Synthesis and Properties of New Molecule-Based Magnets Containing Mn(II), Cu(II) and Nitronyl Nitroxide Radical Cation

Abstract

Neste trabalho, descrevemos a obtenção de dois novos compostos de cobre(II), ou precursores, (Pr-Rad) 2 3DMSO.6H 2 O (4), respectivamente. As propriedades magnéticas dos precursores 1 e 2 mostram a presença de interações ferromagnéticas entre os radicais cátions e o cobre (II), na faixa de temperatura entre 20 e 300 K. Os magnetos moleculares 3 e 4 exibem magnetização espontânea com temperatura crítica, T c , de 23 K e 24 K, respectivamente.In this work, we describe the synthesis of two new copper(II) compounds, (Pr-Rad) 2 [Cu(opba)].H 2 O (1) and (Bu-Rad) 2 [Cu(opba)].2H 2 O (2) where opba stands for orthophenylenebis(oxamato) and R-Rad + are nitronyl nitroxide radical cations. From 1 and 2, two new molecule-based magnets [Pr-Rad] 2 [Mn 2 {Cu(opba)} 3 ].3.3DMSO.5H 2 O (3) and [Bu-Rad] 2 [Mn 2 {Cu(opba)} 3 ].3DMSO.6H 2 O (4) were obtained, respectively. The magnetic properties of precursors 1 and 2 show the presence of ferromagnetic interaction between the radical cations with copper(II), in the temperature range of 20-300 K. The magnets 3 and 4 exhibit spontaneous magnetization at critical temperatures, T c , of 23 K and 24 K, respectively. Keywords: supramolecular chemistry, molecule-based magnets, molecular materials, catenanes, ferrimagnetism IntroductionAs evidenced by the remarkable increase in publications on the topic, the field of molecule-based magnetism is flourishing. However, the critical temperature of the molecule-based magnets remains low and up to now there have not been compounds of this type used for any technological application. Four molecule-based magnets have been reported to remain magnetically ordered near room temperature.1-3 One of them decomposes at 350 K, and the other three demagnetize near 315 K. The crystal structures of these compounds have not all been determined.One of the outstanding features of molecule-based materials is that the magnetic properties may be transformed by quite small and subtle modifications in the molecular chemistry. Variations in the organic molecules may lead to modifications in the magnetism of the material. Sometimes the molecular fragments only serve as spacers and are not involved directly in the interaction between neighboring atoms. 4 In other cases, the organic part, although not possessing magnetic moment or not being responsible for the transmission of the interaction is essential to the exchange process. 5 In the last few years, numerous magnetic molecular units carrying spin and able to establish 3 ], (pbaOH = 2-hydroxy-1,3-propylenebis(oxamato)) with T c = 4.6 K.In the beginning of the nineties, we initiated a research in the direction to increase the dimensionality of the compounds using a more 'organic' building block: [Cu(opba)] 2-where opba stands for ortho-phenylenebis(oxamato) (see Figure 1a). We succeeded in designing two-dimensional magnets of formula [cat] Figure 1b). This compound, a magnet with T c of 22 K, presents a rare interlocked structure. Moreover, by the time of the description of this compound, no molecular magnet...

Single‐wall carbon nanotube interactions with copper‐oxamato building block of molecule‐based magnets probed by resonance Raman spectroscopy

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