How well do we understand the synthesis of (ET) 2I 3 by electrocrystallization? ESR and X-ray identification of (ET) 2I 3 crystals which are mixtures of phases and observation of high-T c states of (ET) 2I 3, ranging from 2.5–6.9 K

Abstract

A previously unreported, perhaps widely occurring, phenomenon has been observed in the ESR examination of α- and ß-(ET) 2I 3 crystals prepared by electrocrystallization. Crystals that are in themselves α-ß-mixtures have been identified. The unusual mixed-phase crystals were first discovered in attempts to alloy (ET) 2I 3 and triiodides of closely related donors but have subsequently been detected in simple (ET) 2I 3 electrocrystallizations. In all cases where mixed-phase systems have been isolated, crystals have been noted growing on the bottom of the anodic portion of the H-cell. It is not known at present whether the α/ß-crystals were formed on the bottom, on the anode, or at both sites, although experiments are in progress to clarify this point. A second novel observation that has been made in investigating the mixed-phase systems is that crystals of (ET) 2I 3 have been found that have high-T c states, ranging from 2.5 to 6.9 K (rf penetration depth). It appears that α-, and ß-, and ß ∗ (or α t)-(ET) 2I 3 phases may all occur in one “single” crystal, thereby producing a range of T cs from 1.5–8 K. In the minimum, these findings suggest that crystals of (ET) 2I 3 prepared by electrocrystallization should be carefully screened. In all likelihood, the results have significant ramifications for electrocrystallization preparations in general. An ESR spectroscopic procedure has been developed for identifying and quantifying the composition of ß-(ET) 2I 3 crystals that are mixtures of phases.