A series of (Me(3)TACN)Fe-II derivatives with soft coligands have been investigated, where Me(3)TACN is N,N',N "-trimethyl-1,3,7-triazacyclononane. Treatment of Me(3)TACN with FeCl2 afforded a compound with the empirical formula (Me(3)TACN)FeCl2 (1). Compound 1, which is a versatile precursor reagent, was shown by single-crystal X-ray diffraction to be the salt [(Me(3)TACN)(2)Fe2Cl3][(Me(3)TACN)FeCl3], containing isolated [(Me(3)TACN)(2)Fe2Cl3](+) and [(Me(3)TACN)FeCl3](-) subunits. Treatment of 1 with NaBPh4 gave the known [(Me(3)TACN)(2)Fe2Cl3]BPh4, while the addition of Me(3)TACN to FeCl42- gave [(Me(3)TACN)FeCl3](-). Oxygenation of 1 afforded [(Me(3)TACN)FeCl2](2)(mu-O), which was shown crystallographically to be centrosymmetric with a pair of distorted octahedral Fe centers. The Fe-N bond trans to the Fe-O bond is elongated by 0.2 A relative to the other Fe-N distances. Solutions of 1 and thiolates absorb CO to give [(Me(3)TACN)Fe(SPh)(CO)(2)]BPh4 and (Me(3)TACN)Fe(S2C2H4)(CO) (v(CO) = 1896 cm(-1)). Treatment of 1 with excess CN- afforded [(Me(3)TACN)Fe(CN)(3)](-), isolated as its PPh4+ salt 5. Crystallographic and spectroscopic studies show that 5 is low spin with a C-3 nu structure; its Fe-N distances contracted by 0.23 Angstrom relative to those in [(Me(3)TACN)FeCl3](-). Aqueous solutions of 1 bind CO upon the addition of CN- to produce (Me(3)TACN)Fe(CN)(2)(CO) (6). Analogous to 6 is (Me(3)TACN)Fe(CN)(2)(CNMe), prepared by methylation of 5. The metastable dicarbonyl [(Me(3)TACN)FeI(CO)(2)]I was prepared by treatment of FeI2(CO)(4) with Me3TACN and was crystallographically characterized as its BPh4- salt. Values of E-1/2 for [(Me(3)TACN)FeCl3](-), 5, and 6 are -0.409, -0.640, and 0.533 V vs Fc/Fc(+), respectively.