Tu N. Nguyen

A Supramolecular Aggregate of Four Exchange-Biased Single-Molecule Magnets

The reaction between 3-phenyl-1,5-bis(pyridin-2-yl)pentane-1,5-dione dioxime (pdpdH(2)) and triangular [Mn(III)(3)O(O(2)CMe)(py)(3)](ClO(4)) (1) affords [Mn(12)O(4)(O(2)CMe)(12)(pdpd)(6))](ClO(4))(4) (3). Complex 3 has a rectangular shape and consists of four [Mn(III)(3)O](7+) triangular units linked covalently by the dioximate ligands into a supramolecular [Mn(3)](4) tetramer. Solid-state dc and ac magnetic susceptibility measurements revealed that [Mn(3)](4) contains four Mn(3) single-molecule magnets (SMMs), each with an S = 6 ground state. Magnetization versus dc-field sweeps on a single crystal gave hysteresis loops below 1 K that exhibited exchange-biased quantum tunneling of magnetization steps, confirming 3 to be a supramolecular aggregate of four weakly exchange-coupled SMM units.

Ga3+/Ln3+ Metallacrowns: A Promising Family of Highly Luminescent Lanthanide Complexes That Covers Visible and Near-Infrared Domains

Luminescent lanthanide(III)-based molecular scaffolds hold great promises for materials science and for biological applications. Their fascinating photophysical properties enable spectral discrimination of emission bands that range from the visible to the near-infrared (NIR) regions. In addition, their strong resistance to photobleaching makes them suitable for long duration or repeated biological experiments using a broad range of sources of excitation including intense and focalized systems such as lasers (e.g., confocal microscopy). A main challenge in the creation of luminescent lanthanide(III) complexes lies in the design of a ligand framework that combines two main features: (i) it must include a chromophoric moiety that possesses a large molar absorptivity and is able to sensitize several different lanthanide(III) ions emitting in the visible and/or in the near-infrared, and (ii) it must protect the Ln(3+) cation by minimizing nonradiative deactivation pathways due to the presence of -OH, -NH and -CH vibrations. Herein, a new family of luminescent Ga(3+)/Ln(3+) metallacrown (MC) complexes is reported. The MCs with the general composition [LnGa4(shi)4(C6H5CO2)4(C5H5N) (CH3OH)] (Ln-1, Ln = Sm(3+)-Yb(3+)) were synthesized in a one pot reaction using salicylhydroxamic acid (H3shi) with Ga(3+) and Ln(3+) nitrates as reagents. The molecular structure of [DyGa4(shi)4(C6H5CO2)4(C5H5N) (CH3OH)] was obtained by X-ray analysis of single crystals and shows that the complex is formed as a [12-MCGa(III)shi-4] core with four benzoate molecules bridging the central Dy(3+) ion to the Ga(3+) ring metals. The powder X-ray diffraction analysis demonstrates that all other isolated complexes are isostructural. The extended analysis of the luminescence properties of these complexes, excited by the electronic states of the chromophoric ligands, showed the presence of characteristic, sharp f-f transitions that can be generated not only in the NIR (Sm, Dy, Ho, Er, Yb) but also in the visible (Sm, Eu, Tb, Dy, Tm). All Ln-1 complexes possess very high quantum yield values with respect to other literature compounds, indicating a good sensitization efficiency of the [12-MCGa(III)shi-4] scaffold. Especially, as of today, the Yb-1 complex exhibits the highest NIR quantum yield reported for a lanthanide(III) complex containing C-H bonds with a value of 5.88(2)% in the solid state. This work is a significant step forward toward versatile, easily prepared luminescent lanthanide(III) complexes suitable for a variety of applications including highly in demand biological imaging, especially in the NIR domain.

Slow magnetization relaxation in unprecedented Mn(III)4Dy(III)3 and Mn(III)4Dy(III)5 clusters from the use of N-salicylidene-o-aminophenol.

The first use of N-salicylidene-o-aminophenol in 3d/4f chemistry has led to Mn(III)(4)Dy(III)(5) and Mn(III)(4)Dy(III)(3) clusters with unprecedented metal topologies and stoichiometries; both compounds exhibit out-of-phase signals indicative of the slow magnetization relaxation of a single-molecule magnet.

Covalently Linked Dimer of Mn3 Single-Molecule Magnets and Retention of Its Structure and Quantum Properties in Solution

[Mn3O(O2CMe)3(dpd)3/2)]2(I3)2 has been obtained from the reaction of 1,3-di(pyridin-2-yl)propane-1,3-dione dioxime (dpdH2) with triangular [Mn(III)3O(O2CMe)(py)3](ClO4). It comprises two [Mn(III)3O](7+) triangular units linked covalently by three dioximate ligands into a [Mn3]2 dimer. Solid state dc and ac magnetic susceptibility measurements reveal that each Mn3 subunit of the dimer is a separate single-molecule magnet (SMM) with an S = 6 ground state and that the two SMM units are very weakly ferromagnetically exchange coupled. High-frequency EPR spectroscopy on a single crystal displays signal splittings indicative of quantum superposition/entanglement of the two SMMs, and parallel studies on MeCN/toluene (1:1) frozen solutions reveal the same spectral features. The dimer thus retains its structure and inter-Mn3 coupling upon dissolution. This work establishes that covalently linked molecular oligomers of exchange-coupled SMMs can be prepared that retain their oligomeric nature and attendant inter-SMM quantum mechanical coupling in solution, providing a second phase for their study and demonstrating the feasibility of using solution methods for their deposition on surfaces and related substrates for study.

Dimeric and tetrameric supramolecular aggregates of single-molecule magnets via carboxylate substitution.

