R. Rudert

N-n-Alkyl N,N-dimethylammonioacetic acid bromides: the first complete series of crystal and molecular structure determinations of an ­amphiphilic compound with alkyl chain lengths n = 1,..., 16

The molecular and crystal structures of 16 N-n-alkyl N,N-dimethylammonioacetic acid bromides with chain lengths between n = 1 and n = 16 have been determined. All compounds from n = 5 to n = 16 form bilayers with interdigitated chains. The even-numbered chains display the chain packing type M2(II). The chain packing of the odd-numbered chain compounds is less regular. The head groups of all compounds are connected via electrostatic N+...Br- interactions, and by OH...Br- hydrogen bonds. The compounds with short chains are packed in different ways. Their molecular conformation depends on the crystal packing.

Structural effect on the adsorption properties of aqueous solutions of straight-chain and cyclic dodecyl sulfates

Abstract The adsorption properties of aqueous solutions of sodium alkyl sulfates and their oxyethylates have been studied systematically. The effect of defined structural changes on the adsorption parameter values calculated on the basis of Frumkins surface equation of state has been demonstrated. In particular, a comparison has been made between n -dodecyl and cyclododecyl as hydrophobic groups in sodium alkyl sulfate and its ethers. The limiting areas obtained by surface tension measurements have been discussed on the basis of the crystal structure data of n -dodecyl sulfate and theoretical calculations on the three-dimensional shape of selected conformers of cyclododecyl sulfate.

Electrostatic lattice coefficients and binding energy of orthorhombic La2-xSrxCuO4

Three valency models for orthorhombic La2-xSrxCuO4 were investigated for increasing Sr concentrationsx (0≤x≤0.21): 1. Cu2+→Cu3+, 2. apex O2−→O− and 3. in-plane O2−→O−. All calculations were done by using structural parameters valid for the temperature range from 10 to 22 K. We thereby calculated the electrostatic interaction energy which, next to ionization potentials and electron affinities, comprises a major of the binding energyEBof crystals. Second-order effects were accounted for by calculating the strength of ionic dipole moments induced by crystal electric fields at relevant lattice sites. Their largest strengths are comparable to the dipole moment of the water molecule. Three out of five dipoles in La2-xSrxCuO4 vanish during the transition from the orthorhombic to the tetragonal phase. The binding energy differences between the different models suggest that the system is in a state of model 1. However, the differences are very small, being in the order of 0.3 to 0.76 eV atx=0.13.

Synthesis, crystal and molecular structure of N,N-dimethyl-3-[tris(trimethylsiloxanyl)silyl]pyrrolinium chloride

Abstract The synthesis of N,N-dimethyl-3-[tris(trimethylsiloxanyl)silyl]pyrrolinium chloride was carried out by hydrosilylation of 1,4-dichlorobut-2-yne with tris(trimethylsiloxanyl)silane followed by the reaction of the product with dimethylamine. The structure of the crystalline white solid was determined by an X-ray diffraction study. The SiOSi angles range from 145.8(3)° to 161.4(4)°. The molecules are packed in bilayers with a head-head arrangement.

Effect of the Alkanoyl Group Position at the Glycerol Backbone on the Monolayer Characteristics Demonstrated by 2-Monopalmitoyl-rac-glycerol

