Infrared spectra of adsorbed pyridine have been used to obtain qualitative information on the nature of the interaction of pyridine with different rhodium catalysts supported on palygorskite and silica. Based on these data, qualitative definitions of the adsorption sites of these catalysts have been deduced. The catalysts were prepared with natural palygorskite, and palygorskite dehydrated in vacuo at 150°C and 400°C. In this way, catalysts were obtained that had different water contents and, therefore, different acidities. Lewis-bound pyridine was detected by infrared spectroscopy from room temperature to 500°C. The greatest acidity was found in a catalyst prepared with the palygorskite support dehydrated at 150°C before preparation of the catalyst. With this catalyst, strongly hydrogen-bound pyridine was observed when evacuation was carried out at temperatures between 150°C and 300°C. Catalysts prepared with the palygorskite support pretreated at 400°C did not exhibit strongly hydrogen-bound pyridine, and Lewis acidity decreased significantly. As expected, hydrogen-bound pyridine was also detected for rhodium supported on silica. However, it was desorbed at temperatures below 150°C. The results of the acidity studies follow the same pattern as those for 1 -hexene double-bond migration under hydrogénation reaction conditions.

The exchange of Rh(NBD)(Pϕ3)2+, Rh(NBD)(PMe2ϕ)3+, Rh(COD)(Pϕ3)2+, and Rh(PMe2ϕ)4+ on hectorite was studied in methanol/dichloromethane, acetone, dimethylformamide, and acetonitrile. At low initial Rh+ concentration and short contact times, ion exchange was the predominant process, and its selectivity and maximum capacity were solvent-dependent. High initial Rh+ concentrations, long contact times, and the most polar solvents favored intersalation and salt precipitation. In all experiments monolayers of complex formed in the interlamellar space and were very tightly held. The complexes retained their integrity on the surface even after removal of all solvent molecules.

Zaykovite, ideally Rh3Se4, is a new mineral, the first natural rhodium selenide. It was discovered in the assemblages of platinum-group minerals from the Kazan gold placer, South Urals, Russia. The mineral occurs as crystals up to 40 μm in size within the grains of Pt3Fe alloy, in association with unnamed Pd–Sb–Te phase and Au–Pd alloy. In reflected light, zaykovite has a grey colour with bluish-greenish tint; it shows weak bireflectance and anisotropy. Reflectance values [Rmax/Rmin (%) for COM approved wavelengths (nm)] are: 30.1/29.3(470), 32.2/31.0(546), 33.4/32.0(589) and 35.1/33.7(650). The chemical composition corresponds to the empirical formula (Rh2.26Pt0.46Ir0.25Ru0.01Pd0.01Fe0.01)Σ3.00(Se2.77S1.21Te0.02)Σ4.00 Zaykovite is monoclinic, space group C2/m, a = 10.877(1), b = 11.192(1), c = 6.4796(6) Å, β = 108.887(2)°, V = 746.3(1) Å3, Z = 6 and Dcalc = 8.32 g cm–1. The crystal structure has been solved and refined to R1 = 0.016 based on 858 unique observed reflections. The strongest lines of the powder X-ray diffraction pattern [d(Å), (I), (hkl)] are: 5.43(37)($\bar{1}$11), 3.275(75)(310), 3.199(100)($\bar{1}$31), 3.061(87)(002), 2.568(62)(400), 2.545(41)(041), 3.413(34)($\bar{2}$41) and 1.697(34)(441). Zaykovite is a Se analogue of kingstonite, Rh3S4. A continuous series of solid solutions between kingstonite and zaykovite was encountered in the samples from the Kazan placer. The possible sources of this unique Rh–Se mineralisation in the South Urals could be serpentinised dunite–harzburgite or gabbro–clinopyroxenite–dunite complexes in the vicinity.

The synthesis and X-ray powder diffraction data for the organometallic [Rh2(bim)2(cod)2]Cl2∙2H2O species are reported. Its crystal and molecular structures were determined by simulated annealing and full-profile Rietveld refinement methods. [Rh2(bim)2(cod)2]Cl2∙2H2O was found to crystallize in the orthorhombic Cmca space group. The lattice parameters were determined to be a=21.3574(6), b=10.7764(3), c=14.2795(4) Å, V=3286.5(2) Å3, for Z=4. The crystal structure was found to contain dimeric [Rh2(bim)2(cod)2]2+ cations, in which the bim ligands bridge Rh(cod) fragments with an intermetallic separation of ca. 8.90 Å. The crystal structure is completed by chloride ions and hydrogen-bonded water molecules, situated in the small cavities of the large cation substructure. The conformation of the bim ligand, lying on a crystallographic mirror plane, is rigorously Cs.