Perchlorinated vanadyl tetrapyrazinoporphyrazine: spectral, redox and magnetic properties

Perchlorinated vanadyl tetrapyrazinoporphyrazine and its reduced form obtained by reduction by potassium graphite in the presence of cryptand in o-dichlorobenzene have been synthetized. The reaction leads to the formation of a crystalline anionic salt cryptand(K+)2[(TPyzPzCl84−)VIVO]2− (1), where reduction is ring-centered and results in [TPyzPzCl84−] tetraanions. This causes a difference between shorter and longer bond lengths of 0.078 Å, disrupting macrocycle aromaticity. Reduction of [Cl8TPyzPzVIVO] leads to a strong blue-shift of the Q band (about 100 nm) in both solid state and THF solution. The starting compound is easily reduced to a monoanion, but preparation of the dianionic form requires further study. Magnetic properties of 1 are governed by VIV ions (S = 1/2), while [TPyzPzCl84−] tetraanions are diamagnetic. The EPR spectra of 1 show a strongly anisotropic signal due to the hyperfine interaction of an unpaired electron of VIV with a 51V nucleus (I = 7/2).