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

Abstract

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.

Salt of Ring‐Reduced Iron(II) Octaethyltetrapyrazinoporphyrazine Containing Trimetallic Dianions with Peripherally Coordinated ZnCl2 Units: {FeII(TPyzPzEt8)4–(ZnCl2)2}2–

“…Therefore, the Soret band is observed at 332 nm, but main peak of the Q‐band are observed at 644 nm. This spectrum is quite similar to that of unsubstituted H 2 TPyzPz having the Soret and the Q‐bands at 330 and 644 nm, respectively …”

“…That leads to partial loss of aromaticity of the system and alternation of the C‐N meso bonds in such a way that two pairs of oppositely located C‐N meso bonds are elongated and two other pairs of oppositely located bonds are shortened. The difference between them is 0.06–0.08 Å , . There is no obvious alternation of the C‐N meso bonds in the TPyzPzEt 8 macrocycle in 1 in contrast to reduced tetrapyrazinoporphyrazine macrocycles.…”

“…Reduction of dianionic phthalocyanine and tetrapyrazinoporphyrazine macrocycle to the radical trianionic and tetraanionic state leads to a strong blue shift of both Soret and Q‐bands and the appearance of new bands in the NIR range at 930–1070 nm , . As a rule, the intensity of the NIR bands for the tetraanionic macrocycle is essentially weaker in comparison with that for the radical trianionic macrocycle , .…”

“…Shorter bonds are formed with meso ‐nitrogen atoms (N meso ) and longer bonds are formed with pyrazine (N pyrazine ) and pyrrole (N pyr ) nitrogen atoms. Reduction of unsubstituted metal‐free H 2 TPyzPz and Ti IV O(AceTPrzPz) is accompanied by the reduction of the macrocycle to di‐ and tetraanionic state for (H 2 TPyzPz) 2– and {Ti IV O(AceTPrzPz) 4– } 2– , respectively , . That leads to partial loss of aromaticity of the system and alternation of the C‐N meso bonds in such a way that two pairs of oppositely located C‐N meso bonds are elongated and two other pairs of oppositely located bonds are shortened.…”

“…TPyzPz macrocycle has stronger acceptor properties than phthalocyanines due to the presence of eight additional electronegative nitrogen atoms in the macrocycle . Only two anionic compounds of TPyzPzs are known now , . At the reduction of metal‐free tetrapyrazinoporphyrazine (H 2 TPyzPz) and titanyl tetra(acenaphthenapyrazino) porphyrazine {Ti IV O(AceTPrzPz)} by sodium fluorenone ketyl in the presence of cryptand[2.2.2] or PPNCl, crystalline compounds containing diamagnetic H 2 TPyzPz 2–[34] and {Ti IV O(AceTPrzPz 4– )} 2–[35] dianions were obtained.…”