Cynthia L. M. Pereira

Magnetic Poles Determinations and Robustness of Memory Effect upon Solubilization in a DyIII-Based Single Ion Magnet

The [Dy(tta)3(L)] complex behaves as a single ion magnet both in its crystalline phase and in solution. Experimental and theoretical magnetic anisotropy axes perfectly match and lie along the most electro-negative atoms of the coordination sphere. Both VSM and MCD measurements highlight the robustness of the complex, with persistence of the memory effect even in solution up to 4 K.

A two-dimensional oxamate- and oxalate-bridged Cu(II)Mn(II) motif: crystal structure and magnetic properties of (Bu4N)2[Mn2{Cu(opba)}2ox].

A new compound of formula (Bu4N)2[Mn2{Cu(opba)}2ox] (1) [Bu4N(+) = tetra-n-butylammonium cation, H4opba = 1,2-phenylenebis(oxamic acid), and H2ox = oxalic acid] has been synthesized and magneto-structurally investigated. The reaction of manganese(II) acetate, [Cu(opba)](2-), and ox(2-) in dimethyl sulfoxide yielded single crystals of 1. The structure of 1 consists of heterobimetallic oxamato-bridged Cu(II)Mn(II) chains which are connected through bis-bidentate oxalate coordinated to the manganese(II) ions to afford anionic heterobimetallic layers of 6(3)-hcb net topology. The layers are interleaved by n-Bu4N(+) counterions. Each copper(II) ion in 1 is four-coordinate in a square planar environment defined by two amidate-nitrogen and two carboxylate-oxygen atoms from the two oxamate groups of the obpa ligand. The manganese(II) ion is six-coordinate in a somewhat distorted octahedral surrounding that is built by two oxalate-oxygen and four carbonyl-oxygen atoms from two [Cu(opba)](2-) units. The magnetic properties of 1 in the temperature range 1.9-300 K correspond to those expected for the coexistence of intralayer antiferromagnetic interactions of the type copper(II)-manganese(II) across oxamato and manganese(II)-manganese(II) through oxalato bridges plus a weak spin canting in the very low temperature domain. Simulation of the magnetic data through quantum Monte Carlo methodology reveals the magnitude of the intralayer magnetic interactions [J(CuMn) = -32.5(3) cm(-1), and J(MnMn) = -2.7(3) cm(-1)], their values being within the range of those previously observed in lower nuclearity systems.

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.

Solvent-driven dimensionality control in molecular systems containing CuII, 2,2′-bipyridine and an oxamato-based ligand

A discrete dicopper(II) system, [Cu(bipy)(H2mpba)]2·2H2O (1), and its isomeric chain, [Cu(bipy)(H2mpba)]·dmso (2) [bipy = 2,2′-bipyridine and H4mpba = N,N′-1,3-phenylenebis(oxamic acid)], were obtained by modifying the ratio of the H2O–dmso solvent mixture, and their interconversion was also monitored by changing the solvents during the synthesis. The solvents play an essential role in the formation and crystallization of these complexes, presenting different dimensionalities and connectivities. The double deprotonated H2mpba2− adopts the bidentate/monodentate (1) and bis-bidentate (2) bridging modes toward the (2,2′-bipyridyl)copper(II) units affording a dinuclear compound (1) and a linear chain (2), respectively. Variable-temperature magnetic measurements show the occurrence of weak intradinuclear (1) and intrachain (2) antiferromagnetic interactions.

Oxotris(oxalate)niobate(V): An oxalate delivery agent in the design of building blocks

Abstract This work concerns the oxalate delivery process that occurs when using (NH4)3[NbO(C2O4)3]·6H2O as a suitable oxalate source in the synthesis of two compounds, [Cu(dmphen)(C2O4)(H2O)] (1) and [{Cu(dmphen)(CH3OH)}2(μ-C2O4)](ClO4)2 (2) (dmphen = 2,9-dimethyl-1,10-phenanthroline). {[Fe{HB(pz)3}(CN)2(μ-CN)]2[{Cu(dmphen)}2(μ-C2O4)]}∙xCH3OH (3) (2.0 ≤ x ≤ 2.4) was obtained by reacting 2 and PPh4[Fe{HB(pz)3}(CN)3]∙H2O [ = tetraphenylphosphonium and = tris(pyrazolyl)borate]. Crystal structures of 1–3 have been determined by single-crystal X-ray diffraction experiments: 1 is a mononuclear trigonal bipyramidal copper(II) species, 2 is a centrosymmetric oxalato-bridged dicopper(II) complex, and 3 consists of centrosymmetric tetranuclear units with intramolecular iron–copper and copper–copper distances around 5.010(1) and 5.1833(9) Å, respectively. Variable-temperature magnetic measurements of 2 and 3 were carried out from 50 to 350 (1) and 1.9 to 300 K (3). A strong antiferromagnetic interaction between copper(II) ions occurs in 2 (J = −340 cm−1, the spin Hamiltonian being defined as ). Analysis of the magnetic data of 3 shows magnetic interactions across the oxalate (J1 = −341 cm−1) and single cyanide (J2 = +12.9 cm−1) … (J2 = +12.9 cm−1) bridges . Simple symmetry considerations of the interacting magnetic orbitals in 2 and 3 provide a clear picture of the exchange pathways involved in these complexes.

Towards oxalate-bridged iron(II), cobalt(II), nickel(II) and zinc(II) complexes through oxotris(oxalato)niobate(V): an open air non-oxidizing synthetic route

Four compounds with the formula [M2(dmphen)4(μ-C2O4)](ClO4)2·2dmso [M = Fe (1), Co (2) and Zn (4); dmphen = 2,9-dimethyl-1,10-phenanthroline] and [Ni2(dmphen)4(μ-C2O4)]3[NbO(C2O4)3]2·16H2O (3) have been synthesized using the tris(oxalato)oxoniobate(V) complex anion as the oxalate source, and their structures have been determined by single crystal X-ray diffraction. X-ray quality crystals of highly insoluble oxalate-bridged species were obtained by taking advantage of the slow release of oxalate by the tris(oxalato)oxoniobate(V) complex anion. The structures of 1–4 all contain oxalate-bridged dimetal(II) units with didentate dmphen molecules acting as end-cap ligands; electroneutrality is achieved by perchlorate (1–4) and oxotris(oxalato)niobate(V) (3) anions. Each divalent metal ion in 1–4 is tris-chelated in a six-coordinate distorted octahedral environment. The niobium(V) ion in 3 is seven-coordinate in a distorted pentagonal bipyramidal geometry built from one oxo group and six oxygen atoms from three didentate oxalate ligands. The values of the metal–metal separation across the bis-chelating oxalate are 5.626(1) (1), 5.575(1) (2), 5.434(1) to 5.447(1) (3) and 5.603(1) A (4). The cryomagnetic measurements in the temperature range of 2.0 to 300 K for compounds 1–3 show the occurrence of antiferromagnetic interactions between the divalent metal ions across the oxalate bridge. The nature and amplitude of these magnetic interactions are rationalized by simple symmetry considerations and compared with those previously reported for related oxalate-bridged systems.

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].

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).