We report a structural, magnetic, and charge-transport study of the new “molecular metal” produced by the iodine oxidation of (tetrabenzoporphyrinato)nickel(II), Ni(TBP). The compound is of composition NKTBP)I1.0 and crystallizes in space group D4h2−P4/mcc of the tetragonal system with two formula units in a cell of dimensions a = 14.081 (25) Å and c = 6.434 (11) Å at 113 K. Full-matrix least-squares refinement of 65 variables gave a final value of the conventional R index on F2 of 0.122 for 954 unique reflections. The crystal structure consists of planar Ni(TBP) units stacked metal-over-metal with a NiNi spacing of 3.217 (5) Å at 116 K and with the units staggered by 41°. Running parallel to these stacks are chains of disordered I3− ions. Their existence requires a mixed valency (partially oxidized) formulation whose average charge, or ionicity, of 0.33 may be represented by writing [Ni(TBP)]033+(I3−)1/3. Both structure and formulation of this new compound are the same as we recently found for (phthalocyaninato)nickel(II) iodide, Ni(Pc)I. The complex Ni(TBP)I has a room temperature conductivity of ca. 330 S cm−1, which rises to a maximum of 600 S cm−1 at ca. 95 K and decreases in an activated fashion at lower temperatures. The susceptibility is Pauli-like, being low (ca. 0.1 spins/Ni(TBP)) and roughly temperature independent above 100 K. However, the carrier spin g values and line widths are anomalous; both are unusually large at room temperature (gav = 2.03, Г = 105 G) and increase strongly as the temperature is lowered. These observations lead us to conclude that this conductive molecular crystal exhibits a novel, doubly mixed valence state. Intermolecular mixed valency along a Ni(TBP) stack may be made explicit by writing the stoichiometric formula as [Ni(TBP)]2[Ni(TBP)]+(I3−). In addition, there is a rapid interconversion between ligand and metal-oxidized electronic tautomers: [NiII(TBP)+] ⇋ [NiIII(TBP)].
ASJC Scopus subject areas
- Colloid and Surface Chemistry