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 (FeTPyzPACl 8 , 1) was obtained by a direct tetramerization reaction of 1,2-dichloro-4,5-dicyanopyrazine and iron(II) acetylacetonate in 1-chloronaphthalene at 220 o C. 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 − ) 0.26 FeTPyzPACl 8 }∙2C 6 H 4 Cl 2 (2) was obtained as single crystals by slow diffusion of hexane into the o-dichlorobenzene solution. It contains the {(CN − ) 2 (FeTPyzPACl 8 )} dianions (74 %) together with mixed {(FeTPyzPACl 8 )(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) A and the axial Fe–C(C≡N) bond length is 1.962(6) A. 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.