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By fusing Lu2O3 and TeO2 in a molar ratio of 1:3 in a CsCl flux, colorless single crystals of the lutetium(III) oxotellurate(IV) Lu2Te3O9 could be obtained as first representative of the structurally so far unknown C-type for the composition M2Te3O9. The title compound crystallizes triclinically in space group P with a = 689.67(4) pm, b = 1320.91(8) pm, c = 1450.06(9) pm, α = 110.057(3)°, β = 90.606(3)°, γ = 100.125(3)°, and Z = 6. The crystal structure contains six different Lu3+ cations in eightfold (Lu1 and Lu2: trigonal dodecahedra) and sevenfold (Lu3 and Lu6: monocapped trigonal prisms; Lu4 and Lu5: pentagonal bipyramids) oxygen coordination. These lutetium–oxygen polyhedra (d(Lu–O) = 214–274 pm) are condensed to serrated layers according to 2∞{[Lu6O26]34–} that are stacked along [100]. The oxotellurate(IV) partial structure consists of basically nine crystallographically independent [TeO3]2– (d(Te–O) = 184–196 pm) units connecting the above-mentioned layers to a three-dimensional framework. Strong secondary Te4+···O2– interactions between adjacent [TeO3]2– entities as common feature in the crystal structures of all known ternary lanthanoid(III) oxotellurates(IV) are also present in the crystal structure of Lu2Te3O9. Depending upon the range of these secondary contacts taken into account, the [TeO3]2– units are linked to form one-dimensional strands (d(Te···O) = 237–272 pm) like in B-type Dy2Te3O9 or even two-dimensional layers emerge (d(Te···O) = 237–285 pm).

Ho11ClTe16O48: An Extremly Chlorine-Poor Chloride Oxotellurate(IV) of Trivalent Holmium While attempting to synthesize Ho2Te3O9 by reacting Ho2O3 with TeO2 (800 °C, 12 d) chloride from the CsCl flux was incidently mobilized and as by-product, Ho11ClTe16O48 (triclinic, ; a = 551.52(3), b = 1193.54(6), c = 1834.63(9) pm, α = 100.814(3), β = 95.443(3), γ = 100.175(3)°; Z = 1), the first example of this new composition in the field of lanthanoid(III) chloride oxotellurates(IV) has been obtained. The six crystallographically different Ho3+ cations experience a six-, seven- and eightfold coordination through oxygen atoms (d(Ho3+−O2−) = 221 – 280 pm), leading to octahedral, triangle-square polyhedral, capped trigonal prismatic and square antiprismatic coordination figures. Initially, the corresponding [HoOn] polyhedra convene to layers parallel to the (001) plane via edge and corner sharing which again combine to a [Ho11O48]63− network via other individual [(Ho6)O6] octahedra and [(Ho2)2O4/2O4/1] chains along [100], whose three-dimensional characteristic is unique among the lanthanoid(III) oxotellurates(IV) known to date. The eight crystallographically independent Te4+ cations exhibit coordination numbers of 3 and 3+1 in relation to oxygen, except Te1 with 3+1 O2−plus 1 Cl− as anionic neighbours. Apart from isolated [TeO3]2− polyhedra (Ψ1 tetrahedra: d(Te4+−O2−) = 184 – 196 pm) only double and triple groupings occur even in considering secondary Te4+···O2− contacts (d′(Te4+···O2−) = 218 – 264 pm). As with HoCl[TeO3], the tellurium-oxygen partial structure does not get beyond a “zero-dimensional” expression. The Te4+ cations adjust so well while lining the empty cavities within the network, that still only two Te4+-decorated channel types (oval and round) remain unoccupied, offering space for the non-bonding electron pairs (“lone pairs”). The Cl− anions reside in the bigger oval channels (d(Cl−−Te4+) = 286, 352 and 358 pm, 2 × each). In the default of binding Ho3+−Cl− contacts, the correct description of this new compound would thus be holmium(III) oxochlorotellurate(IV) Ho11[Te16O48Cl] according to Ho11[TeO3]2[Te2O6]2[Te3O9]2{Cl[Te2O6]2}. The presence of chloride was not only detected by the structure refinement on the basis of X-ray diffraction data, but also even in such small quantities by elementary analysis with the electron-beam microprobe.

