Molecular Structure, Optical and Magnetic Properties of Dianionic Free‐Base Tetrapyrazinoporphyrazine Macrocycle

Free‐base tetrapyrazinoporphyrazine (H2TPyzPz) has been synthesized and the reduction of this macrocycle by an excess of sodium fluorenone ketyl in the presence of 2.2.2‐cryptand yields {Na(2.2.2‐cryptand)}2(H2TPyzPz)⋅2C6H4Cl2 (1) salt containing H2TPyzPz2‐ dianions. Blue shift of both Soret and Q‐bands is observed in the spectrum of 1 and a new band is observed at 822 nm. Reduction is accompanied by alternation of the C‐Nimine bonds in the macrocycle. The difference between short and long bonds of 0.092 Å is essentially higher than that for free‐base phthalocyanine radical anions (0.040 Å). This difference can be explained by population of LUMO of H2TPyzP by two electrons in singlet ground state. According to the calculations distortion almost disappears in triplet excited state since in this state two additional electrons occupy orbitals which bonding and antibonding properties are interchanged. Salt 1 shows a weak narrow EPR signal indicating diamagnetism of H2TPyzPz2‐. Calculations also show singlet ground state for the dianions whereas the excited triplet state is positioned by 1130 K higher than the ground state and is not populated at room temperature. Free‐base tetrapyrazinoporphyrazine (H2TPyzPz) was synthesized and crystalline salt {Na(2.2.2‐cryptand)}2 (H2TPyzPz)⋅2C6H4Cl2 (1) with the H2TPyzPz2‐ dianions was obtained allowing molecular structure, optical and magnetic properties of dianionic H2TPyzPz2‐ macrocycles to be analyzed for the first time.