Tailoring magnetic interactions of organic solids: Modification of triphenylverdazyl

Abstract

The synthesis of the free radicals 1‐(4'‐bromophenyl)‐3,5‐diphenyl‐verdazyl (Br‐TPV), 1‐(4'‐isopropyl‐phenyl)‐3,5‐diphenyl‐verdazyl (IP‐TPV), 1,3,5,6‐tetraphenyl‐verdazyl (Ph‐TPV), 6‐(1′‐naphthyl)‐1,3,5‐tri‐phenyl‐verdazyl (1N‐TPV), 6‐(2′‐naphthyl)‐1,3,5‐triphenyl‐verdazyl (2N‐TPV), 6‐(4′‐bromophenyl)‐1,3,5‐triphenyl‐verdazyl (BrPh‐TPV) and 1,3,5,6,6‐pentaphenyl‐verdazyl (PhPh‐TPV) is described. Their magnetic properties (static magnetic susceptibility, ESR) are reported for crystalline samples. They are compared with those of 1,3,5‐triphenyl‐verdazyl (TPV) which behaves as a quasi‐onedimensional antiferromagnet in the crystalline form. Exchange interaction is increased by a factor larger than 3 compared with TPV by the introduction of the additional ring in Ph‐TPV. For Ph‐TPV and PhPh‐TPV also the crystal structure was derived by X‐ray analysis. These results are discussed with special emphasis on their meaning for the tailoring of magnetic interactions in organic solids.

New concepts for molecular magnets

“…The susceptibility of Ph-TPV (Fig. 18) follows accurately the magnetic susceptibility expected for an one-dimensional Heisenberg antiferromagnet apart from a small deviation at low temperatures due Curie-like defect spins (Dormann et al 1992). Although the inter-molecular distances are roughly the same for Ph-TPV and TPV the intra-chain exchange constant of J 1d ak B À34 K for Ph-TPV is considerably larger and the Ne  el temperature T N 0X9 K smaller than for TPV.…”

Electronic Interactions in Verdazyl Biradicals

“…Electrochemical Behavior. Despite the many EPR studies of verdazyls, very few substituted verdazyls have been studied electrochemically. ,,,− The available literature reports have focused on the electrochemistry of 1,3,5-triphenylverdazyl in determining the effect of solvent on reaction entropies and disproportionation equilibria. , Oxidation of 1,3,5-triphenylverdazyl to the cation was reported to be reversible, but the reduction to the anion is only quasireversible. , E 1/2 potentials were not stated, but the peak separation between the anodic and cathodic peaks was given as Δ E P ox = 60 mV and Δ E P red = 110 mV, respectively. , It is likely that the stability of the mono and dications of 1 and of 4 − 7 are related to the stability of the analogous cations.…”

Can DFT calculations help the molecular designer to construct molecule based magnetic materials?

“…-0.011) on the N-phenyl group, and the next shortest between the same nitrogen and the ortho-carbon(3)(spin pop. +0.048), 3.60 Å [21]. As this distance difference is only just significant (possibly), judging from the X-ray data, and the ortho/meta spin density ration is 0.048/(-)0.011 = -4.4, the antiferromagnetic coupling in this compound can still be attributed to this N(1)-C(3) interaction.…”