Magnetism: ferromagnetic interactions

Concerning molecule-based magnets, the first spin-ladder was synthesized (/ -EPYNN)[Ni (dmit)2] (/ -EPYNN = / -7V-ethylpyridinium o-nitronyl nitroxide). Within the crystal lattice, the radical cation /7-EPYNN units are arranged in ID chains with ferromagnetic interactions. The chains of [Ni(dmit)2] moieties in the ladder formation exhibit coexistent antiferromagnetic interactions.1031,1032... 

The magnetic data of the polymeric complex at low temperature (T < 20 K) yield much higher values than those calculated using Eq. 1 and show strong ferromagnetic interactions. The magnetic behavior of the complex is different from those of discrete Cu-Ln complexes, which normally show antiferromagnetic interactions [81-85],... 

The magnetic susceptibility of p-[Fe(Cp )2][Pt(mnt)2] follow a Curie-Weiss behavior with 6 - 9.8 K. The dominant ferromagnetic interactions are assigned to the magnetic intrachain D+A interactions from the type I chains, as the contribution from the D+ [ A2]2 D+ unit chains is expected to respect only to the cations due to the strong dimerization of the anions, S - 0 for [A2]2. ... 

Following the idea of McConnell [44] who proposed in 1967 that a stacking arrangement such as.., D+ A D+ A D+ A-... of donor and acceptor could lead to molecule-based magnets, the combination between metal bis-dithiolene complexes and metalloceniums was performed originally only to promote cooperative ferromagnetic interactions [45]. 

The temperature dependence of the molar magnetic susceptibility (x) of an assembly of paramagnetic spins without interaction is characterized by the Curie behavior with x = C/T where C = /Vy2( 2.S (.S + l)/3k. It is a very common situation in the organometallic chemistry of radical species when the spin density is essentially localized on the metal atom. Since, in most cases, this atom is surrounded by various innocent ligands, intermolecular interactions are very weak and in most cases are reflected by a small contribution described by a Curie-Weiss behavior, with x = C/(T 0) where 0 is the Curie-Weiss temperature. A positive value for 0 reflects ferromagnetic interactions while a negative value — the most common situation — reflects an antiferromagnetic interaction. 

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