Lanthanide(III) Nitrate Complexes of Two 17 Membered N3O2-Donor Macrocycles

The interaction of lanthanide(III) ions with two N₃O₃-macrocycles, L¹ and L², derived from 2,6-bis(2-formylphenoxymethyl)pyridine and 1,2-diaminoethane has been investigated. Schiff-base macrocyclic lanthanide(III) complexes LnL¹(NO₃)₃ · xH₂O (Ln = Nd, Sm, Eu or Lu) have been prepared by direct reaction of L¹ and the appropriate hydrated lanthanide nitrate. The direct reaction between the diamine macrocycle L² and the hydrated lanthanide(III) nitrates yields complexes LnL²(NO₃)₃· H₂O only for Ln = Dy or Lu. The reduction of the Schiff-base macrocycle decreases the complexation capacity of the ligand towards the Ln(III) ions. The complexes have been characterised by elemental analysis, molar conductivity data, FAB mass spectrometry, IR and, in the case of the lutetium complexes, ¹H NMR spectroscopy.     

Two Lanthanide(III) Complexes based on the Schiff Base N,N′‐Bis(salicylidene)‐1,5‐diamino‐3‐oxapentane: Synthesis,Characterization, DNA‐binding Properties,and Antioxidation

The Schiff base N,N′‐bis(salicylidene)‐1,5‐diamino‐3‐oxapentane (H₂L) and its lanthanide(III) complexes, PrL(NO₃)(DMF)(H₂O) ( 1 ) and Ho₂L₂(NO₃)₂ · 2H₂O ( 2 ), were synthesized and characterized by physicochemical and spectroscopic methods. Single crystal X‐ray structure analysis revealed that complex 1 is a discrete mononuclear species. The Pr^III ion is nine‐coordinate, forming a distorted capped square antiprismatic arrangement. Complex 2 is a centrosymmetric dinuclear neutral entity in which the Ho^III ion is eight‐coordinate with distorted square antiprismatic arrangement. The DNA‐binding properties of H₂L and its Ln^III complexes were investigated by spectrophotometric methods and viscosity measurements. The results suggest that the ligand H₂L and its Ln^III complexes both connect to DNA in a groove binding mode; the complexes bind more strongly to DNA than the ligand. Moreover, the antioxidant activities of the Ln^III complexes were in vitro determined by superoxide and hydroxyl radical scavenging methods, which indicate that complexes 1 and 2 have OH ^· and O₂^{– ·} radical scavenging activity.     

Structures and magnetic properties of two series of Schiff base binuclear lanthanide complexes

Until now, although there are many examples of studying the magnetic properties of Schiff base binuclear lanthanide complexes, the relationship between the structure and magnetic properties of the complexes still is worth further investigation in order to improve the magnetic properties of Schiff base lanthanide complexes. In this work, we successfully obtained two series of binuclear Ln complexes by in situ reaction of 4-diethylaminosalicylaldehyde, benzoic hydrazide and different lanthanide salts at 80°C under solvothermal conditions, namely, [Ln₂(L)₃(NO₃)₃]·CH₃CN·CH₃OH·H₂O [Ln = Dy ( 1 ), Ho ( 2 ), Gd ( 3 ) L = deprotonated 4-diethylamino salicylaldehyde benzoylhydrazine], [Ln₂(L)₄(CH₃COO)]CH₃COO·CH₃CN [Ln = Dy ( 4 ), Ho ( 5 ), Gd ( 6 )]. The complex 1 contains three Schiff base ligands L, two Dy (III) ions, and three NO₃⁻. The ligand H₁L is formed by in situ Schiff base reaction with 4-diethylaminosalicylaldehyde and benzoic hydrazide with the participation of Ln (NO₃)₃. When replacing Ln (NO₃)₃ with Ln (OAc)₃, obtained three μ₂-OAc bridged binuclear Ln (III) complexes. The magnetic study showed that complex 4 exhibits field-induced single-molecule magnet (SMM) behavior while complex 1 does not show any SMMs behavior. In addition, we have studied the magnetocaloric effect of complexes 3 and 6 , their maximum −ΔS_m values are 21.37 J kg⁻¹ K⁻¹ and 15.32 J kg⁻¹ K⁻¹, respectively, under ΔH = 7 T and T = 2 K.     

