Emerson F. Pedroso

Cluster glass-like behavior in a 2D bimetallic molecule-based magnet

The compound of formula Na2[Co2{Cu(opba)}3]/2DMSO/6H2O has been synthesized where opba stands for ortho phenylenebis(oxamato) and DMSO is dimethylsulfoxide. Magnetic properties have been investigated in the 2/300 K temperature range. The compound presents a large coercive field, around 3.5 kOe at 4.2 K, and the A.C. susceptibility measurements has revealed a cluster glass-like behavior. # 2003 Elsevier Science Ltd. All rights reserved.

New properties of the [3-MeRad]2[Mn2{Cu(opba)}3] system [3-MeRad+=radical cation, opba=ortho-phenylenebis(oxamato)]: a molecule-based magnet with two-dimensional behavior

Abstract Three compounds have been synthesized, the formulae of which are [3-MeRad] 2 [Cu(opba)]·4H 2 O ( 1 ), [3-MeRad] 2 [Mn 2 {Cu(opba)} 3 ]·6DMSO·8H 2 O ( 2 ), and [3-MeRad] 2 [Mn 2 {Cu(opba)} 3 ]·3DMSO·2.5H 2 O ( 3 ), where opba is ortho -phenylenebis(oxamato) and 3-MeRad + is 2-(3- N -methyl-pyridinium)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide. Their magnetic properties have been investigated in the 1.8–300 K temperature range. By reaction of 1 and MnCl 2 ·3H 2 O in DMSO, small crystals of 2 were obtained. Single crystal X-ray analysis was employed to determine the lattice parameters for 2 : a =15.9(2); b =17.8(2); c =18.0(3) A; α = γ =90(1); β =114(1)°. The temperature dependence of the magnetic susceptibility in the form of the χ M T versus T plot reveals a typical ferrimagnetic behavior for 2 , although the low field FC and ZFC curves show an antiferromagnetic-like interaction below 13 K. Above 200 Oe this interaction disappears as in weak metamagnets. With a thermal-vacuum treatment applied to 2 , solvent molecules are removed affording 3 which presents long-range order around 15 K. The results indicate that the bimetallic compounds present a structure consisting of two-dimensional honeycomb-like networks without interlocking of the M 6 Cu 6 hexagons.

Solvent effects on the dimensionality of oxamato-bridged manganese(II) compounds

Abstract Two new oxamate-containing manganese(II) complexes, [{Mn(H2edpba)(H2O)2}2]n (1) and [Mn(H2edpba)(dmso)2]∙dmso∙CH3COCH3∙H2O (2) (H4edpba = N,N′-ethylenediphenylenebis(oxamic acid) and dmso = dimethylsulfoxide), have been synthesized and the structures of 1 and 2 were characterized by single crystal X-ray diffraction. The structure of 1 consists of neutral honeycomb networks in which each manganese(II) is six-coordinate by one H2edpba2− ligand and two carboxylate–oxygens from two other H2edpba2− ligands building the equatorial plane. Each manganese is connected to its nearest neighbor through two carboxylate(monoprotonated oxamate) bridges in an anti-syn conformation. A dmso solution of single crystals of 1 was placed under acetone atmosphere affording 2, whereas putting 2 in equimolar water:ethanol mixture results in 1. The molecular structure of 2 is made up of mononuclear manganese(II) units which are interlinked by weak C–H⋯π and edge-to-face π-stacking interactions leading to supramolecular chains along the crystallographic b axis. Magnetic measurements reveal the occurrence of an antiferromagnetic coupling between two manganese(II) ions through anti-syn carboxylate bridges for 1 [J = −1.18 cm−1, the Hamiltonian being defined as H = −J S1.S2] and very weak intrachain ferromagnetic interactions in 2 [J = + 0.046 cm−1, H = −J ∑iSi.Si + 1].

Synthesis, crystal structure and magnetic properties of [Co(bpcam)2]ClO4·dmso·H2O, [Co(bpcam)2]2[Co(NCS)4]·dmso·H2O and [Ni(bpcam)2]·H2O [Hbpcam = bis(2-pyrimidylcarbonyl)amide]

The preparation, spectroscopic characterization, structural study and magnetic investigation of three new complexes of formula [Co(bpcam)2]ClO4·dmso·H2O (1), [Co(bpcam)2]2[Co(NCS)4]·dmso·H2O (2) and [Ni(bpcam)2]·H2O (3) [Hbpcam = bis(2-pyrimidylcarbonyl)amide] are reported. Each bpcam group in 1–3 acts as a tridentate ligand being coordinated to the cobalt(III) (1 and 2)/nickel(II) (3) ions through three nitrogen atoms in a mer-arrangement. Six-coordinate cobalt(III) and nickel(II) occur in 1 and 3 respectively, whereas six-coordinate cobalt(III) and four-coordinate cobalt(II) coexist in 2. Cyclic voltammetry of 1 in acetonitrile shows the occurrence of one quasi reversible CoIII ↔ CoII process. Direct current (dc) variable-temperature magnetic susceptibility measurements on polycrystalline samples of 2 and 3 were carried out in the temperature range 1.9–295 K. The magnetic behaviour of 2 obeys to the zero-field splitting effects (DCo) of the 4A2 ground term of the pseudotetrahedral [Co(NCS)4]2− complex anion. A Curie law for a magnetically isolated nickel(II) ion in the high temperatures domain occurs for 3, the small decrease of χMT below 10 K being due zero-field splitting effects. The analysis of the magnetic susceptibility data of 2 and 3 through the spin Hamiltonian H = DM[Sz2 − S(S + 1)/3] + gMβHS [M = Co(2) and Ni(3)] led to the following set of values: gM = 2.37 (2) and 2.12 (3) and |DM| = 34.7 (2) and 1.72 cm−1 (3).

SÍNTESE, CARACTERIZAÇÃO E ESTUDO DAS PROPRIEDADES MAGNÉTICAS DE UM POLÍMERO DE COORDENAÇÃO CONTENDO COBALTO(II) E COBRE(II)

This work describes the synthesis and characterization of two new compounds with ligand opy (N-(2-pyridyl)oxamate): the copper(II) precursor [Me4N]2[Cu(opy)2].5H2O and CoIICuII coordination polymer {[CoCu(opy)2]}n×4nH2O. This latter compound was obtained by reaction of [Me4N]2[Cu(opy)2].5H2O and CoCl2.6H2O in water. The heterobimetallic CoIICuII chain was characterized by elemental analysis, IR spectroscopy, thermogravimetry and magnetic measurements. Magnetic characterization revealed typical behavior of one-dimensional (1D) ferrimagnetic chain as shown in the curves of temperature (T) dependence of magnetic susceptibility (χM), in the form of χMT versus T, and dependence of magnetization (M) with applied field (H).