Synthesis,Structures, and Single‐Molecule Magnetic Properties of Three Dy2 Complexes

To explore the influences of the subtle structural variations in the ligand backbones on the single‐molecule magnetic properties of dinuclear dysprosium(III) complexes, three ligands—H₂L₁ (H₂L₁=N₁,N₃‐bis(salicylaldehyde)diethylenetriamine), H₂L₂ (H₂L₂=N₁,N₃‐bis(3‐methoxysalicylidene)diethylenetriamine), and H₂L₃ (H₂L₃=N₁,N₃‐bis(5‐chlorosalicyladehyde)diethylenetriamine)—were synthesized and employed to prepare the expected dinuclear dysprosium(III) complexes. The three ligands differ in terms of the substituents at the benzene rings of the salicylaldehyde moieties. The reactions of Dy(NO₃)₃ ? 6 H₂O, pivalic acid, and the ligands H₂L₁, H₂L₂, and H₂L₃ generated complexes with the formulae [Dy₂(L₁)₂(piv)₂] ( 1 ), [Dy₂(L₂)₂(piv)₂] ( 2 ), and [Dy₂(L₃)₂(piv)₂] ? 2 MeCN ( 3 ), respectively. The purposeful attachment of the functional groups with varied sizes at the benzene rings of the salicylaldehyde backbones resulted in slight differences in the Dy‐O‐Dy bond angles and the Dy ??? Dy bond lengths in 1 – 3 ; consequently, the three complexes exhibited distinct magnetic properties. They all showed slow magnetization relaxation with energy barriers of 40.32 ( 1 ), 31.67 ( 2 ), and 33.53 K ( 3 ). Complete active space self‐consistent field (CASSCF) calculations were performed on complexes 1 – 3 to rationalize the slight discrepancy observed in the magnetic behavior. The calculated results satisfactorily explained the experimental outcomes.     

Zinc(II) and Nickel(II) Complexes Based on Schiff Base Ligands: Synthesis,Crystal Structure,Luminescent and Magnetic Properties

Three new phenolate oxygen bridged transition metal complexes [Zn₃(HL¹)₃(μ₃‐CH₃O)]·(ClO₄)₂(H₂O)₃ ( 1 ), [Ni₂(HL¹)₂(μ_1,1‐N₃)(o‐vanillin)]·H₂O ( 2 ), [Ni₃(HL²)₂(PhCOO)₂(PhCOOH)₂(EtOH)₂] ( 3 ) have been synthesized by metal ions and potentially multidentate Schiff base ligands (H₂L¹ = 2‐((1‐hydroxy‐2‐methylpropan‐2‐ylimino) methyl)‐6‐methoxyphenol; H₃L² = (E)‐1‐((2‐hydroxy‐3‐methoxy‐benzylidene)amino)ethane‐1,2‐diol). All the three complexes 1 , 2 , and 3 have been characterized by elemental analysis, FT‐IR spectroscopy, and single‐crystal X‐ray diffraction studies. Crystal structures reveal that complex 1 is a trinuclear incomplete cubane‐like zinc cluster whereas complex 2 is a dinuclear nickel complex bridged by azide, and compound 3 is a trinuclear nickel complex. The luminescent property for complex 1 and magnetic behaviors for complexes 2 and 3 have been investigated.     

