Direct Determination of Carrier Parameters in Indium Tin Oxide Nanocrystals.

We develop here a comprehensive experimental approach to independently determine charge carrier parameters, namely, carrier density and mass, in plasmonic indium tin oxide nanocrystals. Typically, in plasmonic nanocrystals, only the ratio between these two parameters is accessible through optical absorption experiments. The multitechnique methodology proposed here combines single particle and ensemble optical and magneto-optical spectroscopies, also using 119Sn solid-state nuclear magnetic resonance spectroscopy to probe the surface depletion layer. Our methodology overcomes the limitations of standard fitting approaches based on absorption spectroscopy and ultimately gives access to carrier effective mass directly on the NCs, discarding the use of literature value based on bulk or thin film materials. We found that mass values depart appreciably from those measured on thin films; consequently, we found carrier density values that are different from reported literature values for similar systems. The effective mass was found to deviate from the parabolic approximation at a high carrier density. Finally, the dopant activation and defect diagram for ITO NCs for tin doping between 2.5 and 15% are determined. This approach can be generalized to other plasmonic heavily doped semiconductor nanostructures and represents, to the best of our knowledge, the only method to date to characterize the full Drude parameter space of 0-D nanosystems.

Magnetic Circular Dichroism Elucidates Molecular Interactions in Aggregated Chiral Organic Materials.

Chiral materials formed by aggregated organic compounds play a fundamental role in chiral optoelectronics, photonics and spintronics. Nonetheless, a precise understanding of the molecular interactions involved remains an open problem. Here we introduce magnetic circular dichroism (MCD) as a new tool to elucidate molecular interactions and structural parameters of a supramolecular system. A detailed analysis of MCD together with electronic circular dichroism spectra combined to ab initio calculations unveils essential information on the geometry and energy levels of a self-assembled thin film made of a carbazole di-bithiophene chiral molecule. This approach can be extended to a generality of chiral organic materials and can help rationalizing the fundamental interactions leading to supramolecular order. This in turn could enable a better understanding of structure-property relationships, resulting in a more efficient material design.

Size Selectivity in Heterolanthanide Molecular Complexes with a Ditopic Ligand.

The similar reactivity of lanthanides generally leads to statistically populated polynuclear complexes, making the rational design of ordered hetero-lanthanide compounds extremely challenging. Here we report on the site selectivity in hetero-lanthanide tetranuclear complexes afforded by the relatively simple ditopic pyterpyNO ligand (4'-(4-pyridil)-2,2':6',2"-terpyridine N-oxide). The sequential room temperature reaction of RE2 (tta)6 (pyterpyNO)2 (where RE=Y, (1); Eu, (2), Dy, (3) Htta=2-thenoyltrifluoroacetone) with La(tta)3 dme (dme=dimethoxyethane) yielded Y2 La2 (tta)12 (pyterpyNO)2 (4), Dy2 La2 (tta)12 (pyterpyNO)2 (5) and Eu2 La2 (tta)12 (pyterpyNO)2 (6). Single crystals X-ray diffraction studies showed that 4, 5 and 6 are isostructural, featuring a tetranuclear structure with two different metal coordination sites with coordination numbers 8 (CN8) and 9 (CN9). The two smaller cations are mainly bridged by the O-donor atoms of the NO groups of two pyterpyNO ligands (CN8), while the larger lanthanum centres are bound by a terpyridine unit (CN9). Size selectivity has been studied with structural and magnetic studies in the solid state and through 19 F NMR and photoluminescence studies in solution, showing a direct dependence on the difference of ionic radii of the ions and yielding a 91 % selectivity for 4. Furthermore, 19 F NMR, X-ray and PL studies pointed out that the nature of the product is independent from the synthetic route for compound Eu2 Y2 (tta)12 (pyterpyNO)2 (7), keeping the ion selectivity also for a self-assembly reaction. Unexpectedly, these studies have evidenced that selectivity is not exclusively governed by electrostatic interactions related to size dimensions.

Direct detection of spin polarization in photoinduced charge transfer through a chiral bridge.

