STRUCTURAL, ELECTRICAL, MAGNETIC, AND SPECTROSCOPIC PROPERTIES OF RING-OXIDIZED MOLECULAR-METALS PRODUCED BY IODINATION OF METAL-FREE AND NICKEL TETRABENZPORPHYRINS

Detailed studies of the structure, conductivitity, magnetoresistance, optical spectra, and magnetic properties (susceptibility, EPR) for the new molecular metal tetrabenzporphyrin iodide (H-2(tbp)I) and the ele ctrical, spectral, and magnetic properties of Ni(tbp)I are reported. P aramagnetic transition-ion impurities were carefully excluded during t he synthesis of H-2(tbp)I and Ni(tbp)I, and both materials show much h igher, metal-like conductivites than previously seen for less-pure Ni( tbp)I. Comparison of the specular reflectance data for Ni(tbp)I and H- 2(tbp)I allows a distinction between purely ring pi-transitions and me tal-involved charge-transfer transitions, and the spectra fix the ener gy levels of the pi orbitals involved in conduction. Transport, magnet ic, and optical properties show that both H-2(tbp)I and Ni(tbp)I are r ing-based conductors that have metal-like conductivities, varying as s imilar to 1/T, down to ca. 30-40 K. However, the remaining level of de fects is higher in the tbp conductors than in H-2(pc)I, and whereas th e latter is metallic down to the mK temperature range, the defects in the (tbp) compounds localize the conduction electrons at similar to 10 K (Ni(tbp)I) and similar to 30 K (H-2(tbp)I), leading to transport th rough one-dimensional variable-range hopping. EPR g-values for H-2(tbp )I and Ni(tbp)I are close to that for the free electron and are nearly temperature-independent. The line widths for both samples are extreme ly narrow and also are nearly temperature-independent. These results s how that Ni(tbp)I does not display doubly-mixed valence, as thought ea rlier: Paramagnetic impurities significantly altered the EPR signals o f the prior samples. H-2(tbp)I crystallizes in the space group P4/mcc with cell constants of a = 14.173(10) Angstrom and c = 6.463(4) Angstr om. Full-matrix least-squares refinement of 63 variables gave an R ind ex of 0.061 on F-0(2).