The Ternary System BaF2/CuF2/AlF3 and the Crystal Structure of Ba45Cu28Al17F197

Abstract

The ternary system BaF 2 /CuF 2 /AlF 3 is investigated by X-ray diffraction techniques and an isothermal section at 620°C is established. It exhibits ten quaternary phases and among them Ba 45 Cu 28 Al 17 F 197 . This fluoride has a triclinic cell: a = 14.024(1) A Ê , b = 23.778(1) A Ê , c = 25.480(1) A Ê , a = 90.44(1)°, b = 90.26(1)°, c = 107.03(1)°, Z = 2. Its crystal structure was solved in the space group P1 (n o 1), from X-ray single crystal data using 41976 unique reflections. It is built up from a complex arrangement of aluminium and copper fluorine polyhedra, which are regular [AlF 6 ] and strongly distorted [CuF 6 ] octahedra, [CuF 6 ] trigonal prisms and [Cu 2 F 10 ] bipolyhedral units constituted either by two octahedra, or one octahedron and one trigonal prism, connected by an edge. These polyhedra are organized in planes of about two octahedra thickness, which form a succession of sheets running perpendicularly to the [100] direction of the cell. Each sheet is constituted by infinite chains of distorted polyhedra connected by edges and vertices and linked together by the vertices of blocks of four and six polyhedra, involving aluminium fluorine octahedra and copper fluorine bipolyhedral units or octahedra. The barium ions, 10 to 14coordinated to fluorine atoms, ensure the electroneutrality of the structure. They are inserted inside the planes. wurde ro È ntgenographisch untersucht und ein isothermer Schnitt seines Phasendiagramms bei 620°C erstellt. Es zeigt zehn quaterna È re Phasen, darunter Ba 45 Cu 28 Al 17 F 197 . Dieses Fluorid hat eine trikline Zelle: a = 14,024(1) A Ê ; b = 23,778(1) A Ê ; c = 25,480(1) A Ê ; a = 90,44(1)°; b = 90,26(1)°, c = 107,03(1)°; Z = 2. Seine Kristallstruktur wurde in der Raumgruppe P1 (Nr. 1) unter Verwendung von 41976 unabha È ngigen Einkristallreflexen gelo È st. Sie besteht aus einer komplexen Anordnung von Aluminium-und Kupfer-Fluoridpolyedern, na Èmlich regula È ren [AlF 6 ]-und stark verzerrten [CuF 6 ]-Oktaedern, trigonalen Prismen [CuF 6 ] und zweikernigen Bausteinen [Cu 2 F 10 ], die entweder aus zwei Oktaedern oder Oktaeder und trigonalem Prisma durch Kantenverknu È pfung gebildet werden. Die genannten Einheiten sind in Ebenen organisiert, die etwa zwei Oktaeder dick sind und eine Folge von Schichten senkrecht zur [100]-Richtung der Zelle bilden. Jede Schicht ist aus verzerrten Polyedern aufgebaut, die u È ber Kanten und Ecken zu unendlichen Ketten verknu È pft sind. Die Querverbindung der Ketten erfolgt u È ber die Ecken von Polyedern, die zu viert oder sechst Blo È cke bilden, bestehend aus [AlF 6 ]-Oktaedern und Einheiten von [Cu 2 F 10 ] oder [CuF 6 ]. Die Bariumionen sind mit Koordinationszahlen von 10 bis 14 in die Schichten eingebettet und besorgen den Ladungsausgleich.

Complex Superstructures of Mo2P4O15

“…The most complex material which we would view as nonmolecular is (for this discussion we categorize the polyoxometallates grown from solution-based species as molecular in nature) Ba 45 Cu 28 Al 17 F 197 with 574 unique atoms. 56 A second source of complexity can be associated with materials prepared at high temperatures and which undergo site ordering on cooling. One such example is R-La 2 Mo 2 O 9 (312 atoms), which, apart from the title phase, is the most complex oxide in the ICSD.…”

The Crystal Structure of Ba3Cu2Al2F16: a Relative of Ba4Cu2Al3F21

“…The crystal structure of Ba 3 Cu 2 Al 2 F 16 is closely related to that of Ba 4 Cu 2 Al 3 F 21 , another fluoride from the ternary system BaF 2 -CuF 2 -AlF 3 [1,5]. Both structures involve the same two types of sheets and differ only in the proportion and in the stacking sequence of the sheets along the c-direction, corresponding to two different compositions and to two different symmetries.…”

“…The investigation by X-ray techniques of the ternary system BaF 2 -CuF 2 -AlF 3 [1] revealed the existence of numerous fluorides with crystal structures involving new modes of linkage between polyhedra; among them Ba 2 CuAlF 9 [2], Ba 2-Cu 2 AlF 11 [3], Ba 5 Cu 2 Al 3 F 23 [4], Ba 4 Cu 2 Al 3 F 21 [5], Ba 45-Cu 28 Al 17 F 197 [1], the structures of which have been described in previous papers. This work establishes the structure distorted copper-fluorine octahedra [CuF 6 ], linked by edges, which form infinite chains interconnected by three vertices of isolated [AlF 6 ] octahedra.…”

“…Only the proportion and the stacking sequence of the two kinds of sheets in the c-direction differ, according to two different compositions and two different symmetries. of an already mentioned compound in the ternary system: Ba 3 Cu 2 Al 2 F 16 [1].…”

Mo2P4O15? the most complex oxide structure solved by single crystal methods?

“…The four larger structures include complex molecular species (such as Na 15 [Mo 144 O 409 (OH) 28 (H 2 O) 56 ]-(H 2 O) 250 ) from the group of Mu ¨ller [9][10][11] and the complex ternary phase Ba 45 Cu 28 Al 17 F 197 . 12 In each case the structural complexity is perhaps unsurprising given the chemical composition of the DOI: 10.1039/b408413f materials. Aside from the title material the most complex crystallographically ordered extended oxide structure determined reliably from single crystal methods in the ICSD appears to be Ru(PO 3 ) 3 with 105 atoms in the asymmetric unit.…”