Conductive Molecular Crystals. Structural, Magnetic, and Charge-Transport Properties of (5,10,15,20-Tetramethylporphyrinato)nickel(II) Iodide

(5,10,15,20-Tetramethylporphyrinato)nickel(II), Ni(tmp), has been partially oxidized by reaction with iodine. We report the structural, magnetic, and charge-transport properties of single crystals of the resulting compound, Ni(tmp)I. The compound crystallizes in space group[formula omitted] of the tetragonal system with four formula units in a cell of dimensions a[formula omitted]. Full-matrix least-squares refinement of 69 variables gives a final value for the R index on F² of 0.079 for 1418 observations. The structure consists of S₄-ruffled Ni(tmp) molecules, stacked metal-over-metal, with a Ni-Ni spacing along the stack of 3.466 (3) Å. Adjacent Ni(tmp) units in the unit cell are staggered by 37°. Severely disordered chains of iodine are located in channels surrounding the Ni(tmp) stacks. The iodine is identified as I₃- from diffuse X-ray scattering and resonance Raman spectroscopy. Splitting of the I₃- bands in the resonance Raman spectrum becomes evident at low temperature. Single-crystal room-temperature conductivity along the needle axis averages 110 Ω1 cm^-1, slightly less than that of large-ring porphyrinic conductors. The temperature dependence of the conductivity of Ni(tmp)I is metal-like above 115 K and activated at lower temperatures. Single-crystal EPR studies indicate that the oxidation of the Ni(tmp) moiety is ligand centered. The magnetic suscepttbility is metal-like, being temperature independent above 28 K but anomalously high (~1/3 spin/macrocycle), indicative of enhanced Coulomb correlations. This suscepttbility enhancement may arise from the mixing in of a magnetic triplet state that is available because of the electronic structure of small porphyrinic macrocycles. The suscepttbility decreases sharply as the temperature is lowered below 28 K.