MONONUCLEAR CHROMIUM(III), MANGANESE(II) AND IRON(LII) COMPLEXES OF THE PENTADENTATE LIGAND 1,4-BIS(2-PYRIDYLMETHYL)-1,4,7-TRIAZACYCLONONANE

Chromium(III), manganese(II) and iron(III) complexes of dmptacn [1,4-b is(2-pyridylmethyl)-1,4,7-triazacyclononane] with general formula [M(d mptacn)Cl](n+) have been prepared by reaction of the macrocycle with;t he corresponding metal chloride salts and their physicochemical proper ties examined. Magnetic susceptibility, Mossbauer and ESR measurements have shown that the iron(III) complex [Fe(dmptacn)Cl]-[PF6](2) . MeOH exhibits spin-crossover behaviour, existing in the low-spin form belo w 50 K and as a mixture of low-and high-spin forms at 298 K. The struc ture of [Cr(dmptacn)Cl][CIO4](2) confirmed that the isomer formed has the secondary nitrogen adjacent to the chloro ligand and that there is significant distortion from octahedral geometry in the complex, both common features of complexes of dmptacn. Two enantiomeric forms of the complex are found in the unit cell, vis-a-vis in one enantiomer the d elta delta delta conformation of the tacn ring is coupled with a lambd a lambda conformation of the pyridyl arms while the opposite conformat ions are observed in the other.