Toward Crystal Design in Organic Conductors and Superconductors

We have seen that many different types of intermolecular interactions in organic conducting cation radical salts. Hydrogen bonding between the donor molecules and the anions is weak but not negligible. The ionic Madelung energy is insufficient to completely intersperse anions and cations, thus the layers favored by the van der Waals interactions remain intact. The search for new conducting and superconducting salts has been mainly by trial-and-error methods, even though simple substitutions have been employed in order to obtain isostructural analogs of successful (e.g., superconducting) salts. However, even seemingly minor substitutions sometimes destroy the packing type, and different crystal structures result. Simulations with the aim at predicting crystal structures have not succeeded, mainly because the different interaction types are of comparable energy, and the delocalized and partial charges render the calculations of the ionic terms extremely unreliable. Clearly, the development of suitable crystal modeling techniques with predictive capabilities is one of the great needs of the field