The association of the [Ln(hfac)3(H2O)2] metallic building blocks with the new ligand [1,1’-binaphthalene]-8,8’-diylbis(diphenylphosphine oxide) (L) led to the formation of three mononuclear complexes of formula [Ln(hfac)3(L)] (LnIII = Eu (1), Dy (2) and Yb (3)). The mononuclear character of the compounds is due to the bidentate coordination mode adopted by L to link the metal. L allows the observation of the characteristic visible 5D0 7FJ (J = 0-4) EuIII- and near infrared 2F5/2 2F7/2 YbIII- emissions while 2 is only weakly emissive due to the mismatch between the energy positions of the triplet excited state of the ligand and DyIII emissive state. The magnetic data reveal a field-induced Single-Molecule Magnet (SMM) behavior for 2 and 3 with an efficient suppression of the Quantum Tunneling of the Magnetization (QTM). The slow magnetic relaxation occurs through a Raman process while the Orbach contribution is discarded as confirmed by the correlation with the MJ states energy splitting provided by the luminescence spectrum of 3.
Photodynamic therapy (PDT) uses a combination of molecular oxygen, light and a photosensitizer (PS) to generate singlet oxygen or reactive oxygen species (ROS), which can eradicate tumoral cells. All currently approved PSs for cancer treatment are molecular PSs. To date, no nanoparticlebased PSs are used clinically although it has widely been shown that nanotechnology may help to improve the properties of molecular PSs; for instance, molecular PSs suffer from some intrinsic limitations that undermine their therapeutic efficacy. In the present minireview, the most critical weaknesses exhibited by molecular PSs are described, and the potential use of nanoparticles (NPs) to address them and to reach the clinics is discussed.
Spin crossover (SCO) active solid solutions with formula [FexZn1-x(Me1,3bpp)2](ClO4)2 (x = 0.10, 0.15, 0.22, 0.33, 0.41, 0.48, 0.56 and 0.64, Me1,3bpp is a bis-pyrazolylpyridine) and the complex [Zn(Me1,3bpp)2](ClO4)2 have been prepared and characterized by single crystal X-ray diffraction. The structural data and the powder diffraction patterns of all the compounds have been compared with the reported isostructural molecular crystal [Fe(Me1,3bpp)2](ClO4)2. Increasing amounts of Zn diminishes monotonically the cooperativity of the SCO of the parent Fe(II) complex (T1/2=183 K) and cause a decrease of T1/2 in line with the negative chemical pressure exerted by the Zn(II) complexes on the Fe(II) lattice. The gradual variation of the magnetic properties as the composition changes are paralleled by the evolution of the structural parameters at the molecular, intermolecular and crystal lattice scales. Thermal trapping of a portion of the Fe(II) centers of these alloys by quenching the crystals to 2 K unveils that, upon warming, the temperature of relaxation of the metastable states is almost constant for all compositions.
Magnetic relaxation times are the central observable in defining the characteristics of single-molecule magnets. It is not uncommon to observe multiple distinct relaxation timescales for a pure material, and sometimes only one relaxation timescale is observed in samples containing multiple components. Herein we examine the conditions required for two distinct relaxation processes to be observable in alternating current susceptibility experiments. We find that there must be at least one order of magnitude difference in the two relaxation times I log10[taumu,1/taumu,2] I > 0.922, even when the intrinsic distributions of the two processes are infinitely sharp (alpha = 0 in the generalised Debye model). In the case where only one process is observable, we provide an expression to estimate the two underlying relaxation times, allowing extraction of “hidden” information from AC susceptibility data.
We report the synthesis of a pyrazine-based bis-tridentate diarylethene (DAE) ligand and the corresponding dinuclear yttrium and dysprosium complexes that all show T-type photochromism. Large changes in the photochromic behaviour are induced by metal coordination, including a tuning of the bleaching rate by several orders of magnitude, characterized through VT-NMR and supported by theoretical calculations. The dysprosium dinuclear complex shows a single-molecule magnet (SMM) behaviour, under an external applied magnetic field, significantly modulated upon photoisomerization. This feature is further analyzed through ab initio calculations.
