April 2000 issue
Rietveld refinements of monoclinic and triclinic AlPO4 tridymites show that their tetrahedral framework structures are isotypic with the silica analogues. The two forms of tridymite differ in distortions of the six-membered rings of tetrahedra, resulting in different superstructures. Both modifications co-exist at room temperature.
SrCrP2O7 belongs to the structure family of α-Ca2P2O7. It consists of a three-dimensional network of [SrO9], [CrO5] and [P2O7] groups. Lattice constants of the whole series of isotypic compounds SrMP2O7 (M2+ = Cr, Zn or Cd) are compared with respect to the electronic configuration of M2+.
addenda and errata
electronic papers (inorganic compounds)
Nonapotassium cerium tetraphosphorus hexadecasulfide is a zero-dimensional material isostructural with the rubidium analogue.
electronic papers (metal-organic compounds)
Recrystallization of trans-[Co(acac)2(PMePh2)(H2O)]PF6 (acac is pentane-2,4-dionato) from aqueous methanol gave purple prisms of the title compound. The molecular structure of the complex cation having a coordinated methanol ligand was revealed with a Co—O(methanol) distance of 2.059 (3) Å.
The title Nd compound is isomorphous with the corresponding Y compound, but with a larger unit cell.
The coordination geometry around the Ni atom is square planar with a slight tetrahedral distortion. The five-membered chelate ring has a distorted gauche conformation with the phenyl groups in axial and equatorial orientations.
The title compound, (Et4N)[ZnI4], is isostructural with the previously reported tetrabromocadmate, whose coordinates were used as the starting parameters for both of the refinements presented here. The asymmetric unit comprises one anion and three cations, all of which are in special positions. The anion has five nearest-neighbour cations in the form of a square pyramid.
Both the monoclinic and triclinic forms of the neutral title complex show an octahedral nickel(II) centre coordinated by two facial tridentate pyridylate ligands. The O-donor atoms of each ligand are trans.
The CoIII ion is six-coordinate in a nearly octahedral environment (one Cl, one O and four N atoms) and the ZnII ion is four-coordinate in a distorted tetrahedral environment (three Cl and one O atom).
The central Co atom of the title complex has a distorted octahedral coordination. The three Co—O bond distances are in the range 1.887 (2)–1.910 (2) Å, while the three Co—N bond distances are in the range 1.919 (2)–1.934 (2) Å. The ethanol solvate molecule is involved in an O—H⋯O intermolecular hydrogen bond.
The crystal structure of the title compound contains discrete monomeric molecules of the carbene complex and solvent molecules separated by normal van der Waals distances. The Pd atom is four-coordinate in an essentially square-planar environment, with the chlorine ligands mutually cis; Pd—P = 2.2495 (7), Pd—Cl = 2.3508 (7) and 2.3600 (7), Pd—C = 1.948 (2) and N—C(carbene) = 1.274 (3) Å.
The title compound crystallizes as discrete ions, which form interionic hydrogen bonds of the type N—H⋯F.
electronic papers (organic compounds)
The absolute configuration at the new stereogenic centre, formed during the key step of the total synthesis, was established by X-ray analysis of the title compound.
The absolute configuration was determined for the title compound, which was prepared in a synthetic study on the natural products bryostatins. There are two independent molecules which show similar conformations, except for the orientation of the methoxy groups.
The absolute configuration was determined for the optically active title compound, which was prepared in a synthetic study on the natural products bryostatins.
In the four title compounds, (I)–(IV
>), respectively, the donor and acceptor molecules are stacked alternately to form one-dimensional columns, but with different relative orientations of the alkyl substituents and thenitro groups.