Magnetic assemblies based on Mn(III) salen analogues

Assembled Mn(III) salen-type quadridentate Schiff-base (SB) complexes, [Mn^III(SB)]ⁿ⁺, with various metal-containing/non-metal building blocks and their synthetic strategies are summarized. With the Mn(III) salen-type complexes, it is possible to have two coordination labile sites in trans- or cis-position as the SB ligand takes a quasi-planar chelate form and a stereoscopic chelate form, respectively, being a coordination-acceptor building block. Particularly in the quasi-planar form, the coordination labile sites face the direction of the Jahn-Teller elongated axis occupying the d_z2 orbital with an unpaired electron. Due to this characteristic orbital arrangement, the activity and magnetic-electronic properties of the Mn(III) salen-type complexes can be tuned, at will, by modulating the SB ligand that is equatorially located around the Mn(III) ion and coupled with the empty d_{x2 - y2} orbital. Both the structural aspects, and magnetic characteristics of assembled compounds are of great interest. This point is the main theme in this review. The high-spin Mn(III) salen-type complexes (S = 2) display strong magnetic uniaxial anisotropy, in which the magnetic easy axis can be unambiguously found as the Jahn-Teller axis. Thus, out-of-plane assembly of the quasi-planar Mn(III) salen-type complexes makes it possible to align the easy axes of the Mn(III) ions. This strategy creates unique magnetic systems involving molecular superparamagnets such as single-molecule magnets and single-chain magnets. So far, variously assembled systems employing Mn(III) salen-type complexes as oligomers, one-dimensional chains, and two- or three-dimensional networks have been designed. By following this review, we would know that the Mn(III) salen-type complexes have the potential as a versatile magnetic source for the design of unique magnetic materials with multiple assembling structures.