Optimizing white light emission in Dy(iii) complexes: impact of energy transfer from mono and bidentate ligands on luminescence

Complexes of dysprosium(iii) ions with 1,1,1,5,5,5-hexafluoro-2,4-pentanedione featuring various mono and bi-dentate neutral ligands have been prepared and thoroughly investigated. The synthesized complexes exhibit an octa-coordinated environment, achieved by stoichiometrically combining organic ligands and Dy(iii) ions. This octa-coordination environment of Dy(iii) ion was confirmed by FT-IR spectroscopy, thermogravimetry and elemental analysis. Near-white light (NWL) is emitted when complexes were exposed to UV radiation, indicating a significant flow of energy from the sensitizing moieties towards the Dy(iii) ion. This NWL emission might have resulted due to a balance between the intensities corresponding to emission peaks at 480 nm (blue) and 575 nm (yellow) in Dy1-Dy3. Emission spectra recorded at different excitation wavelength were utilized to study the tunability of CIE color coordinates. In addition to their high thermal stability, the complexes display bipolar paramagnetic shifts in their NMR spectra. The 4F9/2 → 6H13/2 transition, contributing ∼62% of the total emission, stands out as a promising candidate for laser amplification due to its dominance in the emission spectra. Additionally, NWL emission observed in a solid Dy(iii) complex opens intriguing possibilities for its application in next-generation white-light emitting devices.

Efficient synthetic route to heterobimetallic trinuclear complexes [Ln-Mn-Ln] and their single molecule magnetic properties

A series of mononuclear lanthanoidate complexes isolated as [Bu₄N][Ln(QCl₄)] 1Ln (QCl = 5-chloro-8-quinolinolate; Ln = Eu, Gd, Tb, Dy, Ho, and Er) have been prepared, characterised, and used as facile precursors to obtain a series of new heterobimetallic complexes as crystalline materials. Reaction of 1Ln with manganese nitrate forms [Ln₂Mn(QCl)₈] (2Ln, where Ln = Tb, Dy, Er and Yb) which have been structurally characterised in the cases of 2Tb and 2Yb. The heteroleptic trinuclear complex [Dy₃(QCl)₈Cl(OH₂)], 3, has also been obtained. Compounds 1Dy, 1Tb, and 1Er display slow relaxation of magnetisation below 10K, particularly for the prolate Er³⁺ ion. These results also suggest that the positive effects of the change from mononuclear to trinuclear lanthanoid complexes enhance their single molecule magnetic (SMM) behaviour, as evidenced by the well resolved frequency dependent AC out-of-phase susceptibility maxima seen in the 2Ln systems, that have been analysed quantitatively. The synthesis used here provides a promising strategy in obtaining heterobimetallic complexes with quinolinolate ligands and also constructing efficient heterobimetallic SMMs.

Two Heterometallic Nanoclusters [DyIII4NiII8] and [DyIII10MnIII4MnII2]: Structure, Assembly Mechanism, and Magnetic Properties

A full understanding of the assembly mechanisms of coordination complexes is of great importance for a directional synthesis under control. We thus explored here the formation mechanisms of the two new heterometallic nanoclusters [Dy^III₄Ni^II₈(μ₃-OH)₈(L)₈(OAc)₄(H₂O)₄]·3.25EtOH·4CH₃CN (1) and [Dy^III₁₀Mn^III₄Mn^II₂O₄(OH)₁₂(OAc)₁₆(L)₄(HL)₂(EtOH)₂]·2EtOH·2CH₃CN·2H₂O (2) with different cubane-based squarelike ring structures, which were obtained from the reactions of 4-bromo-2-[(2-hydroxypropylimino)methyl]phenol (H₂L) with Dy(NO)₃·6H₂O and the transition metal salt Ni(OAc)₂·4H₂O or Mn(OAc)₂·4H₂O. The high-resolution electrospray ionization mass spectrometry (HRESI-MS) tests showed that the skeletons of clusters 1 and 2 have a high stability under the measurement conditions for HRESI-MS. The intermediates formed in the reaction courses of clusters 1 and 2 were tracked using time-dependent HRESI-MS, which helped to determine the proposed hierarchical assembly mechanisms for 1 (H₂L → NiL → Ni₂L₂ → Ni₃L₄ → Ni₄L₄ → DyNi₄L₅ → Dy₂Ni₆L₆ → Dy₃Ni₆L₆ → Dy₃Ni₇L₇ → Dy₄Ni₈L₈) and 2 (H₂L → MnL → DyMnL → DyMn₂L → Dy₂Mn₂L_x → Dy₈Mn₂L₂ → Dy₁₀Mn₂L₂ → Dy₁₀Mn₆L_x and H₂L → DyL → Dy₄L₂ → Dy₆L₂ → Dy₈Mn₂L₂ → Dy₁₀Mn₂L₂ → Dy₁₀Mn₆L_x). This is one of the rare examples of investigating the assembly mechanisms of 3d-4f heterometallic clusters. Magnetic studies indicated that the title complexes both show slow magnetic relaxation behaviors and cluster 1 is a field-induced single-molecule magnet.

