Conclusions
The current state of the SMM field is astounding when compared with merely five years ago. First the U eff = 1000 K mark was breached,[13c] followed closely by another jump to 1800 K,[13b] then hysteresis at 60 K,[14a] followed by 80 K.[14c] However, there are clear hurdles to overcome in the future. The current generation of best-in-class SMMs are all organometallic complexes or separated ion pairs (often both),[36,37] these factors make deposition on surfaces for devices challenging for the former, and even more so for the latter. Furthermore, the overwhelming majority of thesestate-of-the-art SMMs are stabilized with substituted cyclopentadienyl ligands; unfortunately, there is in principle a limit to how many substituted cyclopentadienes can be synthesized which still afford the [Dy(CpR)2]+cation, and new innovations are needed in molecular design to deliver new generations of SMMs.
In our opinion the field needn’t worry about running out of direction. To quote our friend and inspiration (or the leader), behind a lot of this work, “can’t you just stick some fluorines on that?”. There will always be demand for new and even more challenging targets for synthetic chemists, and in turn the theoreticians will be asked to develop easy-to-understand models from first principles. The culmination of these lines of thought, and of all the topics discussed above is the following: 1) a more complete understanding of how the dynamical behavior of ligands around metals interacts with electron and nuclear spins needs to be developed, which will likely need to be extended to multi-metallic systems; 2) molecular systems will need to be developed to benchmark these theoretical advancements; 3) robust high-performance SMMs which are not air and moisture sensitive need to be developed, in order to facilitate their potential technological applications; 4) the design of new SMMs needs to shift towards systems capable of displaying longer (and more useful) relaxation times in the liquid nitrogen temperature regime. The complexity of these challenges speaks to the exciting opportunities lying ahead.