About Lanthanide Oxotantalates with the Formula MTaO4 (M = La – Nd, Sm – Lu) Besides being a by-product of solid state syntheses in tantalum ampoules the lanthanide(III) oxotantalates of the formula MTaO4 can be easily prepared by sintering lanthanide sesquioxide M2O3 and tantalum(V) oxide Ta2O5 with sodium chloride as flux. Under these conditions two structure types emerge depending upon the M3+ cationic radius. For M = La – Pr the MTaO4-type tantalates crystallize in the space group P21/c with lattice constants of a = 762(±1), b = 553(±4), c = 777(±4) pm, β = 101(±1)° and four formula units per unit cell. With M = Nd, Sm – Lu, the monoclinic cell dimensions (space group P2/c) shrink to the lattice constants like a = 516(±9), b = 551(±9), c = 534(±9) pm, β = 96.5(±0.3)° and there are only two formula units present. Both structures show a coordination sphere of eight oxygen atoms for the lanthanide trications shaped as distorted square antiprism for the structure with the larger lanthanides (in the following referred to as A-type) and as trigonal dodecahedron for the structure with the smaller ones (called as B-type in the following). The coordination environment about the Ta5+ cations can be described as a slightly distorted octahedron (CN = 6) for the A-type structure of MTaO4 and a heavily distorted one (CN = 6) for the B-type. The difference between the two types results from the interconnection of these [TaO6]7− octahedra. Whereas they are connected via four vertices to form corrugated layers according to parallel the bc-plane in the A-type, the octahedra of the B-type MTaO4 structure share edges to built up zig-zag chains along the c axis.

Bei Versuchen zur Darstellung von anionisch derivatisierten Holmium-Oxotelluraten durch Reaktion von Holmiumtrichlorid (HoCl3) mit Tellurtrioxid (TeO3; molares Verhaltnis 1:2, 800°C, 10 d) in evakuierten Kieselglasampullen wurden transparente, grunlich gelbe und derbe Einkristalle des Holmium(III)-Chlorid-Oxotellurats(IV) HoClTe2O5 (triklin, P1; a = 762, 07(6), b = 796, 79(6), c = 1010, 36(8) pm, α = 100, 987(4), s = 99, 358(4), γ = 91, 719(4)°; Z = 4) erhalten. Die Kristallstruktur beinhaltet achtfach koordinierte (Ho1)3+- (nur umgeben von Oxid-Anionen) und siebenfach koordinierte (Ho2)3+-Kationen (umgeben von einem Chlorid- und sechs Oxid-Anionen). Uber Kantenverknupfungen treten beide Sorten von Holmium-Polyedern jeweils fur sich zu Ketten entlang [100] zusammen und kombinieren ihrerseits abwechselnd uber O6 und O9 zu 2{[Ho2O10(Cl1)]15—}-Schichten parallel (001). Alle vier kristallographisch unterschiedlichen Te4+-Kationen sind jeweils von drei nahen Sauerstoffatomen (d(Te—O) = 188 — 195 pm) und stets auch einem weiter entfernten Sauerstoffteilchen umgeben. Durch die stereochemische Aktivitat der nicht-bindenden Elektronenpaare (“lone pairs”) ergeben sich ψ1-trigonal-bipyramidale Koordinationsfiguren. Die ψ1-tetraedrischen [TeO3]2—-Primareinheiten formieren sich durch Eckenverknupfung zu diskreten [Te2O5]2—-Doppeln mit ekliptischer Konformation, welche nach Art eines Fischgratenmusters parallel (001) auf beiden Seiten der 2{[Ho2O10Cl]15—}-Schichten angeordnet sind. Der Zusammenhalt der 2{[Ho2(Cl1)Te4O10]+}-Schichten erfolgt ausschlieslich uber Cl2—Te1-Kontakte mit einem ungewohnlich langen Abstand von 335 pm. Da (Cl1)— zur Koordinationssphare von (Ho2)3+ zahlt und (Cl2)— nur von Te4+ umgeben ist, sollte die Verbindung korrekterweise als Holmium(III)-Chlorid-Oxochlorotellurat(IV) gemas Ho2Cl[Te4O10Cl] (Z = 2) formuliert werden. HoClTe2O5: A Telluriumdioxide-rich Holmium(III) Chloride Oxotellurate(IV) While attempting to synthesize anionically