Jochen Glaser

Crystal structures, phase-transition, and photoluminescence of rare earth carbodiimides.

Rare earth carbodiimides with the general formula RE 2(CN 2) 3 crystallize with two modifications. A monoclinic( C2/m) modification is obtained for RE = Y, Ce-Tm and a rhombohedral ( R3 c) modification for RE = Tm-Lu. The space group R3 c is confirmed by single-crystal structure determination on Lu 2(CN 2) 3 and indexed powder patterns of RE = Tm, Yb and Lu. The use of diverse chemical syntheses conditions for Tm 2(CN 2) 3 revealed the dimorphic character of this compound. In addition, pressure experiments on Tm 2(CN 2) 3 have induced a phase-transition from rhombohedral to monoclinic. This transformation comprises an increase of the coordination number of Tm from 6 to 7, and a unit-cell volume reduction in the order of 20 %. The photoluminescence behavior of lanthanide doped Gd 2(CN 2) 3:Ln samples is presented with different activators (Ln = Ce, Tb) revealing a broad band emission of Gd 2(CN 2) 3:Ce, quite similar to that of the well-known YAG:Ce.

Über die Koexistenz von tetragonalem und monoklinem CaC2: Strukturelle und spektroskopische Untersuchungen an Erdalkalimetallacetyliden, MC2 (M = Ca, Sr, Ba)

Fur die Erdalkalimetallacetylide CaC2, SrC2 und BaC2 kann die Existenz von jeweils drei polymorphen Strukturen angenommen werden, die monokline Tieftemperaturform, die tetragonale Form und die kubische Hochtemperaturform. Einkristallstrukturanalysen und 13C-MAS-NMR-Messungen ergaben, das die C22–-Ionen in den tetragonalen Strukturen axialsymmetrisch angeordnet sind. Allerdings enthielten die von uns synthetisierten CaC2-Proben stets Anteile von monokliner und tetragonaler Phase. Raman-Spektren von CaC2-Proben zeigten die Prasenz zweier verschiedener C2-Streckschwingungsbanden. Die aus der Koexistenz dieser beiden Phasen resultierende Problematik bei der Interpretation von 13C-MAS-NMR-Spektren wird diskutiert. On the Coexistence of Tetragonal and Monoclinic CaC2: Structural and Spectroscopic Studies on Alkaline Earth Metal Acetylides, MC2 (M = Ca, Sr, Ba) The alkaline earth acetylides CaC2, SrC2 and BaC2 can be considered to occur in three polymorphic structures each. The monoclinic low-temperature form, the tetragonal form, and the cubic high-temperature form. No deviation from axial symmetry is obtained for the C22– ions in the tetragonal structure determinations, as confirmed by X-ray single-crystal structures and 13C MAS NMR studies. The CaC2 samples prepared by us were always a mixture of monoclinic and tetragonal phase. Their Raman spectra exhibited two distinct C2 streching vibrations. Problems arising from the coexistence of these two phases for the interpretation of 13C MAS NMR spectra are discussed.

W6Cl18: Neue Synthesen, neue Strukturverfeinerung, elektronische Struktur und Magnetismus

Die Verbindung W6Cl18 wurde nach zwei Methoden dargestellt; durch Oxidation von W6Cl12 mit CCl4 im Autoklav und durch Reaktion von W6Cl12 mit Cl2 im Stromungsrohr. Beim Erhitzen unter Normaldruck geht W6Cl18 bei 400 °C in W6Cl12 uber. Die Kristallstruktur von W6Cl18 wurde aus Rontgen-Pulverdaten nach der Rietveld-Methode verfeinert. Die ungewohnlichen elektronischen Verhaltnisse des 18-Elektronen-Clusters [W6Cl12]Cl6 werden mit denen des elektronenprazisen 24-Elektronen-Clusters [W6Cl8]Cl4 verglichen. Die Verbindung ist paramagnetisch mit zwei Elektronen in antibindenden Energiezustanden. W6Cl18: New Syntheses, New Structure Refinement, Electronic Structure, and Magnetism Pure W6Cl18 was synthesized after two methods, by oxidizing W6Cl12 with CCl4 in an autoclave, and by reaction of W6Cl12 in a chlorine gas flow. At temperatures above 400 °C and under atmospheric pressure W6Cl18 transforms into W6Cl12. The crystal structure of W6Cl18 was refined after the Rietveld method on X-ray powder data. The unusual electronic conditions of the 18 electron cluster [W6Cl12]Cl6 are compared with those of the electron-precise 24 electron cluster [W6Cl8]Cl4. The compound exhibits paramagnetic behaviour with two electrons in antibonding energy levels.

Synthesis and Properties of Tetracyanamidosilicates ARE[Si(CN2)4]

Tetracyanamidosilicates of the type ARE[Si(CN(2))(4)] with A = K, Rb, and Cs and RE = Y and La-Lu have been prepared by a solid-state metathesis reaction. The potassium compounds with RE = La-Gd crystallize orthorhombically in the space group P2(1)2(1)2. Rubidium as well as cesium compounds crystallize tetragonally in the space group I4. The luminescent properties of ARE[Si(CN(2))(4)]:Ln compounds with RE = Y, La, and Gd doped with 5 mol % Ln = Ce, Eu, or Tb were investigated. Temperature-dependent magnetic susceptibilities were measured for KGd[Si(CN(2))(4)]. The value of the magnetic moment is 7.3 mu(B)/Gd(3+) ion, which is in line with the expected value for the [Xe]4f(7) configuration of Gd(3+).