A New Family of Trinuclear Nickel(II) Complexes as Single‐Molecule Magnets

Three new trinuclear nickel (II) complexes with the general composition [Ni₃L₃(OH)(X)](ClO₄) have been prepared in which X=Cl^? ( 1 ), OCN^? ( 2 ), or N₃^? ( 3 ) and HL is the tridentate N,N,O donor Schiff base ligand 2‐[(3‐dimethylaminopropylimino)methyl]phenol. Single‐crystal structural analyses revealed that all three complexes have a similar Ni₃ core motif with three different types of bridging, namely phenoxido (μ₂ and μ₃), hydroxido (μ₃), and μ₂‐Cl ( 1 ), μ_1,1‐NCO ( 2 ), or μ_1,1‐N₃ ( 3 ). The nickel(II) ions adopt a compressed octahedron geometry. Single‐crystal magnetization measurements on complex 1 revealed that the pseudo‐three‐fold axis of Ni₃ corresponds to a magnetic easy axis, being consistent with the magnetic anisotropy expected from the coordination structure of each nickel ion. Temperature‐dependent magnetic measurements indicated ferromagnetic coupling leading to an S=3 ground state with 2J/k=17, 17, and 28 K for 1 , 2 , and 3 , respectively, with the nickel atoms in an approximate equilateral triangle. The high‐frequency EPR spectra in combination with spin Hamiltonian simulations that include zero‐field splitting parameters D_Ni/k=?5, ?4, and ?4 K for 1 , 2 , and 3 , respectively, reproduced the EPR spectra well after a anisotropic exchange term was introduced. Anisotropic exchange was identified as D_i,j/k=?0.9, ?0.8, and ?0.8 K for 1 , 2 , and 3 , respectively, whereas no evidence of single‐ion rhombic anisotropy was observed spectroscopically. Slow relaxation of the magnetization at low temperatures is evident from the frequency‐dependence of the out‐of‐phase ac susceptibilities. Pulsed‐field magnetization recorded at 0.5 K shows clear steps in the hysteresis loop at 0.5–1 T, which has been assigned to quantum tunneling, and is characteristic of single‐molecule magnets.     

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.     

Chelation of CeIII and PrIII by N,N′‐Bis(pyridoxylideneiminato)ethylene,a Schiff Base Ligand Derived from Vitamin B6: Synthesis,Structural Features and TGA Evaluations of [M(Hpyr2en)(pyr2en)]·nH2O (M = CeIII,n = 2; PrIII,n = 8)

The neutral Schiff base N,N′‐bis(pyridoxylideneiminato)ethylene (H₂pyr₂en) reacts with CeCl₃ · 4H₂O and PrCl₃ · 4H₂O to give [Ce(Hpyr₂en)(pyr₂en)] · 2H₂O ( 1 ) and [Pr(Hpyr₂en)‐(pyr₂en)] · 8H₂O ( 2 ). In the two bimolecular chelate systems, the endo hydroxyl groups of the rings undergo deprotonation by transferring one proton to the pyridinic nitrogen atoms. This confirms the ability of the pyridoxal containing ligand H₂pyr₂en to form stable heavy metal chelates with unusual coordination polyhedra. Complexes 1 and 2 show coordination number 8, and represent a distorted quadratic antiprismatic arrangement. To date no other references have been made to the complexation of Ce and Pr by any vitamin B₆ derivative. The synthesis and the structure elucidation of 1 and 2 represent a contribution to the research on prevention and therapy of damages caused by heavy elements.     

Single‐Molecule Magnetism in Three Dy2 Complexes from the Use of a Pentadentate Schiff Base Ligand and Different Benzoates

Three dinuclear dysprosium(III) complexes, [Dy₂L₂(O₂CPh)₂]?2 MeOH ( 1 ), [Dy₂L₂{(2‐NO₂)O₂CPh}₂] ( 2 ), and [Dy₂L₂{(2‐OH)O₂CPh}₂] ? MeOH ? MeCN ( 3 ) (H₂L=N₁,N₃‐bis(4‐chlorosalicyladehyde)diethylenetriamine), have been synthesized and structurally characterized. Complexes 1 – 3 possess similar Ln₂ cores and differ in substituents at the benzyl rings of benzoates. Direct current (dc) magnetic susceptibility studies in the 2–300 K range showed weak antiferromagnetic interactions between two dysprosium(III) ions in 1 – 3 . The alternating current (ac) magnetic susceptibility measurements indicated that they all exhibited SMM behavior. The strategic attachment of the ?NO₂ group (in 2 ) and the ?OH functionality (in 3 ) on the skeleton of the benzoic acid led to subtle variations of the bond lengths and bond angles in the coordination environments of the central dysprosium(III) ions, consequently resulting in the enhancement of the energy barriers for 2 and 3 . Complete‐active‐space self‐consistent field (CASSCF) calculations were employed to rationalize the experimental outcomes. Theoretical calculations confirm the existence of antiferromagnetic interactions in 1 – 3 , and the calculated dc magnetic susceptibility data agree well with those obtained experimentally. The computational results reveal more axial g tensors, as well as higher first excited Kramers doublets in 2 and 3 ; thus resulting in higher energy barriers in compounds 2 and 3 .     

