Physical measurements have been made on samples of u-and P-RuCI, of relatively high purity. From X-ray powder patterns, the existence of a superstructure has been detected in a-RuCI,, and the structure of P-RuCI, has been found to be of the P-TiCI, type with linear chains of ruthenium atoms lying in distorted octahedra of chlorine atoms. The infrared spectra have been obtained down to 70 cm.-l; the nine bands observed for P-RuCI, indicate that the space group is the trigonal P3cl (C3,"), which means that there are -RuCI,-RuCI,-RuCI,-units in the chains. There is a strong band attributed to a RU-CI stretching vibration at the relatively high frequency of 376 crn.-I. The magnetic susceptibilities, obtained from 8 to 740°K for u-RuCI,, and from 8 to 560°K for (3-RuCI,,show that cr-RuCI, is antiferromagnetic below 13"K, and P-RuCI, below ca. 600°K. but in neither case has the antiferromag netism been detected by neutron diffraction. The temperature dependence of the susceptibilities has been compared with the predictions of crystal field theory for a-RuCI,, and with the theory of linear Heisenberg chains for p-RuCI,. KOLBIN and R Y A B O V~showed that there were two forms of anhydrous ruthenium trichloride. In an interim Communication we reported the cell dimensions of the @-form and the contrasting magnetic behaviour of the two forms; this difference was used to determine the purity of various preparations, and led to methods suitable for preparing relatively pure batches. The results now reported have been obtained by measurements on such batches.The general conclusions to be drawn from this work is that ruthenium trichloride falls into the class of trihalides first noticed by Klemm et aL4 This class has two forms. The a-form, typified by a-TiC1, and also shown by CrCl, and FeCl,, has a laminar structure;

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The magnetic behaviour of ruthenium dioxide up to 1000°K is interpreted in terms of J being ca. -3000 cm.-l in dioxo-bridged chains of ruthenium atoms. The high electrical conductivity as well as certain structural features imply that the average oxidation state of the ruthenium atoms is substantially greater than +4.The oxide hydrate has a high surface area ; it is formulated as Ru02+,, yH,O since there can be an excess (chemisorbed) of oxygen particularly after removal of some of the water. Values of x up to 0.1 2 have been found whereas y is often 1 to 1.3. The susceptibility, though generally similar to that of RuO,, varies from sample to sample: its behaviour is discussed in relation both to the influence of adsorbed groups and also to some terminal ruthenium atoms behaving as mononuclear Ru(V), i.e., being in the d3 state. Expected spectral bands in the infrared have not been detected owing to the presence of electronic conductance bands. Solid State Physics Divisions, A.E.R.E., Harwell. Berkshire IN a recent note,l Cotton and Mague conclude that ruthenium dioxide has the rutile structure ; however, they point out that the closest Ru-Ru distance (3.107 A) excludes metal-metal coupling as the cause of the very of this second term and certain other properties to strong super-exchange, via the dioxo-bridges, in the chains (A) which exist in the c direction. Strong bondlow magnetic susceptibility. In this paper we report \RU/O\ /OARL,/ magnetic susceptibility measurements from 1.3 to from 298-673"~ together with other properties of the / \o/Ru\o/ \ 1033"~, supplementing previously available values (A) dioxide. The susceptibility per g.-atom of ruthenium, defined as XA-Xdia, has a temperature independent term ( N a ) which is relatively large, about 185 x lo* e.m.u. ; the temperature dependent term is small, about 20 x e.m.u. at room temperature and about 85x lo4 e.m.u. at 1000"~. We attribute the smallness ing within the chains is also indicated by the contraction along the c axis with increase of temperature that we have observed.The shape of the susceptibility-temperature curve is completely different from that predicted3 for a mononuclear 4d4 svstem in an octahedral environment but 1 F.

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