Ligand Recognition Processes in the Formation of Homochiral C3‐Symmetric LnL3 Complexes of a Chiral Alkoxide

The reaction of a chiral racemic bidentate ligand HL¹ (tBu₂P(O)CH₂CH(tBu)OH) with mid to late trivalent lanthanide cations affords predominantly homochiral lanthanide complexes (RRR)‐[Ln(L¹)₃] and (SSS)‐[Ln(L¹)₃]. A series of reactions are reported that demonstrate that the syntheses are under thermodynamic control, and driven by a ligand ‘self‐recognition’ process, in which the large asymmetric bidentate L¹ ligands pack most favourably in a C₃ geometry around the lanthanide cation. The synthesis of bis(L¹) adducts [Ln(L¹)₂X] (X=N(SiMe₃)₂, OC₆H₃tBu‐2,6) is also reported. Analysis of the diastereomer mixtures shows that homochiral (L¹)₂ complexes are favoured but to a lesser extent. The complexes Ln(L¹)₃ and [Ln(L¹)₂(OC₆H₃tBu‐2,6)] have been studied as initiators for the polymerization of ε‐caprolactone and its copolymer with lactide, glycolide and its copolymer with lactide, and ε‐caprolactam.     

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.     

2,4-Bis(diphenylphosphorylmethyl)mesitylene: Synthesis and complex formation with lanthanide nitrates. Crystal structure of [Nd(L1(NO3)3 · Me2CO]

A new bisphosphoryl ligand, 2,4-bis(diphenylphosphorylmethyl)mesitylene (L¹), has been synthesized. Upon the interaction of L¹ with lanthanide nitrates, stable mononuclear chelates [Ln(L¹) _n (NO₃)₃] (Ln = Ce(III), Nd(III), Er(III); n = 1, 2) were obtained. The structure of the complexes in solid state and in solution was studied by vibrational (IR and Raman) spectroscopy, X-ray diffraction, and conformational (molecular mechanics) analysis.     

Synthesis,Characterization, Antimicrobial Activities,and Structural Studies of Lanthanide (III) Complexes with 1-(4-Chlorophenyl)-3-(4-fluoro/hydroxyphenyl)prop-2-en-1-thiosemicarbazone

Twelve coordinate lanthanide (III) complexes with the general composition [Ln L₃X_n(H₂O)_n] where Ln = Pr(III), Sm(III), Eu (III), Gd (III), Tb (III), Dy (III), X = Cl^?1, NO₃ ^?2, n = 2–7, and L is 1-(4-chlorophenyl)-3-(4-fluoro/hydroxyphenyl)prop-2-en-1- thiosemicarbazone have been prepared. The lanthanide complexes (5) were derived from the reaction between 1-(4-chlorophenyl)-3-(4-fluoro/hydroxyphenyl)prop-2-en-1-thiosemicarbazone (4) with an aqueous solution of lanthanide salt. Chalcone thiosemicarbazone ligand (4) was prepared by the reaction of [1-(4-chlorophenyl)-3-(4-fluoro/hydroxyphenyl)]prop-2-enone (chalcone) (3) with thiosemicarbazide in the presence of hot ethanol. All the lanthanide-ligand 1:3 complexes have been isolated in the solid state, are stable in air, and characterized on the basis of their elemental and spectral data.

Thiosemicarbazone ligands behave as bidentate ligands by coordinating through the sulfur of the isocyanide group and nitrogen of the cyanide residue. The probable structure for all the lanthanide complexes is also proposed. The chalcone thiosemicarbazone ligands and their lanthanide complexes have been screened for their antifungal and antibacterial studies. Some of the synthesized lanthanide complexes have shown enhanced activity compared with that of the free ligand.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Preparation and structures of polymeric lanthanide nitrate complexes of CH3C[CH2P(O)Ph2]3

The synthesis of complexes between lanthanide nitrates and MeC(CH₂P(O)Ph₂)₃ (=L) in ethanol or methanol leads to the formation of polymeric complexes Ln(NO₃)₃L as alcohol solvates. The ligand adopts a chelating–bridging mode. The structures of the complexes La(NO₃)₃L · EtOH and Pr(NO₃)₃L · MeOH are reported and the coordination of L is discussed in terms of that of the related free ligand EtC(CH₂P(O)Ph₂)₃. Infrared spectroscopy implies structural differences between the early and later lanthanide complexes.     

