Iron magnetic behaviour

This compound can be considered as a precursor of more elaborate bpym-based magnetic systems so that formal substitution of the water molecules by more appropriate peripheral ligands, such as bpym and 2,2 -bithi-azoline (bt) together with NCS" or NCSe" counter-ions, allows us to fine tune the ligand field strength around the iron(II) atom, resulting in a rich variety of magnetic behaviour in the [Fe(L)(NCX)2]2(bpym) series. 

These compounds are first characterised by their magnetic behaviour. The spin-only high spin value of Fe(III) is 5.92 B.M., while a normal range for its low spin values in cubic symmetry is 2.0-2.3 B.M. [24-26]. Among the compounds listed in Table 1, these extreme cases are met by the low spin tris(l-pyrrole-dithiocarbamato)iron(III) hemikis(dichloromethane)... 

Both Mbssbauer spectroscopy and magnetometry are based on the magnetic behaviour of (essentially) iron in a crystal structure, but operate on different dimensional scales. Whereas Mbssbauer spectroscopy yields information about charge and coordination, magnetometric methods are more sensitive to the type of magnetic coupling and to the magnetic domain status of particles. 

Some of the polycrystalline spin crossover systems of iron(II) described above retain their spin equilibrium property upon dissolution in appropriate solvents. The Evans NMR method of measuring the change of the paramagnetic shift with temperature is the most common technique to study the magnetic behaviour of such systems. The spin transition characteristics has been observed to depend on various chemical modi-... 

Wilson et al.37) have first reported on the sT2(Oh) 1 A Oj,) spin transition taking place in six-coordinate iron(II) complexes with the hexadentate ligand tris-[4-[(6-R)-2-pyridyl]-3-aza-3-butenyl]amine, where R is either H or CH3 (see Sect. 8.4). Three of these systems, viz. II, III, and IV of Sect. 8.4, show spin crossover in the solid state, and two of them, viz. II and III, also in solution, whereas IV remains fully high-spin and I fully low-spin. The pronounced differences in the magnetic behaviour between the four members of the [Fe(6-Mepy)n(py)m tren](PF6)2 series (see Sect. 

In the formation of complexes between non-magnetic ions, as in most of the ions outside the iron group, the magnetic behaviour fails to be a point of difference between the two types of bonding. 

The thermal decompositions of nickel(II)-cobalt(II) oxalate solid solutions were studied using TG and TM [103], A series of the mixed binary Ni(II)-Co(II) oxalate samples was prepared at 25% (atom) intervals across the system. Physical mixtures were also prepared by mixing the pure end members. The DTG and DTM curves showed that the decomposition proceeds to completion in two overlapping stages. The kinetics of the individual steps were not studied. From the DTG curves, the authors stated that the physical mixtures behaved as individual oxalates, while the coprecipitate decomposed as a single entity. The TM curves showed that the products formed from the physical mixture and the coprecipitate were distinctly different. The magnetic behaviour of the product from the coprecipitate was consistent with the behaviour predicted for a Ni-Co alloy, but the products from the physically mixed oxalate do not show the transition temperature predicted for an alloy. The kinetics of decomposition of iron-nickel mixed oxalates have been studied by Doremieux et al. [104]. 

Comparisons may be made between the above two transition metal o-bonded metal-loporphyrins. In the rhodium complex the metal atom is almost in the plane of the macrocycle and this is not exactly the case for the ferric complex. It is not clear if this conformation difference is due only to a difference between the metal atoms. One explanation is that the o-bonded ligands are not the same (C Hs or CH3 with two different hybridization schemes). As shown above, this leads to different magnetic behaviour and in this case the out-of-plane distance could be different. One would expect a slightly larger out-of-plane distance for the methyl species because of its spin state. However, the steric interactions of a methyl group are far less than those of the phenyl ring and Fe(TPP)(CH3) could have the iron atom more in the porphyrin plane, thus favoring hexacoordination. ... 

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