Two Decanuclear DyIIIxCoII10-x (x = 2, 4) Nanoclusters: Structure, Assembly Mechanism, and Magnetic Properties

The aggregation and formation of heterometallic nanoclusters usually involves a variety of complex self-assembly processes; thus, the exploration of their assembly mechanisms through process tracking is more challenging than that for homometallic nanoclusters. We explored here the effect of solvent on the formation of heterometallic clusters, which gave two heterometallic nanoclusters, [Dy₂Co₈(μ₃-OCH₃)₂(L)₄(HL)₂(OAc)₂(NO₃)₂(CH₃CN)₂]·CH₃CN·H₂O (1) and [Dy₄Co₆(L)₄(HL)₂(OAc)₆(OCH₂CH₂OH)₂(HOCH₂CH₂OH)(H₂O)]·9CH₃CN (2), with the H₃L ligand formed from the in situ condensation reaction of 3-amino-1,2-propanediol with 2-hydroxy-1-naphthaldehyde in the presence of Co(OAc)₂·4H₂O and Dy(NO)₃·6H₂O. It is worth noting that the skeleton of cluster 1 has a high stability under high-resolution electrospray ionization mass spectrometry (HRESI-MS) conditions with a gradually increasing energy of the ion source. Cluster 2 underwent a multistep fragmentation even under a zero ion-source voltage for the measurement of HRESI-MS. Further analysis showed that cluster 2 underwent a possible fragmentation mechanism of Dy₄Co₆L₆ → Dy₂Co₆L₅/DyL → DyCo₂L₃/DyCo₂L → DyL/Co₂L₂. Most notably, the species emerging in the formation process of cluster 1 were tracked using time-dependent HRESI-MS, from which we proposed its possible formation mechanism of H₂L → Co₂L₂ → Co₂DyL₂/Co₃L₂ → Co₃DyL₂ → Co₄DyL₂ → Co₅Dy₂L₄ → Co₈Dy₂L₆. As far as we know, it is the first time to track the formation process of Dy-Co heterometallic clusters through HRESI-MS with the proposed assembly mechanism. The magnetic properties of the two titled Dy^III_xCo^II_10-x (x = 2, 4) clusters were studied. Both of them exhibit slow magnetic relaxation, and 1 is a single-molecule magnet at zero direct-current field.

Mononuclear Dysprosium Alkoxide and Aryloxide Single-Molecule Magnets

Recent studies have shown that mononuclear lanthanide (Ln) complexes can be high‐performing single‐molecule magnets (SMMs). Recently, there has been an influx of mononuclear Ln alkoxide and aryloxide SMMs, which have provided the necessary geometrical control to improve SMM properties and to allow the intricate relaxation dynamics of Ln SMMs to be studied in detail. Here non‐aqueous Ln alkoxide and aryloxide chemistry applied to the synthesis of low‐coordinate mononuclear Ln SMMs are reviewed. The focus is on mononuclear Dy^III alkoxide and aryloxide SMMs with coordination numbers up to eight, covering synthesis, solid‐state structures and magnetic attributes. Brief overviews are also provided of mononuclear Tb^III, Ho^III, Er^III and Yb^III alkoxide and aryloxide SMMs.

