Thermo-induced structural transformation with synergistic optical and magnetic changes in ytterbium and erbium complexes

Novel stable ytterbium acetylacetonate-quinaldinate complexes as single-molecule magnets and surprisingly efficient luminophores

The first Yb complexes comprising a quinoline-2-carboxylate (quinaldinate, Q-) ligand, namely 1D-polymeric [Yb(acac)2(Q)]n (1, acac- is the acetylacetonate (pentane-2,4-dionate) anion) and mononuclear [Yb(acac)2(Q)(Phen)] (2, Phen is 1,10-phenanthroline), are reported. The bifunctionality of both complexes as field-induced single-molecule magnets (SMMs) and near IR luminophores has been revealed. The SMM properties of 1 and 2 have been discussed in terms of the geometry and composition of the coordination environment. Also, 1 is the first example of 1D-polymeric SMMs with the capped octahedral surrounding of Yb3+. The photoluminescence quantum yields (PLQYs) of 1 and 2 are 2 and 4%, respectively. The origins of this difference are discussed. Surprisingly, the PLQY value of 2 is high for compounds comprising a lot of C-H vibrational quenchers, being the highest one for reliably characterized Yb β-diketonate complexes, and surpassing those for complexes with a broad range of anionic ligands. In this respect, the role of the Phen ligand is to tune the coordination mode of Q- thereby decreasing the energy of coordinating C-O oscillators rather than to act as a typical antenna ligand. These results can give rise to an alternative route to elaborate efficient Yb-based luminophores via the substitution of the β-diketonate ligands controlled by the introduction of appropriate neutral ligands.

Layered lanthanide phosphonates Ln(2-qpH)(SO4)(H2O)2 (Ln = La, Ce, Pr, Nd, Sm): polymorphism and magnetic properties

Polymorphic layered lanthanide coordination polymers provide opportunities to study the effect of intralayer and interlayer interactions on their magnetic dynamics. Herein we report a series of layered lanthanide phosphonates, namely, α-Ln(2-qpH)(SO4)(H2O)2 (Ln = Sm) (α-Ln), β-Ln(2-qpH)(SO4)(H2O)2 (Ln = Pr, Nd, Sm) (β-Ln) and γ-Ln(2-qpH)(SO4)(H2O)2 (Ln = La, Ce, Pr, Nd, Sm) (γ-Ln) (2-qpH2 = 2-quinolinephosphonic acid), which crystallize in monoclinic P21/c (α-Ln), triclinic P1̄ (β-Ln) and orthorhombic Pbca (γ-Ln) space groups, respectively. The structural differences between the β- and γ-phases lie not only in the intralayer but also in the interlayer. Within the layers, the Ln2O2 dimers are aligned parallel in the β-phase, but are non-parallel in the γ-phase. In the interlayer, there are π-π interactions between the quinoline groups in the α- and β-phases but not in the γ-phase. Magnetic studies reveal a field-induced slow relaxation of the magnetisation at low temperatures for compounds γ-Ce, β-Nd, and γ-Nd, and the impact of polymorphism on the magnetic dynamics of Nd(III) compounds is discussed.

Convective heat and mass transfer rate on 3D Williamson nanofluid flow via linear stretching sheet with thermal radiation and heat absorption

A mathematical analysis is communicated to the thermal radiation and heat absorption effects on 3D MHD Williamson nanoliquid (NFs) motion via stretching sheet. The convective heat and mass boundary conditions are taken in sheet when liquid is motion. As a novelty, the effects of thermal radiation, heat absorption and heat and mass convection are incorporated. The aim is to develop heat transfer. Williamson NFs are most important source of heat absorption, it having many significant applications in "energy generation, HT, aircraft, missiles, electronic cooling systems, gas turbines" etc. The suitable similarity transformations have been utilized for reduce basic governing P.D. E's into coupled nonlinear system of O.D. E's. Obtained O.D. Es are calculated by help of R-K-F ("Runge-Kutta-Fehlberg")4th order procedure with shooting technique in MATLAB programming. We noticed that, the skin friction coefficient is more effective in Williamson liquid motion when compared with NFs motion with higher numerical values of stretching ratio parameter, Williamson liquid motion is high when compared to NFs motion for large values of magnetic field. We compared with present results into previous results for various conditions. Finally, in the present result is good invention of previous results.