Two C3-symmetric guanidine-based copper triangles bridged by acetates in a cis manner and by chloride anions in a trans manner, respectively gave rise to two antiferromagnetically coupled hexanuclear CuII compounds, namely [Cu6L2Cl(μ-OAc)(DMF)3]·DMF (Cu6) and [Cu6L2(μ-Cl)2(DMF)4] (Cu6Cl)(where L stands for fully deprotonated tris (2-hydroxybenzylidene) triaminoguanidinium chloride, H5L). The experimental magnetic data of the two compounds were analyzed theoretically. A relatively good agreement with the experimental data was obtained when using the wavefunction theory (CASSCF) in combination with DFT (B3LYP) calculations for the very strong antiferromagnetic coupling within the Cu3 triangles (Javg = − 300 cm−1 for Cu6 and Javg = − 250 cm−1 for Cu6Cl), leading to spin-frustrated systems. It is worth mentioning that the electronic structure of each CuII center remains very similar in each complex with a Kramers ground state well separated from the first excited state (over 12000 cm−1) and weakly anisotropic (g∥ ≈ 2.40 and g⊥ ≈ 2.10).
5 nm nanocrystals of CoFe Prussian blue analogue totally exempt from any alkali cation were prepared. Their photomagnetic properties were compared to those of the corresponding powder made of 150 nm particles as well as to those of 5 nm nanocrystals of CoFe PBAs embedded in comparable silica matrices, made of CoIIFeIII pairs and prepared under various conditions. The photomagnetic investigation of the nanoparticles exempt of any alkali cation clearly shows that they are transformed by light and the comparison of their photomagnetic properties to those of the powder made of particles of bigger size with the same chemical composition suggests that the species involved in the switching properties are surface species. Furthermore, the comparison of the magnetic properties of nanoparticles prepared under various conditions also suggests that the aggregation state of the nanoparticles in the porous channels of the silica matrix, by modulating inter-particle interactions, plays a predominant role in the magnetic properties of the nanoparticles assemblies.
This article relates the synthesis and characterization of novel heterobimetallic complexes containing a low-valent lanthanide, a tetradentate redox non-innocent ligand, viz. the 4,5,9,10-tetraazaphenanthrene, taphen ligand and transition metal fragments of PdMe2 and PtMe2. The experimental results are supported by a theoretical study. Investigation of their reduction properties allowed the formation of isostructural original heterotrimetallic complexes containing two Cp*2Yb fragments and the (taphen)MMe2 (M = Pd and Pt) motifs. These complexes are stable in non-coordinating solvent such as toluene but decompose in coordinating solvents such as thf. Investigation of the internal electron transfer shows that the taphen ligand behaves as a two-electrons reservoir but is capable of transferring back only one electron in thf. This reversible electron(s) transfer is rare in organolanthanide chemistry and show the potential interest of these complexes in reductive chemistry. Additionally, the trinuclear complexes feature odd X-ray crystal structures in which a deviation of symmetry is observed. The latter observation was studied in depth using quantum chemistry calculations highlighting the role of non-covalent weak interactions.
The synthesis, characterization and use of a new donor-acceptor molecular dyad in single component organic solar cells are reported. The dyad, composed of a triazatruxene-based push-pull 'donor' unit linked to a C60 'acceptor' unit through a non-conjugated σ connector, led to promising power conversion efficiencies of 0.6% when embedded in simple devices exhibiting the architecture: indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene): polystyrene sulfonic acid (PEDOT:PSS)/dyad/Al.
Light-Induced Excited Spin-State Trapping has been studied since 1982 in solution and 1984 in solid state as it offers a reversible way of photoswitching the electronic configuration of spin crossover systems. Since then, the lifetime of the photo-induced state was deeply investigated through kinetics measurements. In 1998, a fast and easy way to record the limit temperature above which the photo-induced state is erased, denoted T(LIESST), was introduced. This procedure has been widely used in the spin crossover community due to its easiness and its efficiency to provide detailed information on the photo-induced state. Correlations between T(LIESST) and structural parameters have been proposed for instance. However, it intrinsically contains drawbacks that can lead to misinterpretation of behaviours and can lead to an over estimation of its scope. This review aims to present and discuss not only the correct way to measure T(LIESST) but also the essential contributions it has brought and the limits not to be exceeded in its interpretation.
