The synthesis, X-ray structure, and magnetic susceptibility characterization of a hydroxo-bridged complex, (mu-hydroxo)bis((tetraphenylporphinato)manganese (III)) perchlorate, {[Mn-(TPP)](2)(OH)}ClO4, are described. The complex is readily prepared by a controlled hydrolysis of monomeric diaquo(tetraphenylporphinato)manganese-(III) perchlorate. Interestingly, the bridging hydroxo complex appears to be more stable than the putative mu-oxo complex in halocarbon solvents. The X-ray structure determination shows a complex in which two five-coordinate manganese(III) ions are bridged by a single hydroxo ligand with an average Mn-O distance of 2.026(1) Angstrom and a Mn-O(H)-Mn bridge angle of 160.4(8)degrees.The two porphyrin planes are nearly coplanar, and the two metal ions are separated by 3.993 Angstrom. The average Mn-Np distance is 2.008(7) Angstrom. The two manganese ions are displaced by 0.19 and 0.20 Angstrom from their respective 24-atom mean planes. Both of the two porphyrin rings are moderately S-4 ruffled and have a near-staggered orientation (the N-Mn-Mn’-N’ dihedral angle is 29.9 degrees). The four interring pairs of meso-phenyl groups of the binuclear cation are extremely crowded, with a nearly perpendicular orientation for each pair. The solid-state magnetic susceptibility was measured over the temperature range 2-300 K. The observed behavior is typical of an exchange-coupled binuclear complex. The data were fit to the total spin Hamiltonian (H-tot = H(1) + H(2) - 2J (S) over right arrow(1) .(S) over right arrow(2)) of a zero-field-split, high-spin d(4)-d(4) dimer in its actual crystallographic geometry, using numerical techniques. The hydroxide bridge supports a relatively strong antiferromagnetic coupling (2J = -74.0 cm(-1)) between two zero-field-split (D = -10.8 cm(-1)) manganese(III) ions. Crystal data: a = 16.807(7) Angstrom, b = 17.061(6) Angstrom, c = 17.191(5)Angstrom, alpha = 85.64(3)degrees, beta = 79.75(3)degrees, gamma = 61.95(2)degrees, triclinic, space group , V = 4281(3) Angstrom(3), Z = 2, R(1) = 0.0707 for 14 802 observed data based on F-0 greater than or equal to 4.0 sigma(F-0), R(2w) = 0.2007 for 21 696 total unique data, least-squares refinement on F-2 using all data.