Synthesis and Structural Investigations of [Mn < inf > 3 < /inf > O < inf > 4 < /inf > (phen) < inf > 4 < /inf > (H < inf > 2 < /inf > O) < inf > 2 < /inf > ](NO < inf > 3 < /inf > ) < inf > 4 < /inf > ·2.5H < inf > 2 < /inf > O: A Water-Bound Complex Obtained by Cerium(IV) Oxidation

Abstract

The trinuclear manganese complex [Mn3O4(phen)4(H2O) 2](NO3)4·2.5H2O, 1 (where, phen = 1,10-phenanthroline), has been synthesized by the Ce(IV) oxidation of a concentrated solution of manganese(II) acetate and phen in 1.6 N nitric acid. The complex crystallizes in the triclinic space group P1̄ with a = 10.700(2) Å, b = 12.643(3) Å, c = 20.509(4) Å, α = 78.37(3)°, β= 83.12(3)°, γ = 82.50(3)°, and Z = 2. The structure was solved by direct methods and refined by least-squares techniques to the conventional R (Rw) factors of 0.055 (0.076) based on 4609 unique reflections with Fo ≥ 6.0σ(Fo). The structure of the cation consists of an oxo-bridged Mn3O44+ core, with the geometry of the manganese atoms being octahedral. The coordination polyhedron of one of the manganese atoms (Mn(1)) consists of two μ oxo ligands and two pairs of nitrogen atoms of two phen moieties, whereas that of each of the remaining two manganese atoms consists of three μ-oxo ligands, two nitrogen atoms of a phen moiety, and the oxygen atom of a water molecule. The complex represents the second example for water coordination to manganese(IV) centers in complexes with a Mn3O44+ core. Optical spectra in ligand buffer (pH 4.5) reveal complete conversion of the complex into a MnIIIMnIV species. The observed room-temperature (298 K) magnetic moment of 3.75 μB indicates the presence of strong antiferromagnetic coupling in the complex.