO)₈(H₂O)(THF)₃]·THF·C₇H₁₆ (Ln = Sm^III (4), Eu^III (5), Gd^III (6), Tb^III (7), Dy^III (8), Ho^III (9), Lu^III (10) and Y^III (11)) have been prepared. All compounds were prepared by the reaction between [Fe₂BaO(CCl₃COO)₆(THF)₆] and the corresponding Ln^III nitrate salt. The crystal structures of 1–4, 8 and 9 have been determined; these isostructural molecules have a non-planar {Fe₃Ln(μ₃-O)₂} “butterfly” core. Magnetic susceptibility measurements show dominant intramolecular antiferromagnetic exchange interactions for all the complexes. ⁵⁷Fe Mössbauer spectroscopy shows three different environments for the Fe^III metal ions, all in their high-spin state S = 5/2 (confirming that no electron transfer from Ce^III to Fe^III occurs in 1). At the time scale of the Mössbauer spectroscopy (about 10⁻⁷ s), evidence of magnetization blocking, i.e. slow relaxation of the magnetization, is observed below 3 K for 7, which was confirmed by ac susceptibility measurements.     

RuII and RuIII Chloronitrile Complexes: Synthesis,Reaction Chemistry,Solid State Structure,and (Spectro)Electrochemical Behavior

The synthesis of [Ti₆O₄(OiPr)₈(O₂CPh)₈] ( 3 ) and [RuCl(N≡CR)₅][RuCl₄(N≡CR)₂] ( 4a , R = Me; 4b , R = Ph), [Ru(N≡CPh)₆][RuCl₄(N≡CPh)₂] ( 5 ) and [H₃O][RuCl₄(N≡CMe)₂] ( 7a ) is discussed. Crystallization of 5 from CH₂Cl₂ gave trans-[RuCl₂(N≡CPh)₄] ( 6 ). The solid-state structures of 3 , 4a , b , 5 , 6 and 7a are reported. Complex 4b forms a 3D network, while 6 displays a 2D structure, due to π-interactions between the benzonitrile ligands. The (spectro)electrochemical behavior of 4a , b and 6 was studied at 25 and –72 °C and the results thereof are compared with [NEt₄][RuCl₄(N≡CMe)₂] ( 7b ) and [RuCl(N≡CPh)₅][PF₆] ( 8 ). The electrochemical response of the cation and the anion in 4a , b are independent from each other. [RuCl(N≡CR)₅]⁺ possesses one reversible Ru^II/Ru^III process. However, [RuCl₄(N≡CMe)₂]^– was shown to be prone to ligand exchange and disproportionation upon formation of either a Ru^IV and Ru^II species at 25 °C, while at –72 °C the rapid conversion of the electrochemically formed species is hindered. In situ IR and UV/Vis/NIR studies confirmed the respective disproportionation reaction products of the aforementioned oxidation and reduction, respectively.     

Mononuclear Fe(III) and tetranuclear [Fe(III)Gd(III)]2 complexes with a Schiff-base ligand derived from the o-vanillin: Synthesis, crystal structures and magnetic properties

The mononuclear high-spin iron(III) complexes [Fe(3-MeOsalpn)Cl(H₂O)] (1) and [Fe(3-MeOsalpn)(NCS)(H₂O)]·0.5CH₃CN (2) and the tetranuclear oxo-bridged compound [{Fe(3-MeOsalpn)Gd(NO₃)₃}₂(μ-O)]·CH₃CN (3) [3-MeOsalpn²⁻ = N,N′-propylenebis(3-methoxysalicylideneiminate)] have been prepared and magneto-structurally characterised. The iron(III) ion in 1 and 2 is six-coordinated in a somewhat distorted octahedral surrounding with the two phenolate-oxygens and two imine-nitrogens from the Schiff-base building the equatorial plane and a water (1 and 2) and a chloro (1)/thiocyanate-nitrogen (2) in the axial positions. The neutral mononuclear units of 1 and 2 are assembled into centrosymmetric dinuclear motifs through hydrogen bonds between the axially coordinated water molecule of one iron centre and methoxy-oxygen atoms from the Schiff-base of the adjacent iron atom. The values of the intradimer metal-metal distance within the supramolecular dimers are 4.930 (1) and 4.878 Å (2). The tetranuclear of 3 can be described as two {Fe^III(3-MeOsalpn)} units connected through an oxo-bridge, each one hosting a [Gd^III(NO₃)₃] entity in the outer cavity defined by the two phenolate- and two methoxy-oxygen atoms. The values of the intramolecular Fe?Fe and Fe?Gd distances in 3 are 3.502 and 3.606 Å, respectively. The analysis of the magnetic data of 1-3 in the temperature range 1.9-300 K shows the occurrence of weak intermolecular antiferromagnetic interactions in 1 and 2 [J = −0.76 (1) and −0.75 cm⁻¹ (2) with the Hamiltonian defined as H = −JS_Fe1·S_Fe1] whereas two intramolecular antiferromagnetic interactions coexist in 3, one very strong between the two iron(III) ions (J₁) through the oxo bridge and the other much weaker between the iron(III) and the Gd(III) ions (J₂) across the double phenoxo oxygens [J₁ = −275 cm⁻¹ and J₂ = −3.25 cm⁻¹, the Hamiltonian being defined as H=-J₁S_Fe1·S_Fe1^′-J₂(S_Fe1·S_Gd1+S_Fe1^′·S_Gd1^′)]. These values are analysed in the light of the structural data and compared with those of related systems.     

