Anion-Induced Self-Assembly of Luminescent and Magnetic Homoleptic Cyclic Tetranuclear Ln4(Salen)4 and Ln4(Salen)2 Complexes (Ln = Nd, Yb, Er, or Gd)

Single molecule magnet behavior and luminescence of {Ln4} and {LnZn} complexes

A serials of tetranuclear coordination clusters [Ln4L2(HL)2(μ3-OH)2(NO3)2](NO3)2 [Ln = Dy (1•3CH3CN•5H2O), Gd (2•4CH3CN•5H2O), H2L = 6,6'-dimethoxy-2,2'-[2,2-dimethylpropane-1,3-diylbis-(nitrilomethylidyne)] diphenol] and dinuclear complexes [LnZnL(NO3)3(H2O)]•2CH3CN [Ln = Dy (3), Er (4), Yb (5), Lu...

Substitution Effects Regulate the Formation of Butterfly-Shaped Tetranuclear Dy(III) Cluster and Dy-Based Hydrogen-Bonded Helix Frameworks: Structure and Magnetic Properties

The generation of two types of complexes with different topological connections and completely different structural types merely via the substitution effect is extremely rare, especially for -CH₃ and -C₂H₅ substituents with similar physical and chemical properties. Herein, we used 3-methoxysalicylaldehyde, 1,2-cyclohexanediamine, and Dy(NO₃)₃·6H₂O to react under solvothermal conditions (CH₃OH:CH₃CN = 1:1) at 80 °C to obtain the butterfly-shaped tetranuclear Dy^III cluster [Dy₄(L¹)₄(μ₃-O)₂(NO₃)₂] (Dy₄, H₂L¹ = 6,6'-((1E,1'E)-(cyclohexane-1,3-diylbis(azanylylidene))bis(methanylylidene))bis(2-methoxyphenol)). The ligand H₂L¹ was obtained by the Schiff base in situ reaction of 3-methoxysalicylaldehyde and 1,2-cyclohexanediamine. In the Dy₄ structure, (L¹)^2- has two different coordination modes: μ₂-η¹:η²:η¹:η¹ and μ₄-η¹:η²:η¹:η¹:η²:η¹. The four Dy^III ions are in two coordination environments: N₂O₆ (Dy1) and O₉ (Dy2). The magnetic testing of cluster Dy₄ without the addition of an external field revealed that it exhibited a clear frequency-dependent behavior. We changed 3-methoxysalicylaldehyde to 3-ethoxysalicylaldehyde and obtained one case of a hydrogen-bonded helix framework, [DyL²(NO₃)₃]_n·2CH₃CN (Dy-HHFs, H₂L² = 6,6'-((1E,1'E)-(cyclohexane-1,3-diylbis(azanylylidene))bis(methanylylidene))bis(2-ethoxyphenol)), under the same reaction conditions. The ligand H₂L² was formed by the Schiff base in situ reaction of 3-ethoxysalicylaldehyde and 1,2-cyclohexanediamine. All Dy^III ions in the Dy-HHFs structure are in the same coordination environment (O₉). The twisted S-shaped (L²)^2- ligand is linked by a Dy(III) ion to form a spiral chain. The spiral chain is one of the independent units that is interconnected to form Dy-HHFs through three strong hydrogen-bonding interactions. Magnetic studies show that Dy-HHFs exhibits single-ion-magnet behavior (U_eff = 68.59 K and τ₀ = 1.10 × 10^-7 s, 0 Oe DC field; U_eff = 131.5 K and τ₀ = 1.22 × 10^-7 s, 800 Oe DC field). Ab initio calculations were performed to interpret the dynamic magnetic performance of Dy-HHFs, and a satisfactory consistency between theory and experiment exists.

Enhanced near-infrared luminescence in Ln2Cd2 (Ln = Nd, Yb) heterotetranuclear complexes

Due to the effect of the combination of the rigid structure and synergistic interactions of two ligands on energy transfer, the Cd–Ln complexes show excellent NIR luminescence properties with the QYs reaching 0.34% for Nd³⁺ and 2.13% for Yb³⁺.

