Band 211, Heft 6

We developed a new micro manipulator for mounting individual sub-micrometer sized single crystals within a scanning electron microscope. The translations are realized via a commercially available piezomicroscope, adapted for high vacuum usage and realize nanometer resolution. With this novel instrument it is routinely possible to mount individual single crystals with sizes down to 0.1 μ m. In addition, the full range of SEM techniques is available to accurately characterize the size and composition of the sample. As a first example we present the mounting of a single crystal of 30 · 10 −3 μ m 3 volume.

Variations in the structures of seven fluosilicate hexahydrates of bivalent metals, belonging to the apparently isomorphous series of compounds MG 6 · LR 6 , have been summarised. Four of these seven crystals undergo phase transition on lowering the temperature. Of these, the fluosilicate hexahydrates of Mg, Mn and Fe have Laue group [unk] m : the corresponding Co-compound is an unique case, with a disordered structure of Laue group [unk], suffering a transition. A geometrical relationship between the three orientations of the monoclinic cell of the twinned low temperature phase and the hexagonal cell of its room temperature structure has been established. The mechanism of transition has been described in terms of rotations, through different angles of the metal-water and fluosilicate octahedra in neighboring columns. Angles of rotations for the different octahedra, that reduce the symmetry from rhombohedral to monoclinic, have been calculated and a rough model of the structure of the low temperature phase has been refined using intensity data measured for a few single spots appearing in the Weissenberg photographs of the twinned crystal at low temperature. The structure thus obtained is found to be similar to that of the lower symmetry phase of magnesium fluosilicate hexahydrate, the higher temperature structure of which is quite different from that of the cobalt compound.

A previous determination of the structure of zinc fluotitanate hexahydrate was considered unsatisfactory because an abnormal anisotropic thermal parameter was attributed to the F atom. The structure (space group R [unk], hexagonal cell parameters a = 9.585(4) Å, c = 9.925(5) Å) has been redetermined and refined, using 243 reflections with I > 3 σ ( I ) measured diffractometrically with Mo K α radiation, reaching R = 0.047 and wR = 0.059. The structure obtained is disordered, with two equally occupied sites F1 and F2 for the F-atom, and is isostructural with ZnSiF 6 · 6 H 2 O, except for the occupancy ratio F1:F2 which is 1:2 in the latter case. Low temperature study below the reported transition point revealed a three-component twin with monoclinic cells appearing in three orientations with a pseudo-trigonal symmetry about the former three-fold axis. Angles of rotation of different octahedra in neighboring columns, that reduce the symmetry from rhombohedral to monoclinic, have been calculated. The monoclinic phase is found to be isostructural with the lower temperature phase of MgSiF 6 · 6H 2 O.

The structures of three hydrated germanates K 3 HGe 7 O 16 · 3.1 H 2 O, Rb 3 HGe 7 O 16 · 3.1 H 2 O and Cs 3 HGe 7 O 16 · 2.3 H 2 O have been determined in space group I 23, no. 197, Z = 8, with a = 15.34960(4) Å, 15.45998(4) Å and 15.56660(4) Å, respectively, from Rietveld refinement of powder diffraction patterns collected using synchrotron radiation. The structure of these germanates consists of a three-dimensional framework of tetrahedrally and octahedrally coordinated Ge atoms, with charge compensating cations and water molecules occupying the interconnecting channels. The cations occupy sites near the centres of two types of window approximately 3.3 Å across. One window is nearly circular whilst the other is more elliptical. On partial dehydration, the body-centred superstructure is lost for the Rb and Cs compounds. The structures of Rb 3 HGe 7 O 16 · 0.69 H 2 O and Cs 3 HGe 7 O 16 · 0.70 H 2 O have been refined in space group P [unk]3 m , no. 215, Z = 1, with a = 7.66990(1) Å and 7.73347(3) Å, respectively. In these materials the window apertures are now identical and are circular. For the partially dehydrated K form a 2 × 2 × 2 face-centred cubic structure forms, with a lattice parameter similar to the body-centred hydrated form, a = 15.0844(2) Å.

The title compound [PtCl 2 (C 4 Me 4 )(SbPh 3 )] ( 1 ) crystallizes from methylene chloride/ n -hexane in the monoclinic space group P 2 1 / n with lattice constants a = 8.303(1) Å, b = 17.378(2) Å, c = 17.640(2) Å, β = 90.86(1)°, Z = 4. The crystal structure was solved by the heavy atom method. The refinement converged to a final wR 2 = 0.051 for 4310 reflections ( R 1 = 0.024 for 3810 observed reflections). In the solid state the exactly planar cyclobutadiene ligand is asymmetrically coordinated with respect to the Pt atom having two shorter and two longer Pt – C bonds (Pt – C distances in the range 2.105(4) Å – 2.195(5) Å). The methyl carbon atoms show a remarkable difference concerning the bend out of the C 4 plane, away from the Pt atom (out-of-plane displacement in the range of 0.083(6) Å to 0.401(6) Å). The Pt – Sb bond length amounts to 2.5911(4) Å. The Pt – Cl bonds in 1 are longer than those in the corresponding stibine-free complex [PtCl 2 (C 4 Me 4 )] ( 2 ) (2.449(1) Å/2.458(1) Å vs. 2.338(2) Å/2.323(3) Å). This corresponds to a low-frequency shift of the (PtCl) stretching and deformation modes in 1 compared to that observed in 2 .