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Chloromenite, Cu9O2(SeO3)4Cl6, is the product of volcanic activity. To conduct various physical studies both natural and synthetic samples of chloromenite were used which resulted in a long-standing controversy regarding its crystal structure. We carried out the temperature dependent single crystal X-ray diffraction study in the range 100 – 370 K and established that the reflection conditions are consistent with a primitive monoclinic cell with the only possible P21/n space group. Raman scattering evidences a complex interplay of crystal lattice and spin degrees of freedom. The observation of a sequence of short range fluctuation effects points to the existence of competing interactions or nearly degenerate energy scales. To gain microscopic understanding of the magnetic properties of Cu9O2(SeO3)4Cl6 the first principles density functional theory calculations have been performed. Basing on the new data on magnetization and the hierarchy of exchange interaction parameters a model of Cu9O2(SeO3)4Cl6 magnetic structure is suggested.

The oxyhalides Pb3TeO4X2 ( X = Cl , Br, I) have been prepared from Pb3O2X2 and TeO2. All three compounds are isostructural and adopt the Nd2O2Te (PbBiO2I) structure type ( I 4 / m , Z = 1 ) according to single-crystal and powder X-ray and electron diffraction data. Contrary to previous results, the Pb/Te cation ordering was found to be nearly the same as Pb/I in schwartzembergite, Pb5IO4(OH)2Cl3 but not Pb/Sb in nadorite PbSbO2Cl. We discuss the factors affecting Pb/M cation ordering in layered (Sillen-type) multinary oxyhalides of lead.

Using various synthetic approaches, we have prepared over 50 new multinary bismuth oxyhalides which crystallize in four layered structure types. Most of the compounds belong to the three previously reported structure types involving fluorite- and CsCl-like metal–oxygen vs. metal–halogen layers as well as single or double halide ion sheets. The majority of Bi2−xAxQ0.6O2Z2 (A=Li, Na, K, Ca, Sr, Ba, Pb; Q=Rb, Cs; Z=Cl, Br, I) compounds crystallize in the tetragonal structure of Pb0.6Bi1.4Cs0.6O2Cl2 (Y2) while both Bi1.4Ba0.6Q0.6O2I2 (Q=Rb, Cs) oxyiodides adopt its orthorhombically distorted, partially ordered version. Due to the lower degree of substitution, the fluorite-like layers in the Y2 structure accommodate more A cations than previously known for related Bi compounds. However, very large Tl+ or Rb+ give compounds with another, as yet unknown, structure. We discuss the influence of size and charge of A cations and stoichiometry of [Bi2−xAxO2] fluorite layers on structure and stability of layered oxyhalides of bismuth. Also, we predict formation of isostructural compounds with smaller Q cations like Tl+ and K+.

Three new bismuth oxyhalides, Pb x Bi 2− x Cu x O 2 X 2 (X = Cl, x ≈ 0.35–0.70; X = Br, x ≈ 0.35–0.65; X = I, x ≈ 0.35–0.55) have been predicted and synthesized from PbO, BiOX, and CuX. All three compounds adopt a very deficient LaOAgS (stuffed PbFCl) structure. Atomic parameters have been determined for Pb 0.6 Bi 1.4 Cu 0.6 O 2 Cl 2 and Pb 0.6 Bi 1.4 Cu 0.6 O 2 Br 2 ( P 4/ nmm , Z = 1) as well as for a structurally and compositionally related Pb 0.6 Bi 1.4 Cs 0.6 O 2 Br 2 ( I 4/ mmm , Z = 2). Comparison of these structural data with bond distances and angles in related Pb 0.6 Bi 1.4 Q 0.6 O 2 X 2 oxyhalides (Q = Rb, Cs, Tl; X = Cl, Br) reveals that replacement of CsCl-like [Q 0.6 X 2 ] layers by anti-fluorite-like [Cu 0.6 X 2 ] has a small effect on the Pb 0.6 Bi 1.4 –O and Pb 0.6 Bi 1.4 –X distances and a larger one on bond angles. We predict existence of isostructural compounds among multinary oxyhalides of bismuth and fluorohalides of lead. It is also likely that more complicated structures involving [Cu x X 2 ] layers can be realized.