Microwave dielectric properties of Cu(tatbp)I

Cu(tatbp)I (tatbp = triazatetrabenzporphyrinato) is a quasi-one-dimensional molecular conductor that incorporates in its structure a dense array of S = 1 2 moments localized on a metal spine Cu⁺² sites and interacting strongly with charge carriers on the p-π molecular orbitals of the tatbp aromatic ring. The microwave dielectric properties have been measured at 13 GHz between 2 and 300K. The a.c. conductivity is in agreement with the d.c. measurement, and its magnitude is similar to that found in other good molecular conductors. The conductivity increases from a room temperature value of σ ∼ 3 × 10²Ω^-1cm^-1 to a maximum of ca. 7 × 10²Ω^-1cm^-1 at T ∼ 90K; it decreases by almost three orders of magnitude at lower temperatures, but remains practically constant below 6K at σ ∼ 1Ω^-1cm^-1. In the same range the dielectric constant decreases with temperature, the slope being less pronounced below 7K. This temperature behaviour of both properties is not believed to be associated with a normal metal-insulator or semiconductor transition but to be related to the presence of local moments on the metal spine.