6364
The Structures of the Cations of Werner's Green and Red p- Amido-p-peroxo-bis { bis(ethy1enediamine)cobalt(II1) 1 Salts
method of Werner.' They are monoclinic, space group P ~ $ I ,with a = 8.78, b = 23.97, c = 12.50 A, /3 = 95.8", 2 = 4, D, = 1.72, D, = 1.71 g ~ m - ~ The . intensities of 28 12 independent reflections were estimated Sir: visually from Weissenberg photographs about a and c. In 1910 Werner' described the preparations and The red compound, ~~-[(en),Co(0~H)(NH~)Co(en)~]chemical properties of a large number of bridged di(N03)4.2HzO (11), was prepared by the method of cobalt compounds. Among them were two nitrate Werner' and crystallized from saturated aqueous salts of doubly bridged cations, one red and the other solution. The crystals are also monoclinic, space green, which Werner presumed to be isomeric; the green group P21/n, with a = 8.23, b = 15.41, c = 20.48 A, compound he formulated as [(en)2Co(NHz)(Oz)Co- /3 = 98.9", Z = 4, D, = 1.77, D, = 1.79 g and3. (en)z](N03)4and the red one as [(en)2Co(NH.HN08)- The intensities of 2689 reflections were measured on an (Oz)Co(en)2](N03)3. 2H20. Isomerism was later ruled automated diffractometer using Fe K a X radiation. out when Malatesta2 found the green compound to be Both structures were solved by Patterson and electronparamagnetic, and Thompson and Wilmarth found the density methods and refined by least squares. At the red compound to be diamagnetic. Recently Mori and present stage the R index for I is 0.087 and for 11, Weil, 4 4 on the basis of kinetic and spectroscopic 0.075. measurements, inferred that the arrangement of the O2 The cation in the paramagnetic compound (I) is shown bridge is different in the two compounds and deduced in Figure 1. The approximate planarity of the fivethat a proton is involved in the bridging group of the membered -Co-N-Co-0-0ring and the length of the diamagnetic species, as first proposed by Thompson 0-0 bond, 1.36 (h0.03) A, suggest that the unpaired and Wilmarth. electron is concentrated in the Oz bridge, which thus We have now carried out X-ray diffraction analyses becomes a superoxo group; similar geometry has reof the two compounds. We find the green, paramagcently been found in a number of related compounds.6-8 netic compound to correspond to the formulation The cation of I1 is shown in Figure 2. The three bonds to the briding oxygen atom are noncoplanar. H H
[
HzO
N >o(enh];N03-)h.
(en)Co