Tuning the Magnetic Interactions and Relaxation Dynamics of Dy2 Single‐Molecule Magnets

Efficient modulation of single‐molecule magnet (SMM) behavior was realized by deliberate structural modification of the Dy₂ cores of [Dy₂( a ′ povh )₂(OAc)₂(DMF)₂] ( 1 ) and [Zn₂Dy₂( a′povh )₂(OAc)₆] ? 4 H₂O ( 2 ; H₂ a ′ povh =N′‐[amino(pyrimidin‐2‐yl)methylene]‐o‐vanilloyl hydrazine). Compound 1 having fourfold linkage between the two dysprosium ions shows high‐performance SMM behavior with a thermal energy barrier of 322.1 K, whereas only slow relaxation is observed for compound 2 with only twofold connection between the dysprosium ions. This remarkable discrepancy is mainly because of strong axiality in 1 due to one pronounced covalent bond, as revealed by experimental and theoretical investigations. The significant antiferromagnetic interaction derived from bis(μ₂‐O) and two acetate bridging groups was found to be crucial in leading to a nonmagnetic ground state in 1 , by suppressing zero‐field quantum tunneling of magnetization.     

Magnetic Relaxation in Single‐Electron Single‐Ion Cerium(III) Magnets: Insights from Ab Initio Calculations

Detailed ab initio calculations were performed on two structurally different cerium(III) single‐molecule magnets (SMMs) to probe the origin of magnetic anisotropy and to understand the mechanism of magnetic relaxations. The complexes [Ce^III{Zn^II(L)}₂(MeOH)]BPh₄ ( 1 ) and [Li(dme)₃][Ce^III(cot′′)₂] ( 1 ; L=N,N,O,O‐tetradentate Schiff base ligand; 2 ; DME=dimethoxyethane, COT′′=1,4‐bis(trimethylsilyl)cyclooctatetraenyldianion), which are reported to be zero‐field and field‐induced SMMs with effective barrier heights of 21.2 and 30 K respectively, were chosen as examples. CASSCF+RASSI/SINGLE_ANISO calculations unequivocally suggest that m_J|±5/2〉 and |±1/2〉 are the ground states for complexes 1 and 2 , respectively. The origin of these differences is rooted back to the nature of the ligand field and the symmetry around the cerium(III) ions. Ab initio magnetisation blockade barriers constructed for complexes 1 and 2 expose a contrasting energy‐level pattern with significant quantum tunnelling of magnetisation between the ground state Kramers doublet in complex 2 . Calculations performed on several model complexes stress the need for a suitable ligand environment and high symmetry around the cerium(III) ions to obtain a large effective barrier.     

Dysprosium Single-Molecule Magnets with Bulky Schiff Base Ligands: Modification of the Slow Relaxation of the Magnetization by Substituent Change

The synthesis, and magnetic and photoluminescence investigations of two bifunctional dysprosium complexes based on tridentate Schiff base ligands is reported. Magnetic investigations reveal a genuine single-molecule magnet (SMM) behavior, with out-of-phase signals up to 60 K, and tunable emission arising from the Schiff base ligands.     