derivatized holmium oxotellurates by reacting holmium chloride (HoCl3) with tellurium oxide (TeO3; molar ratio 1 : 3, 800°C 10 d) in evacuated silica ampoules, transparent, greenish yellow and coarse single crystals of holmium(III) chloride oxotellurate(IV) HoClTe2O5 (triclinic, P1; a = 762.07(6), b = 796.79(6), c = 1010.36(8) pm, α = 100.987(4), s = 99.358(4), γ = 91.719(4)°; Z = 4) were obtained. The crystal structure contains eightfold coordinated (Ho1)3+ (only surrounded by oxygen atoms) and sevenfold coordinated (Ho2)3+ cations (surrounded by one chloride and six oxide anions). Each sort of holmium polyhedra convenes independently to chains along [100] by edge-sharing which again combine alternately via O6 and O9 to form 2{[Ho2O10(Cl1)]15—} layers parallel (001). Each of the four crystallographically different Te4+ cations are surrounded by three close oxygen atoms (d(Te—O) = 188 — 195 pm) and always one more situated further away. The stereochemical activity of the non-bonding electron pairs (“lone pairs”) leads to ψ1-trigonal bipyramidal coordination figures. The ψ1-tetrahedral [TeO3]2— basic units form discrete [Te2O5]2— doubles with ecliptic conformation which are arranged in a fish-bone pattern parallel to (001) on both sides of the 2{[Ho2O10Cl]15—} layers. The coherence of the 2{[Ho2(Cl1)Te4O10]+} layers is exclusively maintained via Cl2—Te1 contacts with an extraordinary long distance of 335 pm. As (Cl1)— belongs to the coordination sphere of (Ho2)3+ and (Cl2)— is only surrounded by Te4+, the compound should be correctly named holmium(III) chloride oxochlorotellurate(IV) Ho2Cl[Te4O10Cl] (Z = 2).

Ho2O[SiO4] kristallisiert monoklin mit der Raumgruppe P21/c (a = 904, 15(9), b = 688, 93(7), c = 667, 62(7) pm, β = 106, 384(8)°, Z = 4) im A-Typ der Selten-Erd(III)-Oxid-Oxosilicate. Es entsteht in Form gelber, plattchenformiger Einkristalle als Nebenprodukt eines Versuchs zur Darstellung von Ho3Cl[SiO4]2 nach Umsetzung von Ho2O3 und SiO2 im Verhaltnis 4 : 6 mit einem Uberschus an HoCl3 als Flusmittel durch siebentagiges Tempern bei 1000 °C in evakuierten Kieselglasampullen. Die beiden kristallographisch unterschiedlichen Ho3+-Kationen weisen Koordinationszahlen von 8+1 und 7 auf, mit 2+1-fach uberkappten trigonalen Prismen bzw. Oktaedern, deren eine Ecke sich durch zwei statt einem koordinierenden Teilchen zur Kante umformt, als Koordinationsfiguren. Das nicht an Silicium gebundene O2—-Anion ist tetraedrisch von vier Ho3+-Kationen umgeben und bildet mit diesen durch Kanten- und Eckenverknupfung eine Schicht gemas {[(O5)(Ho1)1/1(Ho2)3/3]4+} parallel (100) aus, in deren rautenformigen Maschen die isolierten Oxosilicat-Tetraeder [SiO4]4— zu liegen kommen. Ho2S[SiO4] kristallisiert orthorhombisch mit der Raumgruppe Pbcm (a = 605, 87(5), b = 690, 41(6), c = 1064, 95(9) pm, Z = 4). Auch dieses stellt ein Nebenprodukt dar, das bei der Synthese von Ho2OS2 durch Reaktion eines Gemenges von Ho2O3, Ho und S mit der Wand der als Behalter verwendeten evakuierten Kieselglasampulle in einem Uberschus an CsCl als Flusmittel bei 800 °C einkristallin entsteht. Die Struktur der gelben, plattchenformigen, luft- und wasserbestandigen Einkristalle unterscheidet ebenfalls zwei Ho3+-Kationen mit doppelt uberkappten trigonalen Prismen bzw. Trigondodekaedern als Koordinationspolyedern fur CN = 8. Die S2—-Anionen sind annahernd quadratisch planar von vier Ho3+-Kationen umgeben, befinden sich jedoch vollstandig auserhalb dieser Ebene. Die [SHo4]10+-Quadrate bilden durch Eckenverknupfung eine stark gewellte Schicht gemas {[(S)(Ho1)2/2(Ho2)2/2]4+} senkrecht zu [100]. Die isolierten Oxosilicat-Tetraeder [SiO4]4— kommen hier