Synthesis,Characterization and Photoluminescence of Lanthanide Metal‐organic Frameworks,Constructed from Triangular 4,4′,4″‐s‐triazine‐1,3,5‐triyl‐p‐aminobenzoate Ligands

Eight isomorphous metal‐organic frameworks: [Ln₂(TATAB)₂(H₂O)(DMA)₆]·5H₂O (Ln = Sm ( 1 ), Eu ( 2 ), Gd ( 3 ), Tb ( 4 ), Dy ( 5 ), Er ( 6 ), Tm ( 7 ), Yb ( 8 )); TATAB = 4,4′,4″‐s‐triazine‐1,3,5‐triyl‐p‐aminobenzoate, DMA = N,N‐dimethylacetamide), were synthesized by the self‐assembly of lanthanide ions, TATAB, DMA and H₂O. Single‐crystal X‐ray crystallography reveals they are three dimensional frameworks with 2‐fold interpenetration. Solid‐state photoluminescence studies indicate ligand‐to‐metal energy transfer is more efficient for compounds 2 and 4 which exhibit intense characteristic lanthanide emissions at room temperature.     

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.     

A EuIII‐MOF with Bis(2‐carboxyethyl)isocyanurate for Luminescence Sensing of Fe3+ and SCN– Ions

The water‐stable 3D lanthanide‐organic framework (Ln‐MOF) {[Eu(bci)(H₂O)] · 2H₂O}_n ( 1 ) [H₂bci = bis(2‐carboxyethyl)isocyanurate] was synthesized under hydrothermal conditions. Compound 1 ‐ Eu exhibits a 3D open‐framework connected by Eu–(μ‐O)₂–Eu chains and bci ligands. Meanwhile, 1 ‐ Eu exhibits highly efficient luminescent sensing for environmentally relevant Fe³⁺ and SCN^– ions through luminescence quenching. These results indicated that it could be utilized as a multi‐responsive luminescence sensor.     

Anionically Substituted 1,1′,1″‐Methylidynetris[1H‐pyrazole] Ligands for the Formation of Neutral Lanthanide Complexes in Water: Synthesis,Characterization, and Photophysical Properties

The six‐step synthesis of the new podand‐type ligand 6,6′,6″‐[methylidenetri(1H‐pyrazole‐1,3‐diyl)]tris[pyridine‐2‐carboxylic acid] (LH₃) is described. Reaction of LH₃ with LnCl₃ ?6 H₂O (Ln=Eu, Gd, Tb) in MeOH resulted in the isolation of [LnL]?HCl complexes characterized by elemental analysis, mass and IR spectroscopy. Photophysical studies of the Eu and Tb complexes in aqueous solutions revealed the characteristic luminescence features of the metal atoms, indicative of an efficient ligand‐to‐metal energy‐transfer process. Determination of the luminescence quantum yields in H₂O showed the Tb complex to be highly luminescent (?=15%), while, for the Eu complex, the quantum efficiency was only 2%. Excited‐state‐lifetime measurements in H₂O and D₂O evidenced the presence of ca. three H₂O molecules in the first coordination sphere of the complexes. Investigation of the Gd complex allowed the determination of the ligand‐centered triplet state and showed the ligand to be well suited for energy transfer to the metal. The luminescence properties of the complexes are described, and the properties of the ligand as a suitable complexation pocket is questioned.     

Lanthanide(II) Complexes Supported by N,O‐Donor Tripodal Ligands: Synthesis,Structure, and Ligand‐Dependent Redox Behavior