Multilateral Solid‐State Metathesis Reactions for the Preparation of Materials with Heteroanions: The [Si(CN2)4]4− Ion

The search for nonoxidic inorganic compounds has led beyond simple metal borides, carbides, nitrides, and silicides to the development of interesting materials in whose structures several nonmetallic elements are combined. For example, in the structures of the well-known compounds Ti(C,N) and Mo2BN, [2] the anions are combined, but are present without bonds between the heteroatoms. An extension to this type of compound comprises metal compounds with element combinations of boron, carbon, nitrogen, and silicon. These elements are bridged to form complex units or ions through heteropolar, covalent bonds. The systematic development of the nitridoborate, nitridosilicate and carbodiimide compound classes has brought about important advances for materials chemistry. These families can be regarded as metal-salt derivatives of the binary nonmetallic materials BN, Si3N4, and C3N4. An extension to these compound types in the form of the cyanamidosilicates is reported herein with the example of the first tetracyanamidosilicates, which can be conceived as metal-salt derivatives of Si(CN2)2. [6] Compounds with this type of heteroanion possess a number of interesting, often unpredictable properties as high-temperature resistant ceramic materials (Si3N4), [7]

Compounds with the electron-rich [W6Cl18]2- cluster anion.

Cluster compounds of the general formula A(2)[W(6)Cl(18)] containing singly charged A cations (A = K, Rb, Ag, Tl, NH(4), N(C(2)H(5))(4), N(n-C(3)N(7))(4), N(n-C(4)H(9))(4)) and [W(6)Cl(18)](2-) anions have been synthesized. Compounds were obtained by W(6)Cl(18) reduction using methanol and the corresponding metal or (alkyl-)ammonium salts. The use of CoCp(2) as reducing agent in inert solvents such as tetrahydrofurane also leads to the ionic compound (Co(C(5)H(5))(2))(2)[W(6)Cl(18)]. All compounds described here evidence the existence of octahedral clusters of the M(6)X(12) type with 20 cluster electrons occupying metal centered states, thus exceeding the conventional number of 16 electrons for this cluster type. Electrospray ionization (ESI) mass spectra were recorded for the neutral compound W(6)Cl(18) and for the ionic salts K(2)[W(6)Cl(18)], Cs(2)[W(6)Cl(18)], and (Co(C(5)H(5))(2))(2)[W(6)Cl(18)], showing that the cluster W(6)Cl(18) unit in these compounds is preserved in solution. The base peak in the ESI spectra for all compounds corresponds to the [W(6)Cl(18)](2-) anion, so that neutral W(6)Cl(18) is prone to undergo a two electron reduction process. This result is confirmed by cyclic voltammetry experiments, which makes of W(6)Cl(18) a very clean mild oxidizing agent. The preparation of the complete series of ionic A(2)[W(6)Cl(18)] (A = K, Cs, CoCp(2)) clusters allows to systematically investigate their structural trends as function of the distinctive cations, which is the main focus of the present work.

Ca3(BN2)N — eine fehlende Verbindung im quasi-binären System Ca3N2-BN

Ca3BN3 wurde als hellgraues Pulver aus Reaktionen aquimolarer Mengen von Ca3N2 und BN bei 1000 °C hergestellt. Die Kristallstruktur wurde aus einem Pulver-Rontgendiagramm nach der Rietveld-Methode verfeinert. Ca3BN3 kristallisiert tetragonal in der Raumgruppe P4/mmm mit den Gitterparameter a = b = 354, 94(1) pm und c = 821, 36(3) pm. Die Kristallstruktur enthalt linear gebaute (BN2)3—-Ionen mit B—N-Bindungslangen von 135, 2(4) pm und ist topologisch mit der orthorhombischen (Pmmm) Hochdruck-Modifikation von Mg3BN3 identisch. Ca3(BN2)N, the missing Compound in the Quasi Binary Ca3N2-BN System Ca3BN3 was synthesized as a light-gray powder from reactions of equimolar amounts of Ca3N2 and BN at 1000 °C. The crystal structure was refined from a X-ray powder pattern by the Rietveld method. Ca3BN3 crystallizes tetragonal with the space group P4/mmm having lattice parameters of a = b = 354.94(1) pm, and c = 821.36(3) pm. The crystal structure contains linear (BN2)3—-ions with B—N bond lengths of 135.2(4) pm and is topologically identical with the orthorhombic (Pmmm) structure of the high-pressure modification of Mg3BN3.