It is well assessed that the charge transport through a chiral potential barrier can result in spin-polarized charges. The possibility of driving this process through visible photons holds tremendous potential for several aspects of quantum information science, e.g., the optical control and readout of qubits. In this context, the direct observation of this phenomenon via spin-sensitive spectroscopies is of utmost importance to establish future guidelines to control photo-driven spin selectivity in chiral structures. Here, we provide direct proof that time-resolved electron paramagnetic resonance (EPR) can be used to detect long-lived spin polarization generated by photoinduced charge transfer through a chiral bridge. We propose a system comprising CdSe quantum dots (QDs), as a donor, and C60, as an acceptor, covalently linked through a saturated oligopeptide helical bridge (χ) with a rigid structure of ∼10 Å. Time-resolved EPR spectroscopy shows that the charge transfer in our system results in a C60 radical anion, whose spin polarization maximum is observed at longer times with respect to that of the photogenerated C60 triplet state. Notably, the theoretical modelling of the EPR spectra reveals that the observed features may be compatible with chirality-induced spin selectivity, but the electronic features of the QD do not allow the unambiguous identification of the CISS effect. Nevertheless, we identify which parameters need optimization for unambiguous detection and quantification of the phenomenon. This work lays the basis for the optical generation and direct manipulation of spin polarization induced by chirality.

Magnetoplasmonics beyond Metals: Ultrahigh Sensing Performance in Transparent Conductive Oxide Nanocrystals.

Active modulation of the plasmonic response is at the forefront of today's research in nano-optics. For a fast and reversible modulation, external magnetic fields are among the most promising approaches. However, fundamental limitations of metals hamper the applicability of magnetoplasmonics in real-life active devices. While improved magnetic modulation is achievable using ferromagnetic or ferromagnetic-noble metal hybrid nanostructures, these suffer from severely broadened plasmonic response, ultimately decreasing their performance. Here we propose a paradigm shift in the choice of materials, demonstrating for the first time the outstanding magnetoplasmonic performance of transparent conductive oxide nanocrystals with plasmon resonance in the near-infrared. We report the highest magneto-optical response for a nonmagnetic plasmonic material employing F- and In-codoped CdO nanocrystals, due to the low carrier effective mass and the reduced plasmon line width. The performance of state-of-the-art ferromagnetic nanostructures in magnetoplasmonic refractometric sensing experiments are exceeded, challenging current best-in-class localized plasmon-based approaches.

Ball milled glyco-graphene oxide conjugates markedly disrupted Pseudomonas aeruginosa biofilms.

The engineering of the surface of nanomaterials with bioactive molecules allows controlling their biological identity thus accessing functional materials with tuned physicochemical and biological profiles suited for specific applications. Then, the manufacturing process, by which the nanomaterial surface is grafted, has a significant impact on their development and innovation. In this regard, we report herein the grafting of sugar headgroups on a graphene oxide (GO) surface by exploiting a green manufacturing process that relies on the use of vibrational ball mills, a grinding apparatus in which the energy is transferred to the reacting species through collision with agate spheres inside a closed and vibrating vessel. The chemical composition and the morphology of the resulting glyco-graphene oxide conjugates (glyco-GO) are assessed by the combination of a series of complementary advanced techniques (i.e. UV-vis and Raman spectroscopy, transmission electron microscopy, and Magic Angle Spinning (MAS) solid-state NMR (ssNMR) providing in-depth insights into the chemical reactivity of GO in a mechanochemical route. The conjugation of monosaccharide residues on the GO surface significantly improves the antimicrobial activity of pristine GO against P. aeruginosa. Indeed, glyco-GO conjugates, according to the monosaccharide derivatives installed into the GO surface, affect the ability of sessile cells to adhere to a polystyrene surface in a colony forming assay. Scanning electron microscopy images clearly show that glyco-GO conjugates significantly disrupt an already established P. aeruginosa biofilm.

Invisible Thermoplasmonic Indium Tin Oxide Nanoparticle Ink for Anti-counterfeiting Applications.

