Organic–inorganic molecular aggregates and their association within long-range ordered crystalline assemblies: relevance to the template effect in solid-state chemistry

Abstract

A series of conducting radical cation salts of 1,2-bis(4,5-dimethyltetrathiafulvalen-4′-yl)ethane [bis(DMTTF)ethane], a bifunctional donor with two quasi-degenerate redox functionalities, has been prepared by electrocrystallization; two kinds of binary radical cation salts, [bis(DMTTF)ethane]₃[Re₆Q₆Cl₈], Q = Se, 1; S, 2 and [bis(DMTTF)ethane]₂[Re₆Q₅Cl₉], Q = Se, 3; S, 4 and a ternary phase [bis(DMTTF)ethane]₅[Re₆Se₆Cl₈][Re₆Se₅Cl₉], 5, have been obtained. All five compounds present the same one-dimensional (1D) structural organization in which a stack of donor molecules is surrounded by cluster anions. The degree of oligomerization of the radical cation moieties within the stack is shown to be controlled solely by the cluster anion charge. Thus, the long-range ordered merging of 1 and 3 has led to the formation of the molecular alloy 5. The electronic properties of 1–5 deduced from the band structure calculations and the magnetic properties observed by single-crystal EPR are analysed in relation with the structural changes and the spin distribution on the TTF moieties. The role of the organic chalcogen-inorganic chalcogen interactions is also discussed. In particular, the spin-Peieris transition observed in 1 and absent in 2 is shown to be associated with significant donor-anion interactions only present in 1. Finally, the relation between the degree of purity of 1 and the absence of a pseudo-gap in the spin-Peieris transition is demonstrated.