(4aS,5R,7R,8S,8aR)-8-(1,3-Dioxolan-2-yl)-7,8-dimethyl-5-(1-methyl­ethen­yl)perhydro­naphthalen-2-one

In the chiral title compound, C18H28O3, the two six-membered rings of the perhydronaphthalenone adopt a rigid chair–chair conformation and the five-membered dioxolanyl ring adopts an envelope conformation. The crystal structure is stabilized only by weak inter­actions

High-pressure phases and transitions of the layered alkaline earth nitridosilicates SrSiN2 and BaSiN2

We investigate the high-pressure phase diagram of SrSiN2 and BaSiN2 with density-functional calculation. Searching a manifold of possible candidate structures, we propose new structural modifications of SrSiN2 and BaSiN2 attainable in high-pressure experiments. The monoclinic ground state of SrSiN2 transforms at 3 GPa into an orthorhombic BaSiN2 type. At 14 GPa a CaSiN2-type structure becomes the most stable configuration of SrSiN2. A hitherto unknown Pbcm modification is adopted at 85 GPa and, finally, at 131 GPa a LiFeO2-type structure. The higher homologue BaSiN2 transforms to a CaSiN2 type at 41 GPa and further to a Pbcm modification at 105 GPa. Both systems follow the pressure-coordination rule: the coordination environment of Si increases from tetrahedral through trigonal bipyramidal to octahedral. Some high-pressure phases are related in structure through simple group–subgroup mechanisms, indicating displacive phase transformations with low activation barriers

(S)-6-Methyl-∊-caprolactone

The chiral title compound, C7H12O2, a lactone derivative, features a seven-membered ring that adopts a chair conformation. The crystal structure is stabilized by weak C—H⋯O inter­actions occurring in the (100) plane. The absolute configuration was assigned on the basis of the enantioselective synthesis

1,4-Bis(4-pyridylmeth­yl)piperazin-1-ium perchlorate fumaric acid hemisolvate

In the title salt, C16H21N4 +·ClO4 −·0.5C4H4O4, fumaric acid mol­ecules, situated across crystallographic inversion centres, are O—H⋯N hydrogen bonded to two protonated 1,4-bis­(4-pyridylmeth­yl)piperazine cations, forming trimolecular units. These construct one-dimensional supra­molecular ribbons by N—H⋯N hydrogen bonding, and further aggregate via π–π inter­actions [shortest C⋯C contact = 3.640 (1) Å] and perchlorate-mediated C—H⋯O inter­actions

CORRESPONDENCE

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75533/1/j.1471-0528.1980.tb05024.x.pd

2,2,6,6-Tetra­kis(biphenyl-2-yl)-4,4,8,8-tetra­methyl­cyclo­tetra­siloxane

The title compound, [–Si(C12H9)2OSi(CH3)2O–]2, was obtained unintentionally as the product of an attempted crystallization of caesium bis­(biphenyl-2,2′-di­yl)fluoro­silicate from dimethyl­formamide. In the crystal, the mol­ecule is located on an inversion center and the siloxane ring adopts a twist-chair conformation with the two dimethyl-substituted Si atoms lying 0.7081 (5) Å out of the plane defined by the two bis­(biphenyl-2-yl)-substituted Si atoms and the four O atoms. In each Si(C12H9)2 unit, the orientation of one terminal phenyl ring relative to the phenyl­ene ring of the other biphenyl moiety suggests a parallel displaced π–π stacking inter­action [centroid distance = 4.2377 (11) Å and dihedral angle = 15.40 (9)°]

Redetermination of tetra­kis(N,N-diethyl­dithio­carbamato)tin(IV)

The crystal structure of the title compound, [Sn(C5H10NS2)4], was originally determined by Harreld & Schlemper [Acta Cryst. (1971), B27, 1964–1969] using intensity data estimated from Weissenberg films. In comparison with the previous refinement, the current redetermination reveals anisotropic displacement parameters for all non-H atoms, localization of the H atoms, and higher precision of lattice parameters and inter­atomic distances. The complex features a distorted S6 octa­hedral coordination geometry for tin and a cis disposition of the monodentate dithio­carbamate ligands