Monomolecular magnet

Top view of Mn12, called "la Drosophila of the magnet molecules”.

monomolecular magnets (in English, single-molecule magnet) or magnet molecules are systems in which You can get permanent magnetization and magnetic hysteresis (usually at extremely low temperatures) not through three-dimensional magnetic ordering, but through a purely monomolecular phenomenon.

The name magnet is not strictly adequate, since real magnets involve a very large number of coupled centers. However, the scientific community has adopted it for being evocative of the magnetic properties of this type of molecule.

Commonly cited requirements for a system to behave this way are:

• a fundamental state with a thorn of high value
• a dedoblation to high zero field (due to high magnetic anthropy)

The combination of these properties can lead to an energy barrier such that, at low temperatures, the system is trapped in one of the high spin energy valleys.

Molecular magnets exhibit a temperature magnetic susceptibility product that increases with decreasing temperature, and can be characterized by a shift, both in position and intensity, of the peak in b.c. magnetic susceptibility.

The first molecular magnet was Mn12, a manganese dodecanuclear complex, which is maintained by oxo bridges and acetate anions; currently there are a multitude of systems and strategies to develop them, not only with transition metals but also with lanthanides.

Molecular magnets are interesting both from a purely theoretical point of view, due to their quantum behavior, and from a practical point of view (still in the speculative stage) both as candidates for qubits for quantum computing, and for cooling systems at very low temperatures (below 1 K).

Molecular-based magnet

A molecular-based magnet is a molecular material that presents magnetic hysteresis of cooperative origin, like traditional magnets (metal oxides). Organic magnets, for example, are molecular magnets.

History

Lock temperature box diagram (maximum temperature of magnetic hysteresis) compared to the year of publication for magnet molecules based on a single lanthanide ion.

Although the term "single-molecule magnet" was first used in 1996, the first single-molecule magnet was reported in 1991. The Mn₁₂O₁₂(MeCO₂)₁₆(H₂O)₄ complex (Mn₁₂Ac₁₆), first described in 1980, shows low relaxation of magnetization at low temperatures. This manganese oxide compound presents a central Mn(IV)₄O₄ cube surrounded by a ring of 8 units of 8 Mn(III) connected through oxo ligands of bridge.

In 2006 it was known that the deliberate structural distortion of a Mn₆ compound through the use of a nucleus derived from salicylaldoxime changes the intra-triangular magnetic exchange from antiferromagnetic to ferromagnetic resulting in a state fundamental S = 12.

A record magnetization was recorded in 2007 for [Mn(III)₆O₂(sao)₆(O2CPh) ₂(EtOH)₄], with S = 12, D = -0.43 cm⁻¹, and thus U = 62 cm⁻¹ or 86 K at a blocking temperature of 4.3 K. This was achieved by replacing the acetate (OAc) ligands with the bulkier salicylaldoxime, thereby distorting the manganese ligand sphere. It was prepared by mixing manganese perchlorate, benzoic acid sodium salt, a salicylaldoxime derivative and tetramethylammonium hydroxide in water and collecting the filtrate.

In 2011, the University of Nottingham reported that a depleted uranium dinuclear complex could be mistaken for a monomolecular magnet by chemist Stephen Liddle.