Spin Pairing and Magnetic Coupling in Quasi One-Dimensional Semiconductors with a Trimeric Stacking Structure. Structural, Charge-Transport, and Magnetic Studies of [Ni(tatbp)]₃[ReO₄]₂·C₁₀H₇Cl and [Cu(tatbp)]₃[ReO₄]₂·C₁₀H₇Cl

Electrochemical oxidation of (triazatetrabenzoporphyrinato)nickel(II) or (triazatetrabenzoporphyrinato)copper(II), Ni(tatbp) or Cu(tatbp), dissolved in 1-chloronaphthalene in the presence of the perrhenate ion affords the new molecular conductors [Ni(tatbp)]₃[ReO₄]₂·C₁₀H₇Cl and [Cu(tatbp)]₃[ReO₄]₂·C₁₀H₇Cl. The isostructural compounds are composed of partially ligand-oxidized (+2/3) M(tatbp) molecules that form trimerized stacks. Trimerization of the conducting stacks renders the compounds semiconductors with conductivity along the needle axis (crystallographic a) in the range of 2.5 ⨯ 10^-4-3.0 ⨯ 10^-4 Ω^-1 cm^-1 and an activation energy for conduction in the range of 0.24-0.26 eV. Magnetic susceptibility measurements on the Ni(II) derivative show that the valence band has the diamagnetic ground state expected for a semiconductor. Nonetheless, the valence-band electrons are shown to mediate a strong intratrimer Cu-Cu coupling characterized by a Weiss constant θ =-5.2 K in the Cu(II) analogue. The magnetic properties are rationalized in terms of a band structure derived by considering the trimers as weakly interacting supermolecules, with θ dominated by intratrimer interactions. A structure determination was performed on the Cu(II) analogue. It crystallizes in space group C_i¹-Pi of the triclinic system with one formula unit in a cell of dimensions a = 9.167 (6) Å, b = 15.849 (10) Å, c = 16.065 (10) Å, α = 65.87 (2)°, β = 72.11 (3)°, and γ = 84.01 (2)° (volume = 2126ų) at 110 K. The Cu-Cu distance for adjacent macrocycles within a trimer is 3.190 (3) Å and that between trimers is 3.482 (4). The ReO₄^- anions lie within channels formed between the stacks as does a disordered 1-chloronaphthalene solvent molecule. The final refinement of 4988 observations having F₀² > 3σ(F₀²) involved an anisotropic model for Cu and Re, an isotropic model for the other non-hydrogen atoms, and fixed positions for the hydrogen atoms (295 variables). The refinement converged to values of R(F) = 0.085 and R_W(F) = 0.091.