im Gegensatz zum Oxid-Oxosilicat nicht innerhalb der ebenfalls rautenformigen Maschen dieser Schichten zu liegen, sondern in Blickrichtung [100] sowohl ober- als auch unterhalb der (Ho2)3+-Kationen. Ho2O[SiO4] and Ho2S[SiO4]: Two Chalcogenide Derivatives of Holmium(III) ortho-Oxosilicate Ho2O[SiO4] crystallizes monoclinically with the space group P21/c (a = 904.15(9), b = 688.93(7), c = 667.62(7) pm, β = 106.384(8)°, Z = 4) in the A-type structure of rare-earth(III) oxide oxosilicates. Yellow platelet-shaped single crystals were obtained as by-product during an experiment to synthesize Ho3Cl[SiO4]2 by reacting Ho2O3 and SiO2 in the ratio 4 : 6 with an excess of HoCl3 as flux at 1000 °C for seven days in evacuated silica ampoules. Both crystallographically different Ho3+ cations show coordination numbers of 8+1 and 7 with coordination figures of 2+1-fold capped trigonal prisms and octahedra, in which one of the vertices changes to an edge by two instead of one coordinating atoms, respectively. The O2— anion not linked to silicon is surrounded tetrahedrally by four Ho3+ cations which built a layer parallel (100) by vertex- and edge-sharing of the [OHo4]10+ units according to {[(O5)(Ho1)1/1(Ho2)3/3]4+}. Within rhombic meshes of these layers the isolated oxosilicate tetrahedra [SiO4]4— come to lie. Ho2S[SiO4] crystallizes orthorhombically in the space group Pbcm (a = 605.87(5), b = 690.41(6), c = 1064.95(9) pm, Z = 4). It also emerged as a single-crystalline by-product obtained during the synthesis of Ho2OS2 by reaction of a mixture of Ho2O3, Ho and S with the wall of the evacuated silica tube used as container with an excess of CsCl as flux at 800 °C. The structure of the yellow platelet-shaped, air and water resistant crystals also distinguishes two Ho3+ cations with bicapped trigonal prisms and trigondodecahedra as coordination polyhedra for CN = 8. The S2— anions are almost square planar surrounded by four Ho3+ cations, but situated completely outside this plane. The [SHo4]10+ squares form strongly corrugated layers perpendicular to [100] by corner-sharing according to {[(S)(Ho1)2/2(Ho2)2/2]4+}. Contrary to the oxide oxosilicates the isolated oxosilicate tetrahedra [SiO4]4— do not lie within the rhombic meshes of these layers, but above and below the (Ho2)3+ cations while viewing along [100].

Synthesis and Crystal Structure of the Holmium(III) Chloride Oxotellurate(IV) HoClTeO3 Orange coloured, rod—shaped single crystals of the holmium( III) chloride oxotellurate(IV) HoClTeO3 (orthorhombic, Pnma; a = 730.25(5), b = 696.54(5), c = 905.18(7) pm; Z = 4) are obtained during attempts to synthesize holmium(III) oxochlorotellurates(IV) by reaction of holmium oxychloride (HoOCl) and tellurium dioxide (TeO2; 1:1—2molar ratio, 800 °C, 40 d) in evacuated silica tubes. The crystal structure contains sevenfold coordinated Ho 3+ cations surrounded by five oxide and two chloride anions forming a pentagonal bipyramid. Interconnection of the [Ho(O1)(O2)4Cl2] polyhedra occurs via two edges made of four equatorial oxygen atoms (O2) under formation of {[Ho(O1)(O2)4/2Cl2/1]5-} chains running parallel [010]. These arrange as hexagonal closest packing of rods and are linked to each other by Cl- anions to a three—dimensional {[Ho(O1)1/1(O2)4/2Cl2/2]4-} network. All Te4+ cations are embedded therein and exhibit ψ1—tetrahedral coordination figures as discrete anionic [Te(O1)(O2)2]2- pyramids due to the stereochemical activity of the non—binding electron pairs („lone pairs”). They stabilize the {[HoO3Cl]4-} network via covalent bonds to one axial (O1) and two equatorial oxygen atoms (O2) of each [HoO5Cl2] polyhedron.

