Syntheses, Structures and Photophysical Properties of New Heterodinuclear Cd–Ln Coordination Complexes (Ln = Sm, Eu, Tb, Nd, Ho, Er)

Cadmium-Inspired Self-Polymerization of {LnIIICd2} Units: Structure, Magnetic and Photoluminescent Properties of Novel Trimethylacetate 1D-Polymers (Ln = Sm, Eu, Tb, Dy, Ho, Er, Yb)

A series of heterometallic carboxylate 1D polymers of the general formula [Ln^IIICd₂(piv)₇(H₂O)₂]_n·nMeCN (Ln^III = Sm (1), Eu (2), Tb (3), Dy (4), Ho (5), Er (6), Yb (7); piv = anion of trimethylacetic acid) was synthesized and structurally characterized. The use of Cd^II instead of Zn^II under similar synthetic conditions resulted in the formation of 1D polymers, in contrast to molecular trinuclear complexes with Ln^IIIZn₂ cores. All complexes 1–7 are isostructural. The luminescent emission and excitation spectra for 2–4 have been studied, the luminescence decay kinetics for 2 and 3 was measured. Magnetic properties of the complexes 3–5 and 7 have been studied; 4 and 7 exhibited the properties of field-induced single-molecule magnets in an applied external magnetic field. Magnetic properties of 4 and 7 were modelled using results of SA-CASSCF/SO-RASSI calculations and SINGLE_ANISO procedure. Based on the analysis of the magnetization relaxation and the results of ab initio calculations, it was found that relaxation in 4 predominantly occurred by the sum of the Raman and QTM mechanisms, and by the sum of the direct and Raman mechanisms in the case of 7.

Some aspects of the formation and structural features of low nuclearity heterometallic carboxylates

Heterometallic carboxylate complexes are of paramount interest in pure and applied coordination chemistry. Despite that plurality of such type compounds have been published to date, synthetic aspects of their chemistry often remain in the shadow of intriguing physical properties manifesting by these species. Present review summarizes reliable data on direct synthesis of low nuclearity molecular compounds as well as coordination polymers on their base with carboxylate-bridged {M2Mg} (M = Co2+, Ni2+, Cd2+), {M2Li2} (M = Co2+, Ni2+, Zn2+, VO2+), {M2Ln2} and {M2Ln} (M = Cu2+, Zn2+, Co2+) metal cores. Structural features and stabilization factors are considered and principal outcomes are confirmed by quantum-chemical calculations. Particular attention is paid to consideration of ligand-exchange reactions that allow controllable modification of heterometallic metal core under mild conditions giving diverse molecular complexes with modified ligand environment or Metal-Organic Frameworks with permanent porosity.

Enhancement of the luminescence properties of high-nuclearity Cd-Ln (Ln = Eu and Nd) nanoclusters by the introduction of more energy transfer donors

Two Cd-Ln clusters [Ln₈Cd₂₄L₁₂(1,4-BDC)₄(OAc)₃₈(OH)₂] (Ln = Eu (1) and Nd (2)) were constructed using a flexible Schiff base and rigid 1,4-BDC ligands. The Cd-Ln clusters exhibit interesting nano-drum-like structures which allow direct visualization by TEM. The introduced 1,4-BDC units act as efficient energy transfer donors for lanthanide luminescence, resulting in superior luminescence properties of 1 and 2.

Lanthanide doped coordination polymers with tunable afterglow based on phosphorescence energy transfer

Lanthanide ion doped coordination polymers (CPs) exhibit an unusual red/green afterglow with long photoemission lifetimes (10.54 ms for Eu³⁺ and 57.66 ms for Tb³⁺) due to the phosphorescence energy transfer at room temperature.

Anisotropic lanthanide-based nano-clusters for imaging applications

We have developed a new class of lanthanide nano-clusters that self-assemble using flexible Schiff base ligands. Cd-Ln and Ni-Ln clusters, [Ln8Cd24(L1)12(OAc)39Cl7(OH)2] (Ln = Nd, Eu), [Eu8Cd24(L1)12(OAc)44], [Ln8Cd24(L2)12(OAc)44] (Ln = Nd, Yb, Sm) and [Nd2Ni4(L3)2(acac)6(NO3)2(OH)2], were constructed using different types of flexible Schiff base ligands. These molecular nano-clusters exhibit anisotropic architectures that differ considerably depending upon the presence of Cd (nano-drum) or Ni (square-like nano-cluster). Structural characterization of the self-assembled particles has been undertaken using crystallography, transmission electron microscopy and small-angle X-ray scattering. Comparison of the metric dimensions of the nano-drums shows a consistency of size using these techniques, suggesting that these molecules may share similar structural features in both solid and solution states. Photophysical properties were studied by excitation of the ligand-centered absorption bands in the solid state and in solution, and using confocal microscopy of microspheres loaded with the compounds. The emissive properties of these compounds vary depending upon the combination of lanthanide and Cd or Ni present in these clusters. The results provide new insights into the construction of novel high-nuclearity nano-clusters and offer a promising foundation for the development of new functional nanomaterials.

