Density functional theory study of the magnetic properties of rare earth complexes: the magnetic coupling mechanism in YIII and GdIII complexes with nitronyl nitroxide

The magnetic coupling interactions of the nitronyl nitroxide radicals bound to diamagnetic (Y^III) and paramagnetic (Gd^III) rare earth ions in two model magnetic systems based on novel rare earth organic radical complexes Ln(hfac)₃(NITPhOCH₃)₂ (Ln = Y^III 1, Gd^III 2; hafc = hexafluoroacetylacetonate; NITPhOCH₃ = 4′-methoxyo-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) have been investigated by density functional theory (DFT). The magnetic coupling mechanisms were also explored from the viewpoint of molecular orbital and spin density populations. DFT calculations show that the empty 4d-orbitals of Y^III and 5d-orbitals of Gd^III play an important role in the antiferromagnetic coupling between the two nitronyl nitroxide radical ligands, and that the ferromagnetic coupling between the Gd^III ion and the radical magnetic centers can be attributed to the nearly complete localization of the isotropic 4f-shell and singly occupied magnetic orbital (Π^*) of the nitronyl nitroxide.     

Two tri-spin complexes based on gadolinium and nitronyl nitroxide radicals: Structure and ferromagnetic interactions

Three Radical-Ln(III)-Radical complexes based on nitronyl nitroxide radicals have been synthesized, structurally and magnetically characterized: [Gd(hfac)₃(NITPhOEt)₂] (1) (hfac=hexafluoroacetylacetonate, and NITPhOEt=4′-ethoxy-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide), [Gd(hfac)₃(NITPhOCH₂Ph)₂] (2) (NITPhOCH₂Ph=4′-benzyloxy-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) and [Lu(hfac)₃(NITPhOCH₂Ph)₂] (3). The X-ray crystal structure analyses show that the structures of the three compounds are similar and all consist of the isolated molecules, in which central ions Gd^III or Lu^III are coordinated by six oxygen atoms from three hfac and two oxygen atoms from nitronyl radicals. The magnetic studies show that in both of the two Gd^III complexes, there are ferromagnetic Gd^III-Rad interactions and antiferro-magnetic Rad-Rad interactions in the molecules (with J_Rad−Gd=0.27 cm⁻¹, j_Rad-Rad=−2.97 cm⁻¹ for 1: and J_Rad−Gd=0.62 cm⁻¹, j_Rad-Rad=−7.01 cm⁻¹ for 2). An analogous complex of [Lu(hfac)₃ (NITPhOCH₂Ph)₂] (3) containing diamagnetic Lu^III ions has also been introduced for further demonstrating the nature of magnetic coupling between radicals.     

Syntheses,Structures, and Properties of Two New Tri‐spin Lanthanide‐Nitronyl Nitroxide (LnIII = GdIII and HoIII) Complexes

Abstract. Two radical–Ln^III–radical complexes, [Ln(hfac)₃(NITPh‐Ph)₂] [Ln = Gd ( 1 ) and Ho ( 2 ), hfac = hexafluoroacetylacetonate; and NITPh‐Ph = 4′‐biphenyl‐4, 4, 5, 5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide] were synthesized and characterized by X‐ray diffraction, elemental analysis, magnetic measurements, as well as IR and UV/Vis spectroscopy. X‐ray crystal structure analysis revealed that the structures of both complexes are isomorphous, the central Ln^III ions are coordinated by six oxygen atoms from three hfac ligand molecules and two oxygen atoms from nitronyl radicals. The temperature dependencies of the magnetic susceptibilities were studied. They showed that in the Gd^III complex, ferromagnetic interactions between Gd^III and the radicals and antiferromagnetic interactions between the radicals coexist in this system (with J_Rad–Gd = 0.1 cm^–1, J_Rad–Rad = –0.309 cm^–1).     

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.     

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.     

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.     