In this study, we present a thermoplasmonic transparent ink based on a colloidal dispersion of indium tin oxide (ITO) nanoparticles, which can offer several advantages as anti-counterfeiting technology. The custom ink could be directly printed on several substrates, and it is transparent under visible light but is able to generate heat by absorption of NIR radiation. Dynamic temperature mapping of the printed motifs was performed by using a thermal camera while irradiating the samples with an IR lamp. The printed samples presented fine features (in the order of 75 µm) and high thermal resolution (of about 250 µm). The findings are supported by thermal finite-element simulations, which also allow us to explore the effect of different substrate characteristics on the thermal readout. Finally, we built a demonstrator comprising a QR Code invisible to the naked eye, which became visible in thermal images under NIR radiation. The high transparency of the printed ink and the high speed of the thermal reading (figures appear/disappear in less than 1 s) offer an extremely promising strategy toward low-cost, scalable production of photothermally active invisible labels.

Star-Shaped Magnetic-Plasmonic Au@Fe3O4 Nano-Heterostructures for Photothermal Therapy.

Here, we synthesize a Au@Fe3O4 core@shell system with a highly uniform unprecedented star-like shell morphology with combined plasmonic and magnetic properties. An advanced electron microscopy characterization allows assessing the multifaceted nature of the Au core and its role in the growth of the peculiar epitaxial star-like shell with excellent crystallinity and homogeneity. Magnetometry and magneto-optical spectroscopy revealed a pure magnetite shell, with a superior saturation magnetization compared to similar Au@Fe3O4 heterostructures reported in the literature, which is ascribed to the star-like morphology, as well as to the large thickness of the shell. Of note, Au@Fe3O4 nanostar-loaded cancer cells displayed magneto-mechanical stress under a low frequency external alternating magnetic field (few tens of Hz). On the other hand, such a uniform, homogeneous, and thick magnetite shell enables the shift of the plasmonic resonance of the Au core to 640 nm, which is the largest red shift achievable in Au@Fe3O4 homogeneous core@shell systems, prompting application in photothermal therapy and optical imaging in the first biologically transparent window. Preliminary experiments performing irradiation of a stable water suspension of the nanostar and Au@Fe3O4-loaded cancer cell culture suspension at 658 nm confirmed their optical response and their suitability for photothermal therapy. The outstanding features of the prepared system can be thus potentially exploited as a multifunctional platform for magnetic-plasmonic applications.

Stoichiometrically Controlled Assembly of Lanthanide Molecular Complexes of the Heteroditopic Divergent Ligand 4'-(4-Pyridyl)-2,2':6',2″-terpyridine N-Oxide in Hypodentate or Bridging Coordination Modes. Structural, Magnetic, and Photoluminescence Studies.

Mononuclear rare-earth tris-ß-diketonato complexes RE(tta)3dme [RE = Y (1), La (2), Dy (3), or Eu (4); Htta = 2-thenoylacetone; dme = 1,2-dimethoxyethane] react cleanly at room temperature in a 1:1 molar ratio with the heteroditopic divergent ligand 4'-(4-pyridyl)-2,2':6',2″-terpyridine N-oxide (pyterpyNO) to yield RE2(tta)6(pyterpyNO)n, where n = 2 for RE = Y (5), Dy (6), or Eu (7) and n = 3 for RE = La (8). The crystal structure of 5 revealed a dinuclear compound with two pyterpyNO's bridging through the oxygen atom in a hypodentate mode leaving the terpyridine moieties uncoordinated. Using a metal:pyterpyNO molar ratio of 2 for RE = Y (9), Dy (10), or Eu (11), it was possible to isolate the molecular complexes RE4(tta)12(pyterpyNO)2, while using a 5:3 molar ratio, the product La5(tta)12(pyterpyNO)3 (12) can be obtained. 89Y nuclear magnetic resonance spectroscopy revealed two different yttrium centers at room temperature for 9. An X-ray diffraction study of 10 showed a symmetrical tetranuclear structure resulting from the coordination of two Dy(tta)3 fragments to the two hypodentate terpyridines of the dinuclear unit and presenting two different coordination sites for metals with coordination numbers of 8 and 9. Magnetic studies of 6 and 10 revealed the presence of an antiferromagnetic interaction between the two Dy(III) atoms bound by the NO bridges. These compounds displayed a slow relaxing magnetization through Orbach (6) and Raman (10) processes in the absence of an applied magnetic field; the rate increased upon application of a 1 kOe field. 7 and 11 showed a bright red emission typical of Eu3+. The two complexes have similar emission properties mainly determined by the employed ß-diketonato ligands.