含不同芳香取代基的肼基二硫代甲酸甲酯-Ga3+配合物的合成及抑菌活性

设计合成了4种含不同芳香取代基团的肼基二硫代甲酸甲酯配体（2-乙酰基吡啶肼基二硫代甲酸甲酯（L¹-H）、2-甲酰基吡啶肼基二硫代甲酸甲酯（L²-H）、2-甲酰基噻吩肼基二硫代甲酸甲酯（L³-H）、2-甲酰基水杨醛肼基二硫代甲酸甲酯（L⁴-H））的镓配合物,对它们的抑菌活性进行了测试,并讨论了配体分子中不同芳香取代基对配合物抑菌活性的影响。在模拟生理条件下,L与Ga³⁺生成较稳定的单核配合物[Ga（L¹）₂]NO₃（1）、[Ga（L²）₂]NO₃（2）、[Ga（L³）₂]NO₃（3）、[Ga（L⁴）₂]NO₃（4）,各配合物对金黄色葡萄球菌和大肠杆菌表现出比Ga（NO₃）₃·9H₂O强的抑制活性,抑制金黄色葡萄球菌的能力高于大肠杆菌,其中,1和2的活性比相应配体高,其余2个配合物与其配体之间无明显活性差异。L¹和L²分子中吡啶基的较强吸电子效应可能是1和2具有较强抑菌活性的主要原因。4种配合物抑制黑曲霉生长的活性同样高于Ga（NO₃）₃·9H₂O,其中3最强,并显著高于L³,其余配合物与相应配体间无活性差异。     

含不同芳香取代基的肼基二硫代甲酸甲酯-Ga~(3+)配合物的合成及抑菌活性

设计合成了4种含不同芳香取代基团的肼基二硫代甲酸甲酯配体(2-乙酰基吡啶肼基二硫代甲酸甲酯(L1-H)、2-甲酰基吡啶肼基二硫代甲酸甲酯(L2-H)、2-甲酰基噻吩肼基二硫代甲酸甲酯(L3-H)、2-甲酰基水杨醛肼基二硫代甲酸甲酯(L4-H))的镓配合物,对它们的抑菌活性进行了测试,并讨论了配体分子中不同芳香取代基对配合物抑菌活性的影响。在模拟生理条件下,L-H与Ga3+生成较稳定的单核配合物[Ga(L1)2]NO3(1)、[Ga(L2)2]NO3(2)、[Ga(L3)2]NO3(3)、[Ga(L4)2]NO3(4),各配合物对金黄色葡萄球菌和大肠杆菌表现出比Ga(NO3)3·9H2O强的抑制活性,抑制金黄色葡萄球菌的能力高于大肠杆菌,其中,1和2的活性比相应配体高,其余2个配合物与其配体之间无明显活性差异。L1-H和L2-H分子中吡啶基的较强吸电子效应可能是1和2具有较强抑菌活性的主要原因。4种配合物抑制黑曲霉生长的活性同样高于Ga(NO3)3·9H2O,其中3最强,并显著高于L3-H,其余配合物与相应配体间无活性差异。     

2,2′‐Bipyrimidine as Efficient Sensitizer of the Solid‐State Luminescence of Lanthanide and Uranyl Ions from Visible to Near‐Infrared

Treatment of Ln(NO₃)₃?nH₂O with 1 or 2 equiv 2,2′‐bipyrimidine (BPM) in dry THF readily afforded the monometallic complexes [Ln(NO₃)₃(bpm)₂] (Ln=Eu, Gd, Dy, Tm) or [Ln(NO₃)₃(bpm)₂]?THF (Ln=Eu, Tb, Er, Yb) after recrystallization from MeOH or THF, respectively. Reactions with nitrate salts of the larger lanthanide ions (Ln=Ce, Nd, Sm) yielded one of two distinct monometallic complexes, depending on the recrystallization solvent: [Ln(NO₃)₃(bpm)₂]?THF (Ln=Nd, Sm) from THF, or [Ln(NO₃)₃(bpm)(MeOH)₂]?MeOH (Ln=Ce, Nd, Sm) from MeOH. Treatment of UO₂(NO₃)₂?6H₂O with 1 equiv BPM in THF afforded the monoadduct [UO₂(NO₃)₂(bpm)] after recrystallization from MeOH. The complexes were characterized by their crystal structure. Solid‐state luminescence measurements on these monometallic complexes showed that BPM is an efficient sensitizer of the luminescence of both the lanthanide and the uranyl ions emitting visible light, as well as of the Yb^III ion emitting in the near‐IR. For Tb, Dy, Eu, and Yb complexes, energy transfer was quite efficient, resulting in quantum yields of 80.0, 5.1, 70.0, and 0.8 %, respectively. All these complexes in the solid state were stable in air.     