The preparation and characterization of a series of complexes of the Yb and Eu cations in the oxidation state II and III with the tetradentate N,O‐donor tripodal ligands (tris(2‐pyridylmethyl)amine (TPA), BPA^? (HBPA=bis(2‐pyridylmethyl)(2‐hydroxybenzyl)amine), BPPA^? (HBPPA=bis(2‐pyridylmethyl)(3.5‐di‐tert‐butyl‐2‐hydroxybenzyl)amine), and MPA^2? (H₂MPA=(2‐pyridylmethyl)bis(3.5‐di‐tert‐butyl‐2‐hydroxybenzyl)amine) is reported. The X‐ray crystal structures of the heteroleptic Ln²⁺ complexes [Ln(TPA)I₂] (Ln=Eu, Yb) and [Yb(BPA)I(CH₃CN)]₂, of the Ln²⁺ homoleptic [Ln(TPA)₂]I₂ (Ln=Sm, Eu, Yb) and [Eu(BPA)₂] complexes, and of the Ln³⁺ [Eu(BPPA)₂]OTf and [Yb(MPA)₂K(dme)₂] (dme=dimethoxyethane) complexes have been determined. Cyclic voltammetry studies carried out on the bis‐ligand complexes of Eu³⁺ and Yb³⁺ show that the metal center reduction occurs at significantly lower potentials for the BPA^? ligand as compared with the TPA ligand. This suggests that the more electron‐rich character of the BPA^? ligand results in a higher reducing character of the lanthanide complexes of BPA^? compared with those of TPA. The important differences in the stability and reactivity of the investigated complexes are probably due to the observed difference in redox potential. Preliminary reactivity studies show that whereas the bis‐TPA complexes of Eu²⁺ and Yb²⁺ do not show any reactivity with heteroallenes, the [Eu(BPA)₂] complex reduces CS₂ to afford the first example of a lanthanide trithiocarbonate complex.     

The First Europium(III) β‐Diketonate Complex Functionalized Polyhedral Oligomeric Silsesquioxane

The first europium(III) β‐diketonate complex functionalized polyhedral oligomeric silsesquioxane (POSS) has been obtained by immobilization of such a complex at a silicon vertex of the POSS cage through the complexation of Eu³⁺ ions with thenoyltrifluoroacetone‐functionalized POSS. The new molecular hybrid material is liquid at room temperature, and shows bright‐red emission when irradiated with UV light due to energy transfer from the thenoyltrifluoroacetone ligand to the coordinated Eu³⁺ ions. Thermal analysis has revealed a significant improvement in the thermal stability of the material compared with tris(2‐thenoyltrifluoroacetonate)europium(III) dihydrate, [Eu(TTA)₃] ? 2 H₂O. In the context of recent advances in printable electronic technology, this novel luminescent organic liquid with the characteristic emission of Eu³⁺ may potentially be useful in the development of next‐generation organic devices such as flexible displays.     

Multifunctional Lanthanide‐Based Metal–Organic Frameworks with a Polyheterotopic Ligand: Doped with Ytterbium(III) for Luminescence Enhancement and Selective Dye Adsorption

The chemistry of metal–organic frameworks has been progressing fast with its exciting potential in multifunctional applications. A series of three‐dimensional lanthanide‐based metal–organic frameworks, {[Ln(HTPO)(NO₃)(H₂O)]⋅x(CH₃CN)⋅y(H₂O)}_n (Ln=Eu ( 1 ), Tb ( 2 ), Gd ( 3 ), Sm ( 4 ), Dy ( 5 ), Nd ( 6 )), {[Eu(TPO)(HCOO)_0.5]⋅(H₃O)_0.5}_n ( 7 ), {[Eu(TPO)(DMF)]⋅(solv)_x}_n ( 8 ; DMF= N,N‐dimethylformamide), and {[Eu(TPO)(DMA)]⋅(solv)_x}_n ( 9 ; DMA=dimethylacetamide) were synthesized with semirigid C₃‐symmetric ligand tris(4‐carboxylphenyl)phosphine oxide (H₃TPO). In these frameworks, the H₃TPO ligand exists in a totally different configuration. Framework 1 exhibits good breathing properties for absorbing more guest molecules through a solvent‐induced single‐crystal‐to‐single‐crystal (SC–SC) transformation involving a configuration transformation of the organic linker in the framework. The ytterbium ion was doped into 1 to improve the luminescent performance (lifetime and quantum yield) of the red europium emission. Among a series of Eu_1−xYb_xTPO samples, Eu_0.88Yb_0.12TPO showed enhanced luminescence intensity (≈5.1 times that of the pure europium system), and the lifetime increased from 1073.08 to 1236.57 μs. Moreover, the porosity of these frameworks allows them to efficiently adsorb dye molecules with high selectivity and efficiency.     

