Optical, magnetic, and electronic properties of peripherally fused macrocycles: Molybdocene porphyrazines

Metal-free and copper porphyrazines, [H₂pz] and [Cu pz], have been fused at the periphery with molybdocene dithiolene, [Cp₂Mo]. The optical, magnetic, and electronic properties of the resulting neutral and cationic complexes are studied, using first-principles density functional theory implemented by the discrete variational method. Analysis of the charge and spin distribution shows that the porphyrazine core is strongly coupled with the peripheral complex. The calculated optical absorption is found to be in reasonable agreement with experimental spectra, lending support to our theoretical model. Under appropriate circumstances one observes interaction of unpaired spins localized in the vicinity of both metal sites. The calculated spin distribution shows that [Cp₂Mo][Cu pz] and [Cp₂Mo][H₂pz]⁺ have a magnetic moment of 1 μ_B while [Cp₂Mo][Cu pz]⁺ and [Cp₂Mo][H₂pz] have no moment, in good agreement with the results of X-band EPR spectra. The Cu-Mo magnetic interaction is antiferromagnetic, being mediated by pyrrol nitrogens, meso nitrogens, carbons, and sulfurs.