Self-Assembly of Antiferromagnetically-Coupled Copper(II) Supramolecular Architectures with Diverse Structural Complexities

The self-assembly of 2,6-diformyl-4-methylphenol (DFMP) and 1-amino-2-propanol (AP)/2-amino-1,3-propanediol (APD) in the presence of copper(II) ions results in the formation of six new supramolecular architectures containing two versatile double Schiff base ligands (H₃L and H₅L1) with one-, two-, or three-dimensional structures involving diverse nuclearities: tetranuclear [Cu₄(HL²⁻)₂(N₃)₄]·4CH₃OH·56H₂O (1) and [Cu₄(L³⁻)₂(OH)₂(H₂O)₂] (2), dinuclear [Cu₂(H₃L1²⁻)(N₃)(H₂O)(NO₃)] (3), polynuclear {[Cu₂(H₃L1²⁻)(H₂O)(BF₄)(N₃)]·H₂O}_n (4), heptanuclear [Cu₇(H₃L1²⁻)₂(O)₂(C₆H₅CO₂)₆]·6CH₃OH·44H₂O (5), and decanuclear [Cu₁₀(H₃L1²⁻)₄(O)₂(OH)₂(C₆H₅CO₂)₄] (C₆H₅CO₂)₂·20H₂O (6). X-ray studies have revealed that the basic building block in 1, 3, and 4 is comprised of two copper centers bridged through one μ-phenolate oxygen atom from HL²⁻ or H₃L1²⁻, and one μ-1,1-azido (N₃⁻) ion and in 2, 5, and 6 by μ-phenoxide oxygen of L³⁻ or H₃L1²⁻ and μ-O²⁻ or μ₃-O²⁻ ions. H-bonding involving coordinated/uncoordinated hydroxy groups of the ligands generates fascinating supramolecular architectures with 1D-single chains (1 and 6), 2D-sheets (3), and 3D-structures (4). In 5, benzoate ions display four different coordination modes, which, in our opinion, is unprecedented and constitutes a new discovery. In 1, 3, and 5, Cu(II) ions in [Cu₂] units are antiferromagnetically coupled, with J ranging from −177 to −278 cm⁻¹.     

Synthesis, structure, and magnetic properties of heterometallic trinuclear complexes {MII��LnIII��MII} (MII = Ni, Cu; LnIII = La, Pr, Sm, Eu, Gd)

Trinuclear heterometallic complexes containing the {M₂Ln(Piv)₆(NO₃)} (M^II = Ni, Cu; Ln^III = Nd, Pr, Sm, Eu, Gd; Piv^? is the anion of pivalic acid) and {Cu₂Ln(Piv)₈)]^? (Ln^III = Eu, Gd) metal cores were synthesized, their structures and magnetic properties were studied. For the most compounds, it was shown that their magnetic properties can be interpreted taking no interaction of the 3d-metal ions and a lanthanide into account. Ferromagnetic exchange interactions were found to exist between the unpaired electrons of the paramagnetic centers in the exchange clusters of the gadolinium-containing heterometallic complexes {M-Gd-M} (M = Ni or Cu).