One‐dimensional Europium(III) Coordination Polymer Based on 3‐Pyridylacrylic Acid

Under hydrothermal conditions, the reaction of racemic 3‐pyridyl‐3‐aminopropionic acid (rac‐HPAPA) with Eu(ClO₄)₃· 6H₂O affords a 1‐D chain complex, [Eu(3‐PYA)₃(H₂O)]_n ( 1 ) (3‐PYA=3‐pyridylacrylate), which represents an example of neutral 1‐D coordination polymeric material based on 3‐HPYA (HPYA= pyridylacrylic acid) ligand with strong red fluorescent emission in the solid state.     

Three Lanthanide Metal‐Organic Frameworks Based on an Ether‐Decorated Polycarboxylic Acid Linker: Luminescence Modulation,CO2 Capture and Conversion Properties

Three new isostructural 3D lanthanide metal–organic frameworks (Ln‐MOFs), {H[LnL(H₂O)]?2 H₂O}_n ( 1‐Ln ) (Ln=Eu³⁺, Gd³⁺ and Tb³⁺), based on infinite lanthanide‐carboxylate chains were constructed by employing an ether‐separated 5,5′‐oxydiisophthalic acid (H₄L) ligand under solvothermal reaction. 1‐Eu and 1‐Tb exhibit strong red and green emission, respectively, through the antenna effect, as demonstrated through a combination of calculation and experimental results. Moreover, a series of dichromatic doped 1‐Eu_xTb_y MOFs were fabricated by introducing different concentrations of Eu³⁺ and Tb³⁺ ions, and they display an unusual variation of luminescent colors from green, yellow, orange to red. 1‐Eu with channels decorated by ether O atoms and the open metal sites displays good performance for CO₂ capture and conversion between CO₂ and epoxides into cyclic carbonates.     

Lanthanide(III) Complexes of 4,10‐Bis(phosphonomethyl)‐1,4,7,10‐tetraazacyclododecane‐1,7‐diacetic acid (trans‐H6do2a2p) in Solution and in the Solid State: Structural Studies Along the Series

Complexes of 4,10‐bis(phosphonomethyl)‐1,4,7,10‐tetraazacyclododecane‐1,7‐diacetic acid (trans‐H₆do2a2p, H₆ L ) with transition metal and lanthanide(III) ions were investigated. The stability constant values of the divalent and trivalent metal‐ion complexes are between the corresponding values of H₄dota and H₈dotp complexes, as a consequence of the ligand basicity. The solid‐state structures of the ligand and of nine lanthanide(III) complexes were determined by X‐ray diffraction. All the complexes are present as twisted‐square‐antiprismatic isomers and their structures can be divided into two series. The first one involves nona‐coordinated complexes of the large lanthanide(III) ions (Ce, Nd, Sm) with a coordinated water molecule. In the series of Sm, Eu, Tb, Dy, Er, Yb, the complexes are octa‐coordinated only by the ligand donor atoms and their coordination cages are more irregular. The formation kinetics and the acid‐assisted dissociation of several Ln^III–H₆ L complexes were investigated at different temperatures and compared with analogous data for complexes of other dota‐like ligands. The [Ce( L )(H₂O)]^3? complex is the most kinetically inert among complexes of the investigated lanthanide(III) ions (Ce, Eu, Gd, Yb). Among mixed phosphonate–acetate dota analogues, kinetic inertness of the cerium(III) complexes is increased with a higher number of phosphonate arms in the ligand, whereas the opposite is true for europium(III) complexes. According to the ¹H NMR spectroscopic pseudo‐contact shifts for the Ce–Eu and Tb–Yb series, the solution structures of the complexes reflect the structures of the [Ce(H L )(H₂O)]^2? and [Yb(H L )]^2? anions, respectively, found in the solid state. However, these solution NMR spectroscopic studies showed that there is no unambiguous relation between ³¹P/¹H lanthanide‐induced shift (LIS) values and coordination of water in the complexes; the values rather express a relative position of the central ions between the N₄ and O₄ planes.     

