H. Schenk

Insertion reactions involving palladium complexes with nitrogen ligands I. Reactivity towards carbon monoxide of methylpalladium(II) complexes containing bidentate α-diimine ligands: crystal structures of four methylpalladium(II) and acylpalladium(II) complexes

Abstract Neutral compounds of the type (2,2′-bipyridine)Pd(CH3)(Cl) and 6-R′C5H3N-2-C(H)=NR)Pd(CH3)(Cl) ( R = i Pr ; R ′ = H : i Pr  PyCa ) ( R = t Bu ; R ′ = H : t Bu-PyCa ) ( R = i Pr ; R ′ = CH 3 : i Pr -6- Me  PyCa ) (R = CH2CH2C6H5;R′ = H: PhePyCa) ( R = t Bu ; R ′ = CH 3 : t Bu -6- Me  PyCa ) ( R = i Pr ; R′ = C ( H ) O : i Pr  IPA ) have been synthesized starting from (1,5-cyclooctadiene)Pd(CH3)(Cl) and ionic compounds of the type [(N-N)Pd(CH3)]BF4 (NN = bipy, iPrPyCa, tBuPyCa or iPr-6-MePyCa) by treatment of the methyl(chloro)palladium compounds with silver tetrafluoroborate. All products have been characterized by spectroscopic methods. Reaction of the compounds with carbon monoxide gives that neutral acyl compounds (NN)Pd(C(O)CH3)(Cl) and ionic acyl compounds [(NN)Pd(C(O)CH3)]BF4 (NN = bipy, iPrPyca, tBuPyCa, iPr-6-MePyCa or PhePyCa). The crystal structures of (iPr-6-MePyCa)Pd(CH3)(Cl), (iPrIPA)Pd(CH3)(Cl), (bipy)Pd(C(O)CH3)(Cl) and (iPrPyCa)Pd(C(O)CH3(Cl), have been determined. Comparison of data for the PdNCC5H4N moieties of the complexes concerned show that the geometries are almost identical, the largest r.m.s. deviation (between (iPr-6-MePyCa)Pd(CH3)(Cl) and (bipy)Pd(C(O)CH3)(Cl)) being 0.2 A. The PdC bond distances in the two acetylpalladium complexes are 0.05 A shorter than those in the two methylpalladium complexes. The PdN bond distances for the nitrogen atoms situated trans to the organic group are shorter by 0.11 A in the case of acetyl ligands. An unprecedented influence of the steric properties of the ligands on the half-life for the CO insertion is observed; substituents adjacent to the nitrogen donor atoms cause strongly acceleration.

Real-Time X-Ray Powder Diffraction Investigations on Cocoa Butter. I. Temperature-Dependent Crystallization Behavior

The crystallization behavior of cocoa butter has been investigated by means of real-time X-ray powder diffraction. Two procedures have been followed: cooling from 60°C at a constant rate until maximum solidification has taken place; and cooling from 60°C in 2 min to a constant solidification temperature. It appears that all polymorphic forms of cocoa butter, with the exception of the β form, can be formed from liquid. The solidification temperature appears to be the most important crystallization parameter.

Application of simulated annealing approach for structure solution of molecular crystals from X-ray laboratory powder data

Abstract Simulated annealing approach was successfully applied to solve three unknown molecular structures from X-ray laboratory powder data using a priory known structural fragments. Some possible developments of the method are discussed.

Real-time X-ray powder diffraction investigations on cocoa butter. III. Direct β-crystallization of cocoa butter: Occurrence of a memory effect

Direct β-crystallization of different samples of cocoa butter has been investigated. The influence of the thermal history of cocoa butter on its phase behavior is defined as a memory effect. The chemical composition of cocoa butter has been related to the occurrence of the short-term β-memory effectvia statistical analysis of the results. We explain how this effect can be attributed mainly to stearic acid and its related triacylglycerols. The total phase behavior of cocoa butter is discussed on the basis of the results obtained from the series of three papers of which this is the last.

Structural study of lanthanum oxysulfate (LaO)2SO4

Abstract The structure of lanthanum oxysulfate (LaO) 2 SO 4 was studied with neutron, electron, and X-ray diffraction using the Rietveld refinement method. The unit cell is determined to be monoclinic ( a = 14.349(1), b = 4.2852(5), c = 8.386(1) A , β = 107.00(1), Sp.gr. C2 c ). The structure is similar to that of grandreefite and consists of the alternative sulfate and (LaO) layers. Every sulfate oxygen is coordinated with two lanthanum atoms. The experimental data were confirmed by the energy minimization calculations.

