Constraints and restraints in crystal structure analysis

The restraint-based procedure in least-squares refinement is critiqued and the advantages of using internal coordinates are discussed

Finding crystal structures from few diffraction data by a combination of a random search with genetic algorithms

A new procedure for performing structural analysis of crystalline materials from diffraction data by random search and genetic algorithms is described

Crystal structure of the stereoregular ethylene-alt-styrene copolymer synthesized with a zirconocene-based catalyst

A stereoregular alternating ethylene-styrene copolymer, also stretchable in fiber form, has been obtained with rac-isopropylidenebis( l-indenyl)zirconium dimethyldiamide activated by the methylalumoxane catalytic system. From X-ray diffraction fiber spectra, an isotactic structure has been assigned to this copolymer as well as the previously described stereoregular ethylene-styrene copolymers. The polymer has zigzag planar chain conformation with phenyl groups oriented perpendicularly to the chain axis. The crystallographic symmetry in B2/m. Lattice constants (monoclinic, unique axis c): a = 10.23, b = 15.53, c = 5.12 Angstrom; gamma = 98.6 degrees. The disagreement index for measured reflections is R-1 = 0.10

La diffrazione dei cristalli

Numerosi e ottimi testi trattano la diffrazione dei raggi X e il suo uso nelle indagini strutturali, essi però sono per lo più in lingua inglese e poco si prestano come testi didattici. Questo libro si propone di colmare tale lacuna. Di particolare rilievo il capitolo sull’uso delle coordinate interne nella modellazione delle molecole nelle procedure di risoluzione delle strutture per tentativo, un argomento poco trattato da altri testi, anche perché, in anni recenti, ha ricevuto nuovi impulsi proprio grazie agli autori