A fourfold interpenetrating cadmium(II) metal–organic framework based on 2,4,6‐tris(pyridin‐4‐yl)‐1,3,5‐triazine with reversible photochromic properties

2,4,6‐Tris(pyridin‐4‐yl)‐1,3,5‐triazine (tpt), as an organic molecule with an electron‐deficient nature, has attracted considerable interest because of its photoinduced electron transfer from neutral organic molecules to form stable anionic radicals. This makes it an excellent candidate as an organic linker in the construction of photochromic complexes. Such a photochromic three‐dimensional (3D) metal–organic framework (MOF) has been prepared using this ligand. Crystallization of tpt with Cd(NO₃)₂·4H₂O in an N,N‐dimethylacetamide–methanol mixed‐solvent system under solvothermal conditions afforded the 3D MOF poly[[bis(nitrato‐κ²O,O′)cadmium(II)]‐μ₃‐2,4,6‐tris(pyridin‐4‐yl)‐1,3,5‐triazine‐κ³N²:N⁴:N⁶], [Cd(NO₃)₂(C₁₈H₁₂N₆)]_n, which was characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis and single‐crystal X‐ray diffraction. The X‐ray diffraction crystal structure analysis reveals that the asymmetric unit contains one independent Cd^II cation, one tpt ligand and two coordinated NO₃^? anions. The Cd^II cations are connected by tpt ligands to generate a 3D framework. The single framework leaves voids that are filled by mutual interpenetration of three independent equivalent frameworks in a fourfold interpenetrating architecture. The compound shows a good thermal stability and exhibits a reversible photochromic behaviour, which may originate from the photoinduced electron‐transfer generation of radicals in the tpt ligand.     

Self‐Assembly versus Stepwise Synthesis: Heterometal–Organic Frameworks Based on Metalloligands with Tunable Luminescence Properties

A new family of heterometal–organic frameworks has been prepared by two synthesis strategies, in which IFMC‐26 and IFMC‐27 are constructed by self‐assembly and IFMC‐28 is obtained by stepwise synthesis based on the metalloligand (IFMC=Institute of Functional Material Chemistry). IFMC‐26 is a (3,6)‐connected net and IFMC‐27 is a (4,8)‐connected 3D framework. The metalloligands {Ni(H₄L)}(NO₃)₂ are connected by binuclear lanthanide clusters giving rise to a 2D sheet structure in IFMC‐28 . Notably, IFMC‐26‐Eu _x Tb _y and IFMC‐28‐Eu _x Tb _y have been obtained by changing the molar ratios of raw materials. Owing to the porosity of IFMC‐26 , Tb³⁺@IFMC‐26‐Eu and Eu³⁺@IFMC‐26‐Tb are obtained by postencapsulating Tb^III and Eu^III ions into the pores, respectively. Tunable luminescence in metal–organic frameworks is achieved by the two kinds of doping methods. In particular, the quantum yields of heterometal–organic frameworks are apparently enhanced by postencapsulation of Ln^III ions.     

catena‐Poly­[europium(III)‐tri‐μ‐2,3‐di­methoxy­benzoato]

The title compound, [Eu(C₉H₉O₄)₃]_n or [Eu(2,3‐DMOBA)₃]_n, where 2,3‐DMOBA is 2,3‐di­methoxy­benzoate, is an infinite one‐dimensional non‐centrosymmetric coordination polymer. The unique Eu^III atom is bridged by six carboxyl­ate ligands; it is ennea‐coordinated and has a distorted tricapped trigonal prism geometry. The Eu—O distances are in the range 2.315 (3)–2.959 (5) Å.     