Synthesis,Crystal Structure,and Magnetic Property of New Trispin Ln(III)‐Nitronyl Nitroxide Complexes

Four Ln(III) complexes based on a new nitronyl nitroxide radical have been synthesized and structurally characterized: {Ln(hfac)₃[NITPh(MeO)₂]₂} (Ln = Eu( 1 ), Gd( 2 ), Tb( 3 ), Dy( 4 ); NITPh(MeO)₂ = 2‐(3′,4′‐dimethoxyphenyl)‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide; hfac = hexafluoroacetylacetonate). The single‐crystal X‐ray diffraction analysis shows that these complexes have similar mononuclear trispin structures, in which central Ln(III) ion is eight‐coordinated by two O‐atoms from two nitroxide groups and six O‐atoms from three hfac anions. The variable temperature magnetic susceptibility study reveals that there exist ferromagnetic interactions between Gd(III) and the radicals, and antiferromagnetic interactions between two radicals (J_Gd‐Rad = 3.40 cm^?1, J_Rad‐Rad = ?9.99 cm^?1) in complex 2 . Meanwhile, antiferromagnetic interactions are estimated between Eu(III) (or Dy(III)) and radicals in complexes 1 and 4 , and ferromagnetic interaction between Tb(III) and radicals in complex 3 , respectively.     

Structure and Magnetic Investigation of a Series of Rare Earth Heterospin Monometallic Compounds of Nitronyl Nitroxide Radical

Five rare earth heterospin complexes [Ln(hfac)₃(NITptBuPh)₂], [Ln^III = Eu ( 1 ), Tb ( 2 ), Dy ( 3 ), Ho ( 4 ), Er ( 5 )] (hfac = hexafluoroacetylacetonate), were synthesized with the radical ligand NITptBuPh [2‐(4′‐tert‐butylphenyl)‐4, 4,5, 5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide]. These complexes exhibit similar structures. All of them crystallize in the monoclinic space group P2₁/c, and consist of discrete mononuclear molecules. The central Ln^III ion is eight‐coordinate with a distorted dodecahedral environment. The NITptBuPh radical acts as monodentate ligand towards Ln^III ion through the NO group. The magnetic studies suggested weak antiferromagnetic interactions between Ln^III ion and radicals in 1 , 3 , 4 , and 5 , but weak ferromagnetic interaction in 2 .     

Exchange coupling and magnetic anisotropy in a family of bipyrimidyl radical‐bridged dilanthanide complexes: Density functional theory and ab initio calculations

The origin of the magnetic anisotropy energy barriers in a series of bpym^? (bpym = 2,2′‐bipyrimidine) radical‐bridged dilanthanide complexes [(Cp*₂Ln)₂(μ‐bpym)]⁺ [Cp* = pentamethylcyclopentadienyl; Ln = Gd^III ( 1 ), Tb^III ( 2 ), Dy^III ( 3 ), Ho^III ( 4 ), Er^III ( 5 )] has been explored using density functional theory (DFT) and ab initio methods. DFT calculations show that the exchange coupling between the two lanthanide ions for each complex is very weak, but the antiferromagnetic Ln‐bpym^? couplings are strong. Ab initio calculations show that the effective energy barrier of 2 or 3 mainly comes from the contribution of a single Tb^III or Dy^III fragment, which is only about one third of a single Ln energy barrier. For 4 or 5 , however, both of the two Ho^III or Er^III fragments contribute to the total energy barrier. Thus, it is insufficient to only increase the magnetic anisotropy energy barrier of a single Ln ion, while enhancing the Ln‐bpym^? couplings is also very important. © 2014 Wiley Periodicals, Inc.     

Four tri-spin lanthanide–nitronyl nitroxide (LnIII = GdIII,DyIII, ErIII,and HoIII) complexes: syntheses,structures, and magnetic properties

Four radical–Ln(III)–radical complexes, [Ln(hfac)₃(NITPhSCH₃)₂] (Ln?=?Gd (1), Dy (2), Er (3), Ho (4); hfac?=?hexafluoroacetylacetonate; NITPhSCH₃?=?4′-thiomethylphenyl-4,4,5,5tetramethyl-imidazoline-1-oxyl-3-oxide), have been synthesized, and structurally and magnetically characterized. The X-ray crystal structures show that the structures of the four complexes are similar, consisting of isolated molecules in which Ln(III) ions are coordinated by six oxygen atoms from three hfac and two oxygen atoms from nitronyl radicals. The temperature dependencies of magnetic susceptibilities for the four complexes show that in the Gd(III) complex, ferromagnetic interactions between Gd(III)–radical and antiferromagnetic interactions between the radicals coexist with J _Rad–Gd?=?1.09?cm^?1, J _Rad–Rad?=??1.85?cm^?1.     

