Ce3Cl5[SiO4] und Ce3Cl6[PO4]: Ein chloridreiches Chloridsilicat und -phosphat des Cers im Vergleich

Abstract

Professor Josef Goubeau in memoriamInhaltsu È bersicht. Bei der Umsetzung von CeCl 3 mit CeO 2 , Cer und SiO 2 bzw. P 2 O 5 im molaren Verha È ltnis von 5 : 3 : 1 : 3 bzw. 8 : 3 : 1 : 2 in evakuierten Quarzglasampullen (7 d, 850°C) fallen Ce 3 Cl 5 [SiO 4 ] (orthorhombisch, Pnma; a = 1619,7(2), b = 415,26(4), 1423,6(1) pm; Z = 4) bzw. Ce 3 Cl 6 [PO 4 ] (hexagonal, P6 3 /m; a = 1246,36(9), c = 406,93(4) pm; Z = 2) als farblose, sta È bchenfo È rmige, luft-und wasserunempfindliche Einkristalle an. Ûberschu È ssiges Certrichlorid fo È rdert als Fluûmittel das Kristallwachstum und ist nach der Reaktion leicht durch Auswaschen mit Wasser wieder zu entfernen. Diskrete [SiO 4 ] 4± -bzw. [PO 4 ] 3± -Tetraeder bestimmen als isolierte Einheiten die Kristallstrukturen. Beide, das Chloridsilicat Ce 3 Cl 5 [SiO 4 ] und das Chloridphosphat Ce 3 Cl 6 [PO 4 ], zeigen strukturelle Øhnlichkeiten mit CeCl 3 (UCl 3 -Typ), indem man formal vier bzw. drei Cl ± -Anionen in der verdreifachten Formel (Ce 3 Cl 9 ) durch jeweils eine [SiO 4 ] 4± -bzw. [PO 4 ] 3± -Einheit ersetzt. Dadurch erho È ht sich die Koordinationszahl fu È r Ce 3+ von neun in CeCl 3 auf zehn in Ce 3 Cl 5 [SiO 4 ] und Ce 3 Cl 6 [PO 4 ], womit eine drastische Verringerung des molaren Volumens beim Ûbergang von Ce 3 Cl 9 (V m = 186,17 cm 3 /mol) zu Ce 3 Cl 5 [SiO 4 ] (V m = 144,15 cm 3 /mol) bzw. Ce 3 Cl 6 [PO 4 ] (V m = 164,84 cm 3 /mol) einhergeht. Die Koordinationspolyeder um Ce 3+ lassen sich als vierfach u È berkappte trigonale Prismen beschreiben, die zusa È tzlich zu je sieben Cl ± -Anionen jeweils noch drei Sauerstoffatome zweier ortho-Silicat-bzw. ortho-Phosphat-Tetraeder aufweisen. Ce 3 Cl 5 [SiO 4 ] and Ce 3 Cl 6 [PO 4 ]: A Chloride-Rich Chloride Silicate of Cerium as Compared to the PhosphateAbstract. By reacting CeCl 3 with CeO 2 , cerium and SiO 2 , or P 2 O 5 , respectively, in molar ratios of 5 : 3 : 1 : 3 or 8 : 3 : 1 : 2, respectively, in sealed evacuated silica tubes (7 d, 850°C) colorless, rod-shaped single crystals of Ce 3 Cl 5 [SiO 4 ] (orthorhombic, Pnma; a = 1619.7(2), b = 415.26(4), 1423.6(1) pm; Z = 4) and Ce 3 Cl 6 [PO 4 ] (hexagonal, P6 3 /m; a = 1246.36(9), c = 406.93(4) pm; Z = 2) are obtained as products insensitive to air and water. Excess cerium trichloride as flux promotes crystal growth and can be rinsed off again with water after the reaction. The crystal structures are determined by discrete [SiO 4 ] 4± or [PO 4 ] 3± tetrahedra as isolated units. Both, the chloride silicate Ce 3 Cl 5 [SiO 4 ] and the chloride phosphate Ce 3 Cl 6 [PO 4 ], exhibit structural similarities to CeCl 3 (UCl 3 type), when four or three Cl ± anions are each substituted formally by one [SiO 4 ] 4± or [PO 4 ] 3± unit, respectively, in the tripled formula (Ce 3 Cl 9 ). The coordination number for Ce 3+ is thus raised from nine in CeCl 3 to ten in Ce 3 Cl 5 [SiO 4 ] and Ce 3 Cl 6 [PO 4 ], along with a drastic reduction of the molar volume with the transition from Ce 3 Cl 9 (V m = 186.17 cm 3 /mol) to Ce 3 Cl 5 [SiO 4 ] (V m = 144.15 cm 3 /mol) and Ce 3 Cl 6 [PO ...

Inorganic Lanthanide Compounds with Complex Anions

“…Table ) due to a slightly different orientation of the SiO 4 4- tetrahedra (Figure ). With La 3 Cl 5 (SiO 4 ) and Ce 3 Cl 5 (SiO 4 ), two examples of chlorine-rich chloride ortho -silicates are known. , They are isotypic and show a certain similarity to the trichlorides LaCl 3 and CeCl 3 (UCl 3 type of structure) when four Cl - ions of the tripled formula are substituted for SiO 4 4- . For the discrete silicate anions a statistical distribution on two cyrstallographic positions is found.…”

“…The chloride phosphate Ce 3 Cl 6 (PO 4 ), which has been obtained by reacting CeCl 3 , Ce, CeO 2 , and P 2 O 5 in silica tubes, is isotypic with the respective vanadates and shows the Ce 3+ ions in coordination of seven Clions and three oxygen ligands. 280 The structure can be seen as built up from [Ce 3 Cl 6 ] units in the form of three vertex-connected [CeCl 3 ] triangles. These units are arranged in a way that pseudo-hexagonal channels occur along [001] which incorporate the PO 4 3ions.…”

Composition and Crystal Structure of SmSb2O4Cl Revisited – and the Analogy of Sm1.5Sb1.5O4Br

“…[14] The same holds for the tetragonal oxidophosphates(V) and -arsenates(V) Ln 4 O 4 Cl[PO 4 ] (Ln = La, Pr and Nd) [15] and Ln 4 O 4 Cl[AsO 4 ] (Ln = La -Nd, Sm -Gd), [16] where the ψ 1 -tetrahedral [AsO 3 ] 3anions of the first examples are replaced with [PO 4 ] 3and [AsO 4 ] 3-ψ 0 -tetrahedra. The chloride-rich hexagonal cerium(III) compound Ce 3 Cl 6 [PO 4 ] [17] seems to be the only example, where Cland [PO 4 ] 3anions coexist without the aid of extra O 2anions.…”

Hydrogenoxosilicates of the lanthanides

“…Due to the very short distance between the central positions of the face-shared tetrahedra (d(Si 4+ · · ·Si 4+ ) = 59 pm) and the half occupation of the silicon position (8d, sof(Si) = 0.516 (14)), it is obvious that only one of the two partial tetrahedra can be fully occupied with silicon while the other one is not. A similar dilemma has been encountered with the chloride oxosilicates M 3 Cl 5 [SiO 4 ] (Pnma or C2/m; M = La-Nd, Tb) [12][13][14] already. In two of the monoclinic subgroups of Pnma, P2 1 /n11 and P112 1 /a namely, a satisfactory ordered occupation pattern of Si 4+ within the trigonal bipyramids occurs, in which the "upper" partial tetrahedra are filled in a regarded strand and the "lower" tetrahedra in the adjacent strands, so that real discrete [SiO 3 (OH)] 3− anions emerge.…”