Borromean‐Entanglement‐Driven Assembly of Porous Molecular Architectures with Anion‐Modified Pore Space

A series of metal–organic frameworks based on a flexible, highly charged Bpybc ligand, namely 1? Mn?OH^?, 2? Mn?SO₄^2?, 3? Mn?bdc^2?, 4? Eu?SO₄^2? (H₂BpybcCl₂=1,1′‐bis(4‐carboxybenzyl)‐4,4′‐bipyridinium dichloride, H₂bdc=1,4‐benzenedicarboxylic acid) have been obtained by a self‐assembly process. Single‐crystal X‐ray‐diffraction analysis revealed that all of these compounds contained the same n‐fold 2D→3D Borromean‐entangled topology with irregular butterfly‐like pore channels that were parallel to the Borromean sheets. These structures were highly tolerant towards various metal ions (from divalent transition metals to trivalent lanthanide ions) and anion species (from small inorganic anions to bulky organic anions), which demonstrated the superstability of these Borromean linkages. This non‐interpenetrated entanglement represents a new way of increasing the stability of the porous frameworks. The introduction of bipyridinium molecules into the porous frameworks led to the formation of cationic surface, which showed high affinities to methanol and water vapor. The distinct adsorption and desorption isotherms of methanol vapor in four complexes revealed that the accommodated anion species (of different size, shape, and location) provided a unique platform to tune the environment of the pore space. Measurements of the adsorption of various organic vapors onto framework 1? Mn?OH^? further revealed that these pores have a high adsorption selectivity towards molecules with different sizes, polarities, or π‐conjugated structures.     

catena‐Poly­[[di­aqua­(isonicotinato‐O,O′)­europium(III)]‐di‐μ‐isonicotin­ato‐O:O′]

The title complex, [Eu(C₆H₄O₂)₃(H₂O)₂], has a double carboxyl­ate‐bridged infinite‐chain structure, with one chelating carboxyl­ate group on each Eu ion centre, which also binds to two water mol­ecules to yield an eight‐coordinate square‐antiprismatic geometry, with Eu—O bond lengths in the range 2.338 (3)–2.594 (3) Å. The pyridine N atoms of the isonicotinate groups do not coordinate to the Eu ions; instead, they direct the formation of Eu^III coordination polymers via hydrogen bonding with coordinated water mol­ecules.     

A three‐dimensional homochiral metal–organic framework constructed from manganese(II) with S‐carboxymethyl‐N‐(p‐tosyl)‐l‐cysteine and 4,4′‐bipyridine

In the chiral polymeric title compound, poly[aqua(4,4′‐bipyridine)[μ₃‐S‐carboxylatomethyl‐N‐(p‐tosyl)‐l ‐cysteinato]manganese(II)], [Mn(C₁₂H₁₃NO₆S₂)(C₁₀H₈N₂)(H₂O)]_n, the Mn^II ion is coordinated in a distorted octahedral geometry by one water molecule, three carboxylate O atoms from three S‐carboxyatomethyl‐N‐(p‐tosyl)‐l ‐cysteinate (Ts‐cmc) ligands and two N atoms from two 4,4′‐bipyridine molecules. Each Ts‐cmc ligand behaves as a chiral μ₃‐linker connecting three Mn^II ions. The two‐dimensional frameworks thus formed are further connected by 4,4′‐bipyridine ligands into a three‐dimensional homochiral metal–organic framework. This is a rare case of a homochiral metal–organic framework with a flexible chiral ligand as linker, and this result demonstrates the important role of noncovalent interactions in stabilizing such assemblies.     

Tieftemperatur‐Oxidation in flüssigem Ammoniak: [Eu2(Ind)4(NH3)6], das erste Indolat eines Selten‐Erd‐Elementes

Low‐Temperature Oxidation in Liquid Ammonia: [Eu₂(Ind)₄(NH₃)₆], the First Indolate of a Rare Earth Element Intensively yellow to orange coloured, transparent crystals of [Eu₂(Ind)₄(NH₃)₆] were obtained by low‐temperature oxidation of europium metal with indole (C₈H₆NH) in liquid ammonia at —50 °C and subsequent melting of the reaction mixture in excess indole at 120 °C. [Eu₂(Ind)₄(NH₃)₆] has a dimeric structure and contains divalent Eu. The coordination sphere around the europium atoms consists of five N atoms of two cisoid indolate anions and three NH₃ molecules as well as an η⁵‐coordinating π‐system of another indolate ligand, bridging to the next Eu atom with an sp²‐orbital.     