F.B. acknowledges the European Union and the Aarhus Institute of Advanced Studies (Aarhus University) for the Marie Sklodowska-Curie AIAS-COFUND grant (EU-FP7 program, Grant Agreement No. 609033). S.J.L.B. was supported by NSF MRSEC/Columbia program (Center for Precision Assembly of Superstratic and Superatomic Solids, DMR-1420634). The technical staff of the X04SA-MS Beamline of the Swiss Light Source (PSI, Villigen, CH) is gratefully acknowledged. The measurements for PDF were Chem2, 2018, 2-1 12 conducted at NSLS II, a U.S. Department of Energy Office of Science User Facility operated by Brookhaven National Laboratory (Contract No. DE-SC0012704).
The use of metallohelicates as potential antiproliferative agents is mostly exemplified by one sole family of supramolecular compounds that is based on bis-iminopyridine ligands. In the present investigation, two other types of metallocylinders have been selected and their potential DNA-binding and cytotoxic properties have been investigated. Hence, two new neutral iron(III) metallosupramolecular compounds have been prepared from bis-β-diketone ligands, and a known cationic iron(II) helicate from bis-pyrazole ligands has been used for comparison purposes. DNA-interaction experiments and cell studies reveal remarkable biological properties for one of the neutral iron cylinders and the positively charged, pyrazole-based helicate, as illustrated by their antiproliferative behaviours, which are far better than those of two well-known compounds, i.e. the most studied metallohelicate in the field and cisplatin.
a Departament de Química Inorgánica i Orgànica, Universitat de Barcelona, Diagonal 645, 08028, Barcelona-Spain b Institució Catalana de Recerca i Estudis Avançats (ICREA) c Departament de Ciència de Materials i Química Física and IQTCUB, Universitat de Barcelona, Diagonal 645, 08028, Barcelona-Spain d Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS-Université de Rennes 1, 263 Avenue du Genéral Leclerc, 35042 Rennes Cedex, France
In photoactivated chemotherapy, the photocleavable protecting group that prevents the bioactive compound from interacting with biomolecules in the dark is sometimes cytotoxic, which makes interpretation of phototoxicity challenging. For ruthenium polypyridyl complexes new, non-toxic protecting ligands that prevent a toxic metal complex from binding to biomolecules in the dark, but that can be efficiently photosubstituted upon visible light irradiation to recover the high toxicity of the metal complex, are necessary. In this work, we report on the synthesis, stereochemical characterization and cytotoxicity of a series of polypyridyl complexes; [Ru(bpy)2(mtpa)](PF6)2 ([1](PF6)2, bpy = 2,2’-bipyridine), [Ru(bpy)(dmbpy)(mtpa)](PF6)2 ([2](PF6)2, dmbpy = 6,6’-dimethyl-2,2’-bipyridine), and [Ru(dmbpy)2(mtpa)](PF6)2 ([3](PF6)2) based on the non-toxic 3-(methylthio)propylamine protecting ligand (mtpa). The number of methyl groups had a crucial effect on the photochemistry and cytotoxicity of these complexes. The non-strained complex [1]2+ was not capable of fully releasing mtpa and was not phototoxic in lung cancer cells (A549). In the most strained complex [3]2+, thermal stability was lost, leading to poor photoactivation in vitro and a generally high toxicity also without light activation. The heteroleptic complex [2]2+ with intermediate strain showed, upon blue light irradiation, efficient mtpa photosubstitution and increased cytotoxicity in cancer cells, but photosubstitution was not selective. Overall, fine-tuning of the lipophilicity and steric strain of ruthenium complexes appears as an efficient method to obtain phototoxic ruthenium-based photoactivated chemotherapeutic prodrugs, at the cost of synthetic simplicity and photosubstitution selectivity.
