(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.
ASJC Scopus subject areas
- Colloid and Surface Chemistry