X-Ray Triggered Coordination-Bond Breakage in Dysprosium-Organic Framework and its Impact on Magnetic Properties

Photosensitive lanthanide-based single-molecule magnets (Ln-SMM) are very attractive for their potential applications in information storage, switching, and sensors. However, the light-driven structural transformation in Ln-SMMs hardly changes the coordination number of the lanthanide ion. Herein, for the first time it is reported that X-ray (λ=0.71073 Å) irradiation can break the coordination bond of Dy-OH₂ in the three-dimensional (3D) metal-organic framework Dy₂ (amp₂ H₂ )₃ (H₂ O)₆  ⋅ 4H₂ O (MDAF-5), in which the {Dy₂ (OPO)₂ } dimers are cross-linked by dianthracene-phosphonate ligands. The structural transformation proceeds in a single-crystal-to-single-crystal (SC-SC) fashion, forming the new phase Dy₂ (amp₂ H₂ )₃ (H₂ O)₄  ⋅ 4H₂ O (MDAF-5-X). The phase transition is accompanied by a significant change in magnetic properties due to the alteration in coordination geometry of the Dy^III ion from a distorted pentagonal bipyramid in MDAF-5 to a distorted octahedron in MDAF-5-X.

Photo-controllable heterostructured crystals of metal-organic frameworks via reversible photocycloaddition

Metal-organic framework (MOF)-based heterostructures are attractive because they can provide versatile platforms for various applications but are limited by complex liquid epitaxial growth methods. Here, we employ photolithography to fabricate and control MOF-based heterostructured crystals via [4 + 4] photocycloaddition. A layered dysprosium-dianthracene framework, [Dy(NO3)3(depma2)1.5]·(depma2)0.5 (2) [depma2 = pre-photodimerized 9-diethylphosphonomethylanthracene (depma)] underwent a single-crystal-to-single-crystal transition at 140 °C to form [Dy(NO3)3(depma)(depma2)]·(depma2)0.5 (3). The dissociated anthracene moieties are face-to-face π-π interacted allowing a reversible photocycloaddition between 2 and 3. This structural transformation causes a luminescence switch between blue and yellow-green and thus can be used to fabricate erasable 2 + 3 heterostructured crystals for rewritable photonic barcodes. The internal strain at the heterostructure interface leads to photobending and straightening of the crystal, a photomechanical response that is fast, reversible and durable, even operating at 140 °C, making it promising for photoactuation. This work may inspire the development of intelligent MOF-based heterostructures for photonic applications.

Cobalt(II)-dianthracene Frameworks: Assembly, Exfoliation and Properties

Metal-organic frameworks containing responsive organic linkers are attractive for potential applications in sensors and molecular devices. Herein we report three cobalt(II) phosphonates incorporating responsive dianthracene linkers, namely, Co₂ (amp₂ H₂ )₂ (H₂ O)₄  ⋅ 6H₂ O (MDAF-1), Co₂ (amp₂ )(H₂ O)₄  ⋅ 2H₂ O (MDAF-2) and Co(amp₂ H₂ ) ⋅ 2H₂ O ⋅ 0.5DMF (MDAF-3), where amp₂ H₄ is pre-photodimerized 9-anthrylmethylphosphonic acid. MDAF-1 shows a layer structure in which dinuclear Co₂ (PO₃ H)₂ units are inter-connected by dianthracene ligands. In MDAF-2 and MDAF-3, inorganic chains of corner-sharing {CoO₄ } (or {CoO₆ }) and {PO₃ C} are cross-linked by dianthracene ligands into 3D frameworks. All compounds underwent thermo-induced phase transitions, first the de-solvation and then the de-dimerization of dianthracene (as well as the release of the remaining solvent molecules for MDAF-2 and -3), associated with magnetic changes. MDAF-1 can be exfoliated into single-layer nanosheets in water which show light-triggered luminescent changes.