Magneto-Optical Activity in Nonmagnetic Hyperbolic Nanoparticles.

Active nanophotonics can be realized by controlling the optical properties of materials with external magnetic fields. Here, we explore the influence of optical anisotropy on the magneto-optical activity in nonmagnetic hyperbolic nanoparticles. We demonstrate that the magneto-optical response is driven by the hyperbolic dispersion via the coupling of metallic-induced electric and dielectric-induced magnetic dipolar optical modes with static magnetic fields. Magnetic circular dichroism experiments confirm the theoretical predictions and reveal tunable magneto-optical activity across the visible and near infrared spectral range.

Dielectric Effects in FeO x -Coated Au Nanoparticles Boost the Magnetoplasmonic Response: Implications for Active Plasmonic Devices.

Plasmon resonance modulation with an external magnetic field (magnetoplasmonics) represents a promising route for the improvement of the sensitivity of plasmon-based refractometric sensing. To this purpose, an accurate material choice is needed to realize hybrid nanostructures with an improved magnetoplasmonic response. In this work, we prepared core@shell nanostructures made of an 8 nm Au core surrounded by an ultrathin iron oxide shell (≤1 nm). The presence of the iron oxide shell was found to significantly enhance the magneto-optical response of the noble metal in the localized surface plasmon region, compared with uncoated Au nanoparticles. With the support of an analytical model, we ascribed the origin of the enhancement to the shell-induced increase in the dielectric permittivity around the Au core. The experiment points out the importance of the spectral position of the plasmonic resonance in determining the magnitude of the magnetoplasmonic response. Moreover, the analytical model proposed here represents a powerful predictive tool for the quantification of the magnetoplasmonic effect based on resonance position engineering, which has significant implications for the design of active magnetoplasmonic devices.

A bionic shuttle carrying multi-modular particles and holding tumor-tropic features.

The systemic delivery of composite nanoparticles remains an outstanding challenge in cancer nanomedicine, and the principal reason is a complex interplay of biological barriers. In this regard, adaptive cell transfer may represent an alternative solution to circumvent these barriers down to the tumor microenvironment. Here, tumor-tropic macrophages are proposed as a tool to draw and vehiculate modular nanoparticles integrating magnetic and plasmonic components. The end result is a bionic shuttle that exhibits a plasmonic band within the so-called therapeutic window arising from as much as 40 pg Au per cell, magnetization in the order of 150 pemu per cell, and more than 90% of the pristine viability and chemotactic activity of its biological component, until at least two days of preparation. Its synergistic combination of plasmonic, magnetic and tumor-tropic functions is assessed in vitro for applications as magnetic guidance or sorting, with a propulsion around 4 µm s-1 for a magnetic gradient of 0.8 T m-1, the optical hyperthermia of cancer, with stability of photothermal conversion to temperatures exceeding 50∘C, and the photoacoustic imaging of cancer under realistic conditions. These results collectively suggest that a bionic design may be a promising roadmap to reconcile the efforts for multifunctionality and targeted delivery, which are both key goals in nanomedicine.

Precise Size Control of the Growth of Fe3O4 Nanocubes over a Wide Size Range Using a Rationally Designed One-Pot Synthesis.

