A New Charge-Ordered Molecular Conductor: -(BEDT-TTF)₂K⁺(18-crown-6)[Co^II (NCS)₄]?(H₂O)

A new molecular conductor, i.e., kappa-(BEDT-TTF)(2)K+(18-crown-6)[Co-II(NCS)(4)]center dot(H2O), is semiconductive with substantial charge gap values (Delta E) of 0.57 eV (measured) and 0.37 eV (calculated). There is a full band separation despite formal average charge on BEDT-TTF of +0.5 and kappa(kappa)-type packing of BEDT-TTF dimers that favors high conductivity. X-ray crystal structure analysis reveals complete charge ordering with full Coulomb charge on unique BEDT-TTF radical cations A (Q(A) = +1), while unique molecules B are uncharged (Q(B) = 0). Geometries of A (flat) and B (bent) differ considerably and are in accordance with the ascribing charges. Charge segregation is enhanced by forming tight face-to-face BEDT-TTF dimers AA (Q(AA) = +2) and BB (Q(BB) = 0). Strongly interacting double-charged dimers AA form "superstripes" running along a that are interleaved along b with chains of neutral dimers BB. Peculiar extremely thick (13.7 & Aring;) four-decker insulating anion layers cast strong Coulomb potential onto the conductive layers predetermining charge localization in the latter.