catena‐Poly[[[(di‐2‐pyridylamine‐κ2N2,N2′)copper(II)]‐μ‐benzene‐1,3‐dicarboxylato‐κ3O1,O1′:O3] monohydrate], a zigzag coordination polymer with strong π–π interactions

The novel title coordination polymer, {[Cu(C₈H₄O₄)(C₁₀H₉N₃)]·H₂O}_n, synthesized by the slow‐diffusion method, takes the form of one‐dimensional zigzag chains built up of Cu^II cations linked by benzene‐1,3‐dicarboxylate (ipht) anions. An exceptional characteristic of this structure is that it belongs to a small group of metal–organic polymers where ipht is coordinated as a bridging tridentate ligand with monodentate and chelate coordination of individual carboxylate groups. The Cu^II cation has a highly distorted square‐pyramidal geometry formed by three O atoms from two ipht anions and two N atoms from a di‐2‐pyridylamine (dipya) ligand. The zigzag chains, which run along the b axis, further construct a three‐dimensional metal–organic framework via strong face‐to‐face π–π interactions and hydrogen bonds. A solvent water molecule is linked to the different carboxylate groups via hydrogen bonds. Thermogravimetric and differential scanning calorimetric analyses confirm the strong hydrogen bonding.     

N,N′‐Bis(Salicylidene)‐1,2‐Cyclohexanediamine Lanthanide(III) Coordination Polymers: Syntheses,Crystal Structures,and Luminescence Properties

The salen‐type ligand H₂L [H₂L = N,N′‐bis(salicylidene)‐1,2‐cyclohexanediamine] was utilized for the synthesis of two lanthanide(III) coordination polymers [LnH₂L(NO₃)₃MeOH]_n [Ln = Eu ( 1 ) and Ln = Lu ( 2 )]. The single‐crystal X‐ray diffraction analyses of 1 and 2 revealed that they are isomorphous and exhibit one‐dimension neutral structure, in which H₂L effectively functions as a bridging ligand and give rise to a chain‐like polymer. The luminescent properties of polymers in solid state and in solution were investigated and 1 exhibits typical red luminescence of Eu^III ions in solid state and dichloromethane solution and 2 emits the ligand‐centered blue luminescence. The energy transfer mechanisms in these luminescent lanthanide polymers were described through calculation of the lowest triplet level of ligand H₂L.     

Highly Efficient Visible‐to‐NIR Luminescence of Lanthanide(III) Complexes with Zwitterionic Ligands Bearing Charge‐Transfer Character: Beyond Triplet Sensitization

Two zwitterionic‐type ligands featuring π–π* and intraligand charge‐transfer (ILCT) excited states, namely 1,1′‐(2,3,5,6‐tetramethyl‐1,4‐phenylene)bis(methylene)dipyridinium‐4‐olate (TMPBPO) and 1‐dodecylpyridin‐4(1 H)‐one (DOPO), have been prepared and applied to the assembly of lanthanide coordination complexes in an effort to understand the ligand‐direction effect on the structure of the Ln complexes and the ligand sensitization effect on the luminescence of the Ln complexes. Due to the wide‐band triplet states plus additional ILCT excitation states extending into lower energy levels, broadly and strongly sensitized photoluminescence of f→f transitions from various Ln³⁺ ions were observed to cover the visible to near‐infrared (NIR) regions. Among which, the Pr, Sm, Dy, and Tm complexes simultaneously display both strong visible and NIR emissions. Based on the isostructural feature of the Ln complexes, color tuning and single‐component white light was achieved by preparation of solid solutions of the ternary systems Gd‐Eu‐Tb (for TMPBPO) and La‐Eu‐Tb and La‐Dy‐Sm (for DOPO). Moreover, the visible and NIR luminescence lifetimes of the Ln complexes with the TMPBPO ligand were investigated from 77 to 298 K, revealing a strong temperature dependence of the Tm³⁺ (³H₄) and Yb³⁺ (²F_5/2) decay dynamics, which has not been explored before for their coordination complexes.