The physicochemical properties of spinel oxide magnetic nanoparticles depend critically on both their size and shape. In particular, spinel oxide nanocrystals with cubic morphology have shown superior properties in comparison to their spherical counterparts in a variety of fields, like, for example, biomedicine. Therefore, having an accurate control over the nanoparticle shape and size, while preserving the crystallinity, becomes crucial for many applications. However, despite the increasing interest in spinel oxide nanocubes there are relatively few studies on this morphology due to the difficulty to synthesize perfectly defined cubic nanostructures, especially below 20 nm. Here we present a rationally designed synthesis pathway based on the thermal decomposition of iron(III) acetylacetonate to obtain high quality nanocubes over a wide range of sizes. This pathway enables the synthesis of monodisperse Fe3O4 nanocubes with edge length in the 9-80 nm range, with excellent cubic morphology and high crystallinity by only minor adjustments in the synthesis parameters. The accurate size control provides evidence that even 1-2 nm size variations can be critical in determining the functional properties, for example, for improved nuclear magnetic resonance T2 contrast or enhanced magnetic hyperthermia. The rationale behind the changes introduced in the synthesis procedure (e.g., the use of three solvents or adding Na-oleate) is carefully discussed. The versatility of this synthesis route is demonstrated by expanding its capability to grow other spinel oxides such as Co-ferrites, Mn-ferrites, and Mn3O4 of different sizes. The simplicity and adaptability of this synthesis scheme may ease the development of complex oxide nanocubes for a wide variety of applications.

Nickel ferrite nanoparticles for simultaneous use in magnetic resonance imaging and magnetic fluid hyperthermia.

We demonstrate magnetic resonance imaging (MRI) contrast enhancement and ac-field induced heating abilities of tetramethylammoniumhydroxide (TMAH) coated nickel ferrite (NiFe2O4) nanoparticles and discuss the underlying physical mechanisms. The structural characterization revealed that the NiFe2O4 particles synthesized with a modified co-precipitation method have a very narrow size distribution with a 4.4 nm magnetic core and 15 nm hydrodynamic diameters, with relatively small fraction of agglomerates. The as-prepared particles presented superparamagnetic behavior at room temperature. The in vitro hyperthermia experiments, performed in ac-field conditions under human tolerable limits, showed that the suspensions of the synthesized nanoparticles exhibit a maximum specific absorption rate (SAR) value of 11 W/g. The 1H nuclear magnetic resonance (NMR) relaxometry measurements indicated the suspensions of NiFe2O4 have a transverse-to-longitudinal relaxivity ratio r2/r1 greater than two, as required for superparamagnetic MRI contrast agents. On the basis of the parameters obtained from the magnetic measurements, by comparing the relevant theoretical models with the experimental results, we found that the presence of agglomerates, and particularly the interactions within the agglomerated nanoparticles, caused a significant increase in the hyperthermia and MRI efficiencies. On the other hand, from an applicative point of view, both the MRI contrast enhancement and the heating capabilities allow the simultaneous use of nickelferrites in diagnostic and therapeutic applications as theranostic agents.

Addressing the Influence of Localized Plasmon Resonance on the Magneto-Optical Properties of Cobalt Ferrite Nanoparticles.

The optical and magneto-optical (MO) properties of magneto-plasmonic nanocomposite films made up of a transparent polymer with a dispersion of cobalt ferrite (CFO) nanoparticles (NPs) and different concentrations of Au NPs are investigated. The volumetric concentrations of CFO and Au NPs, around 3%, and below 7‰ respectively, are below the percolation limit, and hence the nanocom-posite films constitute models for investigating the influence of the electromagnetic field generated at the surface plasmon resonance of Au NPs on the magneto-optical properties of CFO NPs. The plasmon resonance is present in these magneto-plasmonic composites, red-shifted with respect to the bare Au NPs and covering the spectral region where charge-transfer and crystal field MO transitions can be excited. Moreover, the magneto-optical hysteresis loops were measured in the whole spectral region. We observe that the hysteresis loops shape is a fingerprint of the different MO transitions of the CFO NPs. The strength of the MO peak around 750 nm, corresponding to the Crystal Field transition is damped respect to the corresponding peak of the CFO NPs. The strength of this peak evolves non-monotonically with the Au NPs concentration. On the other hand, the MO band around 550 nm, excited by Charge Transfer transitions, changes sign when Au NPs are present. In addition, a second MO contribution is observed. Our results demonstrate that the interactions between plasmon resonance and MO effects are not only determined by the stronger local electromagnetic fields at the resonance but they depend on the type MO transition that is involved in these oxides. This study helps to understand and design the magneto plasmonic nano-structures and applications, for example in biomedicine and sensing, in which random and weak dipolar interparticle interactions between plasmonic and magnetic nanostructures are present.

