Hans Hartl

Ion chemistry of the hexanuclear methoxo-oxovanadium cluster V6O7(OCH3)12

Abstract The hexanuclear methoxo-oxovanadium cluster V6O7(OCH3)12 (1) is investigated by electrospray ionization in methanol solution. Collision experiments unravel the fragmentation schemes of the molecular ions 1+ and 1− as well as the H+, Na+, and Cs+ adducts of 1. In general, fragmentation of the hexanuclear cluster ions commences with sequential expulsions of two OV(OCH3)3 units to yield the corresponding V4 clusters. However, when an active proton is present in the cluster ion, e.g., in the protonated molecule [ 1 + H ]+, loss of methanol precedes degradation to V4 clusters. In addition, the experiments suggest that electrospray ionization provides as an alternative method for the generation of metal oxide cluster ions VmOn+/− (m=1–4, n=0–11).

Discrepancy between the structural and magnetic dimensionality in the (μ-terephthalato)bis[(diethylenetriamine)Cu(II)]perchlorate complex

Abstract The crystal structure of [(dien)Cu(μ-tp)Cu(dien)](ClO4)2, where tp is the dianion of terephthalic acid and dien is diethylenetriamine, has been determined by direct X-ray methods. The complex crystallizes in the monoclinic space group P21/c with a=8.911(6), b=8.002(5), c=19.61(2) A, β=90.2(1)°, Z=2 and V=1398.3 A3. Solution of the structure of a twin crystal of the compound led to final values of R=0.069 and Rw=0.079 with 174 least-squares parameters for 2263 unique reflections with I>2σ(I). The compound is a perchlorate salt of a dicationic centrosymmetric binuclear copper(II) complex, [(dien)Cu(μ-tp)Cu(dien)]2+ — the crystallographic inversion center being located at the center of the benzene ring of the tp bridging ligand. Within the binuclear unit the copper(II) ions are bridged by tp ligand in a bis-unidentate fashion, the coordination geometry about each Cu(II) ion is distorted octahedral; the CuCu distance in each binuclear entity is 11.006(5) A. Moreover, two Cu(II) centers of two different dimeric units are bridged by an oxygen atom of a carboxylate group. Thus, chains along the b direction and layers parallel to (100) are formed. The variable-temperature (4.2–290 K) magnetic susceptibility data of the complex, interpreted with a dimer law with a molecular field approximation, yielded to J, g and zJ′ values of −3.66 cm−1 2.07 and −0.03 cm−1, respectively. An orbital interpretation of the coupling is proposed.

A Mixed-Valence VIV/VV Alkoxo-polyoxovanadium Cluster Series [V6O8(OCH3)11]n+/−: Exploring the Influence of a μ-Oxo Ligand in a Spin Frustrated Structure

The synthesis and structural characterization of the neutral mixed-valence methoxo-polyoxovanadium cluster [V(6)O(8)(OCH(3))(11)] (1) and its single oxidation product in the hexachloroantimonate salt [V(6)O(8)(OCH(3))(11)][SbCl(6)] (2) are presented here. The cluster comprises a hexauclear polyoxovanadate core of the Lindqvist structure, of which all but one of the mu-bridging oxo ligands are substituted by methoxo. As revealed by cyclic voltammetry, the cluster is highly redox active, displaying several further thermodynamically stable V(IV)/V(V) mixed-valence redox derivatives. Furthermore, valence sum calculations performed on the X-ray structural data as well as results from IR and UV-vis spectrometry characterize them as class II mixed-valence compounds. In the present article, we equally present results from cyclic voltammetry, UV-vis spectrometry, and magnetic measurements obtained for members of the previously reported [V(6)O(7)(OCH(3))(12)] cluster series, which, as opposed to 1 and its derivatives, contain exclusively methoxo ligands as mu-bridging moieties. Magnetic measurements performed on the highly reduced cluster species [V(IV)(5)V(V)(1)O(7)(OCH(3))(12)](-) and [V(IV)(6)O(7)(OCH(3))(12)](2-) reveal net antiferromagnetic exchange interactions between the d-electrons, which at lower temperatures are in part suppressed for reasons attributed to geometric spin frustration. Among the present results, the comparison of the cyclic voltammograms of 1 and [V(6)O(7)(OCH(3))(12)] has proven to be of considerable interest, showing an unexpectedly pronounced discrepancy in all but one of their corresponding redox potentials. In particular, a detailed analysis of the electrochemical conversions indicates that the observed shift is almost entirely the result of a different degree of d-electron spin-spin interactions in corresponding mixed valence species of the cluster series.