Synthesis,spectral and antimicrobial studies of rare earth metal complexes with Schiff-base hydrazone containing quinoline moiety

The synthesis and characterization of lanthanide(III) complexes with the Schiff-base hydrazone, o-hydroxyacetophenone-7-chloro-4-quinoline, (HL) are reported. The complexes were characterized by different physicochemical methods: mass spectrometry, ¹H NMR, ¹³C NMR, and IR, UV-visible, molar conductance and magnetic studies. They have the stoichiometry [Ln(L)₂(NO₃)]·nH₂O where Ln = La(III), Pr(III), Nd(II), Sm(III), Eu(III) and n = 1–3. The spectra of the complexes were interpreted by comparison with the spectrum of the free ligand. The Schiff-base ligand and its metal complexes were tested against one stain Gram +ve bacteria (Staphylococcus aureus), Gram ?ve bacteria (Escherichia coli), and Fungi (Candida albicans). The tested compounds exhibited high antimicrobial activities     

Synthesis, characterization, thermal stability, reactivity, and antimicrobial properties of some novel lanthanide(III) complexes of 2-(N-salicylideneamino)-3-carboxyethyl-4,5,6,7-tetrahydrobenzo[b]thiophene

Two series of new lanthanide(III) complexes of the type [Ln(HSAT)₂(H₂O)₃Cl₃] and [Ln(HSAT)₂(NO₃)₃], where Ln = La, Pr, Nd, Sm, Eu, Gd, Dy, Tm, Yb, or Lu, and HSAT = 2-(N-salicylideneamino)-3-carboxyethyl-4,5,6,7-tetrahydrobenzo[b]thiophene, are synthesized by the reaction of LnCl₃ or Ln(NO₃)₃ with the title ligand in ethanol. The complexes are characterized by elemental analysis, magnetic moment values, molar conductivity, IR, UV-Vis, and ¹H NMR spectral data. Two selected complexes are subject to thermogravimetric analysis, and their kinetic parameters are estimated using Coats-Redfern equation. The complex [La(HSAT)₂(NO₃)₃] underwent facile transesterification when refluxed in methanol. The ligand and some selected complexes are screened for their antimicrobial properties. Antimicrobial activities of the ligand increase on coordination with the metal ion. The text was submitted by the authors in English.     

Trigonal (-3) symmetry octahedral lanthanide(III) complexes of zwitterionic tripodal ligands: luminescence and magnetism

Sandwich coordination complexes, [Ln^III(H₃L)₂]X₃?solvents, of Tb(III), Eu(III), Dy(III), Ho(III) and Er(III) were prepared with two new zwitterionic ester-substituted tripodal amine ligands, tris((2-hydroxy-5-n-butyl benzoate)aminoethyl)-amine (H₃L¹) and tris((2-hydroxy-5-methyl benzoate)aminoethyl)-amine (H₃L²). These ligands were synthesised by condensation of the appropriately substituted salicylaldehyde with tris(2-aminoethyl)amine (tren) followed by in situ reduction of the tris-imine to tris-amine. Subsequent 2:1 reaction with lanthanide(III) ions yields [Ln^III(H₃L)₂]X₃?solvents (L = L¹, L²; X = Cl^?, NO₃^?; solvents = MeOH or H₂O). All complexes were characterised by microanalysis, infrared spectroscopy, high resolution mass spectrometry and solid-state photoluminescence measurements. The crystal structures of [Tb^III(H₃L¹)₂]Cl₃·6MeOH, [Dy(H₃L¹)₂]Cl₃·6MeOH, [Eu^III(H₃L¹)₂]Cl₃·6MeOH and [Tb^III(H₃L¹)₂](NO₃)₃ reveal high-crystallographic ?3 symmetry at the O₆-coordinated octahedral lanthanide(III) ions and that the tripodal ligands are bound in zwitterionic form: the protons from the phenolic oxygens have migrated to the amino nitrogens. Photoluminescence measurements indicate various degrees of energy transfer of the ligand chromophore to the lanthanide ions, as both ligand and lanthanide emission features are observed. Despite the high-crystallographic symmetry and the likely small transverse magnetic anisotropy of the complexes, no evidence of slow relaxation of the magnetisation, characteristic of a single-molecule magnet, was observed for [Tb^III(H₃L¹)₂]Cl₃·MeOH·3H₂O, [Dy^III(H₃L¹)₂]Cl₃·6H₂O, [Ho^III(H₃L¹)₂](NO₃)₃·2H₂O, [Er^III(H₃L¹)₂]·H₂O and [Tb^III(H₃L¹)₂](NO₃)₃ down to 2.0 K.     

