Heterometallic Octanuclear Ni(4)(II)Ln(4)(III) (Ln = Y, Gd, Tb, Dy, Ho, Er) Complexes Containing Ni(2)(II)Ln(2)(III)O(4) Distorted Cubane Motifs: Synthesis, Structure, and Magnetic Properties

The reaction of 2-methoxy-6-[{2-(2-hydroxyethylamino)ethylimino}methyl] phenol (LH3) with lanthanide metal salts followed by the addition of nickel acetate allowed isolation of a family of octanuclear complexes, [Ni4Ln4(μ2-OH)2(μ3- OH)4(μ-OOCCH3)8(LH2)4]·(OH)2·xH2O. Single crystal X-ray diffraction studies of these complexes reveal that their central metallic core consists of two tetranuclear [Ni2Ln2O4] cubane subunits fused together by acetate and hydroxide bridges. The magnetic study of these complexes reveals a ferromagnetic interaction between the LnIII and the NiII center. The magnitude of exchange coupling between the NiII and LnIII center, parametrized from the magnetic data of the Gd analogue, gives J = +0.86 cm−1. The magneto caloric effect, studied for the NiII 4GdIII 4 complex, shows a maximum of magnetic entropy change, −ΔSm = 22.58 J kg−1 K−1 at 3 K for an applied external field of 5 T.Ministerio de Economía y Competitividad (MINECO) and EU Feder Funds (Project CTQ2014-56312-P), the Junta de Andalucía (FQM-195 and the Project of Excellence P11-FQM- 7756), and the University of Granada for financial support

Octanuclear heterobimetallic {Ni4Ln4} assemblies possessing Ln4 square grid [2×2] motifs : synthesis, structure and magnetism

Octanuclear heterobimetallic complexes, [Ln4Ni4(H3L)4(µ3-OH)4(µ2-OH)4]4Cl·xH2O·yCHCl3 (Dy3+ , x = 30.6, y = 2 (1); Tb3+ , x = 28, y = 0 (2) ; Gd3+ , x = 25.3, y = 0 (3); Ho3+ , x = 30.6, y = 3 (4)) (H5L = N1, N3-bis(6-formyl-2-(hydroxymethyl) -4-methylphenol) diethylenetriamine) are reported. These are assembled by the cumulative coordination action of four doubly deprotonated compartmental ligands, [H3L] 2- , along with eight exogenous –OH ligands. Within the core of these complexes, four Ln3+ are distributed to the four corners of a perfect square grid while four Ni2+ are projected away from the plane of the Ln4 unit. Each of the four Ni2+ possesses distorted octahedral geometry while all the Ln3+ are crystallographically equivalent and are present in an elongated square antiprism geometry. The magnetic properties of compound 3 are dominated by an easy-plane single-ion anisotropy of the Ni2+ ions [DNi = 6.7(7) K] and dipolar interactions between Gd3+ centers. Detailed ac magnetometry reveals the presence of distinct temperature-dependent out-of-phase signals for compounds 1 and 2, indicative of slow magnetic relaxation. Magnetochemical analysis of complex 1 implies the 3d and the 4f metal ions are engaged in ferromagnetic interactions with SMM behavior, while dc magnetometry of compound 2 is suggestive of an antiferromagnetic Ni-Tb spin-exchange with slow magnetic relaxation due to a field-induced level crossing. Compound 4 exhibits an easy-plane single-ion anisotropy for the Ho3+ ions and weak interactions between spin centers

A single-ion magnet based on a heterometallic CoIII2DyIII complex

We report a CoIII2DyIII complex, which shows single-ion-magnet behaviour. AC susceptibility data of this compound reveals the presence of slow relaxation of the magnetization in zero-field below 15 K. The relaxation barrier is 88 K

Molecular Indium(III) Phosphonates Possessing Ring and Cage Structures. Synthesis and Structural Characterization of [In₂(<i>t</i>‑BuPO₃H)₄(phen)₂Cl₂] and [In₃(C₅H₉PO₃)₂(C₅H₉PO₃H)₄(phen)₃]·NO₃·3.5H₂O

Two novel indium­(III) phosphonates, [In₂(<i>t</i>-BuPO₃H)₄(phen)₂Cl₂] (<b>1</b>) and [In₃(C₅H₉PO₃)₂(C₅H₉PO₃H)₄(phen)₃]·NO₃·3.5H₂O (<b>2</b>) with phen = 1,10-phenanthroline, have been synthesized by solvothermal reactions involving indium­(III) salts and organophosphonic acids. <b>1</b> is a dinuclear compound where the two indium centers are bridged by a pair of isobidentate phosphonate ligands, [<i>t</i>-BuP­(O)₂OH]⁻, resulting in an eight-membered (In₂P₂O₄) puckered ring. Compound <b>2</b> is trinuclear; the In₃ platform is held together by two bicapping tripodal phosphonate ligands from the top and bottom of the indium plane. In addition, two bridging monoanionic phosphonate ligands serve to bind two pairs of indium centers. Both <b>1</b> and <b>2</b> also contain monodentate monoanionic phosphonate ligands. The solid-state MAS ³¹P NMR spectrum of complex <b>1</b> shows two signals at 21.9 and 29.3 ppm. Compound <b>2</b> contains signal maxima at 25.8 and 28.9 ppm, with a shoulder at 31.5 ppm. Room temperature solid-state fluorescence spectra of <b>1</b> and <b>2</b> are characterized by strong emission bands at 385 nm (λ_ex = 350 nm) and 395 nm (λ_ex = 350 nm), respectively, which are red-shifted with respect to the emission of free phenanthroline

