Ferromagnetic interaction and metallic conductivity of radical ion salts (DIEDO)2M(mnt)2 (M=Ni, Pt)

(DIEDO)2M(mnt)2 (M=Ni, Pt; DIEDO=4,5-diiodo-4′,5′-ethylenedioxytetrathiafulvalene; mnt: maleonitriledithiolate) composed of transition metal complexes and iodine-bonded donor have a unique structure featured with strong coordination-bond-like interaction between iodo group of donor and cyano group of anion. It consists of two donor chains sandwiched between anion chains. The salts are metallic down to 100 K, followed by an onset of a metal–insulator (M–I) transition. TMI becomes lowered at high pressures (21 K at P>11 kbar). The magnetic susceptibility suggests the presence of ferromagnetic interactions (J∼20 K) between localized magnetic moments of M(mnt)2−, which interact with conduction electrons. The origin of ferromagnetic interactions is explained by McConnell’s first model and small overlaps between SOMOs of M(mnt)2−.