High-Coordinate Mononuclear Ln(III) Complexes: Synthetic Strategies and Magnetic Properties

Single-molecule magnets involving monometallic 4f complexes have been investigated extensively in last two decades to understand the factors that govern the slow magnetization relaxation behavior in these complexes and to establish a magneto-structural correlation. The prime goal in this direction is to suppress the temperature independent quantum tunneling of magnetization (QTM) effect via fine-tuning the coordination geometry/microenvironment. Among the various coordination geometries that have been pursued, complexes containing high coordination number around Ln(III) are sparse. Herein, we present a summary of the various synthetic strategies that were used for the assembly of 10- and 12-coordinated Ln(III) complexes. The magnetic properties of such complexes are also described.

Multifunctional Binuclear Ln(III) Complexes Obtained via In Situ Tandem Reactions: Multiple Photoresponses to Volatile Organic Solvents and Anticounterfeiting and Magnetic Properties

The design and synthesis of simple lanthanide complexes with multiple functions have been widely studied and have faced certain challenges. Herein, we successfully synthesized the series of binuclear lanthanide complexes [Ln₂(L1)₂(NO₃)₄] (HL1 = 2-amino-1,2-bis(pyridin-2-yl)ethanol; Ln = Dy (Dy2), Tb (Tb2), Ho (Ho2) Er (Er2)) via the in situ self-condensation of Ln(NO₃)₃·6H₂O-catalyzed 2-aminomethylpyridine (16 steps) under solvothermal conditions. Dy2 was mixed with different volatile organic solvents, and photoluminescence tests demonstrated that it showed an excellent selective photoresponse to chloroform (CHCl₃). Sensing Tb2 on different organic solvents under the same conditions showed that it exhibited excellent selective photoresponse to methanol (CH₃OH). Even under EtOH conditions, Tb2 could selectively respond to small amounts of CH₃OH. To the best of our knowledge, achieving a selective photoresponse to various volatile organic compounds by changing the metal center of the complex is difficult. Furthermore, we performed anticounterfeiting tests on Tb2, and the results showed significant differences between the anticounterfeiting marks under white light and ultraviolet light conditions. The alternating current susceptibilities of Dy2 suggested that it was a typical single-molecule magnet (SMM) (U_eff = 93.62 K, τ₀ = 1.19 × 10^-5 s) under a 0 Oe dc field. Ab initio calculations on Dy2 indicated that the high degrees of axiality of the constituent mononuclear Dy fragments are the main reasons for the existence of SMM behavior.

Metal hydrogen-bonded organic frameworks: structure and performance

Although great progress has been made in the design, synthesis, and performance expansion of porous materials, new porous materials with stable structures still need to be explored further. In recent years, porous molecular crystals formed by intermolecular interactions have attracted wide attention from chemists, especially metal hydrogen-bonded organic frameworks (M-HOFs) formed by connecting metal complexes through hydrogen bonds. Metal complexes with specific properties (e.g., magnetism, luminescence, sensing, and catalysis) can expand and develop the application of M-HOFs further. However, the huge volume, irregular shape, complex coordination modes, and interference of coordination bonds pose certain challenges in the synthesis and performance expansion of M-HOFs. In this frontier, we summarize the latest progress in the use of 3d, 4d, and 4f metal complexes for the synthesis of M-HOFs, and briefly introduce the performance expansion of these M-HOFs, which is expected to help expand new porous materials with stable structures and specific functions.