Fluorescence Properties and Density Functional Theory Calculation of a Structurally Characterized Heterotetranuclear [ZnII2–SmIII2] 4,4′-Bipy-Salamo-Constructed Complex

A new heterotetranuclear complex, [{Zn(L)Sm(NO3)3}2(4,4′-bipy)]·2CH3OH, was synthesized via an unsymmetrical single salamo-like ligand H2L: 6-methoxy-6′-ethoxy-2,2′-[ethylenedioxybis(azinomethyl)]diphenol, with Zn(OAc)2·2H2O, Sm(NO3)3·6H2O, and 4,4′-bipyridine by the one-pot method. The [ZnII2–SmIII2] complex was validated via elemental analysis, powder X-ray diffraction (PXRD) analysis, infrared spectroscopy, and ultraviolet–visible (UV–Vis) absorption spectroscopy. The X-ray single crystal diffraction analysis of the [ZnII2–SmIII2] complex was carried out via X-ray single-crystal crystallography. The crystal structure and supramolecular features were discussed. In addition, while studying the fluorescence properties of the [ZnII2–SmIII2] complex, the density functional theory (DFT) calculation of its structure was also performed.

Water-Stable Europium 1,3,6,8-Tetrakis(4-carboxylphenyl)pyrene Framework for Efficient C2H2/CO2 Separation

Compound {(Me₂NH₂)₃[Eu₇(μ₃-O)₂(TBAPy)₅(H₂O)₆]·12.5DMF} _n (JXNU-5), constructed from the 1,3,6,8-tetrakis(4-carboxylphenyl)pyrene (TBAPy^4-) ligand and one-dimensional (1D) europium carboxylate rods, is presented. JXNU-5 has a three-dimensional framework with 1D channels. The strong coordination bonds between Eu^III ions with high charge densities and carboxylate O atoms as well as strong π···π-stacking interactions between pyrenes lead to a water-resistant JXNU-5, which was verified by powder X-ray diffraction and surface area measurements. The breakthrough simulations and experiments demonstrate that an efficient C₂H₂/CO₂ (50/50 mixture) gas separation at ambient conditions was achieved with JXNU-5. The calculation results show that the dominating interactions between the absorbed C₂H₂ molecules and host framework are hydrogen bonds associated with the carboxylate O atoms exposed on the pores. Thus, an elegant example of a water-stable metal-organic framework for effective C₂H₂/CO₂ separation is demonstrated.

A series of new octanuclear Ln8 clusters: magnetic studies reveal a significant cryogenic magnetocaloric effect and slow magnetic relaxation

A series of new octanuclear Ln₈ clusters. Magnetically, Gd₈ exhibited a significant magnetocaloric effect and a magnetic entropy change is 32.49 J K⁻¹ kg⁻¹ for a field of 7 T at 2 K, while Dy₈ exhibited a frequency dependent slow relaxation of magnetization at a zero applied direct current magnetic field.

Tunable ligand emission of napthylsalophen triple-decker dinuclear lanthanide(iii) sandwich complexes

The ligand 1,1′-((1E,1′E)-(1,2-phenylenebis(azanylylidene))bis(methanylylidene)) bis(naphthalen-2-ol) (H₂L) was used to prepare lanthanide(iii) metal complexes found to self-assemble as triple decker sandwich complexes of the type (Ln₂L₃).

A Novel 3D Salen Neodymium Framework with Near-Infrared (NIR) Properties

The reaction of N,N′-bis(3-hydroxy)ethylene-1,2-diamine (H2salen) with Nd(NO3)3·6H2O and NdCl3·6H2O yields a novel lanthanide complex, namely, Nd(salen)2(NO3)2Cl (1). X-ray crystallographic analysis revealed that H2salen effectively functions as a bridging ligand forming a kind of novel 3D structure complex which is constructed by Salen ligands and mixed lanthanide counter-ions without π–π stacking and hydrogen bond interactions. This is the first Salen-type 3D lanthanide complex to be constructed in this way. The near-infrared (NIR) properties of 1 in the solid state were also studied.

