2,3,5,6-Tetrakis(2-pyridyl)pyrazine (tppz)-containing iron(II) complexes: syntheses and crystal structures

The preparation and crystal structure of two iron(II) complexes of formula PPh4-mer-[Fe(tppz)(CN)(3)] center dot 7H(2)O (1) and [Fe(tPPZ)(2)]-[Fe(NCS)(4)] (2) [tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine; PPh4+ = tetraphenylphosphonium. cation] are reported here. The structure of 1 consists of mononuclear mer-tricyano[2,3,5,6-tetrakis(2-pyridyl)pyrazine]ferrate(II) anions, tetraphenylphosphonium cations and crystallization water molecules. Three carbon atoms from three cyanide groups in a mer arrangement and three nitrogen atoms from a tridentate tppz ligand build a somewhat distorted octahedral surrounding around the iron atom in 1. The values of the Fe-C [1.925(6)-1.947(5) angstrom] and Fe-N [1.870(4)-1.978(4) angstrom] bond lengths in I are consistent with a low-spin iron(II) species, a fact which is corroborated by its diamagnetic character at room temperature. Compound 2 is an ionic salt which is made up of low-[Fe(1)(tPPZ)(2)](2+) and high-spin [Fe(2)(NCS)(4)](2-) iron(II) units. The Fe(1) and Fe(2) iron atoms in 2 are six- and four-coordinated, respectively, six nitrogen atoms from two tridentate tppz ligands building a distorted octahedral environment at Fe(1) [Fe(1)-N = 1.874(4)-1.970(5) angstrom] and four thiocyanate-nitrogen atoms from terminally bound thiocyanate groups forming a tetrahedral surrounding at Fe(2) [Fe(2)-N = 1.966(8)-1.986(7) angstrom]. The versatility as a ligand of tppz toward transition metal ions is analyzed and discussed in the light of the available structures.