Oliver Kahn Lecture: Composition and structure of the V[TCNE]x (TCNE = tetracyanoethylene) room-temperature, organic-based magnet – A personal perspective

VII[TCNE]-z[TCNE]2-1-z/2 (1 < z < 2) is the simplest formulation for the inhomogeneous and nonstoichiometric V[TCNE]x (x = 1 + z/2) room temperature magnet. This is based upon consideration of all of the surface, IR, elemental composition, and magnetic data. A limiting z = 1 2-D, layered structural motif with layers of μ4-[TCNE]−[TCNE]− bonded to four VII sites bridged by diamagnetic μ4-[TCNE]2− is described, and is sufficient to account for the observed Tc exceeding room temperature and the observed relatively high conductivity. The z = 2 limiting structure with the same layers, but bridged by S = 1/2 μ-[TCNE]−[TCNE]− is identified and provides for a 3-D magnetic structure. Nonetheless, the magnet does not diffract, and the featureless morphology observed from TEM studies suggests that it is a glassy material. Attempts to grow crystalline V[TCNE]x by several slow diffusion methods were unsuccessful, and did not result is a magnetically ordered material. This suggests that the V[TCNE]x room temperature magnet is a kinetic phase, and preparing a crystalline kinetic product will be challenging.

The formulation and structure of the V[TCNE]x (TCNE = tetracyanoethylene) room temperature, inhomogeneous, nonstoichiometric, organic-based magnet is reviewed. It is best described as VII[TCNE]·−z[TCNE]2−1-z/2 (1 < z < 2).Figure optionsDownload as PowerPoint slide