Synthesis, Thermochromic Properties and Thermal Behavior of some Schiff Bases.Part I.p,p'-Diaminodiphenylmethane-Schiff Bases and Sulphonamide Schiff Base

Crystalline salicylideneaniline and its derivatives exhibit thermochromic phenomena, i.e., they show a reversible colour change, as a result of a variation in temperature1-3. The presence of the ortho-OH group is considered to be an essential condition for the thermochromic effects4. One study5 has indicated that the presence of an ortho-hydroxyl group is not a structural requirement for the thermochromism of Schiff bases. However, in this literature only differential thermal analysis (DTA) …     

Effects of Zinc(II) on the Luminescence of Europium(III) in Complexes Containing β‐Diketone and Schiff Bases

The UV, excitation, and luminescence spectra of tris(pivaloyltrifluoroacetonato)europium(III) ([Eu(pta)₃]; Hpta=1,1,1‐trifluoro‐5,5‐dimethylhexane‐2,4‐dione=HA) were measured in the presence of bis(salicylidene)trimethylenediamine (H₂saltn), bis[5‐(tert‐butyl)salicylidene]trimethylenediamine (H₂(^tBu)saltn), or bis(salicylidene)cyclohexane‐1,2‐diyldiamine (H₂salchn), and the corresponding Zn^II complexes [ZnB] (B=Schiff base). The excitation and luminescence spectra of the solution containing [Eu(pta)₃] and [Zn(salchn)] exhibited much stronger intensities than those of solutions containing the other [ZnB] complexes. The introduction of a ^tBu group into the Schiff base was not effective in sensitizing the luminescence of [Eu(pta)₃]. The luminescence spectrum of [ZnB] showed a band around 450 nm. The intensity decreased in the presence of [Eu(pta)₃], reflecting complexation between [Eu(pta)₃] and [ZnB]. On the basis of the change in intensity against the concentration of [ZnB], stability constants were determined for [Eu(pta)₃Zn(saltn)], [Eu(pta)₃Zn{(^tBu)saltn}], and [Eu(pta)₃Zn(salchn)] as 4.13, 4.9 and 5.56, respectively (log , where =[[Eu(pta)₃ZnB]]([[Eu(pta)₃]][[ZnB]])^?1). The quantum yields of these binuclear complexes were determined as 0.15, 0.11, and 0.035, although [Eu(pta)₃Zn(salchn)] revealed the strongest luminescence at 613 nm. The results of X‐ray diffraction analysis for [Eu(pta)₃Zn(saltn)] showed that Zn^II had a coordination number of five and was bridged with Eu^III by three donor O‐atoms, i.e., two from the salicylidene moieties and one from the ketonato group pta.     

Synthesis,Structure, Luminescent and Thermal Properties of Ytterbium(III) and Dysprosium(III) Complexes with 5‐Sulfoisophthalic Acid Sodium Salt

Two rare earth metal‐organic framework compounds [Ybsip(H₂O)₅] · 3H₂O ( 1 ) and [Dysip(H₂O)₄] ( 2 ) (NaH₂sip: 5‐sulfoisophthalic acid sodium salt) were synthesized hydrothermally, and characterized by single‐crystal X‐ray diffraction, elemental analysis, and FT‐IR spectroscopy. In complex 1 , each Yb^III atom is nine‐coordinate with a distorted monocapped tetragonal prismatic arrangement. Two carboxylate groups of each sip^3– molecule adopt the same μ₁‐η¹:η¹ chelating coordination model connecting two Yb^III atoms. The oxygen atoms of the sulfonate group do not participate in coordination with Yb^III. The whole sip^3– molecule acts as a μ₂ bridge to form an one‐dimensional (1D) chain structure. The 1D chains are linked by hydrogen bonding to generate two‐dimensional layers, and are further combined together to form a three‐dimensional structure. In complex 2 , the Dy^III atom is nine‐coordinate with a distorted monocapped tetragonal antiprismatic arrangement. In each sip^3– anion, two carboxylate groups take the same μ₁‐η¹:η¹ chelating coordination mode, only an oxygen atom of sulfonate group bond to Dy^III ion. The whole ligand sip^3– acts as a μ₃ bridge linking three different Dy^III ions to generate a wave‐like two‐dimensional network with (6,3) topological structure. The two‐dimensional networks are further linked by O–H ··· O hydrogen bonds to form a three‐dimensional structure. The thermal and luminescent properties of both complexes are investigated.     

