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.