Synthesis of iron(II) octachlorotetrapyrazinoporphyrazine, molecular structure and optical properties of the (X-)2FeTPyzPACl8 dianions with two axial anionic ligands (X- = CN-, CL-)

Abstract

Iron(II) octachlorotetrapyrazinoporphyrazine (FeTPyzPACl8, 1) was obtained by a direct tetramerization reaction of 1,2-dichloro-4,5-dicyanopyrazine and iron(II) acetylacetonate in 1-chloronaphthalene at 220 oC. It was dissolved in o-dichlorobenzene by a complex formation reaction with the CN anions by adding bis(triphenylphosphoranylidene) ammonium cyanide (PPNCN). Salt(PPN+)2{(CN-)1.74(Cl-)0.26FeTPyzPACl8}2C6H4Cl2 (2) was obtained as single crystals by slow diffusion of hexane into the o-dichlorobenzene solution. It contains the {(CN-)2 (FeTPyzPACl8)} dianions (74 %) together with mixed {(FeTPyzPACl8)(CN-)(Cl-)} dianions (26 %). The conformation of tetrapyrazinoporphyrazine macrocycle in 2 was determined by single crystal X-ray analysis. Central 24-atom PA macrocycle is nearly planar but dichloropyrazine groups noticeably deviate relatively the mean 24-atom plane or are twisted. The iron(II) atoms are located exactly in the PA plane, the average equatorial Fe-N(PA) bond length is 1.941(3) Å and the axial Fe-C(C≡N) bond length is 1.962(6) Å. The position of Q- and Soret bands in the spectrum of 1 is at 656, 475 and 327 nm. The addition of two axial anionic ligands provides a greater number of bands in the visible range observed at 657, 550, 438, 415 and 326 nm. © ISUCT Publishing.