From bowls to capsules: assembly of hexanuclear NiII rings tailored by alkaline cations.

An anionic hexanuclear NiII metallamacrocycle with endo and exo linking sites has been employed as a building block to generate a series of capsules and bowls of nanometric size. The supramolecular arrangement of the {Ni6} rings was tailored by the size of the alkali cations, showing the transition from {Ni6-M2-Ni6} capsules (M = LiI and NaI) to {Ni6-M} bowls (M = KI and CsI). The alkyl co-cations are determinant to stabilize the assemblies by means of CHꞏꞏꞏ interactions on the exo side of the metallamacrocycles. The effect on the topology of the supramolecular assemblies of the cation size, cation charge, Et3NH+ or Me4N+ countercations has been analysed. Magnetic mesurements reveal the presence of ferromagnetic and antiferromagnetic interactions inside the rings that allow a S = 0 ground state

Rare nuclearities in Ni(II) cluster chemistry: an unprecedented {Ni12} nanosized cage from the use of N-naphthalidene-2-amino-5-chlorobenzoic acid.

The self-assembly reaction between NiI2, benzoic acid (PhCO2H) and the Schiff base chelate, N-naphthalidene-2-amino-5-chlorobenzoic acid (nacbH2), in the presence of the organic base triethylamine (NEt3), has resulted in the isolation and the structural, spectroscopic, and physicochemical characterization of the dodecanuclear [Ni12I2(OH)6(O2CPh)5(nacb)5(H2O)4(MeCN)4]I (1) cluster compound in ~30%yield. Complex 1 has a cage-like conformation, comprising twelvedistorted, octahedral NiII ions that are bridged by five 3-OH, one -OH, an I in 55% occupancy, five PhCO2 groups (under the 1: 1: , 1: 2: 3 and 2: 2: 4 modes), and the naphthoxido and carboxylato O-atoms of five doubly deprotonated nacb2 groups. The overall {Ni12} cluster exhibits a nanosized structure with a diameter of ~2.5 nm and its metallic core can be conveniently described as a series of nine edge- or vertex-sharing {Ni3} triangular subunits. Complex 1 is the highest nuclearity coordination compound bearing the nacbH2 chelate, and a rare example of polynuclear NiII complex containing coordinating I ions. Direct current (DC) magnetic susceptibility studies revealed the presence of predominant antiferromagnetic exchange interactions between the NiII ions, while photophysical studies of 1 in the solid-state showed a cyan-to-green centered emission at 520 nm, upon maximum excitation at 380 nm. The reported results demonstrate the rich coordination chemistry of the deprotonated nacb2 chelate in the presence of NiII metal ions, and the ability of this ligand to adopt a variety of di erent bridging modes, thus fostering the formation of high-nuclearity molecules with rare, nanosized dimensions and interesting physical (i.e., magnetic and optical) properties

{Ni4} Cubanes from enantiomerically pure 2-(1-hydroxyethyl)pyridine ligands: supramolecular chirality

Homometallic {NiII4} cubane-like clusters with a rare chiral core have been prepared via the employment of enantiomerically pure 2-(1-hydroxyethyl)pyridine (Hmpm). Comparison with the achiral cubanes derived from the related 2-pyridinemethanol (Hpym) ligand reveals drastic structural changes as a consequence of the transfer of chirality from the ligands to the whole structure. Their magnetic properties have been related to the structural features of their cubane-type cores

High field level crossing studies on spin dimers in the low dimensional quantum spin system Na2_2T2_2(C2_2O4_4)3_3(H2_2O)2_2 with T=Ni,Co,Fe,Mn

In this paper we demonstrate the application of high magnetic fields to study the magnetic properties of low dimensional spin systems. We present a case study on the series of 2-leg spin-ladder compounds Na$_2$T$_2$(C$_2$O$_4$)$_3$(H$_2$O)$_2$ with T = Ni, Co, Fe and Mn. In all compounds the transition metal is in the $T^{2+}$ high spin configuation. The localized spin varies from S=1 to 3/2, 2 and 5/2 within this series. The magnetic properties were examined experimentally by magnetic susceptibility, pulsed high field magnetization and specific heat measurements. The data are analysed using a spin hamiltonian description. Although the transition metal ions form structurally a 2-leg ladder, an isolated dimer model consistently describes the observations very well. This behaviour can be understood in terms of the different coordination and superexchange angles of the oxalate ligands along the rungs and legs of the 2-leg spin ladder. All compounds exhibit magnetic field driven ground state changes which at very low temperatures lead to a multistep behaviour in the magnetization curves. In the Co and Fe compounds a strong axial anisotropy induced by the orbital magnetism leads to a nearly degenerate ground state and a strongly reduced critical field. We find a monotonous decrease of the intradimer magnetic exchange if the spin quantum number is increased

Activities to promote critical information management over Internet in pharmacy students