Structural and Magnetic Studies on Nickel(II) and Cobalt(II) Complexes with Polychlorinated Diphenyl(4-pyridyl)methyl Radical Ligands

New magnetic metal complexes with organic radical ligands, [M(hfac)₂(PyBTM)₂] (M = Ni^II, Co^II; hfac = hexafluoroacetylacetonato, PyBTM = (3,5-dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical), were prepared and their crystal structures, magnetic properties, and electronic structures were investigated. Metal ions in [M(hfac)₂(PyBTM)₂] constructed distorted octahedral coordination geometry, where the two PyBTM molecules ligated in the trans configuration. Magnetic investigation using a SQUID magnetometer revealed that χT increased with decreasing temperature from 300 K in the two complexes, indicating an efficient intramolecular ferromagnetic exchange interaction taking place between the spins on PyBTM and M with J/k_B of 21.8 K and 11.8 K for [Ni^II(hfac)₂(PyBTM)₂] and [Co^II(hfac)₂(PyBTM)₂]. The intramolecular ferromagnetic couplings in the two complexes could be explained by density functional theory calculations, and would be attributed to a nearly orthogonal relationship between the spin orbitals on PyBTM and the metal ions. These results demonstrate that pyridyl-containing triarylmethyl radicals are key building blocks for magnetic molecular materials with controllable/predictable magnetic interactions.     

Assisted Self-Assembly to Target Heterometallic Mn-Nd and Mn-Sm SMMs: Synthesis and Magnetic Characterisation of [Mn7Ln3(O)4(OH)4(mdea)3(piv)9(NO3)3] (Ln=Nd,Sm, Eu,Gd)**

In an assisted self-assembly approach starting from the [Mn₆O₂(piv)₁₀(4-Me-py)₂(pivH)₂] cluster a family of Mn−Ln compounds (Ln=Pr−Yb) was synthesised. The reaction of [Mn₆O₂(piv)₁₀(4-Me-py)₂(pivH)₂] ( 1 ) with N-methyldiethanolamine (mdeaH₂) and Ln(NO₃)₃ ⋅ 6H₂O in MeCN generally yields two main structure types: for Ln=Tb−Yb a previously reported Mn₅Ln₄ motif is obtained, whereas for Ln=Pr−Eu a series of Mn₇Ln₃ clusters is obtained. Within this series the Gd^III analogue represents a special case because it shows both structural types as well as a third Mn₂Ln₂ inverse butterfly motif. Variation in reaction conditions allows access to different structure types across the whole series. This prompts further studies into the reaction mechanism of this cluster assisted self-assembly approach. For the Mn₇Ln₃ analogues reported here variable-temperature magnetic susceptibility measurements suggest that antiferromagnetic interactions between the spin carriers are dominant. Compounds incorporating Ln=Nd^III( 2 ), Sm^III( 3 ) and Gd^III ( 5 ) display SMM behaviour. The slow relaxation of the magnetisation for these compounds was confirmed by ac measurements above 1.8 K.     

N‐Heterocyclic Tridentate Aromatic Ligands Bound to [Ln(hexafluoroacetylacetonate)3] Units: Thermodynamic,Structural, and Luminescent Properties

Herein, we discuss how, why, and when cascade complexation reactions produce stable, mononuclear, luminescent ternary complexes, by considering the binding of hexafluoroacetylacetonate anions (hfac^?) and neutral, semi‐rigid, tridentate 2,6‐bis(benzimidazol‐2‐yl)pyridine ligands ( Lk ) to trivalent lanthanide atoms (Ln^III). The solid‐state structures of [Ln( Lk )(hfac)₃] (Ln=La, Eu, Lu) showed that [Ln(hfac)₃] behaved as a neutral six‐coordinate lanthanide carrier with remarkable properties: 1) the strong cohesion between the trivalent cation and the didentate hfac anions prevented salt dissociation; 2) the electron‐withdrawing trifluoromethyl substituents limited charge‐neutralization and favored cascade complexation with Lk ; 3) nine‐coordination was preserved for [Ln( Lk )(hfac)₃] for the complete lanthanide series, whilst a counterintuitive trend showed that the complexes formed with the smaller lanthanide elements were destabilized. Thermodynamic and NMR spectroscopic studies in solution confirmed that these characteristics were retained for solvated molecules, but the operation of concerted anion/ligand transfers with the larger cations induced subtle structural variations. Combined with the strong red photoluminescence of [Eu( Lk )(hfac)₃], the ternary system Ln^III/hfac^?/ Lk is a promising candidate for the planned metal‐loading of preformed multi‐tridentate polymers.     

