The metal organosiioxanes which have been obtained from trifnnctional organosilicon monomers and polyvaient metals have had polymer structure. We are the first to report that the consecutive reaction of a mixture of [PhSi(ONa)O]3'3H20 and [PhSiOi.5] 8 with NaOH and then with CoC12 (6.6:7.5:20:10 mole ratio) gives a low-molecular-weight crystalline compound (I) having an intense blue color in addition to polycobaltophenylsiloxane. The crystal and molecular structure of (I) were established by x-ray structural analysis~ The unit cell parameters for monoclinic crystals of (I) at -120~ are as follows: a = 18.714(4)~ b = 18.797(4), c = 24~735 (6) ~, ~ = 99.98(2) ~ , V + 8569(3) ~, z = 2, space group P2 I. The crystals consist of {[(PhSi)7013Co]3SiPh} ~anions having normal contacts with each other and Na + cations coordinated by oxygen atoms of the anions and of the molecules of water of crystallization. The unusual, architecturally attractive, cobaltosiloxane framework of the anion (Fig. I) has approximate C 3 symmetry which holds well for the heavy atoms. The bond lengths in the anion are close to normal. The bond angles at the oxygen atoms range from 121 to 157 ~ in the eight-membered cobaltosiloxane rings, from 133 to 158 ~ in the tetrasiloxane rings~ and from 147 to 150 ~ in the atoms bound to the central siliconatom.