Synthesis,structure and luminescence properties of two novel lanthanide complexes with 2-fluorobenzoic acid and 1,10-phenanthroline

Two lanthanide complexes with 2-fluorobenzoate (2-FBA) and 1,10-phenanthroline (phen) were synthesized and characterized by X-ray diffraction. The structure of each complex contains two non-equivalent binuclear molecules, [Ln(2-FBA)₃?·?phen?·?CH₃CH₂OH]₂ and [Ln(2-FBA)₃?·?phen]₂ (Ln?=?Eu (1) and Sm (2)). In [Ln(2-FBA)₃?·?phen?·?CH₃CH₂OH]₂, the Ln³⁺ is surrounded by eight atoms, five O atoms from five 2-FBA groups, one O atom from ethanol and two N atoms from phen ligand; 2-FBA groups coordinate Ln³⁺ with monodentate and bridging coordination modes. The polyhedron around Ln³⁺ is a distorted square-antiprism. In [Ln(2-FBA)₃?·?phen]₂, the Ln³⁺ is coordinated by nine atoms, seven O atoms from five 2-FBA groups and two N atoms of phen ligand; 2-FBA groups coordinate Ln³⁺ ion with chelating, bridging and chelating-bridging three coordination modes. The polyhedron around Ln³⁺ ion is a distorted, monocapped square-antiprism. The europium complex exhibits strong red fluorescence from ⁵D₀?→?⁷F _j ( j?=?1–4) transition emission of Eu³⁺.     

Synthesis,crystal structure,antioxidation and fluorescence of two lanthanide complexes with a noncyclic polyether Schiff base ligand

Two lanthanide (Sm and La) complexes with the Schiff base ligand bis(3-methoxysalicylidene)-3-oxapentane-1,5-diamine (Bod) have been synthesized and characterized by physico-chemical and spectroscopic methods. [Sm(Bod)(NO₃)₃] {bis(3-methoxysalicylidene)-3-oxapentane-1,5-diamine samarium(III) trinitrate} (1) is a discrete mononuclear species and [La(Bod)(NO₃)₃(DMF)]_n {bis(3-methoxysalicylidene)-3-oxapentane-1,5-diamine dimethylformamide lanthanum(III) trinitrate}_n (2) formed an inorganic coordination polymer. In the two complexes, the metal ions are both ten-coordinate and the geometric structure around the Ln(III) ions can be described as distorted hexadecahedral. An antioxidant assay in vitro shows that complexes 1 and 2 exhibit better scavenging activity than both the ligand and the usual antioxidants on hydroxyl and superoxide radicals. Under excitation at room temperature, a red shift in the fluorescence band of the ligand in the complexes compared with that of the free ligand can be attributed to coordination of the rare earth ions to the ligand. Furthermore, 1 produced characteristic Sm(III) luminescence, which indicates the ligand Bod is a good organic chelator to absorb energy and transfer it to the Sm³⁺ ion.     

