Five new (mu-oxo)diiron(III) complexes of the capping tetradentate ligand tris(2-pyridylmethyl)amine (tpa) have been prepared. The diaquo complex [tpa(H2O)FeOFe(H2O)tPa](ClO4)4 (1) and its conjugate base [tpa(OH)-FeOFe(H2O-tpa](ClO4)3 (2) serve as useful starting materials for the preparation of other (mu-oxo)-bridged diiron(III) complexes of tpa containing either terminal ligands or an auxiliary bridging group. For example, the terminal water ligands of 1 can be replaced by chloro ligands to give monobridged [tpa(Cl) FeOFe(Cl)tpa] (ClO4)2 (3) or by sulfato to give dibridged [(tpa)FeO(SO4)Fe(tpa)](ClO4)2(4). Complex 2 shows unusual reactivity; 2 is capable of promoting the hydrolysis of acetonitrile to give a (mu-acetamidato-N,O)-bridged complex, [(tpa)FeO(CH3CONH)Fe(tpa)]-(ClO4)3 (5). Complexes 1-5 show strong antiferromagnetic exchange coupling. The electronic absorption and resonance Raman spectra show distinctions between the mono- and dibridged systems, with 2 defining a borderline case. An X-ray structural analysis of [tpa(OH)FeOFe(H2O)tpa](ClO4)3(2) shows it to be monoclinic, space group P2(1)/c, with a = 12.092(2) angstrom, b = 17.740(4) angstrom, c = 20.633(3) angstrom, and beta = 104.148(8)degrees and with 4 formula units in the unit cell. The structure refined to a final R value of 0.054 for 2904 reflections. The coordinated water and hydroxide groups are linked by an intramolecular hydrogen bond, O...O = 2.419(10) angstrom. The Fe atoms are linked by a mu-oxo bridge; however, in contrast to those of other structurally characterized (mu-oxo)diiron(III) complexes, the two Fe-(mu-O) distances, 1.780(6) and 1.839(6) angstrom, are significantly different. The Fe-O-Fe angle is 138.9(4)degrees, and the Fe...Fe distance is 3.389(2) angstrom. An X-ray structural analysis of [tpa(Cl)FeOFe(Cl)tpa](ClO4)2 (3) shows it to be monoclinic, space group C2/c, with a = 16.308(2) angstrom, b = 17.178(3) angstrom, c = 16.575(2) angstrom, and beta = 11 1.807(7)degrees and with 4 formula units per cell. The structure refined to a final R value of 0.061 for 1946 reflections. The cation has 2-fold symmetry with the bridging oxygen atom on the 2-fold axis : Fe-(mu-O) = 1.785(1) angstrom, Fe-O-Fe = 174.7(5)degrees, and Fe...Fe = 3.565(2) angstrom.