Con el fin de promover la adquisición de habilidades y destrezas que permitan al estudiante de Farmacia desarrollar una actitud activa y crítica frente a la información disponible en Internet, así como saber seleccionar las fuentes de información de Internet adecuadas para su formación, se ha llevado a cabo un proyecto de innovación docente (2008PID-UB/115) cuyo objetivo final es fomentar la gestión crítica de la información. Para ello se han diseñado una serie de ejercicios integrados en una actividad basada en casos clínicos, que forma parte de la evaluación continuada de la asignatura de Fisiopatología de la Licenciatura de Farmacia (UB). Se ha evaluado el proyecto a través de las calificaciones obtenidas en las actividades y las encuestas de opinión de un total de 379 estudiantes. Los resultados evidencian que la mayoría de estudiantes (90%) valoran muy positivamente las actividades planteadas, considerando que favorecen su aprendizaje y formación personal, y les aportan criterios útiles y provechosos para el análisis y selección de información biomédica a través de Internet. Por último, cabe destacar que el proyecto planteado ha demostrado ser aplicable a un grupo numeroso de estudiantes de Grado y constituye una estrategia válida para fomentar competencias transversales relacionadas con la gestión de la información, de gran relevancia para el futuro profesional farmacéutico.It has been carried out an educational innovation project (2008PID-UB/115) whose ultimate goal was to promote critical management information. Its specific objectives were to promote the acquisition of skills and abilities to allow the student of Pharmacy, on the one hand, to develop active and critical attitude towards the information available on Internet and, on the other hand, to select the Internet information sources suitable for their formation. For these purposes, we set up some activities based on a clinical case as a part of the continuous assessment of the subject of Pathophysiology of the Bachelor of Pharmacy (UB). The project was assessed by the scores on the activities and the opinion surveys of a total of 379 students. The results show that most students (90%) highly value the activities planned and they consider that these kinds of activities promoted their learning and their professional training. The students also state that the exercises provided them useful and helpful criteria for the analysis and selection of biomedical information over Internet. Finally, it is noteworthy that the proposed project has proved to be applicable to a large group of undergraduate students. Moreover, it is a valid strategy to promote cross-curricular competencies related to management of information, which is of great relevance for the future pharmacist.Este estudio ha sido subvencionado por la Universidad de Barcelona (Proyecto de Innovación Docente 2008PID-UB/115)

On the possibility of magneto-structural correlations: detailed studies of di-nickel carboxylate complexes

A series of water-bridged dinickel complexes of the general formula [Ni<sub>2</sub>(μ<sub>2</sub>-OH<sub>2</sub>)(μ2- O<sub>2</sub>C<sup>t</sup>Bu)<sub>2</sub>(O<sub>2</sub>C<sup>t</sup>Bu)2(L)(L0)] (L = HO<sub>2</sub>C<sup>t</sup>Bu, L0 = HO<sub>2</sub>C<sup>t</sup>Bu (1), pyridine (2), 3-methylpyridine (4); L = L0 = pyridine (3), 3-methylpyridine (5)) has been synthesized and structurally characterized by X-ray crystallography. The magnetic properties have been probed by magnetometry and EPR spectroscopy, and detailed measurements show that the axial zero-field splitting, D, of the nickel(ii) ions is on the same order as the isotropic exchange interaction, J, between the nickel sites. The isotropic exchange interaction can be related to the angle between the nickel centers and the bridging water molecule, while the magnitude of D can be related to the coordination sphere at the nickel sites

Bosonic representation of one-dimensional Heisenberg ferrimagnets

The energy structure and the thermodynamics of ferrimagnetic Heisenberg chains of alternating spins S and s are described in terms of the Schwinger bosons and modified spin waves. In the Schwinger representation, we average the local constraints on the bosons and diagonalize the Hamiltonian at the Hartree-Fock level. In the Holstein-Primakoff representation, we optimize the free energy in two different ways introducing an additional constraint on the staggered magnetization. A new modified spin-wave scheme, which employs a Lagrange multiplier keeping the native energy structure free from temperature and thus differs from the original Takahashi Scheme, is particularly stressed as an excellent language to interpret one-dimensional quantum ferrimagnetism. Other types of one-dimensional ferrimagnets and the antiferromagnetic limit S=s are also mentioned.Comment: to be published in Phys. Rev. B 69, No. 6, 0644XX (2004

Carbonate-Templated Self-Assembly of an Alkylthiolate-Bridged Cadmium Macrocycle

In the presence of Cd(ClO4)2 and a base, a new mixed N,S-donor alkylthiolate ligand supported both carbonate formation from atmospheric CO2 and the self-assembly of a novel bicapped puckered (CdS)6 molecular wheel. The remarkable stability of the complex was demonstrated by slow intermolecular ligand exchange on the 2J(HH) and J(111/113Cd1H) time scales at elevated temperature. Both CO2 and the base were required to convert amorphous “CdLClO4” precipitated in the absence of air to the carbonate complex. The complex shares structural features with the ζ-carbonic anhydrase class associating cadmium(II) with the biogeochemical cycling of carbon and is the first structurally characterized carbonate complex of any metal involving an alkylthiolate ligand

Topological insights in polynuclear Ni/Na coordination clusters derived from a schiff base ligand

This article presents the syntheses, crystal structures, topological features and magnetic properties of two NiII/NaI coordination clusters (CCs) formulated [NiII3Na(L1)3(HL1 (MeOH)2] (1) and [NiII6Na(L1)5(CO3)(MeO (MeOH)3(H2O)3]·4(MeOH) 2(H2O) [2 4(MeOH) 2(H2O)] where H2L1 is the semi rigid Schiff base ligand (E)-2-(2-hydroxy-3 methoxybenzylideneamino)-phenol). Compound 1 possesses a rare NiII3NaI cubane (3M4-1) topology and compound 2 is the first example in polynuclear Ni/Na chemistry that exhibits a 2,3,4M7-1 topology

A general synthetic route for the preparation of high-spin molecules: Replacement of bridging hydroxo ligands in molecular clusters by end-on azido ligands

Abstract A general method of increasing the ground-state total spin value of a polynuclear 3d-metal complex is illustrated through selected examples from cobalt(II) and nickel(II) cluster chemistry that involves the dianion of the gem-diol form of di-2-pyridyl ketone and carboxylate ions as organic ligands. The approach is based on the replacement of hydroxo bridges, that most often propagate antiferromagnetic exchange interactions, by the end-on azido ligand, which is a ferromagnetic coupler