Synthesis, Characterization, and Crystal Structures of Iron(Ⅱ) and Manganese(II) Complexes with 4,7-bis(2-pyridylmethyl)-1-thia-4,7-diazacyclononane

A new synthesis has been developed for 1-thia-4,7-diazacyclononane and the complexation behavior of a particular derivative has been explored. The pentadentate ligand 4,7-bis(2-pyridylmethyl)-l-thia-4,7-diazacyclononane ([9]<TEX>$N_2SPY_2$</TEX>) and its iron(Ⅱ) and manganese(Ⅱ) complexes were prepared and characterized. Magnetic moments of 5.17 and 5.90 μB respectively, indicate that the iron(Ⅱ) and manganese(Ⅱ) complexes are high spin. Charge transfer transitions (d-π*) occur for [Fe(Ⅱ)([9]<TEX>$N_2SPY_2)(X)]^{n+}$</TEX>at 27027, 25000, and 24390 cm-1 for X=<TEX>$H_2O$</TEX>, Cl-, and OH-, respectively. In acetonitrile solution, the cyclic voltammogram of the manganese(Ⅱ) complex exhibits a redox couple at 0.92 V vs. NHE while the redox potentials for [Fe(Il)([9]<TEX>$N_2SPY_2)(X)]^{n+}$</TEX> are 0.70, 0.66, and 0.37 V vs. NHE for X=<TEX>$H_2O$</TEX>, Cl-, and OH-, respectively. The d-π* charge transfer energy and Fe(Ⅱ)/Fe(Ⅲ) redox potential for [Fe(Ⅱ)([9]<TEX>$N_2SPY_2)(X)]^{n+}$</TEX> increase in the same order: <TEX>$H_2O>Cl^- >OH^-$</TEX>. The crystal structures of the iron(Ⅱ) and manganese(Ⅱ) complexes reveal that the metal ions are sixcoordinate, binding to four nitrogen atoms and a sulfur atom from the pentadentate ligand, as well as a chloride anion, with the chloride and sulfur atoms in cis positions. The two metals have similar coordination geometries, which are closer to trigonal prismatic than octahedral. In both iron and manganese complexes, the M-N(<TEX>$sp_3$</TEX>) trans to Cl- is 0.07 Å longer than the one cis to Cl- , and M-N(<TEX>$sp^2$</TEX>) trans to S is 0.05 longer than the one cis to S atom.