Über Usovite Ba2M″ M″ M2″ F14 und die Hochdruckphasen von BaMnVF7 und BaMnFeF7: Verbindungen mit BaMnGaF7-Struktur

On Usovites Ba₂M^IIM′^IIM₂^IIIF₁₄ and the High Pressure Phases of BaMnVF₇ and BaMnFeF₇: Compounds with BaMnGaF₇ Structure The results of complete single crystal structure determinations of the monoclinic BaMnGaF₇ type compounds Ba₂CaCoV₂F₁₄ (and Ba₂CdMn Fe₂F₁₄) are reported: C2/c, Z = 4, a = 1369.7 (1381.2), b = 538.4 (537.2), c = 1491.6 (1489.5) pm, β = 91.49 (91.11)°, Rg = 0.036 (0.038) for 4389 (2521) reflections. The atoms Ca/Co (Cd/Mn) distribute not completely ordered on the 8? and 6?coordinated sites of this “usovite” structure (Ba₂CaMgAl₂F₁₄). This is also evident for Cd/Fe from Mössbauer spectra of Ba₂CdFeAl₂F₁₄. The lattice constants of this and further seven compounds Ba₂M^IIM′^IIM2_IIIF₁₄ (M^II = Ca, Cd; M′^II = Mg, Mn? Cu; M^II = Al, Ga) are given. Two novel representatives of the same structure with M^II = M′^II = Mn could be prepared in the form of the high pressure phases of BaMn VF₇ and BaMnFeF₇. The magnetic properties of both modifications of the iron compound and of BaMnGaF₇ are reported and discussed.