Electronic structure and properties of Bunz' polymers

The Bunt polymers consist of n-membered rings of carbon atoms connected via n mono- or diethynyl units (m 1, 2 respectively) to other such rings. Coordinated to the three-, four-, and five-membered rings are ML(n) units (L = CO, Cp) which lead to 18-electron rule stability at each metal-organic center. The electronic band structures of the metal-free (often metallic) and metal-complexed (always insulating) materials are derived, and it is shown how the insulating polymer-M(CO)(3) systems may be converted to systems with small bandgaps by the loss of a CO group. Depending on the width of the conduction band, either small bandgap semiconductors, ferromagnetic metals or antiferromagnetic insulators are predicted. The properties of C(6)ML(x) polymers are also investigated (ML(x) = NO, CO, C3H3+). These consist of an ML, unit attached to a graphite sheet. Bending the MNO group converts the linear three-electron donor ''NO+'' unit into an ''NO-'' moiety and generation of a metal. By construction of polymers with specific arrangements of M(CO)(3) and MCp groups, interesting patterns of metallic and insulating units may be envisaged at the atomic level.