![Fig. 9. (a) Scheme of the formation of the 1D VT CP [Co(3,4-dhcSQ)(3,4-dhcCat)(bix)] and assembly into nanoparticles. (b) Scheme of the attachment of carboxyl-functionalized nanoparticles onto a gold surface previously covered with monolayer of amino-terminated alkyl chains through a carbodiimine-mediated coupling reaction. Reproduced with permission from ref. 72. Copyright 2015, John Wiley and Sons.](/figures/fig-9-a-scheme-of-the-formation-of-the-1d-vt-cp-co-34-dhcsq-18e9xl64.webp)
![Fig. 7. The 2D VT coordination polymer [{Co(3,5-dbsq)(3,5-dbdiox)}2(tpom)] [68]. Hydrogen atoms and dioxolene ligands omitted for clarity; color code as per Fig. 5.](/figures/fig-7-the-2d-vt-coordination-polymer-co-35-dbsq-35-dbdiox-2-12h8st88.webp)
![Fig. 3 Structures of 1D cobalt(II) SCO coordination polymers [Co(pyterpy)Cl2] (left) and [Co(enbzpy)(dca)]+ (right) [54, 56]. Color code: Co (cyan), N (blue), C (black), Cl (green); H atoms omitted for clarity.](/figures/fig-3-structures-of-1d-cobalt-ii-sco-coordination-polymers-264pivcy.webp)
![Fig. 5. Structures of 1D cobalt-dioxolene VT coordination polymers (from left to right): [Co(3,6-dbsq)(3,6-dbdiox)(pyz)] and [Co(3,5-dbsq)(3,5-dbdiox)2(NLN)], NLN = bpb, tpb and dpg (Fig 2) [58,60,61,63]. Color code as per Fig. 3 and O (red).](/figures/fig-5-structures-of-1d-cobalt-dioxolene-vt-coordination-wkocu6os.webp)
Q2. What are the future works mentioned in the paper "Switchable cobalt coordination polymers: spin crossover and valence tautomerism" ?
In the case of VT complexes, the possibility of linking the VT moieties through the redox-active ligands has been little pursued and could offer an alternative approach to tuning the characteristics of the VT transition, for instance by increasing the hysteresis loop width. Iron ( II ) SCO coordination polymers provide inspiration for the possibilities with switchable CPs, but cobalt-based systems remain relatively underexplored. In principle, the switchability associated with the VT transition can be intrinsically important for the specific functionality of the particles, or it can instead offer a means of monitoring the composition of the particles, for instance for applications in drug delivery. While VT rather than SCO is probably more promising for cobalt systems, future promising options include combining cobalt-dioxolene moieties into CPs with other metals or metalloligands.
Q3. What is the main challenge in designing appropriate materials?
The main challenge in designing appropriate materials is the very nature of the VT/SCO transition itself, as the characteristic features of the transitions, including transition temperature, abruptness and hysteresis, are highly dependent on factors beyond the molecule.
Q4. What is the origin of Prussian blue?
Prussian blue is an early example of a functional coordination polymer (CP), with its use as a pigment dating back to the early 18th century.
Q5. What is the effect of the reorientation on the SCO?
the perchlorate counterion undergoes reorientation that affects the anion-interactions with the dicyanamide bridge, which seem to play a significant role in the cooperative character of the SCO transition.
Q6. What is the exciting route to switchable materials?
An exciting route to switchable materials suitable for practical applications is thesynthesis of nano- or microparticles of VT CPs.
Q7. What is the SCO transition in a hexafluorophosphate?
The non-coordinating bulky hexafluorophosphate counterion does not take part in the intermolecular interactions around the cobalt center, the result being a much less well-defined SCO conversion.
Q8. What is the VT transition for cobalt-dioxolene?
The VT transitions for many of these compounds can also be induced by light irradiation, with effective TLIESST temperatures in the range 55-83 K (Table 1).
Q9. What is the difference in octahedral geometry for Co(II?
A consequence of the smaller difference in bond lengths for Co(II) SCO systems, and the resulting weaker intermolecular cooperativity, is that the transitions are generally more gradual than for Fe(II) and are often incomplete, with fewer examples of hysteresis.
Q10. What is the difference in octahedral geometry in a HS?
Associated with the increased population of the antibonding eg* orbitals, the SCO transition induces an increase in bond lengths, which is observed mainly for the two axial bonds while the equatorial bonds elongate to a very small extent, resulting in a much less distorted octahedral geometry in the HS state.
Q11. How many different structural families of cobalt CPs have been found to exhibit SCO?
To date, less than 20 different structural families of cobalt CPs have been found to exhibit either SCO or VT transitions (Table 1), with many more examples of VT transitions rather thanSCO.
Q12. What is the VT transition for amorphous nanoparticles?
The use of such a ligand, 4-(2-(pyridin-4-yl)ethyl)benzene-1,2-diol (pbdH2; Fig. 2), with cobalt acetate, affords amorphous spherical nanoparticles of 110 nm diameter from the fast precipitation method [73].