New Dmit-Based Organic Magnetic Conductors (PO-CONH-C2H4N(CH3)3)[M(dmit)2]2 (M = Ni, Pd) Including an Organic Cation Derived from a 2,2,5,5-Tetramethyl-3-pyrrolin-1-oxyl (PO) Radical

We have prepared two dmit-based salts with a stable organic radical-substituted ammonium cation, (PO-CONH-C2H4N(CH3)(3))[Ni(dmit)(2)](2)center dot CH3CN and (PO-CONH-C2H4N(CH3)(3))[Pd(dmit)(2)](2) where PO is 2,2,5,5-Tetramethyl-3-pyrrolin-1-oxyl and dmit is 2-Thioxo-1,3-dithiol-4,5-dithiolate. The salts are not isostructural but have similar structural features in the anion and cation packing arrangements. The acceptor layers of both salts consist of tetramers, which gather to form 2D conducting layers. Magnetic susceptibility measurements indicate that the Ni salt is a Mott insulator and the Pd salt is a band insulator, which has been confirmed by band structure calculations. The cationic layers of both salts have a previously unreported polar structure, in which the cation dipoles order as (sic) along the acceptors stacking direction to provide dipole moments. The dipole moments of nearest neighbor cation layers are inverted in both salts, indicating no net dipole moments for the whole crystals. The magnetic network of the [Ni(dmit)(2)] layer of the Ni salt is two-dimensional so that the magnetic susceptibility would be expected to obey the 1D or 2D Heisenberg model that has a broad maximum around T approximate to theta . However, the magnetic susceptibility after subtraction of the contribution from the PO radical has no broad maximum. Instead, it shows Curie-Weiss behavior with C = 0.378 emu center dot K/mol and = -35.8 K. The magnetic susceptibility of the Pd salt obeys a Curie-Weiss model with C = 0.329 emu center dot K center dot mol(-1) and theta = -0.88 K.