A New Late Permian Burnetiamorph From Zambia Confirms Exceptional Levels of Endemism in Burnetiamorpha (Therapsida: Biarmosuchia) and an Updated Paleoenvironmental Interpretation of the Upper Madumabisa Mudstone Formation

A new burnetiamorph therapsid, Isengops luangwensis, gen. et sp. nov., is described on the basis of a partial skull from the upper Madumabisa Mudstone Formation of the Luangwa Basin of northeastern Zambia. Isengops is diagnosed by reduced palatal dentition, a ridge-like palatine-pterygoid boss, a palatal exposure of the jugal that extends far anteriorly, a tall trigonal pyramid-shaped supraorbital boss, and a recess along the dorsal margin of the lateral temporal fenestra. The upper Madumabisa Mudstone Formation was deposited in a rift basin with lithofacies characterized by unchannelized flow, periods of subaerial desiccation and non-deposition, and pedogenesis, and can be biostratigraphically tied to the upper Cistecephalus Assemblage Zone of South Africa, suggesting a Wuchiapingian age. Isengops is the second burnetiamorph recognized from Zambia and is part of a tetrapod assemblage remarkably similar to others across southern Pangea during the Wuchiapingian. A revised cladistic analysis of Biarmosuchia yielded over 500 most parsimonious trees that generally reaffirm the results of previous analyses for burnetiamorphs: Lemurosaurus is basal, Lobalopex and Isengops are proximate burnetiid outgroups, and Bullacephalus, Burnetia, Mobaceras, Niuksenitia, and Pachydectes are burnetiines. Furthermore, Russian biarmosuchians are scattered throughout the tree and do not form sister taxon relationships with each other. Burnetiamorphs display a wide disparity of cranial adornments and are relatively speciose (13 species), especially when compared to the number of specimens discovered to date (∼16 specimens). As has been suggested in some other tetrapod clades (e.g., ceratopsian dinosaurs), the burnetiamorph fossil record supports an inferred macroevolutionary relationship between cranial adornment and increased speciation rate.

Crystal structure ofcatena-poly[[trimethyltin(IV)]-μ-2-(2-nitrophenyl)acetato-κ2O:O′]

In the title one-dimensional coordination polymer, [Sn(CH3)3(C8H6NO4)]n, the SnIVatom is coordinated by three methyl C atoms and two carboxylate O atoms (one symmetry generated), resulting in an almost regular SnC3O2trigonal pyramid. The C atoms occupy the equatorial sites and the O atoms occupy the axial sites. In the ligand, the dihedral angles between the benzene ring and the pendant acetate and nitro groups are 57.7 (1) and 36.9 (3)°, respectively. The bridging ligand leads to [010] chains in the crystal, with adjacent metal atoms related by a 21screw axis. A weak π–π interaction exists between the centroids of symmetry-related benzene rings at a distance of 3.9131 (19) Å.

Tetrametallic lanthanide(iii) phosphonate cages: synthetic, structural and magnetic studies

Reaction of lanthanide nitrates with phosphonic acids in the presence of pivalic acid and pyridine lead to a trigonal pyramid of lanthanides with phosphonates capping three of the triangular faces.

Bis(tert-butyldimethylsilyl)(2,6-diisopropylphenyl)phosphane: the first structure of an organophosphane with twotert-butyldimethylsilyl (TBDMS) substituents

The title compound, C24H47PSi2, is the first organophosphane bearing twotert-butyldimethylsilyl (TBDMS) groups to be crystallographically characterized, even though TBDMS is a very popular bulky silyl group. The structure is a considerably flattened trigonal pyramid, with the sum of the C/Si—P—C/Si angles being 333.35 (6)°, which can be attributed to the steric pressure from the three bulky groups. The P—Si distances [2.2605 (6) and 2.2631 (6) Å] are normal, while the P—C distance [1.8646 (12) Å] is long (outside the s.u. values) compared with related structures. The plane of the aryl ring approximately bisects the Si—P—Si angle, quite unlike the secondary (tert-butyldimethylsilyl)(2,6-diisopropylphenyl)phosphane bearing only one TBDMS group, in which the single Si atom is perpendicular to the aryl ring. The title structure conforms closely to that predicted from B3LYP/6-31G(d) calculations, although the calculations overestimate the degree of planarity. The compound crystallizes centrosymmetrically in the space groupP\overline{1} as isolated molecules.

The Theory Investigation of the Effect of Substitutions of –CF3 on the Properties of Ru Complex with Phenanthroline

The Ru(phen)32+ complex forms a regular octahedron and the Ru(phen)3 unit is a nearly regular trigonal pyramid with ~90° angles. Lengths between Ru and six nitrogen atoms showed slightly different, and rather insensitive to –CF3 group substituted, as well as the oxidation. There is manifest influence of perfluoro group substitutions on the HOMO and LUMO energies and the substitution of –CF3 enhances the electron-transport abilities, as well as the complex stability. By substitution of –CF3 group show increased λ, with addition one –CF3, a.u 0.02~0.03 ev increase consequently, indicating that the –CF3 in ligand will hinder hole transport. But, the reorganization energies for these complexes are really values compared with other materials for optoelectronic devices.

The crystal structure of Pb5(As3+O3)Cl7 from the historic slags of Lavrion, Greece – a novel Pb(II) chloride arsenite

The crystal structure of new lead chloride arsenite, Pb5(As3+O3)Cl7 [orthorhombic, Pbcn, a = 16.894(2), b = 10.913 (1), c = 16.760(2) Å, V = 3090.1(7) Å3], from the historic slags of Lavrion, Greece, has been solved by direct methods and refined to R1 = 0.069. The structure contains five symmetrically unique Pb, one As, eight Cl and three O sites. The As atom forms three nearly equal As—O bonds which result in the formation of an AsO3 trigonal pyramid with As at the apex. The Pbl. Pb2, Pb3 and Pb4 atoms are bonded to the AsO3 groups via Pb2+—O bonds to form complex [Pb4(AsO3)] chains parallel to the b axis. The Pb(5) atom is coordinated solely by Cl– anions. The resulting Pb(5)Cl7 polyhedra share common edges and corners to produce bent chains parallel to the c axis. A short compilation of structural features of known lead chloride arsenites is given.

(2,4,6-Trimethyldithiobenzoato-κ2 S,S′)bis(triphenylphosphine-κP)gold(I)

The asymmetric unit of the title compound, [Au(C10H8S2)(C18H15P)2], consists of two independent molecules. The Au coordination environment can be described as a highly distorted tetrahedral arrangement (S2AuP2), but is more accurately described as a flattened trigonal pyramid defined by three normal covalent bonds (SAuP2), with a second S atom more distantly bonded to the Au atom.