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.     

Magnetic Relaxation Dynamics of a Binuclear Diluted Er(III)/Y(III) Compound Influenced by Lattice Solvent

It is crucial to investigate the slow relaxation mechanisms of binuclear Er^III‐based single‐molecule magnets (SMMs) and explore strategies for optimizing their magnetic properties. Herein, a doped compound, [Y_1.75Er_0.25(thd)₄Pc] ? 2C₆H₆ ( YEr ? 2C₆H₆ , Hthd=2,2,6,6‐tetramethylheptanedione, H₂Pc=phthalocyanine), was synthesized by doping the paramagnetic erbium(III) compound Er₂ ? 2C₆H₆ in the diamagnetic yttrium(III) matrix Y₂ ? 2C₆H₆ . The doping effect was studied using SQUID magnetization measurements. The results suggest that magnetic‐site dilution improves the magnetic property from a fast relaxation of the pure Er^III compound to a typical SMM relaxation process of the doped sample. In this binuclear system, the dominant single‐ion relaxation is entangled with the neighboring Er^III ion through the intramolecular Er^III???Er^III interaction, which plays an important role in suppressing the quantum tunneling of the magnetization (QTM) process. Furthermore, the influence of lattice solvents on single‐ion relaxation was studied. By releasing the benzene molecules, compound YEr ? 2C₆H₆ can be successfully transformed to a desolvated sample YEr accompanied by structural alteration and improved SMM performance.     

Synthesis and photophysical properties of Ir<Superscript>III</Superscript>-Ln<Superscript>III</Superscript> (Ln = Nd,Yb, Er) bimetallic complexes containing bipyrimidines as bridging ligands

Bipyrimidines have been chosen as (N∧N)(N∧N) bridging ligands for connecting metal centers. Ir^III-Ln^III (Ln = Nd, Yb, Er) bimetallic complexes [Ir(dfppy)₂(μ-bpm)Ln(TTA)₃]Cl were synthesized by using Ir(dfppy)₂(bpm)Cl as the ligand coordinating to lanthanide complexes Ln(TTA)₃·2H₂O. The stability constants between Ir(dfppy)₂(bpm)Cl and lanthanide ions were measured by fluorescence titration. The obvious quenching of visible emission from Ir^III complex in the Ir^III-Ln^III (Ln = Nd, Yb, Er) bimetallic complexes indicates that energy transfer occurred from Ir^III center to lanthanides. NIR emissions from Nd^III, Yb^III, and Er^III were obtained under the excitation of visible light by selective excitation of the Ir^III-based chromophore. It was proven that Ir(dfppy)₂(bpm)Cl as the ligand could effectively sensitize NIR emission from Nd^III, Yb^III, and Er^III.     

Magnetic Blocking from Exchange Interactions: Slow Relaxation of the Magnetization and Hysteresis Loop Observed in a Dysprosium–Nitronyl Nitroxide Chain Compound with an Antiferromagnetic Ground State

The combination of the anisotropic Dy^III ion and organic radicals as spin carriers results in discrete and one‐dimensional lanthanide–radical magnetic materials, namely, [Dy(hfac)₃(NITThienPh)₂] ( 1 ) and [Dy₂(hfac)₆(NITThienPh)₂]_n ( 2 ; hfac=hexafluoroacetylacetonate, NITThienPh=2‐(5‐phenyl‐2‐thienyl)‐4,4,5,5‐tetramethyl‐imidazoline‐1‐oxyl‐3‐oxide). Linking monomeric 1 with the Dy^III ion leads to the formation of polymeric 2 , and the transformation between them is chemically controllable and reversible. The characterization of both static and dynamic magnetic properties shows that the dominant intrachain exchange interaction is important to observe magnetic bistability in 2 rather than that in 1 . Monomeric 1 exhibits paramagnetic behavior, whereas polymeric 2 shows the unusual coexistence of superparamagnetic and two‐step field‐induced metamagnetic behaviors. The antiferromagnetic ground state of 2 does not prevent the dynamic relaxation of the magnetization with the finite‐sized effect in the lanthanide–radical system. Energy barriers to thermally activated relaxation for 2 are 53 and 98 K in the low‐ and high‐temperature regimes, respectively. A hysteresis loop is observed with the coercive field of 99 Oe at 2 K.     