Synthesis and Spectroscopic Properties of Arene-Substituted Pyrene Derivatives as Model Compounds for Fluorescent Polarity Probes

In this paper, the syntheses of a variety of substituted phenyl pyrenes 5a−n by Suzuki cross-coupling and of two decoupled analogues 10 and 17 are reported. These compounds have been investigated by fluorescence spectroscopy. The solvatochromism of their emission bands (Stokes shift) and the quantum yields in methylcyclohexane and acetonitrile have been determined. Furthermore, the crystal structure of a pyrenyl-tris(2,2′-bipyridine)ruthenium(II) complex 19 is presented.

Hexagonal Molybdenum Trioxide : Known for 100 Years and Still a Fount of New Discoveries

In 1906, the preparation of “molybdic acid hydrate” was published by Arthur Rosenheim. Over the past 40 years, a multitude of isostructural compounds, which exist within a wide phase range of the system MoO3−NH3−H2O, have been published. The reported molecular formulas of “hexagonal molybdenum oxide” varied from MoO3 to MoO3·0.33NH3 to MoO3·nH2O (0.09 ≤ n ≤ 0.69) to MoO3·mNH3·nH2O (0.09 ≤ m ≤ 0.20; 0.18 ≤ n ≤ 0.60). Samples, prepared by the acidification route were investigated using thermal analysis coupled online to a mass spectrometer for evolved gas analysis, X-ray powder diffraction, Fourier transform infrared, Raman, magic-angle-spinning 1H- and 15N NMR spectroscopy, and incoherent inelastic neutron scattering. A comprehensive characterization of these samples will lead to a better understanding of their structure and physical properties as well as uncover the underlying relationship between the various compositions. The synthesized polymeric parent samples can be represented by the structural formula (NH4)(x∞)(3)[Mo(y square 1−y)O(3y)(OH)(x)(H2O)(m−n)]·nH2O with 0.10 ≤ x ≤ 0.14, 0.84 ≤ y ≤ 0.88, and m + n ≥ 3 − x − 3y. The X-ray study of a selected monocrystal confirmed the presence of the well-known 3D framework of edge- and corner-sharing MoO6 octahedra. The colorless monocrystal crystallizes in the hexagonal system with space group P6(3)/m, Z = 6, and unit cell parameters of a = 10.527(1) Å, c = 3.7245(7) Å, V = 357.44(8) Å3, and ρ = 3.73 g·cm(−3). The structure of the prepared monocrystal can best be described by the structural formula (NH4)(0.13∞)(3)[Mo(0.86 square 0.14)O2.58(OH)0.13(H2O)(0.29−n)]·nH2O, which is consistent with the existence of one vacancy (square) for six molybdenum sites. The sample MoO3·0.326NH3·0.343H2O, prepared by the ammoniation of a partially dehydrated MoO3·0.170NH3·0.153H2O with dry gaseous ammonia, accommodates NH3 in the hexagonal tunnels, in addition to [NH4]+ cations and H2O. The “chimie douce” reaction of MoO3·0.155NH3·0.440H2O with a 1:1 mixture of NO/NO2 at 100 °C resulted in the synthesis of MoO3·0.539H2O. This material is of great interest as a host of various molecules and cations.

Rubidium- und Caesium-Verbindungen mit dem Isopolyanion [Ta6O19]8– – Synthesen, Kristallstrukturen, thermische und schwingungsspektroskopische Untersuchungen der Oxotantalate A8[Ta6O19] · n H2O (A = Rb, Cs; n = 0, 4, 14)

Die Verbindungen A8[Ta6O19] · n H2O (A = Rb, Cs; n = 0, 4, 14) enthalten das Isopolyanion [Ta6O19]8–, das aus sechs zu einem grosen Oktaeder kantenverknupften [TaO6]-Oktaedern besteht. Sie gehen – wie u. a. die thermoanalytischen Untersuchungen (TG/DSC) zeigen – durch reversible Hydratations/Dehydratationsprozesse ineinander uber und zeigen auch strukturell enge Bezuge. Cs8[Ta6O19] (tetragonal, I4/m, a = 985.9(1) pm, c = 1403.3(1) pm, Z = 2), die isotypen Phasen A8[Ta6O19] · 14 H2O (A = Rb/Cs; monoklin, P21/n, a = 1031.30(6)/1055.4(1) pm, b = 1590.72(9)/1614.9(6) pm, c = 1150.43(6)/1171.4(1) pm, β = 100.060(1)/ 99.97(2)°, Z = 2) und Rb8[Ta6O19] · 4 H2O (monoklin, C2/c, a = 1216.9(4) pm, b = 1459.2(5) pm, c = 1414.7(4) pm, β = 90.734(6)°, Z = 4) wurden auf der Basis von Einkristalldaten strukturell charakterisiert. Die RAMAN-Spektren erlauben daruberhinaus einen detallierten Vergleich der Hexatantalat-Ionen in den vier Verbindungen. Rubidium und Caesium Compounds with the Isopolyanion [Ta6O19]8– – Synthesis, Crystal Structures, Thermogravimetric and Vibrational Spectrocopic Analysis of the Oxotantalates A8[Ta6O19] · n H2O (A = Rb, Cs; n = 0, 4, 14) The compounds A8[Ta6O19] · n H2O (A = Rb, Cs; n = 0, 4, 14) contain the isopoly anion [Ta6O19]8–, which consists of six [TaO6] octahedra connected via corners to form a large octahedron. They transform into each other by reversible hydratation/dehydratation processes, as shown from thermoanalytic measurements (TG/DSC), and show also structural similarities. Cs8[Ta6O19] (tetragonal, I4/m, a = 985.9(1) pm, c = 1403.3(1) pm, Z = 2), the isotypic phases A8[Ta6O19] · 14 H2O (A = Rb/Cs; monoclinic, P21/n, a = 1031.30(6)/1055.4(1) pm, b = 1590.72(9)/1614.9(6) pm, c = 1150.43(6)/1171.4(1) pm, β = 100.060(1)/99.97(2)°, Z = 2) and Rb8[Ta6O19] · 4 H2O (monoclinic, C2/c, a = 1216.9(4) pm, b = 1459.2(5) pm, c = 1414.7(4) pm, β = 90.734(6)°, Z = 4) have been characterised on the basis of single crystal x-ray data. Furthermore the RAMAN spectra allow a detailled comparison of the hexatantalate ions in the four compounds.

