Role of monovalent anions in organic superconductors

From an analysis of the crystallographic structures of 13 (TMTSF)/sub 2/X salts (TMTSF, tetramethyltetraselenafulvalene and X, monovalent anion), at ambient temperature and 125 K, we demonstrate that the interchain Se-Se contacts correlate well with the observed physical properties of the salts. This is in contrast with earlier and less complete analyses which have focused on unit-cell dimensions or intrachain contacts.