A new series of lanthanoid containing Keggin-type germanotungstates with acetate chelators: [{Ln(CH3COO)GeW11O39(H2O)}2] {Ln=Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb}

A series of head-on complexes of lanthanoid containing germanotungstates was isolated from a one pot reaction in an acetate buffer at pH 4.5. This convenient approach brought forward the [{Ln(CH₃COO)GeW₁₁O₃₉(H₂O)}₂]¹²⁻ (Ln=Eu^III, Gd^III, Tb^III, Dy^III, Ho^III, Er^III, Tm^III, and Yb^III) family with acetate chelators in the rarely observed μ₂: η²-η¹ mode. All compounds were structurally characterized using various solid state analytics, such as single crystal X-ray diffraction, FT-IR spectroscopy, and thermogravimetric analysis. The isostructural polyanions crystallize in the monoclinic system (S.G. P2₁/c). Temperature-dependent magnetic susceptibility measurements were performed on the Gd^III-complex which exhibits near perfect Curie-type behavior.     

Exchange interactions in trinuclear multispin complexes [Fe 2III MIIO(p-NitPhCOO)6]?MeCN (M = Co, Ni, p-NitPhCOO- = p-benzoatenitronyl nitroxide radical)

The temperature dependences of the magnetic susceptibilities for the complexes [Fe₂^III M^IIO(p-NitPhCOO)₆]∙MeCN (M = Co, Ni, p-NitPhCOO^–= p-benzoatenitronyl nitroxide radical, MeCN = acetonitrile) revealed the existence of antiferromagnetic exchange coupling among the metal ions in the trinuclear units, as well as between these units and the free radicals in the crystal lattices of the complexes.     

A linear Cu-Gd-Cu-Gd complex derived from the assembly reaction of [NaCuH3L] and [Gd(thd)3(H2O)2] (H3L = meso-1,2-diphenyl-1-(2-oxybenzamido)-2-(2-oxy-3-ethoxybenzylideneamino)ethane and Hthd = 2,2,6,6-tetra-methyl-3,5-heptanedione)

A linear tetranuclear Cu^II-Gd^III-Cu^II-Gd^III complex [Cu^IIL^dpen(meso)Gd^III(thd)₂(H₂O)]₂ was synthesized from the reaction of [NaCu^IIL^dpen(meso)(DMF)] with [Gd^III(thd)₃(H₂O)₂], and the structures and magnetic properties were investigated, where H₃L^dpen(meso) = meso-1,2-diphenyl-1-(2-hydroxybenzamido)-2-(2-hydroxy-3-ethoxybenzylideneamino)ethane and Hthd = 2,2,6,6-tetramethyl-3,5-heptanedione. The Cu^II complex component [NaCu^IIL^dpen(meso)(DMF)] has a one-dimensional (1D) chain structure, in which the Na⁺ ion is coordinated by two phenoxo and an ethoxy oxygen atoms of a Cu^II complex and an amido oxygen atom of the adjacent Cu^II unit to produce the 1D structure, in which the diphenylethylenediamine moieties have the array of {(1R,2S)-Na-(1S,2R)}_1∞. The assembly reaction of the Cu^II and Gd^III components gave a linear complex with the array of Cu(1)-Gd(1)-Cu(2)-Gd(2), in which two diphenylethylenediamine moieties have the same chirality of (1R,2S)-(1R,2S) or (1S,2R)-(1S,2R). Two linear Cu(1)-Gd(1)-Cu(2)-Gd(2) units are linked by hydrogen bonds through two water molecules to give a cyclic structure with a center of symmetry. The temperature dependence of the magnetic susceptibilities and field-dependent magnetization revealed the ferromagnetic interaction between the Cu^II and Gd^III ions within the linear chain.