Solvothermal Synthesis of a 24-Nuclear, Cube-Shaped Squarato-oxovanadium(IV) Framework: [N(nBu)4]8[V24O24(C4O4)12(OCH3)32]

Polydentate bridging ligands can be used to link small polyoxo-alkoxo-metalate units to form supramolecular clusters. In the title compound, twelve μ4 -bridging squarato groups connect eight trinuclear methoxo-oxo-vanadate units to form a tetradodecanuclear cubic framework, in whose cavity six n-butyl groups of the tetra-n-butylammonium cations are anchored.

Two New Isopolyoxotungstates(VI) with the Empirical Composition Cs2W2O7⋅2 H2O and Na2W2O7⋅H2O: An Icosatetratungstate and a Polymeric Compound

The largest isopolyoxotunstate ion known to date, W24 O8424- (structure shown in the picture), isolated as the cesium salt, and a chainlike polyoxotungstate ion made up of planar W4 O16 units, isolated as the sodium salt, hide behind the simple empirical formulas of the title compounds.

Kristallisation und Strukturuntersuchung von Alkali-Parawolframaten / Crystallization and Structure Determination of Alkaline Metal-Paratungstates

The syntheses and crystal structures of the following paratungstates-Z with different alkaline cations are reported and discussed: Na10[H2W12O42] · 20H2O (I), Na10[H2W12O42] · 27H2O (II), Na10[H2W12O47] · 28H2O (III), K10[H2W12O42] · 10H2O (IV), K6Na4[H2W12O42] · 13H2O (V), Cs6Na4[H2W12O42] · 16H2O (VI), Cs8Na2[H2W12O42] · 10H2O (VII), Cs8Na2[H2W12O42] · 12H2O (VIII), K3Na7[H2W12O42] · 24H2O (IX) and K5Na2[H2W12O42] · 12H2O (X). Priority has been set on the description of the coordination of the cations with the oxygen ligands H2W12O4210- and H2O.

Trinuclear thiocyanate-bridged compounds of the type [ML]2[Mn(NCS)4](ClO4)2 (where M = Cu(II), Ni(II); L = N-dl-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene)

The complexes of general formula [ML]2[Mn(NCS)4](ClO4)2 (where M = Cu(II), Ni(II); L = N-dl-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene) were obtained and the crystal structures of both heteronuclear compounds were determined at 173 K. Complex [CuL]2[Mn(NCS)4](ClO4)2 (1) crystallizes in a monoclinic space group, C2/c, with a = 41.297(9) A, b = 7.571(2) A, c = 16.417(4) A, beta = 96.97(15) degrees, Z = 8, whereas complex [NiL]2[Mn(NCS)4](ClO4)2.H2O (2) crystallizes in a monoclinic space group, P2/c, with a = 21.018(5) A, b = 7.627(2) A, c = 16.295(4) A, beta = 104.47(1) degrees, Z = 4. The magnetic behaviour of (1) and (2) has been investigated over the temperature range 1.8-300 K. Complex (1) displays ferromagnetic coupling inside the trinuclear core of CuMnCu and compound (2) behaves like a mononuclear Mn(II) system. The magnetic properties of the second compound (2) with a similar trinuclear structure shows that Ni(II) ions have a diamagnetic character and a rather weak zero-field splitting at the central Mn(II) ion occurs. Finally, the magnitudes of the Cu(II)-M(II) interactions with M = Ni and Mn have been compared and qualitatively justified.