水杨醛牛磺酸Schiff碱镝(Ⅲ)配合物的合成表征及热分解动力学研究(英文)

合成了水杨醛牛磺酸Schiff碱与镝(Ⅲ)的配合物,并通过元素分析、红外光谱、X射线粉末衍射及摩尔电导等对其结构进行了表征.在非等温条件下,采用Achar微分法和Coats-Redfern积分法拟合出配合物的热分解动力学方程.     

Two Isostructural Layered Lanthanide(III) Complexes: Syntheses,Structures, Magnetic and Luminescent Properties

Two N'-(2-hydroxybenzylidene)pyridine N-oxide-carbohydrazide (H₃L)-based coordination complexes with the formula [Ln₂(DMF)₂(OAc)₂(HL)₂]_n (Ln = Dy for 1 and Eu for 2 ) were solvothermally synthesized. Crystal structures, thermal stabilities, magnetic and luminescent properties of the two complexes were fully investigated. Both complexes are isomorphic two-dimensional layers with centrosymmetric {Ln₂} subunits extended by doubly deprotonated HL^2– connectors. Complex 1 with highly anisotropic Dy^III spin exhibits slightly frequency-dependent magnetic relaxations under zero dc field with an effective energy barrier of ca. 6.84 K. Eu^III-based complex 2 displays only one weak fluorescent emission around 532 nm with the absence of characteristic emission of Eu^III ion. These results provide helpful hints of the hydrazide Schiff-functionalized organic ligands on the function modulations of the resulting Ln complexes.     

Polynuclear Complexes with Alkoxo and Phenoxo Bridges from In Situ Generated Hydroxy‐Rich Schiff Base Ligands: Syntheses,Structures, and Magnetic Properties

Complexes of new Schiff base ligands generated in situ from the reaction of 1‐aminoglycerol, aldehydes, and metal ions are reported. [Cu₄(HL¹)₄] ( 1 ) and [Ni₄O(HL¹)₃(H₂O)₃)] ? 6 H₂O ? DMF ? DMSO ( 2 ) have M₄O₄ cubane cores, with the L/M molar ratios of 4:4 and 3:4, respectively. [Mn^III₃Mn^IINaOCl₄(HL¹)₃] ? 3 M eCN ( 3 ) has a unique pentanuclear trigonal propeller‐shaped Mn^III₃Mn^IINa core structure, and the coordination assemblies are linked by hydrogen bonds to afford a 3D channel structure. [Cu₂(HL²)₂] ( 4 ) has a bis(μ₂‐alkoxo)‐bridged Cu₂O₂ core, with the binuclear species linked by hydrogen bonds to afford a 1D double‐chain. [Ni₇(OH)₂(OCH₃)₄(H₂L³)₂(MeOH)₂(H₂O)₂]‐ (ClO₄)₂ ? 10 H₂O ( 5 ) has a heptanuclear structure containing heptadentate di‐Schiff base ligands, with the nickel(II) ions bridged by phenoxo, alkoxo, hydroxo, and methoxo groups to afford a very rare face‐sharing hexadruple defective cubane core with a Ni@Ni₆ arrangement. The lattice water molecules are linked by hydrogen bonds to form helical chains, which are further hydrogen‐bonded to the coordination moieties to afford a 2D network. Variable temperature magnetic susceptibility measurements and nonlinear data‐fitting revealed that the “2+4” type of cubane complex 1 shows medium intradimeric ferromagnetic interactions and weak interdimeric ferromagnetic interactions. For complexes 2 and 5 , coexistent ferro‐ and antiferromagnetic couplings afford a non‐zero spin ground state. However, compound 3 shows antiferromagnetic interactions between Mn^III and Mn^II, and ferromagnetic interactions between the Mn^III centers, resulting in a global antiferromagnetic behavior. In conclusion, the reaction of 1‐aminoglycerol with aldehydes and metal salts afforded polynuclear complexes with a rich structural diversity and remarkable magnetic behavior.