Highly conductive metallomacrocyclic assemblies. Synthetic approaches to molecular metals with variable band-filling

Abstract

The enforced cofacial structure of the polymer [Si(Pc)O]_n has been employed to introduce new oxidation states in phthalocyanine molecular metals. Thus, oxidative electrochemical techniques have produced materials with doping levels as high as {[Si(Pc)O](BF₄)_0.50}_n, {[Si(Pc)O] (p-toluene-sulfonate)_0.85}_n and {[Si(Pc)O](SO₄)_0.09}_n. Controlled potential coulometry and X-ray diffraction studies of the [Si(Pc)O]_n/BF₄⁻ system suggest that ‘break-in’ phenomena have a structural basis (orthorhombic → tetragonal) and that doping is relatively homogeneous. Optical, magnetic, and charge transport properties of the {[Si(Pc)O](BF)_4y}_n series are reported as a function of y. Electrochemical techniques have also been employed to synthesize partially reduced polymers such as {(Et₄N)_0.25[Si(Pc)O]}_n and {[Li_0.25[Si(Pc)O]}_n. Incremental doping of [Si(Pc)O]_n with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) produces materials with doping levels as high as {[Si(Pc)O]DDQ_y}_n, y = 0.91. Optical and charge transport measurements show that as y is progressively increased, the polymer is transformed from a filled band insulator (y = 0.00), to a molecular metal (y ≈ 0.30 – 0.50), to an integral oxidation state Mott insulator $\text{(y ⪆ 0.90)}$.