The influence of the position of the aliphatic chain at the glycerol backbone has been basically unknown. Solely the results of 2-monopalmitoyl-rac-glycerol obtained at ≥13 °C indicated an essential influence of the position of the palmitoyl group at the glycerol backbone, substantiated by a disordered packing of the alkyl chains. Therefore, the present study extends the comprehensive characterization of 2-monopalmitoyl-rac-glycerol monolayers to the low-temperature range for highlighting the effect of the position of the aliphatic chain at the glycerol backbone of monoalkanoylglycerolester monolayers. Systematic studies of the thermodynamic behavior, the morphological features, and the 2D lattice structures of 2-monopalmitoyl-rac-glycerol monolayers at ≤10 °C allow useful conclusions. Large differences between the π-A isotherms of 1- and 2-monopalmitoyl-rac-glycerol monolayers and their thermodynamic analysis indicate that the change of the substitution from position 1 to position 2 of glycerol backbone is consistent with a shortening of the alkyl chain by roughly two CH2 groups. Quantum chemical calculations of the molecular structure and packing calculations are in reasonable agreement with the thermodynamic results. Considerable diversity in the mesoscopic domain topography exists between the monoalkanoylglycerol esters with the aliphatic chain positioned at the end of the glycerol backbone (1-position) and those with the aliphatic chain in the middle of the glycerol backbone (2-position). The new faceted shape of the 2-monopalmitoyl-rac-glycerol domains, before they develop branched fractal-like structures at the edges, is the essential difference to the round or cardioid-like 1-monoalkanoylglycerol domains. In the low-temperature range, well-defined orthorhombic lattice structures exist at all surface pressures. Comparing all GIXD data from the three racemic compounds (1-monostearoyl-rac-glycerol, 1-monopalmitoyl-rac-glycerol, and 2-monopalmitoyl-rac-glycerol) shows that 2-monopalmitoyl-rac-glycerol behaves as 1-monomyristoyl-rac-glycerol, i.e., the shift from position 1 to position 2 of the glycerol backbone is equivalent to a shortening of the alkyl chain.

Sodium 1,12-Dodecylene Disulfate Hydrate

There are two independent dodecylene disulfate molecules in the crystal of 2Na + -C 12 H 24 O 8 S 2 2- .2/3H 2 O, one with a centrosymmetric conformation, its center lying on a crystallographic center of symmetry, the second with an asymmetric conformation, which is partially disordered. The molecules form a layer structure parallel to the ab plane, the polar parts of neighbouring molecular layers connecting via coordination to the Na + ion. Additionally, there are hydrogen bonds between the water molecule and two sulfate groups.

Substitutional disorder, random dipoles and the binding-energy of orthorhombic La₂-XSrXCuO₄

This study investigates the effect of heterovalent, substitutional disorder on the binding energy of La2−xSrxCuO4. First, disorder has been found to create crystal electric fields that fluctuate over different lattice sites and induce ionic dipole moments of varying strength and orientation. The strength of these random dipoles will be presented for increasingx. Second, disorder may slightly displace the ions from their average lattice sites. The large thermal parameters obtained from diffraction experiments are discussed in this context. Finally, the polarization energy related to random dipoles was calculated to be on the order of eV and favourizes the positive charge carriers introduced by Sr doping to be associated with the copper ions. It is concluded that the solid exists in a state containing mixed copper valencies (Cu2+/Cu3+).

3,3'-(1,1,3,3,-Tetramethyldisiloxane-1,3-diyl)bis(N-ethyl-N,N-dimethyl-1-propanaminium) Diperchlorate at 163 K and Room Temperature

In the title compound, C 18 H 46 N 2 OSi 2 2+ .2ClO 4 - , the cations lie in special positions ont the crystallographic twofold axis. The contacts between N + and ClO 4 - build up a three-dimensional net. The Si-O-Si angle is relatively small [between 141.8(3) and 144.4(5)°] and depends ont the measuring temperature

Butyl[3-(1,1,3,3,5,5,5-heptamethyltrisiloxan-1-yl)propyl]dimethylammonium bromide, C16H42NO2Si3+Br-, at 173 and 301 K

The molecules form double layers in head-head arrangements. The non-polar regions of the layers are held together by weak van der Waals interactions and the polar regions mainly by electrostatic interactions. One of the Si-O-Si bond angles is much smaller at low temperature (173 K) than at the room temperature (301 K)

Sodium cyclododecyl sulfate trihydrate, Na+.C12H23O4S–.3H2O

The conformation of the cyclododecyl ring has slightly distorted 422 symmetry. The molecules are packed in a head-to-head arrrangement. The hydrophilic parts of neighbouring molecular layers are connected via coordination to Na + and hydrogen bonds