Slow relaxation of the magnetization in Oximato-bridged heterobimetallic Copper(II)-Manganese(III) chains

Abstract

(3), com oxidação do íon manganês(II) a manganês(III) na presença de ar. Na ausência de monocristais para análise por difratometria de raios X, técnicas de absorção de raios X (EXAFS e XANES) foram usadas a 40 K para caracterização estrutural de 1-3. A análise dos dados de absorção de raios X revelou que 1-3 apresentam cadeias bimetálicas de íons Cu II e Mn III ligados por pontes oximato, em ambiente octaédrico (CuN 4 O 2 e MnO 6 ) alongado. Os estudos de propriedades magnéticas de 1-3 revelaram um comportamento metamagnético devido à coexistência de acoplamentos ferromagnéticos intracadeias fortes [J = +52.5 (1), +49.1 (2) e +52.1 cm -1 (3)] e interações antiferromagnéticas intercadeias fracas [j = −0.070 (1), −0.075 (2) e −0.078 cm -1 (3)]. A ortogonalidade estrita entre o orbital magnético do cobre(II) e aquele do centro magnético de manganês(III), junto com a conhecida habilidade do grupo oximato em mediar interações magnéticas quando atua como ponte entre dois íons metálicos, é responsável pela forte interação ferromagnética intracadeia em 1-3. Medidas de susceptibilidade sob corrente alternada realizadas para 1-3 em temperatura baixa e sob campo magnético dc igual a zero revelaram uma dependência do sinal ac fora de fase com a frequência do campo oscilante, como esperado para magnetos do tipo single-chain.The use of the oximato-containing copper(II) complexes, [Cu(Hdeg) (3) where the starting manganese(II) ion was oxidized to manganese(III) by air. In the lack of single crystals suitable for X-ray diffraction analysis, X-ray absorption techniques (EXAFS and XANES) at 40 K were used for the structural characterization of 1-3. The analysis of the X-ray absorption data reveals that 1-3 are oximato-bridged Cu II -Mn III bimetallic chains with elongated octahedral CuN 4 O 2 and MnO 6 surroundings. The study of the magnetic properties of 1-3 reveals a metamagnetic-like behavior due to the coexistence of strong intrachain ferromagnetic couplings [J = +52.5 (1), +49.1 (2) and +52.1 cm -1 (3)] and weak interchain antiferromagnetic interactions [j = −0.070 (1), −0.075 (2) and −0.078 cm -1 (3)]. The strict orthogonality between the magnetic orbital of the copper(II) ion and those of the manganese(III) center, together with the well known ability of the oximato group to mediate magnetic interactions when acting as a bridge between two metal ions, account for the relatively strong intrachain ferromagnetic coupling in 1-3. Alternating current susceptibility measurements for 1-3 in the low temperature range under zero dc magnetic field reveal a frequency-dependence of the out-of-phase ac signal as expected for single chain magnets.Keywords: metal oximates, heterobimetallic complexes, complex as ligand strategy, exchange coupling, single chain magnets Ruiz et al. 977 Vol. 22, No. 5, 2011 IntroductionSince the first report concerning the use of the dimethylglyoxime (H 2 dmg) as a reagent for nickel(II), 1 oximes as ligands have been widely used in coordination chemistry. Although the primary attention on them wa...

Molecular Engineering To Control the Magnetic Interaction between Single-Chain Magnets Assembled in a Two-Dimensional Network

“…Single-chain magnets (SCMs) are attractive research targets of polymeric molecular materials displaying slow relaxation of the magnetization and hysteresis effects. − Because of their fascinating fundamental nature and potential applications as ultimate memory or quantum spintronic devices, increased synthetic efforts were devoted to obtaining such 1D compounds in the past decade. Their synthesis is a current challenge in which achieving strong uniaxial (Ising) anisotropy and minimizing the interchain magnetic interactions are essential requirements .…”

“…Their synthesis is a current challenge in which achieving strong uniaxial (Ising) anisotropy and minimizing the interchain magnetic interactions are essential requirements . While anisotropy could be achieved by the choice of an appropriate metal ion such as high-spin octahedral Co(II), ,,,,, Mn(III), − ,,, Fe(II), or Re(IV), the tuning of the intermolecular interactions between magnetic nanowires to maintain a sufficiently large ratio of intra- to interchain magnetic interactions is a more complicated task because of the inherent difficulties in controlling the crystal packing. Several ways to avoid intermolecular magnetic interactions have been proposed, including the introduction of bulky ligands between/within the chains ,, and the use of H-bonding nucleobase groups or even structurally ditopic, magnetically inert organic linkers that would allow the ferro- or ferrimagnetic Ising chains to be linked into 2D or 3D networks without significant changing the SCM behavior.…”