Evaluation of potential ferromagnetic coupling units: the bis(TMM) [bis(trimethylenemethane)] approach to high-spin organic molecules

Abstract

due to the more favorable partitioning of [ 3"•2• ] than of [2• ] to products (ki > k-¿, Scheme I). There is no evidence for a significant difference between kx and kx, so nucleophilic assistance to the reaction of 1-1 is minimal.The large Grunwald-Winstein values of m = 1.3 and 1.2 for the solvolysis reaction of 1-1 and the apparent bimolecular substitution reaction of azide ion with 1-1, respectively, are consistent with similar changes in polarity on moving from the ground state to the transition state for these reactions. A detailed evaluation of data for reactions in mixed methanol/water solvents with respect to a stepwise preassociation mechanism would require additional experiments at higher concentrations of azide ion (see Figure 5), which are not feasible because of the limited solubility of sodium azide in aqueous/organic solvents.Summary. These experiments provide a relatively simple protocol for determining if kinetically bimolecular nucleophilic substitution reactions proceed through a carbocation reaction intermediate. The reactions of nucleophilic anions with 1-X are kinetically second order in nucleophile only when the reactions of both the nucleophile and the leaving group anion with the free carbocation 2 are diffusion limited. This is consistent with a stepwise preassociation mechanism for the bimolecular substitution reaction. The relative rate acceleration observed at [Nucleophile] = 1.00 M is small (<40%, Figure 2 and Table II), even for those reactions which particularly favor the observation of a stepwise bimolecular substitution reaction. These results suggest that large rate accelerations should not be expected for nucleophilic substitution reactions in water which follow the stepwise preassociation reaction mechanism.

Spin glass behavior in complexes of iron doped coordinated polymers

“…For example, ferromagnetic coupling units have been found in organic radicals with triplet ground state, which resulted in ferromagnetic behavior in organic material [1,2]. However, anti-ferromagnetic coupling could lead to frustrated interaction in the presence of certain degree of disorder.…”

A computational study of the Dougherty model for the prediction of high-spin states in organic chemistry

“…In the design of large organic molecules with high-spin states, Dougherty [1,2] has proposed a conceptual model (founded on the pioneering work of Itoh [3a]) based on``linking'' basic building units as shown in .) The high-spin state in these systems is stabilized by the presence of a ferromagnetic coupling (FC) unit which couples spincontaining (SC) units with high-spin ground states.…”

“…In the systems studied by Dougherty et al [2] (and those recently synthesized by Adam et al [4]), the SC units are triplets (as isolated molecules) coupled via the FC unit. In this case, Dougherty proposes to model [2] the interaction of two triplets, considering a phenomenological Hamiltonian of the form r À2t 1 Á 2 1 where 1 and 2 are the spin operators for the SC units and t is the coupling parameter (or eective exchange integral). In his model, Dougherty associates t in Eq.…”

“…The energy level diagram for two interacting triplets [2] is given in Fig. 1, from which it can be seen that the sign of t FC determines the multiplicity of the ground state of the molecule.…”

“…Firstly, in the Dougherty model [2], no attempt was made to understand why a triplet FC unit yields a t FC b 0. Accordingly, we shall give a theoretical prescription for the computation of t and the computation of the spin of the FC unit in the molecule itself.…”