Regulation of the Metal Center and Coordinating Anion of Mononuclear Ln(III) Complexes to Promote an Efficient Luminescence Response to Various Organic Solvents

A series of mononuclear lanthanide complexes [Ln(L1)(NO₃)₃], (Ln = Dy(III), 1; Tb(III), 3; and Eu(III), 4; L1 = (N¹E,N²E)-N¹,N²-bis((1-methyl-1H-benzo[d]imidazol-2-yl)methylene)cyclohexane-1,2-diamine) is obtained by reacting N-methylbenzimidazole-2-carbaldehyde (L2) and 1,2-cyclohexanediamine (L3) with Ln(NO₃)₃·6H₂O under solvothermal conditions. L1 ligand is produced via an in situ Schiff base reaction of two molecules of L2 and one molecule of L3. The metal center Ln(III) is in a N₄O₆ environment formed by L1 and NO₃^-. NaSCN is added on the basis of 1 synthesis. One SCN^- replaces one of the three coordinated NO₃^- anions in the 1 structure, and the complex [Dy(L1)(NO₃)₂(SCN)]·CH₃CN (2) is synthesized. The complex 1 shows excellent luminescence response to petroleum ether (PET), an organic solvent. To the best of our knowledge, this study is the first to use a complex for sensing responses to PET. When the metal center is changed, the obtained mononuclear complexes 3 and 4 show an excellent luminescence response to tetrahydrofuran (THF). Lastly, 2 obtained by changing the coordinating anion shows an excellent luminescence response to dichloromethane. Herein, for the first time, we regulate the metal center and coordinating anion of lanthanide complexes to adjust the recognition and response of these complexes to different organic solvents.

Mitochondria-localizing dicarbohydrazide Ln complexes and their mechanism of in vitro anticancer activity

Dicarbohydrazide Ln complexes trigger SK-OV-3/DDP cell apoptosis via a mitochondrial dysfunction pathway.

High in vitro and in vivo antitumor activities of Ln(III) complexes with mixed 5,7-dichloro-2-methyl-8-quinolinol and 4,4'-dimethyl-2,2'-bipyridyl chelating ligands

Three novel Ln(III) complexes, namely, [Pm(dmbpy)(ClQ)₂NO₃] (1), [Yb(dmbpy)(ClQ)₂NO₃] (2), and [Lu(dmbpy)(ClQ)₂NO₃] (3), with mixed 5,7-dichloro-2-methyl-8-quinolinol (H-ClQ) and 4,4'-dimethyl-2,2'-bipyridyl (dmbpy) chelating ligands were first synthesized. The cytotoxic activity of Ln(III) complexes 1-3, H-ClQ, and dmbpy against a panel of human normal and cancer cell lines, namely, human non-small cell lung cancer cells (NCI-H460), human cervical adenocarcinoma cancer cells, human ovarian cancer cells, and human normal hepatocyte cells, were evaluated by using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. The three novel Ln(III) complexes showed a high in vitro antitumor activity toward the NCI-H460 with IC₅₀ of 1.00 ± 0.25 nM for 1, 5.13 ± 0.44 μM for 2, and 11.87 ± 0.79 μM for 3, respectively. In addition, Ln(III) complexes 1 and 2 exerted their in vitro antitumor activity/mechanism mainly via the mitochondrial death pathway and caused a G2/M phase arrest in the following order: 1 > 2. An NCI-H460 tumor xenograft mouse model was used to evaluate the Pm(III) complex 1in vivo antitumor activity. Pm(III) complex 1 showed a high in vivo antitumor activity, and the tumor growth inhibition rate (IR) was 56.0% (p < 0.05). In summary, our study on Pm(III) complex 1 revealed promising results in in vitro and in vivo antitumor activity assays.

A series of dysprosium-based hydrogen-bonded organic frameworks (Dy–HOFs): thermally triggered off → on conversion of a single-ion magnet

A series of dysprosium-based HOFs (Dy–HOFs) were designed and synthesized for the first time under solvothermal conditions. Herein, we achieved the magnetic off → on SIM switching of Dy–HOFs under thermal driving conditions.

Formation of nanocluster {Dy12} containing Dy-exclusive vertex-sharing [Dy4(μ3-OH)4] cubanes via simultaneous multitemplate guided and step-by-step assembly

The formation of high-nuclearity clusters of lanthanide usually involved many complicated self-assembly processes. Thus, tracking the formation process is extremely difficult and research on the assembly mechanism is very rare.