Perchlorinated vanadyl tetrapyrazinoporphyrazine: spectral, redox and magnetic properties

Abstract

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⁻)V^IVO]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 [Cl₈TPyzPzV^IVO] 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 V^IV 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 V^IV with a ⁵¹V nucleus (I = 7/2).