H.-Jürgen Meyer

A new family of two-dimensional lanthanide(III) coordination polymers: synthesis, structures and properties of [Ln(SIP)(H 2 O) 4 ] n (Ln=Eu, Gd, Ce, and NaH 2 SIP=5-sulfoisophthalic acid monosodium salt)

Abstract A new family of lanthanide coordination polymers with the general formula [Ln(SIP)(H2O)4]n (Ln=Eu, Gd, Ce, 1–3; and NaH2SIP=5-sulfoisophthalic acid monosodium salt) was hydrothermally synthesized and characterized by IR, elemental analysis, single-crystal X-ray crystallography and powder X-ray diffractions. X-ray studies indicated that these compounds are isostructural and adopt an electrically neutral and undulating two-dimensional layer structure constructed from fused {[Eu(H2O)4]3(SIP)3} pseudo-hexagonal grids. Thermogravimetric measurements in N2 revealed that all exhibit weight losses corresponding to four water molecules per formula unit around 120 °C and the dehydrated compounds are stable up to ca 510 °C. The fluorescence spectrum showed that [Eu(SIP)(H2O)4]n displays intense red fluorescence in the solid-state. The paramagnetism for [Gd(SIP)(H2O)4]n in the range 5–300 K reveals no magnetic coupling via SIP ligand.

Synthesis of the Guaianolide Ring System via Cycloaddition of a Bicyclic Carbonyl Ylide with Allyl Propiolate

A cyclic carbonyl ylide with a trans-annulated cyclopentane ring was generated by a Rh(2)(OAc)(4)-catalyzed reaction from a diazoketone precursor and trapped with allyl propiolate. The 1,3-dipolar cycloaddition led to the stereoselective formation of an oxygen-bridged polycycle. Via Curtius degradation, the cycloadduct was transformed to the ring skeleton typical of the sesquiterpene family of guaianolides.

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+).

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.

Nitridoborate der Lanthanoide: Synthesewege, Strukturprinzipien und Eigenschaften einer neuen Verbindungsklasse

Untersuchungen auf dem Gebiet der Nitridoborate der Lanthanoide (Ln) haben in den vergangenen Jahren zu neuartigen Verbindungen gefuhrt, die hier zusammen mit einigen ihrer Eigenschaften vorgestellt werden. Nitridoborate werden auf zwei prinzipiell unterschiedliche Arten hergestellt: Enweder wird hexagonales Bornitrid durch Reaktionen mit LnN fragmentiert oder Dinitridoborat-Ionen werden in andere Nitridoborat-Ionen umgewandelt. Ln-Nitridoborate enthalten Molekulanionen wie [BN]n−, [BN2]3−, [B2N4]8−, [B3N6]9− und [BN3]6−, die kombiniert und gemeinsam mit Nitrid-Ionen auftreten konnen. Im Kristall sind die Anionen in Schichten angeordnet und in typischen Formationen von Metallatomen umgeben. Endstandige N-Atome sind von Metallatomen in Form einer quadratischen Pyramide uberdacht, bei den B-Atomen dominieren trigonal-prismatische Umgebungen durch Metallatome. Nitridoborate bilden sowohl salzartige als auch metallreiche Verbindungen und haben das Potenzial fur vieles, was man sich unter interessanten Festkorpereigenschaften vorstellt, was ihnen einen festen Platz in den Materialwissenschaften verschaffen sollte.

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.

From cyanate to cyanurate: cyclotrimerization reactions towards the novel family of metal cyanurates

The novel metal cyanurates LiSr(O3C3N3) and Li3Sr2F(O3C3N3)2 were prepared by exothermic solid state metathesis reactions and characterized by single crystal X-ray diffraction. Crystalline powders were prepared by reactions of alkali earth halides (SrCl2 and SrF2) with Li(OCN) in 1:3 molar ratios, at 450 and 575 °C. The reaction with chloride yielded LiSr(O3C3N3), and the reaction starting from the fluoride yielded LiSr(O3C3N3)·1/2LiF, containing additional LiF in the structure. Both crystal structures revealed the presence of the (O3C3N3)(3-) ions which were formed by cyclotrimerization reaction of (OCN)(-) ions. The reactions were monitored by differential thermal analysis. Infrared spectra of the compounds are reported.