Synthesis, characterization and oscillator-vibrated near-infrared (NIR) luminescence of two pseudo-polymorphic [Yb4((OH)2-Salophen)4] complexes

Through the self-assembly of the (OH)2-Salophen H4L (H4L=N,N'-bis(3-hydroxylsalicylidene)benzene-1,2-diamine) with LnCl3·6H2O or Ln(NO3)3·6H2O (Ln=La, Yb or Gd) in different solvent systems MeCN-EtOH and MeCN-DMF, the mixed (L)(4-) and (H2L)(2-) coordination modes induce the formation of anion-independent while pseudo-polymorphic homoleptic linear tetranuclear complexes [Ln4(H2L)2(L)2(EtOH)2] (Ln=La, 1; Ln=Yb, 2 or Ln=Gd, 3) and [Ln4(H2L)2(L)2(DMF)2] (Ln=La, 4; Ln=Yb, 5 or Ln=Gd, 6), respectively. The result of their photophysical properties shows the characteristic NIR luminescence for both Yb(3+)-based complexes 2 and 5 with emissive lifetimes in microsecond ranges, while the difference of nearby and/or distant oscillator-based (OH and/or CH) vibrations from two coordinated EtOH or DMF molecules within the inner coordination spheres of Yb(3+) ions in the two complexes has a decisive effect on their NIR luminescent properties.

Four new lead(ii)–iridium(iii) heterobimetallic coordination frameworks: synthesis, structures, luminescence and oxygen-sensing properties

Crystalline lead(ii)–iridium(iii) heterobimetallic coordination frameworks were prepared and characterized, and one was mixed with C480 to form a ratiometric oxygen sensor for the determination of oxygen in real gas.

A salen-type Dy4 single-molecule magnet with an enhanced energy barrier and its analogues

A discrete hexadentate salen-type tetranuclear Dy complex with a unique {Ln₄O₈} core exhibits two slow magnetic relaxations with the highest energy barrier of 48.14 K among the reported tetranuclear salen-type dysprosium SMMs.

Two series of reactant's ratio-dependent lanthanide organic frameworks derived from nicotinic acid N-oxide and oxalate: synthesis, crystal structures and luminescence properties

Two series of Ln-MOFs of different structures and consequently different chemo-physical properties were obtained by simply controlling the reactant's ratio.

Anion-directed assembly of helical copper(ii) complexes based on a bispyridylpyrrole ligand: synthesis, structural and magnetic properties

Helical copper(ii) complexes based on a bispyridylpyrrole ligand, namely the helical polymer {[Cu₂(PDP_H)₂(N₃)₂]}n, a discrete double-helical complex [Cu₂(PDP_H)₂(NO₃)₂] and triple-helical complex [Cu₂(PDP_H)₃](OTf), were synthesized by displacement of Cl⁻ in [Cu(PDP_H)Cl].

The exceptionally rich coordination chemistry generated by Schiff-base ligands derived from o-vanillin

Recent and relevant examples of homo- and heterometallic complexes generated by Schiff base ligands derived from o-vanillin, as well as their properties, are discussed.

Near-IR luminescence and field-induced single molecule magnet of four salen-type ytterbium complexes

A series of rigid hexadentate salen-type (H2L) ytterbium complexes, namely, [Yb2L3(CH3OH)]·3CH3CN (1), [Yb2LL'L″(CH3OH)(H2O)2](ClO4)2·CH3OH·H2O (2), [Yb2L(OAc)4(CH3OH)2]·2CH3OH (3), and {[Yb2L(OAc)4]·3H2O}n (4) (H2L = N,N'-bis(2-oxy-3-methoxybenzylidene)-1,2-phenylenediamine, HL' = 2-(2'-hydroxy-3'-methyloxy-phenyl)benzimidazole and HL" = 3-methoxysalicylaldehyde) have been synthesized by reactions of H2L with multifarious Yb(3+) salts. X-ray crystallographic analyses demonstrate that complex 1 is of a triple-decker sandwich-type Yb2L3 structure with a ratio of H2L/Yb = 3:2, 2 and 3 possess the unique Yb2 core with a ratio of H2L/Yb = 2:2 and 1:2, respectively, 4 exhibits one dimensional coordination polymers in which the polymeric structures are formed by acetate (OAc(-)) groups. All complexes 1-4 exhibit near-IR luminescence, which can be rationalized on the basis of the disparate structural effects. The magnetic analysis unveils that all complexes 1-4 are of field-induced single-molecule magnet behavior with the energy barriers (Ueff/kB) of 14.5, 2.0, 9.5, and 2.4 K at 3 kOe direct current fields, respectively.

