Organic magnetic materials

In the gold complex 6-XIII, there are differences in the packing modes which are particularly manifested in the intermolecular contacts involving the radical-bearing aminoxyl N-oxide fragments. This leads to differences in the (N-O)- (N-Q) interactions between the two stmctures (a and fi) which results in differences in the magnetic behaviour. Both exhibit intermolecular antiferromagnetic interactions. The 

A number of other systems involving magnetic properties of organic polymorphs are worthy of brief note here, to demonstrate the variety of issues that have been raised, if not always resolved, and the kinds of opportunities that polymorphic systems provide for investigating these systems. 

Compound 6-XIV (tanane) has a high temperature tetragonal phase that transforms at around 14 °C to an orthorhombic phase, which is both ferroelastic and ferroelectric, and a monoclinic phase has also been reported and prepared (Capiomont et al. 1972 Jang et al. 1980). Structural data (Capiomont et al. 1981) were used to model the transition (Legrand et al. 1982). 

Banister et al. (1996) prepared an organic free radical 6-XV not based on NO. It is concomitantly dimorphic by sublimation, and varying the conditions can lead to either the centrosymmetric P a form (Banister et al. 1995) or the non-centrosymmetric 

Fdd2 fi form (Banister et al. 1996). The result is that in the a structure neighbouring chains are antiparallel, while in they are all parallel. Due to these symmetry considerations the a modification cannot exhibit a so-called spin-canting mechanism (Carlin 1989) which can account for the transition from a low-dimensional antifer-romagnet to a weakly ferromagnetic state. However, these restrictions are absent in the P modification, and this mechanism, based to a large extent on the structural distinction between the two polymorphs, has been used to account for the fact that this p form is the first example of an open-shell molecule to exhibit spontaneous magnetization above liquid helium temperature (36 K). 

---

Aryl nitrenes have been studied extensively over the last decades and are used in several industrial processes such as microlithography. Aryl nitrenes have also been used in photoaffinity labeling bioorganic molecules. The pursuit for organic magnetic material has sparked renewed interested in nitrene intermediates, which are ideal candidates for magnetic material because of their high spin properties. ... 

Structure-property relationships for metal-free organic magnetic materials... 

We now turn to considering exchange linkage between spin units in a more general fashion, as a transition from organic radical spin units to organic magnetic materials. 

A particularly promising variant of organic magnetic materials design is the pairing of different radicals having complementary crystal assembly units. In... 

Structure-property relationships for metal-free organic magnetic materials, 45, 93 Substitution, aromatic, a quantitative treatment of directive effects in, 1, 35 Substitution, nueleophilic vinylic, 7, 1... 

Although magnetic solids are generally thought to be inorganic compounds or metals, there is much current interest in organic magnetic materials. 

Magnetic fields are used to manipulate or organize magnetic materials for Lab-on-Chip applications. 

Structure—property relationships for metal-ffee organic magnetic materials, 45, 93... 

Figure 14.32 C shows the NBMOs of m-xylylene, another prototype high-spin system. This structure also has two more than non- atoms. As such, its NBMO are non-disjoint, and a triplet state for the biradical is preferred. In our discussion of organic magnetic materials in Section 17.3 we will see that this /non- approach to predicting spin states can be extended to a remarkable degree, allowing the rational design of very high-spin organic molecules.

As we will see, two fundamentally different approaches to preparing organic magnetic materials have emerged. Before we describe them, though, we present a very brief overview of some basic principles of magnetism. 

---