Self-assembly of high-nuclearity lanthanide-based nanoclusters for potential bioimaging applications

Two series of Cd-Ln and Ni-Ln clusters [Ln8Cd24L12(OAc)44(48)Cl4(0)] and [Ln8Ni6L6(OAc)24(EtOH)6(H2O)2] were constructed using a flexible ligand. The Cd-Ln clusters exhibit interesting nano-drum-like structures which allows direct visualization by TEM. Luminex MicroPlex Microspheres loaded with the Cd-Sm cluster were visualized using epifluorescence microscopy. Cytotoxicity studies on A549 and AGS cancer cell lines showed that the materials have mild to moderate cytotoxicity.

Tetranuclear Heterometallic {Zn2Eu2} Complexes With 1-Naphthoate Anions: Synthesis, Structure and Photoluminescence Properties

A series of new tetranuclear heterometallic Zn(II) -Eu(III) complexes have been synthesized, that is, (bpy)2 Zn2Eu2 (naph)10 (1), (bpy)2 Zn2Eu2 (naph)8 (NO3)2 (2), and (phen)2 Zn2Eu2 (naph)8 (NO3)2 (3), and other ones, where naph(-) is the 1-naphthoate anion, bpy=2,2'-bipyridyl, and phen=1,10-phenanthroline. The solid-phase complexes consist of large supramolecular ensembles due to stacking interactions between the aromatic ligands. Photoluminescence (PL) measurements were carried out to study PL spectra, lifetimes and quantum yields (QY) of the synthesized complexes at different temperatures. The external QY for the solid phases of complexes under UV excitation was found to exceed 20 %. It has been shown that partial replacement of naphthoate ligands in the coordination environment of Eu(3+) by NO3(-) anions influences the PL properties. To investigate the behavior of these complexes in solvent, we dissolved complex 3 in MeCN, put it on a transparent glass as a substrate, and studied the PL properties at room temperature.

3D Ln–Organic Frameworks Featuring Lantern-Shaped Dihelicate Chains: Synthesis and Magnetic and Photophysical Properties

The in situ hydrothermal reaction of rare earth nitrate (Ln(NO3)3), 5-(4-carboxyl-1H-1,2,3-triazol-1-yl) isophthalic acid (H3ctia), and (NH4)2C2O4 resulted in the formation of a series of 3D 4f coordination polymers ([Ln(tia)(C2O4)0.5(H2O)]) (Ln = Nd (1), Sm (2), Eu (3), Gd (4), Tb (5), Dy (6), and tia2– = 5-(1H-1,2,3-triazol-1-yl) isophthalate). The results of single crystal X-ray diffraction reveal that the dinuclear lantern sub-building units ([Ln2(CO2)4]2+) are linked by C2O42– to form dihelicate chains, which are connected by tia2– to afford a novel 3D metal–organic framework with an unordinary 3-nodal (2,3,8)-connected topological network with the Schläfli symbol of {4.62}2{42.616.89.10}{6}. Complexes 2, 3, 5, and 6 exhibit strong fluorescent emissions in the visible region and complexes 1, 2, and 6 show characteristic fluorescent emissions in the near-infrared region. In addition, the magnetic properties of complexes 4, 5, and 6 were also investigated.

A self-assembling lanthanide molecular nanoparticle for optical imaging

Chromophores that incorporate f-block elements have considerable potential for use in bioimaging applications because of their advantageous photophysical properties compared to organic dye, which are currently widely used. We are developing new classes of lanthanide-based self-assembling molecular nanoparticles as reporters for imaging and as multi-functional nanoprobes or nanosensors for use with biological samples. One class of these materials, which we call lanthanide "nano-drums", are homogeneous 4d-4f clusters approximately 25 to 30 Å in diameter. These are capable of emitting from the visible to near-infrared wavelengths. Here, we present the synthesis, crystal structure, photophysical properties and comparative cytotoxicity data for a 32 metal Eu-Cd nano-drum [Eu(8)Cd(24)L(12)(OAc)(48)] (1). We also explored the imaging capabilities of this nano-drum using epifluorescence, TIRF, and two-photon microscopy platforms.

Self-assembly of NIR luminescent 30-metal drum-like and 12-metal rectangular d-f nanoclusters with long-chain Schiff base ligands

Two classes of heterobimetallic d-f nanoclusters [Ln6Cd24(L(1))11(OAc)43(OH)] and [Ln4Zn8(L(2))2(OAc)20(OH)4] (Ln = Nd and Yb) were prepared using flexible long-chain Schiff base ligands which have (CH2)6 backbones. Their NIR luminescence properties were determined.

Anion dependent self-assembly of 56-metal Cd-Ln nanoclusters with enhanced near-infrared luminescence properties

Two series of Cd-Ln clusters: nano-drum [Ln₈Cd₂₄L₁₂(OAc)₄₈] and nano-double-drum [Ln₁₂Cd₄₄L₂₀Cl₃₀(OAc)₅₄] (Ln = Nd and Yb) were prepared using a flexible Schiff base ligand bearing two aryl-Br groups. Chloride (Cl(-)) ions, together with the interactions of Br with other electronegative atoms, play a key role in the formation of the nano-double-drums. The structures were studied by TEM and photophysical properties were determined.

