Ferromagnetic linking

D conjugated arrays of ferromagnetically linked spin sites remain a topic of active pursuit, with modification due to advances since Malaga s proposal [ref 93] cf. Morita Y, Suzuki S, Sato K, Takui T. Nat Chem 2011 3 197-204. 

Still higher nuclearities, up to 12 in [Mni20i2-(RC00)i6(H20)4] (R = Me, Ph), have been reported.The cores of these two compounds, which are of interest as potential building blocks in the preparation of molecular ferromagnets, consist of a central Mn4 (/Li-0)4 cubane linked by O-bridges to eight Mn atoms. 

The occurence of the magnetic structure of the A-type also demands a 3-dimensional linking of octahedra in corners. The magnetic coupling, however, is of a different kind in the 3 directions The A-type is a magnetic layer structure, in which ferromagnetic sheets are coupled anti-ferromagnetically in the third direction. 

Beads of cross-linked polystyrene containing magnetite crystals (Fe304, a ferromagnetic material) have been prepared and successfully used for solid-phase synthesis [125-127]. The magnetic beads could be readily separated from the reaction mixture with a magnet. 

Naturally, the product of two-electron reduction of the para derivative can be depicted (Scheme 3-54) as an anionic diborataquinoid system. In contrast with the para-dib-orataquinoid dianion, an anionic meta-quinoid system is impossible. Indeed, the meta-sub-stituted isomer depicted in Scheme 3-54 has been characterized as a spin-unpaired triplet species with boron-centered spins (Rajca et al. 1995). This dianion diradical can be viewed as two stable borane anion radicals linked with a ferromagnetic coupling unit, i.e., 1,3-phenylene see Chapter 1. 

The theoretical design of donor oligomers that gives parallel spins upon electron transfer has been reported (Mizouchi et al. 1995). TTF and TSeF were used as the donor units, and they linked with >C=Y [Y s are CH2, O, S, or C(CN)2]. Ferromagnetic interaction between the spins is possible in these systems. 

AgF252,53 and the HP form of PdF254 are also characterized by buckled layers of MF4 squares, but the bonding of the planes is different from that in the previous case. Instead of resulting from MF6 octahedra linked by comers and edges, the distorted octahedra are only shared by comers. In both compounds, the ferromagnetic layers are coupled antiferromagnetically. 

---