Ferromagnetic interaction

LCo(H20)6] ion, and bidentate /V-donor ligands such as cn, bipy and phen form octahedral cationic complexes [Co(L-L)3] , which are much more stable to oxidation than is the hexaammine [Co(NH3)6l . Acac yields the orange [Co(acac)2(H20)2] which has the tram octahedral structure and can be dehydrated to [Co(acac)2l which attains octahedral coordination by forming the tetrameric species shown in Fig. 26.3. This is comparable with the trimeric [Ni(acac>2]3 (p. 1157), like which it shows evidence of weak ferromagnetic interactions at very low temperatures. fCo(edta)(H20)] is ostensibly analogous to the 7-coordinate Mn and complexes with the same stoichiometry, but in fact the cobalt is only 6-coordinate, 1 of the oxygen atoms of the cdta being too far away from the cobalt (272 compared to 223 pm for the other edta donor atoms) to be considered as coordinated. 

Intramolecular ferromagnetic interactions in polynuclear metal complexes. C. J. Cairns and D. H. Busch, Coord. Chem. Rev., 1986, 69,1 (174). 

As addressed in many articles, each of those MO- and VB-based models has its own merits and limitations [50,64,71,75-80]. Keeping these in mind and conceiving the importance of the odd-chain unit in ferromagnetic interaction, Radhakrishnan suggested some simple rules according to odd/even in the length of shortest coupling path [49, 50]. 

We report herein a single crystal polarized neutron investigation of the spin density of two purely organic nitronyl nitroxide free radicals which present ferromagnetic interactions the 2-(6-ethynyl-2-pyridyl)-4,4,5,5-tetramethylimidazoline-l-oxyl-... 

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 charge transfer salt (BDNT)2[Ni(mnt)2] (BDNT = 4,9-bis(l,3-benzodithiol-2-ylidene)-4,9-dihydronaphtho[2,3-c]l,2,5-thiadiazole) also shows ferromagnetic interaction with /=3.4K, which was concluded to arise from the [Ni(mnt)2]- component on the basis of EPR evidence. In the absence of structural data, however, further understanding of this behavior could not be obtained. The anion was shown to be monoanionic, hence the valence of BDNT is +0.5.1051... 

Other [AuCIL] complexes with monophosphines are those derived of o-carborane (427),2506 pyr-anoside group (428),2507 a-dimethylamino(3)ferrocenophan-2-yl,2508 calix[4]arene derived phosphites,25 or aminoxyl radical-substituted phosphines (429),2510 for which ferromagnetic interactions have been observed. 

Number of unpaired electrons/ground spin state defines antiferromagnetic and ferromagnetic interactions quantitates ground sublevel splittings For 57Fe sites oxidation and spin state ... 

A deeper analysis [80] on this Cu - Dy chain showed that NN and NNN interactions are efficient above Tc and that inter spin-ladder ferromagnetic interaction is observed in this family of compounds [79-82]. Attempts were made to use the 3d tectons with other lanthanide precursors, such as hexanuclear lanthanide clusters. Regular chains were obtained with Dy-Cu ferromagnetic interaction but their close packing prevents observation of SCM behaviour [83]. 

Figure 9.5 PHI [25] simulation of the -ASm for an arbitrary system of two s = 7/2 spins with a Mw of 1300 Da. Key as shown, where Para is a paramagnetic system, F is a ferromagnetic interaction between spins...

Interestingly, this compound was known for some years [38, 39] before MCE research came back into vogue. Here, the maximum — ASM for a decoupled system is 42 J kg-1 K-1 and is almost met for AH = 0 - 7 T and 1.8 K. So, we have a reasonably high metal content, with a small, though ferromagnetic, interaction, with the appropriate high spin metals. Heat capacity data allow the adiabatic temperature change to be calculated here, this was found to be 12.7 K below 2 K, one of the best by this measure until recently. 

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],... 

Short-range order ferromagnetic interactions have been reported for several compounds containing 1,2-dithiolene and 1,2-diselenolene complexes,252 254... 

Even more atypical are long-range ferromagnetic interactions resulting in bulk ferromagnetism,271 276 a behaviour reported for example in the case of the two homoleptic 1,2-dithiolene complexes (NH4)[Ni(mnt)2] H20,19,274,275 and (Cp2 Mn)[Ni(dmit)2].276... 

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]. 

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