Charge transfer complexes of metal-free phthalocyanine radical anions with decamethylmetallocenium cations: (Cp*2Co+)(H2Pc˙−)·solvent and (Cp*2Cr+)(H2Pc˙−)·4C6H4Cl2

Abstract

Charge transfer complexes (Cp*₂Co⁺)(H₂Pc˙⁻)·0.5C₆H₄Cl₂·0.7C₆H₅CN·0.3C₆H₁₄ (1) and (Cp*₂Cr⁺)(H₂Pc˙⁻)·4C₆H₄Cl₂ (2) have been obtained as single crystals. Both complexes contain metal-free phthalocyanine (Pc) radical anions and decamethylmetallocenium cations. Reduction of the Pc macrocycle leads to the appearance of new bands at 1026–1030 nm in the NIR range and blue shifts of both Soret and Q-bands of H₂Pc in the spectra of 1 and 2. The geometry of the Pc macrocycles supports the formation of H₂Pc˙⁻ by the alternation of shorter and longer C–N(imine) bonds in the macrocycles in 2. Complex 1 contains pairs of H₂Pc˙⁻ having effective π–π interactions with two sandwiched Cp*₂Co⁺ cations, whereas complex 2 contains stacks composed of alternating Cp*₂Cr⁺ and H₂Pc˙⁻ ions. The magnetic moment of 1 is 1.64 μ_B at 300 K due to the contribution of the H₂Pc˙⁻ spins with the S = 1/2 state and diamagnetism of Cp*₂Co⁺. This is supported by the observation of a narrow EPR signal of 1 with g = 2.0032–2.0036 characteristic of H₂Pc˙⁻. Strong antiferromagnetic coupling of spins with a Weiss temperature of −23 K is observed between H₂Pc˙⁻ in 1. This coupling is probably mediated by the Cp*₂Co⁺ cations. The magnetic moment of 2 is 4.18 μ_B at 300 K indicating the contribution of both paramagnetic H₂Pc˙⁻ (S = 1/2) and Cp*₂Cr⁺ (S = 3/2) species. In spite of the presence of stacks of alternating ions in 2, only weak magnetic coupling is observed with a Weiss temperature of −4 K most probably due to ineffective π–π interactions between Cp*₂Cr⁺ and H₂Pc˙⁻. The EPR spectrum of 2 contains an asymmetric signal attributed to Cr^III (g₁ = 3.9059–3.9220) and a narrow Lorentzian signal from H₂Pc˙⁻ with g₂ = 1.9943–1.9961. In addition to these signals, a broad EPR signal grows in intensity below 80 K with g₄ = 2.1085–2.2438 which can be attributed to both paramagnetic Cp*₂Cr⁺ and H₂Pc˙⁻ species having exchange interactions.