Chains antiferromagnetic

Hydrates. A2MnmF5 H20 compounds (A = K, Rb, Cs) are suitable examples of Heisenberg chain antiferromagnets. The 1-D behavior is enhanced by the ferrodistortive ordering of dj2 orbitals, antiparallel along the c direction. In the ab plane weak d°2 y2 interactions occur between the chains. 

The temperature dependence of the susceptibility is well-described by the alternating chain antiferromagnetic Heisenberg model. 

SPECIFIC HEAT OF THREE MAGNETIC LINEAR-CHAIN ANTIFERROMAGNETS. 

Fig. 78. CsMnCl3 2H20 single crystal. Temperature dependence of Xm Curve fitted for a Heisenberg linear chain antiferromagnet by the method of Weng and Griffith using J/k= -3.00 K, S= [73K18].

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... 

In the cis complexes, the torsion angle is usually smaller than that in trans complexes (Tables 16 and 17), leading to decreased antiferromagnetic coupling. In this case, the chains are helical and the compactness of this helix is a further factor that needs to be considered the more compact the helicoidal structure, the greater the antiferromagnetic coupling. 

The affinity of cyanide groups for lanthanide ions has motivated the use of [M(CN)6]3 tectons (with M = Cr3+, Mn3+, Fe2+, Fe3+, Co3+) that can give rise to a wide variety of one-dimensional cyanide-bridged structures ((E) topologic mode in Scheme 4.2) [90]. Some noticeable compounds are [Ln(DMF)4(H20)2Mn(CN)6]-H20 K chains (DMF, dimethylformamide), where antiferromagnetic coupling was observed between Mn3+ tecton and Sm3+, Tb3+,... 

With a few exceptions, the crystal structure of the salts based on the type I mixed chains consists of parallel arrangements of those chains. In most cases the magnetic behavior of these salts is dominated by ferromagnetic (FM) interactions, due to intrachain D+ A coupling. Several of these salts exhibit metamagnetic (MM) behaviors due to the coexistence of weaker antiferromagnetic (AF) intrachain interactions. 

Most of the salts based on decamethylmetallocenium radical cations and on planar metal bisdichalcogenate radical anions reported so far present crystal structures with mixed linear chain basic motives. The only known exception is [Fe(Cp )2][Ni (mnt)2], which exhibits another type of crystal structure based on a D+ [A2]2 D+ repeat unit [28]. In the case of this compound the magnetic behavior is dominated by the intradimer antiferromagnetic interactions. 

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