Synthesis and characterization of a dinuclear chromium(III) complex with two amido bridges and one hydroxo bridge.: Crystal structure of Na[(tacn)Cr(μ-NH2)2(μ-OH)Cr(tacn)](ClO4)4•H2O (tacn = 1,4,7-triazacyclononane)

Triply bridged dinuclear chromium(III) complexes with 1,4,7-trizacyclononane (tacn) with three amido bridges, or two amido bridges and one hydroxo bridge, were obtained in 15-20% yield in liquid ammonia at 100 degrees C from [Cr(tacn)Cl-3] or [Cr(tacn)(CF3SO3)(3)] after addition of stoichiometric amounts of potassium amide. The chemical properties of these dinuclear complexes in an aqueous medium are described in terms of bridge cleavage and formation, substitution of coordinated ammonia and acid-base properties. The structural properties of the dinuclear chromium(III) complex with one hydroxo and two amido bridges were investigated by X-ray diffraction methods. Na[(tacn)Cr(mu-NH2)(2)(mu-OH)Cr(tacn)](ClO4)(4). H2O forms monoclinic crystals belonging to the space group P2(1)/a with a=14.417(2), b=18.045(2), c=23.480(3) Angstrom and beta=90.244(11)degrees (122K) and Z=8. The two independent complex ions have identical geometry with the very short Cr-Cr distances 2.587(2) and 2.594(2) Angstrom. The crystals undergo small structural changes with time, that involve the interactions of the perchlorate ions.