Synthesis,Crystal Structure,Fluorescent and Antioxidation Properties of Cerium(III) and Europium(III) Complexes with Bis(3‐methoxysalicylidene)‐3‐oxapentane‐1,5‐diamine

Two aliphatic ether Schiff base lanthanide complexes (Ln = Eu, Ce) with bis(3‐methoxysalicylidene)‐3‐oxapentane‐1,5‐diamine (Bod), were synthesized and characterized by physicochemical and spectroscopic methods. [Eu(Bod)(NO₃)₃] ( 1 ) is a discrete mononuclear species and [Ce(Bod)(NO₃)₃DMF]_∞ ( 2 ) exhibits an inorganic coordination polymer. In the two complexes, the metal ions both are ten‐coordinated and the geometric structure around the Ln^III atom can be described as distorted hexadecahedron. Under excitation at room temperature, the red shift in the fluorescence band of the ligand in the complexes compared with that of the free ligand can be attributed to coordination of the rare earth ions to the ligand. Moreover, the antioxidant activities of the two complexes were investigated. The results demonstrated that the complexes have better scavenging activity than both the ligand and the usual antioxidants on the hydroxyl and superoxide radicals.     

Insights into crystal structures,supramolecular architectures and antioxidant activities of self-assembled fluorescent hetero-multinuclear [Cu (II)-Ln (III)] (Ln = La,Ce, Pr and Nd) salamo-like complexes

Newly designed hetero-dinuclear 3d–4f complex [Cu(L)La (NO₃)₂(μ-NO₃)(H₂O)]·EtOH ( 1 ), hetero-tetranuclear 3d–4f complex [Cu(L)Ce (NO₃)₂(μ-NO₃)(OAc)₂]₂·MeOH ( 2 ) and hetero-multinuclear 3d–4f complexes [{Cu(L)Ln (NO₃)₃}₂][Cu(L)Ln (NO₃)₃]₂ (Ln = Pr ( 3 ) and Nd = ( 4 )) have been self-assembled from the reaction of Cu (OAc)₂·H₂O, Ln (NO₃)₃·6H₂O (Ln = La, Ce, Pr and Nd) with an unsymmetric salamo-like bisoxime ligand H₂L (6-Methoxy-6′-ethoxy-2,2′-[ethylenedioxybis (nitrilomethylidyne)]diphenol) based on a Schiff base condensation of 2-[O-(1-ethoxyamide)]oxime-6-methoxyphenol and 3-ethoxysalicylaldehyde. The structures of complexes 1 – 4 were characterized by elemental analyses, PXRD analyses, IR, UV–Vis spectra, and single-crystal X-ray analyses. In addition, the supramolecular interactions and fluorescence properties of complexes 1 – 4 are discussed in detail. Moreover, the antioxidant activities of the complexes 1 – 4 were determined by superoxide radical-scavenging method in vitro, which indicates that the complexes 1 – 4 all show potential antioxidant properties.     

Tunable Emissive Lanthanidomesogen Derived from a Room‐Temperature Liquid‐Crystalline Schiff‐Base Ligand

A novel photoluminescent room‐temperature liquid‐crystalline salicylaldimine Schiff base with a short alkoxy substituent and a series of lanthanide(III) complexes of the type [Ln(LH)₃(NO₃)₃] (Ln=La, Pr, Sm, Gd, Tb, Dy; LH=(E)‐5‐(hexyloxy)‐2‐ [{2‐(2‐hydroxyethylamino)ethylimino]methyl}phenol) have been synthesized and characterized by FTIR, ¹H and ¹³C NMR, UV/Vis, and FAB‐MS analyses. The ligand coordinates to the metal ions in its zwitterionic form. The thermal behavior of the compounds was investigated by polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). The ligand exhibits an enantiotropic hexagonal columnar (Col_h) mesophase at room temperature and the complexes show an enantiotropic lamellar columnar (Col_L) phase at around 120 °C with high thermal stability. Based on XRD results, different space‐filling models have been proposed for the ligand and complexes to account for the columnar mesomorphism. The ligand exhibits intense blue emission both in solution and in the condensed state. The most intense emissions were observed for the samarium and terbium complexes, with the samarium complex glowing with a bright‐orange light (ca. 560–644 nm) and the terbium complex emitting green light (ca. 490–622 nm) upon UV irradiation. DFT calculations performed by using the DMol3 program at the BLYP/DNP level of theory revealed a nine‐coordinate structure for the lanthanide complexes.