Abstract
There has been a renaissance in the interdisciplinary field of Molecular Magnetism since ~2000, due to the discovery of the impressive properties and potential applications of d- and f-metal Single-Molecule Magnets (SMMs) and Single-Ion Magnets (SIMs) or Monometallic Single-Molecule Magnets. One of the consequences of this discovery has been an explosive growth in synthetic molecular inorganic and organometallic chemistry. In SMM and SIM chemistry, inorganic and organic ligands play a decisive role, sometimes equally important to that of the magnetic metal ion(s). In SMM chemistry, bridging ligands that propagate strong ferromagnetic exchange interactions between the metal ions resulting in large spin ground states, well isolated from excited states, are preferable; however, antiferromagnetic coupling can also lead to SMM behavior. In SIM chemistry, ligands that create a strong axial crystal field are highly desirable for metal ions with oblate electron density, e.g., TbIII and DyIII, whereas equatorial crystal fields lead to SMM behavior in complexes based on metal ions with prolate electron density, e.g., ErIII. In this review, we have attempted to highlight the use of few, efficient ligands in the chemistry of transition-metal SMMs and SIMs, through selected examples. The content of the review is purely chemical and it is assumed that the reader has a good knowledge of synthetic, structural and physical inorganic chemistry, as well as of the properties of SIMs and SMMs and the techniques of their study. The ligands that will be discussed are the azide ion, the cyanido group, the tris(trimethylsilyl)methanide, the cyclopentanienido group, soft (based on the Hard-Soft Acid-Base model) ligands, metallacrowns combined with click chemistry, deprotonated aliphatic diols, and the family of 2-pyridyl ketoximes, including some of its elaborate derivatives. The rationale behind the selection of the ligands will be emphasized.
Highlights
This work is devoted to Research Director Vassilis Psycharis on the occasion of his 60th birthday
Magnetization vs. dc magnetic one oxygen atom from a 4.22 MeCO2− ligand and two 3.21 MeCO2− ligands. The latter and an field sweeps on single crystals of 33 display hysteresis loops below 0.7 K whose coercivities increase with additional acetato group link each triangular subunit to a Na+ ion; the two alkali metal ions attached decreasing temperature and with increasing sweep rate, confirming that this giant cluster is one of the to the decanuclear {MnII2MnIII8} loop connect it in an equivalent manner to a neighboring loop giving largest Mn Single-Molecule Magnets (SMMs)
We hope that this review has provided the readers with a taste of the synthetic chemistry and reactivity studies of 3d, 4d- and 5d-metal Single-Ion Magnets (SIMs) and SMMs, with emphasis on some ligands or families of ligands that have been used successfully in this area
Summary
Alfred Stock, a pioneer in borane and silane chemistry, was the first scientist to introduce the term “ligand” in the second decade of the 20th century; the word has its roots in the Latin language where “ligare” means “to bind” [52]. By combining two different organometallic ligands of sufficient bulk (but not too bulky to avoid close approach of the ligands), the groups of Tong, Mansikkamäki and Layfield synthesized the mononuclear complex [(CpiPr5 )DyIII (Cp*)][B(C6 F5 )4 ] (4), Equations (1) and (2), Figure 2; CpiPr5 is the penta-iso-propylcyclopentadienyl(−1) ligand and Cp* is the pentamethylcyclopentadienyl(−1) ligand This design of ligand framework allowed the two key structural parameters—that is, the Dy–Cpcent distances (cent refers to the centroids of the cyclopentadienyl ligands) and the Cp–Dy–Cp bend angle-to be short and wide, respectively, achieving an axial crystal field of sufficient strength to give a SIM that shows magnetic hysteresis above 77 K [36]; this is the first step for the development of nanomagnet devices that function at relatively practical temperatures. Modified from reference [36]
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