Ln–Cd heterometal organic–inorganic hybrid materials based on diverse Ln–Cd oxo-cluster chains: syntheses, structures and visible luminescence

Two types of luminescent Ln–Cd heterometal complexes, I and II, based on diverse Ln–Cd oxo-clusters have been synthesized and characterized.

Three novel d7/d10 metal complexes with N-heterocyclic ligand of 2,6-bis(3-pyrazolyl)pyridine: synthesis, structure, surface photovoltage spectroscopy and photocatalytic activity

We synthesized three novel d⁷/d¹⁰ metal complexes with 2,6-bis(3-pyrazolyl)pyridine and studied their surface photovoltage spectra and photocatalytic activities.

Lanthanide nano-drums: a new class of molecular nanoparticles for potential biomedical applications

We are developing a new class of lanthanide-based self-assembling molecular nanoparticles as potential reporter molecules for imaging, and as multi-functional nanoprobes or nanosensors in diagnostic systems. These lanthanide "nano-drums" are homogeneous 4d-4f clusters approximately 25 to 30 Å in diameter that can emit from the visible to near-infrared (NIR) wavelengths. Here, we present syntheses, crystal structures, photophysical properties, and comparative cytotoxicity data for six nano-drums containing either Eu, Tb, Lu, Er, Yb or Ho. Imaging capabilities of these nano-drums are demonstrated using epifluorescence, total internal reflection fluorescence (TIRF), and two-photon microscopy. We discuss how these molecular nanoparticles can to be adapted for a range of assays, particularly by taking advantage of functionalization strategies with chemical moieties to enable conjugation to protein or nucleic acids.

Four 2D Ln–Cd heterometal–organic coordination polymers based on tetranuclear Ln–Cd oxo-cluster with highly selective luminescent sensing of organic molecules and metal cations

Two series of 2D-layered Ln–Cd heterometal–organic complexes based on tetranuclear [Ln₂Cd₂] oxo-clusters with selective luminescent sensing have been synthesized.

Anion-dependent self-assembly of near-infrared luminescent 24- and 32-metal Cd-Ln complexes with drum-like architectures

Two series of 4d-4f clusters [Ln8Cd24L12(OAc)48] and [Ln6Cd18L9Cl8(10)(OAc)28(26)] (Ln = Nd, Gd, Er, and Yb) with novel drum-like structures were prepared using a flexible Schiff base ligand. Their NIR luminescence properties were determined.

A series of novel lanthanide carboxyphosphonates with a 3D framework structure: synthesis, structure, and luminescent and magnetic properties

By introduction of 1,4-benzenedicarboxylic acid as the second organic ligand, a series of novel lanthanide carboxyphosphonates with a 3D framework structure, namely, [Ln(3)(H(2)L)(HL)(2)(bdc)(2)(H(2)O)]·7H(2)O (Ln = La (1), Ce (2), Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), Tb (8); H(3)L = H(2)O(3)PCH(2)NC(5)H(9)COOH; H(2)bdc = HOOCC(6)H(4)COOH) have been synthesized under hydrothermal conditions. Compounds are isostructural and feature a 3D framework in which Ln(III) polyhedra are interconnected by bridging {CPO(3)} tetrahedra into 2D inorganic layers parallel to the ab plane. The organic groups of H(2)L(-) are grafted on the two sides of the layer. These layers are further cross-linked by the bdc(2-) ligands from one layer to the Ln atoms from the other into a pillared-layered architecture with one-dimensional channel system along the a axis. The thermal stability of compounds has been investigated. Luminescent properties of compounds , and the magnetic properties of compound have also been studied.

Syntheses, structures and photophysical properties of tetranuclear Cd-Ln coordination complexes

Four novel hetero-tetranuclear d-f coordination complexes, [Ln2Cd2(p-toluylate)10(phen)2] (Nd, 1; Pr, 2; Sm, 3) and [Ho2Cd2(p-chloro-benzoate)10(phen)2](4) (phen = 1, 10-phenanthroline), are synthesized by the hydrothermal method, and their structures are studied by single-crystal X-ray diffraction. Structures 1-3 are isomorphous and structure 4 has a similar molecular structure. In the near-infrared (NIR) region or in the visible region, complexes 1-4 show the characteristic emission bands of Ln(III) ions, which are attributed to the sensitization from the ligands and d-block (cadmium-ligand section) to f-block (lanthanide-ligand section). Moreover, in the Cd-Ln complexes, the CdLn separation is very close, so the d-orbital of the Cd(II) ion and the f-orbital of the Ln(III) ion may influence each other, which probably cause the intra-levels to be adjusted. This can have a significant effect on the emission bands in the NIR region, hence the corresponding emission bands of complexes 1, 2 and 4 exhibit shift or splitting compared with isolated Ln(III) ions. At the same time in the UV-Vis-NIR absorption spectra of the complexes, the corresponding absorption bands also show shift or splitting. The shift or splitting of bands in the NIR emission spectra and in the absorption spectra can evidence each other.