Struktur und elektrochemische Untersuchung von Nb3Cl8

Nb3Cl8 wurde durch Reaktion von NbCl5 mit Niob-Metallpulver in einer geschlossenen Quarzglasampulle bei 700 °C dargestellt. Aus einer LiCl-Schmelze isolierte Einkristalle wurden fur die Strukturbestimmung mit einem IPDS-Rontgendiffraktometer (Raumgruppe P 3 m1, Z = 2, Gitterkonstanten a = b = 672,95(7) pm, c = 1223,2(2) pm (bei 100 K), R1 = 0,029, wR2 = 0,064 fur alle unabhangigen Reflexe) und die Messung des elektrischen Widerstandes ausgewahlt. Die Lithium-Einlagerung in die Struktur von Nb3Cl8 wurde elektrochemisch untersucht. Structure and Electrochemical Study of Nb3Cl8 The compound Nb3Cl8 was synthesized from NbCl5 and niobium metal in a sealed quartz ampoule at 700 °C. Single crystals, obtained from LiCl melt were used for X-ray structure determination (space group P 3 m1, Z = 2, lattice parameters a = b = 672.95(7) pm, c = 1223.2(2) pm (at 100 K), R1 = 0.029, wR2 = 0.064 for all independent reflections). Electrical resistivity measurements are reported. Electrochemical intercalation of lithium into the structure of Nb3Cl8 was studied.

Meta)stabiles CaC2

Eine von insgesamt vier Modifikationen von CaC2 ist das sogenannte metastabile Calciumcarbid, CaC2-III, welches rein dargestellt wurde. Es bildet sich beim Erhitzen von monoklinem CaC2-II (C2/c) ab etwa 150 °C und bleibt beim Abkuhlen auf RT stabil. Die Struktur der Phase wurde mittels Rontgen-Pulverdaten verfeinert (C2/m, Z = 4, a = 722,6(1) pm, b = 385,26(7) pm, c = 737,6(1) pm, β = 107,345(2)°). Beim Zerreiben der Phase wird eine Ruckumwandlung in CaC2-II induziert, und beim Erhitzen erfolgt bei 460 °C ein reversibler Phasenubergang in die kubische Modifikation (CaC2-IV). Mittels 13C-MAS-NMR-Messungen werden Unterschiede zwischen den drei bei Raumtemperatur stabilen Strukturen CaC2 I–III aufgezeigt, insbesondere die Prasenz von zwei unterschiedlichen Kohlenstoffatomen in der Struktur der Titelverbindung. (Meta)stable CaC2 One out of four modifications of CaC2 is the so-called metastable Calcium Carbide, CaC2-III, which was synthesized as pure material. It forms by heating monoclinic CaC2-II (C2/c) above 150 °C and remains stable after cooling down to room temperature. The structure was refined from X-ray powder patterns (C2/m, Z = 4, a = 722.6(1) pm, b = 385.26(7) pm, c = 737.6(1) pm, β = 107.345(2)°). After grinding CaC2-III transforms back into CaC2-II. Heating CaC2-III induces a reversible phase transition into the cubic modification (CaC2-IV) at 460 °C. Differences between the three different structures of CaC2 I–III, being stable at ambient conditions are also shown by 13C-MAS-NMR measurements, especially the presence of two distinct types of carbon atoms in the structure of the title compound.

Neue Verbindungen im System Ca/Ni/Si

Im System Ca—Ni—Si wurden die neuen Verbindungen CaNi2Si und Ca3Ni3Si2 hergestellt und ihre Strukturen rontgenographisch an Einkristallen bestimmt. CaNi2Si kristallisiert in der Raumgruppe P63/mmc (Nr. 194) mit den Gitterparametern a = 400, 38(5) pm, c = 988, 6(2) pm und Z = 2 (R1 = 0, 0307, wR2 = 0, 0553 fur alle gemessenen symmetrieunabhangigen Reflexe) als Besetzungsvariante des ReB3-Typs. Fur Ca3Ni3Si2 wurde eine orthorhombische Zelle mit der Raumgruppe Pnma (Nr. 62), Z = 4 und den Gitterparametern a = 926, 59(5) pm, b = 396, 69(2) pm, c = 1814, 1(2) pm gefunden (R1 = 0, 0435, wR2 = 0, 0605 fur alle gemessenen symmetrieunabhangigen Reflexe). Ni und Si bilden gefaltete zweidimensional unendliche Schichten, die durch die Ca-Atome separiert werden. New Compounds in the System Ca/Ni/Si The new compounds CaNi2Si and Ca3Ni3Si2 were synthesized in the Ca—Ni—Si-system and their structures determined by single crystal X-ray diffraction. CaNi2Si crystallizes in the space group P63/mmc (no. 194) with the lattice parameters a = 400.38(5) pm, c = 988.6(2) pm and Z = 2 (R1 = 0.0307, wR2 = 0.0553 for all symmetry-independent reflections) in a site occupancy variant of the ReB3 type. The unit cell of Ca3Ni3Si2 was found to be orthorhombic with a = 926.59(5) pm, b = 396.69(2) pm and c = 1814.1(2) pm (Pnma, no. 62, Z = 4, R1 = 0.0435, wR2 = 0.0605 for all symmetry-independent reflections). The nickel and silicon atoms build puckered two dimensional layers which are separated by the calcium atoms.