Ho2Te4O11 (monoklin, C2/c; a = 1240,73(8), b = 511,21(3), c = 1605,84(9) pm, β = 106,142(7)°; Z = 4) und Ho2Te5O13 (triklin, P1; a = 695,67(5), b = 862,64(6), c = 1057,52(7) pm, α = 89,057(6), β = 86,825(6), γ = 75,056(6)°; Z = 2) entstehen durch Umsetzung von Holmiumsesquioxid mit Tellurdioxid in geeigneten molaren Verhaltnissen (Ho2O3 : TeO2 = 1 : 4 bzw. 1 : 5) innerhalb von acht Tagen in evakuierten Quarzglasampullen bei 800 °C. Der Einsatz von Caesiumchlorid (CsCl) als Flusmittel in etwa funffach molarem Uberschus sorgt fur schnelle und quantitative Reaktionen zu einkristallinen Zielprodukten. In der Kristallstruktur von Ho2Te4O11 erfolgt die Verknupfung von [HoO8]-Polyedern uber Sauerstoffkanten, wodurch sich ein Netz {[Ho2O10]14–} parallel zur (001)-Ebene ausbildet. Der Kristallstruktur von Ho2Te5O13 liegen dagegen nur noch von sauerstoffverknupften [(Ho1)O8]- und [(Ho2)O7]-Polyedern aufgebaute Bander {[(Ho1)2(Ho2)2O20]28–} zugrunde, die langs [100] verlaufen. Gemeinsam ist beiden Strukturen allerdings die stereochemische Aktivitat der nicht-bindenden Elektronenpaare („lone pairs”) samtlicher Te4+-Kationen (Te1 und Te2 in Ho2Te4O11; Te1–Te5 in Ho2Te5O13), die ψ1-polyedrische Koordinationsfiguren mit 3 + 1, 4 bzw. 3 + 2 Sauerstoffatomen um die Zentralteilchen bewirkt. Ho2Te4O11 and Ho2Te5O13: Two Telluriumdioxide-rich Oxotellurates(IV) of Trivalent Holmium Ho2Te4O11 (monoclinic, C2/c; a = 1240.73(8), b = 511.21(3), c = 1605.84(9) pm, β = 106.142(7)°; Z = 4) and Ho2Te5O13 (triclinic, P1; a = 695.67(5), b = 862.64(6), c = 1057.52(7) pm, α = 89.057(6), β = 86.825(6), γ = 75.056(6)°; Z = 2) are obtained by the reaction of holmium sesquioxide with tellurium dioxide in appropriate molar ratios (Ho2O3 : TeO2 = 1 : 4 and 1 : 5, respectively) in evacuated silica tubes within eight days at 800 °C. The application of cesium chloride (CsCl) as flux in about five times molar excess secures fast and complete reactions to the single-crystalline products aimed at. In the crystal structure of Ho2Te4O11 [HoO8] polyhedra are connected via oxygen edges thereby building up a network {[Ho2O10]14–} (001). On the other hand, the crystal structure of Ho2Te5O13 exhibits oxygen-linked [(Ho1)O8] and [(Ho2)O7] polyhedra, which form ribbons {[(Ho1)2(Ho2)2O20]28–} running along [100]. Common to both structures, however, is the stereochemical activity of the non-bonding electron pairs (“lone pairs”) of all the of the Te4+ cations (Te1 and Te2 in Ho2Te4O11, Te1–Te5 in Ho2Te5O13) causing ψ1-polyhedral figures of coordination with 3 + 1, 4 and 3 + 2 oxygen atoms, respectively, around the central atoms.