Increasing the Magnetic Anisotropy of a Natural System: Co-Doped Magnetite Mineralized in Ferritin Shells.

Iron oxide nanoparticles mineralized within the internal cavity of Ferritin protein cage are extremely appealing for the realization of multifunctional therapeutic and diagnostic agents for cancer treatment by drug delivery, magnetic fluid hyperthermia (MFH) and magnetic resonance imaging. Being the maximum mean size imposed by the internal diameter of the protein shell (ca. 8 nm) too small for the use of these systems in MFH, a valuable strategy for the improvement of the hyperthermic efficiency is increasing the magnetic anisotropy by doping the iron oxide with divalent Co ions. This strategy has been demonstrated to be highly efficient in the case of iron oxide nanoparticles mineralized in Human Ferritin (HFt). However, a deterioration of nanoparticles crystallinity and consequently a reduction of the hyperthermic efficiency were observed with increasing Co-doping. In this contribution, we compare two series of Co-doped iron oxide nanoparticles (Co-doping level up to 15%) mineralized into HFt and into Ferritin from the archaea Pirococcus Furiosus (PfFt), the protein structure of which differs for the nucleation sites, with the aim of increasing the crystalline quality of the inorganic cores for larger Co doping. Highly monodisperse nanoparticles of 6-7 nm were obtained in both series. The structural and magnetic characterization indicate that the PfFt series is less subjected to crystallinity deterioration with increasing Co content with respect to the HFt one. Such difference is reflected in the hyperthermic efficiency, which reaches the maximum value for different intermediate Co-doping (10% and 5% for PfFt and HFt, respectively), and goes to zero for further Co-doping increments.

Resonant Inelastic Soft X-ray Scattering Study of Co-Doped Maghemite Nanoparticles.

Cobalt ferrite nanoparticles have been attracting considerable interest in the recent years because of the large number of potential applications, including magnetic storage, magnetic fluid hyperthermia and as contrast agents for magnetic resonance imaging. Physical properties of this class of materials depend critically on a number of parameters, including crystallinity, stoichiometry and cation distribution. In this work we have performed a Resonant Inelastic soft X-ray Scattering (RIXS) study on a series of 5 nm cobalt-doped maghemite nanoparticles to obtain direct quantitative information on cation distribution as a function of cobalt doping. We found that the distribution of divalent cobalt is stable in the investigated doping range and slightly different from that of bulk, stoichiometric cobalt ferrite. These results confirm that cobalt doping can be used to finely tune the magnetic properties of nanostructured ferrites without modifying their structural integrity.

Controlled Dissociation of Iron and Cyclopentadienyl from a Diiron Complex with a Bridging C3 Ligand Triggered by One-Electron Reduction.

The one-electron reduction of a diiron cationic complex revealed unique features: cleavage of the diiron structure occurred despite a multidentate bridging C3 ligand and was accompanied by the clean dissociation of one η5-cyclopentadienyl ring and one iron as isolated units. Thus, the iron(II)-iron(II) µ-vinyliminium complex [Fe2Cp2(CO)(µ-CO){µ-η1:η3-C3(Et)C2HC1N(Me)(Xyl)}][SO3CF3] ([1a]SO3CF3) reacted with cobaltocene in tetrahydrofuran (THF), affording the iron(II) vinylaminoalkylidene [FeCp(CO){C1N(Me)(Xyl)C2HC3(Et)C(═O)}] (2a) in 77% yield relative to the C3 ligand. Analogously, [FeCp(CO){C1N(Me)(Xyl)C2HC3(CH2OH)C(═O)}] (2b) was obtained in 64% yield from the appropriate diiron precursor and CoCp2. The formation of 2a is initiated by the one-electron reduction of [1a]+, followed by a reversible intramolecular rearrangement terminating with the irreversible release of CpH (NMR and gas chromatography-mass spectrometry) and Fe [electron paramagnetic resonance (EPR) and magnetometry]. The key intermediate iron(I) ferraferrocene (3) was detected by EPR and IR spectroelectrochemistry, while the related species 3-H-3 was isolated after the addition of a hydrogen source and then identified by X-ray diffraction. A plausible mechanism for the route from [1a]+ to 3 was ascertained by density functional theory calculations. The dication [1a]2+, displaying both carbonyl ligands in terminal positions, and the anion [3]- were electrochemically generated. The functionalized diiron compounds 4 (52% yield) and 5 (62%) were afforded through the activation of O2 and S8 by a radical intermediate along the reductive pathway of [1a]+. The reaction of [Fe2Cp2(CO)(µ-CO){µ-η1:η3-C(SiMe3)CHCN(Me)(Xyl)}][SO3CF3] ([1c]SO3CF3) with CoCp2 in THF afforded [Fe2Cp2(C≡CSiMe3)(CO)(µ-CO){µ-CNMe(Xyl)}] (6) in 65% yield.

