The reaction of trimethylsilyl-substituted 2-aminopyridines with mixed chloro(dialkylamido)metal complexes (titanium and zirconium) leads via amine elimination to octahedral group 4 metal complexes that contain amine, amido, and aminopyridinato ligands. The X-ray crystal structure analyses of (4-Me-TMS-APy)(NMe(2))(HNMe(2))TiCl(2) (1) (crystallographic data: P2(1)/c (No. 14), monoclinic, a = 16.754(2) Å, b = 14.395(2) Å, c = 17.890(3) Å, beta = 110.28(1) degrees, Z = 8) and (6-Me-TMS-APy)(NEt(2))(HNEt(2))ZrCl(2) (2) (crystallographic data: P2(1)/n (No. 14) monoclinic, a = 10.125(1) Å, b = 16.331(1) Å, c = 15.276(2) Å, beta = 93.90(1), Z = 4) prove the compounds to be mononuclear with a cisoid arrangement of the two chloro ligands embedded in a reactive pocket determined by the steric demand of the three nitrogen containing ligands. Oligo- and polymerization studies with propene and 1-butene reveal the following results. First, 1 is a remarkably active precatalyst in contrast to the very low activity of 2. Second, MAO, a 1:1 mixture of i-Bu(3)Al/B(C(6)F(5))(3) (homogeneous polymerization) and ethylaluminum sesquichloride (if 1 is incorporated in a MgCl(2)-matrix) have shown to be the most active cocatalysts. Third, the polymers and oligomers are atactic.

Chloro(dialkylamido) complexes of the type (R2N)2MCl2(THF)2 (R = Me, Et; M = Zr and R = Me; M = Hf) were synthesized in a conproportionation reaction by adding an equimolar amount of the corresponding M(NR2)4 to an ether slurry of MCl4 in the presence of THF. X‐ray crystal structure determinations of (Et2N)2ZrCl2(THF)2 (1 a) and (Me2N)2ZrCl2 · (THF)2 (1 b) reveal a distorted octahedral coordination geometry where the sterically demanding dialkylamide ligands force the chloride and the THF ligands out of their ideal position. Dynamic NMR investigations indicate an equilibrium of complexes with coordinated THF at low temperature in accordance with the structure determined by X‐ray crystallography and of chloro‐amido complexes that do not bind THF (at higher temperature).

Given just a few strong low-index reflections, a periodic nodal surface (PNS), which divides the unit cell into regions of high and low electron density, can be generated. Fourteen known zeolite structures were examined to verify the validity of the procedure developed and in all cases the framework atoms were found to lie on just one side of the calculated curved surface. In other words, the surface defines a structure envelope. The same approach was applied to a few ionic and organic structures and was found to be equally valid. Since these reflections, with large d spacings, are precisely the ones that are least likely to be involved in overlap in a powder diffraction pattern, such a PNS can also be calculated using powder data. The resulting restriction in the region of the asymmetric unit in which atoms are likely to be found has immediate implications for any of the direct-space methods of structure determination from powder data. The use of this structure envelope as a mask in a straightforward grid search procedure reduced the computer time required to solve several framework structures by as much as two orders of magnitude.

A structure envelope is a special type of periodic nodal surface that separates regions of high electron density from those of low electron density. Once such a surface has been generated, it can be used in combination with direct-space methods to facilitate structure solution from powder data. To generate an informative structure envelope, the phases of the structure factors of a few strong low-order re¯ections must be determined; an algorithm has been developed for this purpose. The program SayPerm combines (a) the use of errorcorrecting codes (e.c.c.'s) to sample phase space ef®ciently, (b) a pseudo-atom approximation of structure fragments to simulate atomic resolution at ca 2.5 A Ê , and (c) phase extension and phase set ranking using the Sayre equation. The effect of using a structure envelope in structure solution was ®rst tested in combination with a subroutine for ®nding zeolite topologies in the program FOCUS. Then extension to molecular structures in combination with a simulated-annealing program was explored. This resulted in the development of the program Safe and the subsequent determination of the structure of a tri-peptide (C 32 N 3 O 6 H 53 ) with 17 variable torsion angles.

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Laue experiments using synchrotron radiation have been carried out on quasicrystalline samples mainly with decagonal symmetry. Apart from Laue spots, Kossel lines and diffuse scattering have been observed on the X-ray film simultaneously. High spatial resolution was achieved by the positioning of the X-ray film at a distance of about 350 mm from the sample. Conclusions about the real structure and the crystal quality could be drawn using information obtained from the appearance of the Kossel lines, and the shape and the splitting of the Laue spots, respectively. The dimensions of the mosaic blocks and their tilting behaviour for one of the samples under investigation have been determined.

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