Abstract
A simple method, using density functional theory (DFT), of predicting spin-state in advance of synthesis is reported. Specifically, an excellent correlation is observed between the switching temperatures (T
) in CDCl
solution of five spin-crossover (SCO)-active [Fe
(L
)
(NCBH
)
] complexes and the DFT-calculated (and observed)
N NMR chemical shift (δ
) of the five different azine-substituted 1,2,4-triazole ligands employed, L
= 4-(4-methylphenyl)-3-phenyl-5-(azine)-1,2,4-triazole, where azine = pyridine, pyridazine, 4-pyrimidine, pyrazine, and 2-pyrimidine. To test the generality of this finding, DFT was also employed to readily predict the δ
values for a family of 16 literature ligands, known as bpp
[X,Y-substituted 2,6-(pyrazol-1-yl)pyridines], which have produced 16 SCO-active [Fe
(bpp
)
](Z)
complexes (Z = BF
or in one case PF
) in (CD
)
CO solution: again an excellent correlation was found between the computed δ
and the observed T
. These correlations represent a key advance in the field, as they allow a simple DFT calculation on a modified ligand to be used to reliably predict, before synthesis of the ligand or complex, the T
that would result from that modification. Achieving such easily predictable tuning of T
, and hence of spin-state, is a significant step forward in the field of SCO and also has big implications in many other fields in which spin-state is key, including catalysis, metallo-enzyme modeling studies, and host-guest chemistry.