Temperature-dependent self-assembly of near-infrared (NIR) luminescent Zn2Ln and Zn2Ln3 (Ln=Nd, Yb or Er) complexes from the flexible Salen-type Schiff-base ligand

Through the self-assembly of the precursor [Zn(L)(MeCN)] (H2L=N,N'-bis(3-methoxy-salicylidene)cyclohexane-1,2-diamine) with LnCl3·6H2O (Ln=La, Nd, Yb, Er or Gd) and NaN3 in alcohol-containing solutions, two series of mixed anions-induced Zn2Ln-arrayed complexes [Zn2(L)2(MeOH)ClLn(N3)]·Cl (Ln=La, 1; Ln=Nd, 2; Ln=Yb, 3; Ln=Er, 4 or Ln=Gd, 5) and Zn2Ln3-arrayed complexes [Zn2(L)3Cl2(μ2-OH)(μ3-OH)2Ln3(N3)2] (Ln=La, 6; Ln=Nd, 7; Ln=Yb, 8; Ln=Er, 9 or Ln=Gd, 10) are obtained at room temperature or under reflux, respectively. In contrast to Zn2Ln-arrayed complexes with the two Zn2+ ions in the inner cis-N2O2 cores and one Ln3+ ion in the outer O2O2 moieties, the demetalation of partial precursors leads to the selective exchange of Zn2+ centers for the Ln3+ ions for the formation of novel heterometallic Zn2Ln3-arrayed complexes with the Ln3+ ions in both the inner cis-N2O2 core and the outer O2O2 moieties of the ligands. The result of their photophysical properties shows that the characteristic near-infrared (NIR) luminescence of Nd3+ or Yb3+ ion has been sensitized from the excited state (both 1LC and 3LC) of the ligand H2L, while relatively lower quantum yields for Zn2Ln3-arrayed complexes than those for Zn2Ln-arrayed complexes, correspondingly, should be due to the luminescent quenching with the involvement of OH- oscillators around the Ln3+ ions.

Sensitized luminescence of Eu(III) complexes with Schiff-base and 1,10-phenanthroline: role of Schiff-base as a sensitizer

The synthesis and characterization of two europium(III) complexes, [Eu(L)(H2O)]Cl and [Eu(L)(phen)(H2O)]Cl (L=N,N'-bis(salicylidene)-3,6-dioxa-1,8-diaminooctanato and phen=1,10-phenanthroline) are reported. Exciting the Eu(III) complexes with near-UV light resulted in sensitized red luminescence by a transfer of energy from the triplet excited states of L to the Eu(III) ion. Introducing phen to the complex increased the quantum yield of the L-sensitized luminescence of [Eu(L)(phen)(H2O)](+) by more than 18 times relative to [Eu(L)(H2O)](+). The optimized structures and the configurational interaction singles (CIS) of the [Eu(L)(phen)(H2O)](+) and [Eu(L)(H2O)](+) molecules were theoretically studied using ab initio Hartree-Fock (HF). The theoretical calculations showed that the first nearly degenerate 1A and 2A excited states, more specifically the π→π(*) transitions of the two phenolate terminals, contributed significantly to the energy transfer process. Although the phen excitation route was forbidden in [Eu(L)(phen)(H2O)](+), the coordination of phen enhanced the absorbing ability of L markedly and caused the energy transfer from the 1A and 2A states to the (5)D1 and (5)D0 states of Eu(III) to predominate over any radiative and nonradiative processes occurring between the excited states and the ground states of the L moiety. Consequently, the quantum yield of the sensitized luminescence was enhanced significantly in [Eu(L)(phen)(H2O)](+).