Synthetic strategy for rational design of single-chain magnets

A magnetically-isolated one-dimensional chain can behave as if "magnet" - this sentence may be opposed to our common sense. In this review, we will show that a "magnet-like" behavior can effectively be found in only a magnetic spin chain. In 2001, which is almost forty years after the pioneering theoretical work of R. J. Glauber [J. Math. Phys., 4, 294 (1963)] on the dynamics of ferromagnetically-coupled Ising spin chains, the first experimental evidence of such behavior has been discovered in a real one-dimensional compound [A. Caneschi et al. Angew. Chem., Int. Ed., 40, 1760 (2001)]. In 2002, we have reported on a one-dimensional compound [Mn ₂(saltmen) ₂Ni(pao) ₂(py) ₂](ClO ₄) ₂ (saltmen ^2- = N,N′-(1,1,2,2- tetramethylethylene)bis(salicylideneiminato), pao ^- = pyridine-2-aldoximato, and py = pyridine) which can be considered as a chain of ferromagnetically-coupled anisotropic S _T = 3 units [J. Am. Chem. Soc., 124, 12837 (2002)]. Magnetic measurements on this compound revealed the presence of slow relaxation and large field-dependent hysteresis of the magnetization at low temperatures. The topology of this chain is very close to the "ideal" chain imagined by Glauber and hence, still to date, the simplest system to probe the Glauber dynamics. By analogy to the Single-Molecule Magnets described in the introduction of this paper, we called this type of material: Single-Chain Magnet (SCM). To obtain simple SCM systems, we have developed a step-by-step synthetic strategy using primary and secondary building blocks to control the chemistry of the targeting materials and the physics of their characteristic magnetic properties. In this review, we will describe this synthetic strategy from the elementary building blocks to the final series of Single-Chain Magnets obtained since 2002. The magnetic properties of all these materials will be discussed in detail. In particular, the experimental SCM behavior will be described and analyzed in relation with the generalization of the Glauber model for real systems.