Molecular Indium(III) Phosphonates Possessing Ring and Cage Structures. Synthesis and Structural Characterization of [In₂(<i>t</i>‑BuPO₃H)₄(phen)₂Cl₂] and [In₃(C₅H₉PO₃)₂(C₅H₉PO₃H)₄(phen)₃]·NO₃·3.5H₂O

Two novel indium­(III) phosphonates, [In₂(<i>t</i>-BuPO₃H)₄(phen)₂Cl₂] (<b>1</b>) and [In₃(C₅H₉PO₃)₂(C₅H₉PO₃H)₄(phen)₃]·NO₃·3.5H₂O (<b>2</b>) with phen = 1,10-phenanthroline, have been synthesized by solvothermal reactions involving indium­(III) salts and organophosphonic acids. <b>1</b> is a dinuclear compound where the two indium centers are bridged by a pair of isobidentate phosphonate ligands, [<i>t</i>-BuP­(O)₂OH]⁻, resulting in an eight-membered (In₂P₂O₄) puckered ring. Compound <b>2</b> is trinuclear; the In₃ platform is held together by two bicapping tripodal phosphonate ligands from the top and bottom of the indium plane. In addition, two bridging monoanionic phosphonate ligands serve to bind two pairs of indium centers. Both <b>1</b> and <b>2</b> also contain monodentate monoanionic phosphonate ligands. The solid-state MAS ³¹P NMR spectrum of complex <b>1</b> shows two signals at 21.9 and 29.3 ppm. Compound <b>2</b> contains signal maxima at 25.8 and 28.9 ppm, with a shoulder at 31.5 ppm. Room temperature solid-state fluorescence spectra of <b>1</b> and <b>2</b> are characterized by strong emission bands at 385 nm (λ_ex = 350 nm) and 395 nm (λ_ex = 350 nm), respectively, which are red-shifted with respect to the emission of free phenanthroline

Synthesis, structure and magnetism of the mixed-valent phosphonate cage, [MnIIMnIII12(μ4-O)6(μ-OH)6(O3P–t-Bu)10(OH2)2(DMF)4]·[2MeOH·4DMF]

The reaction of MnCl2·4H2O with t-BuPO3H2 in the presence of triethylamine afforded the tridecanuclear cage, [MnIIMnIII12(μ4-O)6(μ-OH)6(O3P–t-Bu)10(OH2)2(DMF)4]·[2MeOH·4DMF] (1). The structural analysis of 1 reveals that it is a mixed-valent complex containing a [MnIIMnIII12(μ4-O)6] core. The centre of the core is occupied by a MnII ion which is surrounded by 12 MnIII ions. The latter are connected to each other by six μ-OH− and 10 t-BuPO32− ligands. The vacant coordination sites of six MnIII ions situated in the periphery are occupied by four DMF and two water molecules. Magnetic studies on 1 reveal a frequency-dependent response which is characteristic of single-molecule magnets

Tetranuclear lanthanide(III) complexes in a seesaw geometry: Synthesis, structure, and magnetism

A fundamental problem with the development of courseware is that no instruments exist which enable the likely performance of courseware to be estimated. For such a purpose, the construction of a model of computer-assisted instruction, such as a qualitative block diagram, is essential. The block diagram is then formalized using general systems theory as a framework. The general systems model is then transformed into a set of cooperating procedures in a computer program, which is documented with examples

Photophysical and Primary Self-Referencing Thermometric Properties of Europium Hydrogen-Bonded Triazine Frameworks

Lanthanide hydrogen-bonded organic frameworks (LnHOFs) are recently emerging as a novel versatile class of multicomponent luminescent materials with promising potential applications in optics and photonics. Trivalent europium (Eu3+) incorporated polymeric hydrogen-bonded triazine frameworks (PHTF:Eu) have been successfully obtained via a facile and low-cost thermal pyrolysis route. The PHTF:Eu material shows a porous frame structure principally composed of isocyanuric acid and ammelide as a minor constituent. Intense red luminescence with high colour-purity from Eu3+ is obtained by exciting over a broad absorption band peaked at 300 nm either at room or low temperature. The triazine-based host works as excellent optical antenna towards Eu3+, yielding ~42% sensitization efficiency (ηsens) and an intrinsic quantum yield of Eu3+ emission (ΦEu) as high as ~46%. Temperature-dependent emission studies show that PHTF:Eu displays relatively high optical stability at elevated temperatures in comparison to traditional inorganic phosphors. The retrieved activation energy of 89 meV indicates that thermal quenching mechanisms are attributed to the intrinsic energy level structure of the metal-triazine assembly, possibly via a thermally activated back transfer to ligand triplet or CT states. Finally, by using an innovative approach based on excitation spectra, we demonstrate that PHTF:Eu can work as a universal primary self-referencing thermometer based on a single-emitting center with excellent relative sensitivity in the cryogenic temperature range.</jats:p