P. Galen Lenhert

Molecular Packing and Crystalline Order in Polybenzobisoxazole and Polybenzobisthiazole Fibers

The structures of poly(p-phenylenebenzobisthiazole) (PBZT) and poly(p-phenylenebenzobisoxazole) (PBO) fibers have been investigated by fiber diffraction techniques. d-spacings were obtained from equatorial and meridional scans recorded on a four-circle diffractometer. Intensity data were derived from x-ray rotation patterns taken on Weissenberg and vacuum cylindrical cameras. Unit cells were found to be monoclinic and non-primitive, each containing two chains per cell of dimensions a = 11.79(2), b = 3.539(5), c = 12.514(9) A, γ = 94.0(2) o for PBZT; and = 11.20(1), b = 3.540(2), c = 12.050(3) A, γ = 101.3(1) for PBO. The fiber axes correspond to c. The conformational torsion angle between the bisthiazole and phenylene units and the orientation of chains within the unit cells were obtained from a ‘linked-atom least-squares’ (LALS)refinement procedure. A packing model is proposed for each polymer in which two independent molecular chains are displaced longitudinally by discrete rather than random increments. Primitive unit cells (Z = 1), besides requiring perfect axial registry of molecular chains, suffer from the occurrence of short intermolecular contacts and are rejected from further consideration.

Reactions of coordinated molecules : XXV. The preparation of several bis[(hydroxy)(methyl)]carbenoid complexes of rhenium

Abstract When the rhenium(I) complexes, XRe(CO) 5 (where X is Cl, Br or I), are treated with two molar-equivalents of methyllithium, dianionic complexes of the type, fac -(OC) 3 (X)Re[C(CH 3 )O] 2 – , are formed. The diprotonation of these dianions with HX affords the neutral, bis-carbenoid complexes, fac -(OC) 3 (X)Re[C(CH 3 )(OH)] 2 . When X is methyl, the reaction with methyllithium gives only a monoanion. The iodo, bis-carbenoid complex decomposes in solution with the elimination of acetaldehyde and with the formation of the known dimeric complex, [Re(CO) 4 I] 2 . The X-ray molecular structure determination of this dimeric complex is reported. The 13C NMR data of the chloro and bromo biscarbenoid complexes are also presented.

Reactions of coordinated molecules. 35. Carbon-carbon bond formation between adjacent acyl ligands in (metalla-.beta.-diketonato)difluoroboron complexes of iron, manganese, and rhenium

Quand les complexes de type L n M(CH 3 CO)(RCO)BF 2 sont traites avec KH, ou la tetramethylpiperidine, un proton est elimine du coordinat acetyl pour donner des complexes η 3 -allyl anioniques de type {L n M[η 3 -CH 2 COCO(R)BF 2 ]} − . Etude RX de PPN{cis-(OC) 4 Mn[η 3 -CH 2 COCO(i-Pr)BF 2 ]}

Common boundary in multiple lattices of K2MCu(NO2)6 where M is Ca, Ba, Pb

Abstract Evidence for a {110} boundary in the multiple lattice structures of K 2 MCu(NO 2 ) 6 with M = Ca, Ba, Pb, has been obtained from zero-level precession photographs. The results are discussed in terms of the static-dynamic Jahn-Teller effect.