X-Ray, infrared, and magnetic studies of α- and β-ruthenium trichloride

Abstract

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;

Crystal and Magnetic Structures in Layered, Transition Metal Dihalides and Trihalides

“…Early reports assigned the trigonal space group P3 1 12 [82] (known as the CrCl 3 structure type, although it has been shown that CrCl 3 does not actually adopt it) and the AlCl 3 type [85], and a tendency to form stacking defects has been noted [86]. The Ti 3 O type was also reported [81]. More recently an X-ray and neutron diffraction study reported the monoclinic AlCl 3 structure for small single crystals at and below room temperature, and a phase transition in large single crystals from a trigonal structure at room temperature to the monoclinic AlCl 3 structure type below about 155 K [80].…”

Fluorosulfates of the noble metals. Part 6. Synthesis and magnetic properties of fluorosulfato compounds of ruthenium

“…Depending on the method of preparation two structurally different forms are obtained (12). A black a-form has Ruit in a significantly distorted octahedron (19) resulting in paramagnetism with Curie-Weiss law behavior between 300 and 80 K (10) and a more complicated magnetic behavior at lower temperatures (19). The dark brown @-form is antiferromagnetic below-600 K on account of rather short Ru-Ru bonds (2.83 A) (19); however, the presence of a-RuC1, as contaminant has obscurred the situation somewhat.…”

Crystal structure and magnetism inα−RuCl3: Anab initiostudy

“…We have found that, structures with C2/m 22 and Cmc2 1 space group symmetries are most favorable with almost degenerate energies. Previously suggested P 3 1 12 structure 3,21 yields total energy comparable to those of C2/m and Cmc2 1 structures with the energy difference smaller than 0.4 meV per formula unit (f.u.). Energy differences between different interlayer magnetic orders are smaller than 0.1 meV / f.u., and magnitude of interlayer exchange interactions estimated from interlayer hopping integrals are smaller than 0.05 meV.…”

“…Furthermore, α-RuCl 3 has a three-dimensional crystal structure consisting of RuCl 3 layer stacking, and interlayer coupling and interaction terms can introduce another complication. Experimentally, both P 3 1 12 and C2/m space groups have been suggested as the crystalline symmetry in this compound 3,6,11,21,22 . As an illustrative example, Fig.…”