1D hetero-bimetallic regularly alternated 4f-3d coordination polymers based on N-oxide-4,4'-bipyridine (bipyMO) as a linker: photoluminescence and magnetic properties.

Heterotopic divergent ligand N-oxide-4,4'-bipyridine (bipyMO) has been herein exploited for the preparation of hetero-bimetallic coordination polymers where Ln(hfac)3 and M(hfac)2 nodes regularly alternate (Hhfac = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione), bipyMO being able to selectively use its two potential coordination sites to discriminate the metal ions. The synthesis of three coordination polymers, [Ln(hfac)3M(hfac)2(bipyMO)2]n (Ln = Eu, M = Zn, 1; Ln = Eu, M = Cu, 2, Ln = Dy, M = Co, 3), was carried out by reacting the appropriate [M(hfac)2(bipyMO)]n and [Ln(hfac)3] precursors in toluene in the presence of a given stoichiometric amount of bipyMO. The products were characterized by elemental analysis, X-ray powder diffraction, and FTIR spectroscopy. Single crystal X-ray diffraction studies carried out on 2 showed that it was formed by chains containing the hexa-coordinated 3d metal (Cu(hfac)2[N]2) and the octa-coordinated lanthanide (Eu(hfac)3[O]2) nodes, where [N] and [O] stand for the donor atom of the bridging divergent ligand. The X-ray powder diffraction patterns of the three compounds and the comparison of their cell constant values allowed establishing that the derivatives were isotypic. Photoluminescence (PL) studies on microcrystalline sample powders evidenced a bright red emission for 1 with an absolute PL quantum yield of 0.24. The sensitized emission of Eu3+ can be excited in a wide wavelength range, from UV to visible, up to ≈450 nm. Conversely, europium emissions are not detectable in 2 due to the presence of Cu(hfac)2(bipyMO) moieties whose strong absorption overlaps Eu3+ transitions. Magnetic measurements conducted on 3 revealed the presence of a weak ferromagnetic interaction below 2.1 K. An ac susceptibility study highlighted a slow relaxation of the magnetization of 3 with an applied static magnetic field of 0.1 T, which could be equally fitted with a Orbach-direct or a Raman-direct mechanism. No relaxation dynamics was detected without the application of a static magnetic field.

Spin Helicity in Chiral Lanthanide Chains.

We report here the determination of the helical spin structure of three Ln-based chiral chains of the formula [Ln(Hnic)(nic)2(NO3)]n (Hnic = nicotinic acid; Ln = Tb, Dy, and Er) by means of cantilever torque magnetometry. While the Dy and Er derivatives are strongly axial (easy-axis and easy-plane anisotropy, respectively), the Tb derivative is characterized by a remarkable rhombicity. In agreement with these findings, alternating-current susceptibility reveals slow magnetic relaxation only in the Dy derivative. Dilution of DyIII ions in the diamagnetic Y-based analogue shows that the weak ferromagnetic intrachain interactions do not contribute significantly to the energy barrier for the reversal of magnetization, which is better described as a single-ion process. Single crystals of the two enantiomers of the Dy derivative have also been investigated using hard X-ray synchrotron radiation at the L-edge of the metal revealing optical activity although with negligible involvement of the 4f electrons of the DyIII ion.