SYNTHESIS AND CRYSTAL-STRUCTURE OF THE IRON(II)-IRON(III) COMPLEX [FEL][FECL4]CL -TRIS(PYRAZOL-3-YLMETHYL)-1,4,7-TRIAZACYCLONONANE]

The pyrazole-functionalized macrocycles -tris(pyrazol-3-ylmethyl)-1,4, 7-triazacyclononane, L, and -tris(pyrazol-1-ylmethyl)-1,4,7-triazacycl ononane, L', gave mixed-valence iron complexes of formulae [FeL][FeCl4 ]Cl and [FeL'][FeCl4]Cl, which are considered to contain the high-spin iron(II) [FeL](2+) and, respectively [FeL'](2+) cations, besides [FeC l4](-) and Cl- anions. The diamagnetic compound [FeL'][ClO4](2) has al so been obtained. There is evidence for the iron(II) contained in [FeL ][FeCl4]Cl being formed in the reduction of iron(III), accomplished by primary alcohols in the presence of L . 6HCl. The assignment of the [ FeL][FeCl4]Cl formula to the L derivative is supported by the results of an X-ray structural determination. The iron(II) in the [FeL](2+) ca tion is in a six-co-ordinate environment formed by the donor nitrogen atoms of the L ligand. The Fe-N bond distances are 2.274(4) Angstrom ( macrocycle nitrogens) and 2.120(4) Angstrom (pyrazole nitrogens). Comp arison with the much shorter distances detected for the diamagnetic co mpound [FeL'][ClO4](2) by a (poor-quality) structure determination sup ports the assignment of the iron(II) high-spin nature to the metal ion in the [FeL](2+) cation.