Real-time X-ray powder diffraction investigations on cocoa butter. II. The relationship between melting behavior and composition of β-cocoa butter

The melting behavior of twelve different cocoa butter samples, in the β-phase, has been investigated with real-time X-ray powder diffraction. The melting trajectory of each sample is characterized by three temperature values: a starting point, a point of maximum melting, and a point of complete melting. These points are determined by an analysis of the subsequent X-ray diffraction patterns. A least-squares analysis has been developed which allows the observed melting points to be related to the composition of the cocoa butter. This analysis shows that the melting behavior of cocoa butter can be described as a function of certain binary combinations of its major components.

MONODENTATE AND BRIDGING COORDINATION OF 3,3'-ANNELATED 2,2'-BIPYRIDINES IN ZEROVALENT PALLADIUM- AND PLATINUM-P-QUINONE COMPLEXES

Compounds of the type M(N∩N-κN)(nq)2 and M2(μ2-N∩N)(μ2-pbq)2, in which nq = 1,4-naphthoquinone, pbq = 1,4-benzoquinone, and N∩N is a monodentate or bridging ligand of the α-diimine type, were obtained from reactions of Pd(dba)2 in toluene with the 3,3′-annelated-2,2′-bipyridines: 4,5-diazafluoren-9-one (dafo) and 4,5-diazafluorene (dafe) in the presence of the appropriate p-quinone. In the corresponding reactions with 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 2,2′-bipyrimidine (bpym), N,N′-dicyclohexyl-1,4-diaza-1,3-butadiene (chex-dab), bis[N-(o,o′-diisopropyl)phenylimino]acenaphthene (o,o′-iPr2-bian) and 5,6-dihydro-1,10-phenanthroline (dh-phen) only complexes of the type M(N∩N-κ2N)(Q) were formed (Q = nq, pbq). The structures of the complexes have been established by NMR in solution and by X-ray diffraction in the solid state; crystal structures of Pd(bpy-κ2N)(η2-pbq) (1) Pd(dafo-κN)(η2-nq)2 (14) and Pd2(μ2-dafo)(μ2,η2:η2-pbq)2 (16) have been determined. Of the ligands, dafo and dafe are the only ones apt to form complexes containing a monodentate or bridging N∩N ligand. This behaviour is ascribed to the geometrical constraints of dafo and dafe; the annelation by one carbon atom at the 3,3′-positions in these ligands causes an increase in bite angle from approximately 77° to 82°.

On the determination of accurate intensities from powder diffraction data. II. Estimation of intensities of overlapping reflections

Even the best least-squares algorithm to extract intensities from a powder diagram will not be able to determine the separate intensities of completely overlapping peaks. In this paper a new method (DOREES) is presented to determine these intensities more accurately by applying relations between structure factors derived from direct methods and the Patterson function. The intensities obtained from the least-squares fit are used as a starting set for DOREES. Comparative tests on both artificially generated and real data show that DOREES improves the intensity set considerably.

Organa - a program package for structure determination from powder diffraction data by direct-space methods

A new software package has been developed, named Organa, for ab initio solution of crystal structures from powder diffraction data by direct-space methods. The package contains energy-guiding Monte Carlo and grid-search algorithms and is based on a combined global minimization of the R factor and a potential energy function of the system with the option of local minimization of the cost function for each generated trial structure. Basically, the potential energy function consists of van der Waals interactions, but harmonic potentials can be added to impose soft distance restraints. The program was successfully applied to the structure determination of a series of melamine phosphate compounds. The program is freely available (for all Windows platforms) from the correspondence author upon request.

Structures of mono-unsaturated triacylglycerols. I. The β1 polymorph

An improved crystal structure model has been established for the beta2 polymorph of the symmetric mono-unsaturated triacylglycerol 1,3-distearoyl-2-oleoylglycerol (SOS) and the equivalent beta-V polymorph of Ivory Coast cocoa butter. In addition, the crystal structures of the beta2 polymorphs are reported for the triacylglycerols 1,3-dipalmitoyl-2-oleoylglycerol (POP) and 1-palmitoyl-2-oleoyl-3-stearoylglycerol (POS), which are, together with SOS, the major components of cocoa butter, and that of 1-stearoyl-2-oleoyl-3-arachidoylglycerol (SOA). The existence of beta2-POS and beta2-SOA has not been previously reported in the literature. All structures have been solved from high-resolution laboratory or synchrotron powder diffraction data with the direct-space parallel-tempering program FOX and refined with the Rietveld module of GSAS. All compounds crystallize in similar monoclinic unit cells (Cc) with very long b axes (>127 A). The oleic chains are packed together and sandwiched between saturated chain layers, forming acyl-chain three-packs. An analysis of the beta2 polymorphs and beta1 polymorphs [van Mechelen et al. (2006). Acta Cryst. B62, 1121-1130] shows that they contain the same three-packs and differ only in the symmetry relation between the three-packs. The three-pack build-up provides an explanation of the mechanism of the phase transition that causes the formation of fat bloom on dark chocolate.