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] · 7H2O (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) Å] and Fe–N [1.870(4)–1.978(4) Å] bond lengths in 1 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) Å] 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) Å]. The versatility as a ligand of tppz toward transition metal ions is analyzed and discussed in the light of the available structures.

The preparation and crystal structure of two iron(II) complexes of formula PPh4-mer-[Fe(tppz)(CN)3] · 7H2O (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. Compound 2 is an ionic salt which is made up of low-[Fe(1)(tppz)2]2+ six-coordinated and high-spin [Fe(2)(NCS)4]2− four-coordinated iron(II) units. It is the first structurally characterized example containing the tetrahedral iron(II) unit [Fe(NCS)4]2−.Figure optionsDownload as PowerPoint slide