[Mn3]2 and [Mn3]4 supramolecular aggregates of weakly exchange-coupled Mn(III)3 single-molecule magnets (SMMs) with S = 6 have been prepared by carboxylate substitution on [Mn3O(O2CMe)3(mpko)3](+) [mpkoH = methyl(pyridine-2-yl) ketone oxime)] with the dicarboxylic acids α-truxillic acid and fumaric acid, respectively. The method opens up a new approach to Mn3 SMM aggregates of various size and topology.

Near-Infrared Optical Imaging of Necrotic Cells by Photostable Lanthanide-Based Metallacrowns

Sensitive detection of cell necrosis is crucial for the determination of cell viability. Because of its high resolution at the cellular level and sensitivity, optical imaging is highly attractive for identifying cell necrosis. However, challenges associated with this technique remain present such as the rapid photobleaching of several types of organic fluorophores and/or the interference generated by biological autofluorescence. Herein, we synthesized novel biologically compatible Zn2+/Ln3+ metallacrowns (MCs) that possess attractive near-infrared (NIR) emission and are highly photostable. In addition, these MCs have the ability to label differentially necrotic HeLa cells from living cells. This work is also the first demonstration of (i) the use of the NIR emission arising from a single lanthanide(III) cation for optical biological imaging of cells under single photon excitation, (ii) the first example of a lanthanide(III)-based NIR-emitting probe that can be targeted to a specific type of cell.

A Recyclable Metal–Organic Framework as a Dual Detector and Adsorbent for Ammonia

Recyclable materials for simultaneous detection and uptake of ammonia (NH3 ) are of great interest due to the hazardous nature of NH3 . The structural versatility and porous nature of metal-organic frameworks (MOFs) make them ideal candidates for NH3 capture. Herein, the synthesis of a water-stable and porous 3-dimensional CuII -based MOF (SION-10) displaying a ship-in-a-bottle structure is reported; the pores of the host SION-10 framework accommodate mononuclear CuII -complexes. SION-10 spontaneously uptakes NH3 as a result of two concurrent mechanisms: chemisorption due to the presence of active CuII sites and physisorption (bulk permanent porosity). The color of the material changes from green to blue upon NH3 capture, with the shifts of the UV/Vis absorption bands clearly seen at NH3 concentrations as low as 300u2005ppm. SION-10 can be recovered upon immersion of SION-10⊃NH3 in water and can be further reused for NH3 capture for at least three cycles.

One‐Step Assembly of Visible and Near‐Infrared Emitting Metallacrown Dimers Using a Bifunctional Linker

A family of dimeric LnIII [12-MCGa(III)N(shi) -4] metallacrowns (MCs) (LnIII =Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb) was synthesized using the isophthalate group (ip2- ) as a linker. The [LnGa4 ]2 complexes exhibit remarkable photophysical properties, with large molar absorptivities of ≈4×104 u2009m-1 u2009cm-1 , high quantum yields and long luminescence lifetimes with values of (i)u200531.2(2)% and 1.410(1)u2005ms, respectively for the visible-emitting [TbGa4 ]2 complex and (ii)u20052.43(6)% and 30.5(1)u2005μs for the near-infrared (NIR) emitting [YbGa4 ]2 in the solid state. The NIR emission was obtained not only from Yb, Nd, and Er complexes but also from the less frequently observed emitters such as Pr and Ho. In addition, emission in both visible and NIR domains could be detected for Dy and Sm MCs. ESI-MS and UV/Vis data revealed that the complexes are highly stable in dimethylsulfoxide (DMSO) solution with the 1 H- and COSY-NMR spectra of the diamagnetic [YGa4 ]2 analogue providing evidence for long-term solution stability. This new approach allows one to construct a basis for highly luminescent MCs that may be further modified to be adapted for applications such as optical imaging.

Photocatalytic hydrogen generation from a visible-light responsive metal–organic framework system: the impact of nickel phosphide nanoparticles

Herein, we report the performance of a photocatalytic system based on visible-light active MIL-125-NH2 mixed with nickel phosphide (Ni2P) nanoparticles. This combination boosts the H2 evolution rate to an outstanding value of 894 μmol h−1 g−1 under visible-light irradiation, which is among the highest H2 evolution rates reported to date for metal–organic frameworks (MOFs). The H2 generation rate exhibited by Ni2P/MIL-125-NH2 is almost 3 times higher than that of the Pt/MIL-125-NH2 system, highlighting the impact of the co-catalyst on photocatalytic water splitting. Additionally, our system outperforms the Ni2P/TiO2 system under UV-vis irradiation. The exceptional performance of Ni2P/MIL-125-NH2 is due to the efficient transfer of photogenerated electrons from MIL-125-NH2 to Ni2P, high intrinsic activity of Ni2P and exceptional synergy between them. This system exhibits the highest apparent quantum yields of 27.0 and 6.6% at 400 and 450 nm, respectively, ever reported for MOFs.

Metallacrowns: From Discovery to Potential Applications in Biomolecular Imaging

Biomolecular imaging holds great promise for the future of medical diagnosis, drug design, and therapy guidance. Opportunities for both inxa0vivo applications and inxa0vitro assays ranging from gene expression to pathology to elucidate biochemical processes in cells are amenable to these methods. In recent years, the field has grown rapidly and attracted the attention of not only biologists but also physicists, chemists, and engineers. In this article, we begin with a brief review of molecular imaging agents and several common clinical imaging techniques. We then provide an overview of metallacrowns (MCs) and their structures, followed by a discussion of how MCs have been developed into promising biomolecular probes for imaging.