Magnetocaloric effect in hexacyanochromate Prussian blue analogs

We report on the magnetocaloric properties of two molecule-based hexacyanochromate Prussian blue analogs, nominally CsNi[Cr(CN)_6](H_2O) and Cr_3[Cr(CN)_6]_2x12(H_2O). The former orders ferromagnetically below Tc=90 K, whereas the latter is a ferrimagnet below Tc=230 K. For both, we find significantly large magnetic entropy changes DSm associated to the magnetic phase transitions. Notably, our studies represent the first attempt to look at molecule-based materials in terms of the magnetocaloric effect for temperatures well above the liquid helium range.Comment: 4 pages, 6 figure

Microscopic origins of the ferromagnetic exchange coupling in oxoverdazyl-based Cu(II) complex

The exchange channels governing the experimentally reported coupling constant Jexpt=6 cm−1 value in the verdazyl-ligand based Cu II complex Cu hfac 2 imvdz are inspected using wave function-based difference dedicated configuration interaction calculations. The interaction between the two spin 1/2 holders is summed up in a unique coupling constant J. Nevertheless, by gradually increasing the level of calculation, different mechanisms of interaction are turned on step by step. In the present system, the calculated exchange interaction then appears alternatively ferromagnetic/ antiferromagnetic/ferromagnetic. Our analysis demonstrates the tremendously importance of some specific exchange mechanisms. It is actually shown that both parts of the imvdz ligand simultaneously influence the ferromagnetic behavior which ultimately reaches Jcalc=6.3 cm−1, in very good agreement with the experimental value. In accordance with the alternation of J, it is shown that the nature of the magnetic behavior results from competing channels. First, an antiferromagnetic contribution can be essentially attributed to single excitations involving the network localized on the verdazyl part. In contrast, the ligand-to-metal charge transfer LMCT involving the imidazole moiety affords a ferromagnetic contribution. The distinct nature / of the mechanisms is responsible for the net ferromagnetic behavior. The intuitively innocent part of the verdazyl-based ligands is deeply reconsidered and opens new routes into the rational design of magnetic object

Single chain magnet behaviour in an enantiopure chiral cobalt(II)–copper(II) one-dimensional compound

The self-assembly of an enantiomerically pure, chiral dianionic oxamatocopper(II) complex with cobalt(II) ions leads to neutral oxamato-bridged heterobimetallic chains that combine chirality and slow magnetic relaxation, providing thus the first example of ‘‘chiral single chain magnets (CSCMs).Ruiz Garcia, Rafael, [email protected] ; Lloret Pastor, Francisco, [email protected]

Dialkyl-substituted monoamidinium-templated oxalate-based noncentrosymmetric 2D compounds

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Binuclear heterometallic M(iii)–Mn(ii) (M = Fe, Cr) oxalate-bridged complexes associated with a bisamidinium dication: a structural and magnetic study

International audienceTwo heterometallic oxalate-bridged dinuclear anions associated with a non-H-bond donor bisamidinium cation (Cat 2+), leading to compounds of formula Cat[Mn II (H 2 O) 4 M III (ox) 3 ] 2 Á6H 2 O (M = Fe (1) and Cr (2)), are presented. Their structural analysis reveals that the anion is the combination of a tris(oxalato)metallate(III) moiety with a tetra(aqua)manganese(II) entity. A 3D H-bonded network is formed between the crystallisation and coordination water molecules and the terminal and bridging oxalate ligands. The exchange interaction between both metal ions mediated by the oxalate bridge is À4.9 cm À1 for 1 and +1.6 cm À1 for 2 (H = ÀJS 1 S 2)

Organic radicals, a promising route towards original molecule-based magnetic materials

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Synthesis and Properties of a Thermochromic Spin Crossover Fe^II Complex: An Undergraduate Coordination Chemistry Laboratory Experiment

International audienceIn this third-year undergraduate experiment, a coordination complex [Fe(NH2trz)3]Br2·H2O (NH2trz is 4-amino-1,2,4-triazole, C2H4N4) was synthesized and characterized by IR and UV–visible spectroscopies. This compound exhibits a spectacular reversible purple-white thermochromic transition upon heating–cooling with a large hysteresis centered at room temperature. The thermochromic transition is related to the spin crossover (SCO) from the low-spin state (LS, purple, S = 0, diamagnetic) to the high-spin state (HS, white, S = 2, paramagnetic). During this experiment, students discovered synthetic methods, such as anion metathesis and Ostwald ripening, and physical properties, such as magnetic properties, thermochromism, and bistability phenomenon, altogether leading to possible applications in optical-data storage and display

Dichroïsme magnéto-chiral : un terrain de jeu pour la chimie moléculaire

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