The Effect of the Spacer of Bis(biurea) Ligands on the Structure of A2L3‐type (A=anion) Phosphate Complexes

By tuning the length and rigidity of the spacer of bis(biurea) ligands L, three structural motifs of the A₂L₃ complexes (A represents anion, here orthophosphate PO₄^3?), namely helicate, mesocate, and mono‐bridged motif, have been assembled by coordination of the ligand to phosphate anion. Crystal structure analysis indicated that in the three complexes, each of the phosphate ions is coordinated by twelve hydrogen bonds from six surrounding urea groups. The anion coordination properties in solution have also been studied. The results further demonstrate the coordination behavior of phosphate ion, which shows strong tendency for coordination saturation and geometrical preference, thus allowing for the assembly of novel anion coordination‐based structures as in transition‐metal complexes.     

Volume and adiabatic compressibility of optically active and inactive tartaric acids and tartrates

The differences of partial molal volume and adiabatic compressibility at infinite dilution of optically active diastereoisomers in water are reported. The L and meso tartaric acids and their potassium salts are examined. The results are interpreted in terms of specificity of H bonding between the solvent H₂O and the stereoisomers in the charged and uncharged forms. The results are of interest in relation to biochemical specificities and stereospecific behavior of optical enantiomers.     

Thermodynamic properties of alkali halides. IV. Apparent molal volumes,expansibilities, compressibilities,and heat capacities in urea-water mixtures

The apparent molal volume φ_v, expansibility φ_E, compressibility φ_K, and heat capacity φ_c of NaCl were measured in urea-water mixtures, as a function of salt (<1.5m) and urea (<13m) concentrations at 25°C. At a fixed urea concentration, the transfer functions from H₂O to 3m urea are linear functions of the NaCl aquamolality. At a fixed salt aquamolality, (0.1m), the sign of the transfer functions is in the direction of a decrease in the structure-breaking effect, and the absolute values of the transfer functions tend to level off at high urea concentrations (13m). The functions φ_v, φ_E, φ_K, φ_c, and (?φ_v/?T)_p were measured for the sodium halides and alkali, bromides (chlorides in the case of φ_K) at a fixed salt aquamolality of 0.1m and fixed urea molality of 3m. The corresponding transfer functions from H₂O to 3m urea are opposite those from H₂O to D₂O and similarly are relatively independent of ionic size. This suggests that urea, shows no specific interaction affinity for ions and that the overall number of water molecules influenced by the ions is relatively constant for all alkali halides. The lithium halides are an exception in that Li⁺ seems to have hardly any structure-breaking effect.     

Nanoscale Control of Polyoxometalate Assembly: A {Mn8W4} Cluster within a {W36Si4Mn10} Cluster Showing a New Type of Isomerism

Two near isomeric clusters containing a novel {Mn₈W₄} Keggin cluster within a [W₃₆Mn₁₀Si₄O₁₃₆(OH)₄(H₂O)8]^24? cluster are reported: K₁₀Li₁₄ [W₃₆Si₄O₁₃₆Mn^II₁₀(OH)₄(H₂O)₈] ( 1 ) and K₁₀Li1_3.5Mn_0.25[W₃₆Si₄O₁₃₆Mn^II₁₀(OH)₄(H₂O)₈] ( 1′ ). Bulk characterization of the clusters has been carried out by single crystal X‐ray structure analysis, ICP‐MS, TGA, ESI‐MS, CV and SQUID‐magnetometer analysis. X‐ray analysis revealed that 1′ has eight positions within the central Keggin core that were disordered W/Mn whereas 1 contained no such disorder. This subtle difference is due to a differences is how the two clusters assemble and recrystallize from the same mother liquor and represents a new type of isomerism. The rapid recrystallization process was captured via digital microscopy and this uncovered two “intermediate” types of crystal which formed temporarily and provided nucleation sites for the final clusters to assemble. The intermediates were investigated by single crystal X‐ray analysis and revealed to be novel clusters K₄Li₂₂[W₃₆Si₄Mn₇O₁₃₆(H₂O)₈]?56 H₂O ( 2 ) and Mn₂K₈Li₁₄[W₃₆Si₄Mn₇O₁₃₆(H₂O)₈]?45 H₂O ( 3 ). The intermediate clusters contained different yet related building blocks to the final clusters which allowed for the postulation of a mechanism of assembly. This demonstrates a rare example where the use X‐ray crystallography directly facilitated understanding the means by which a POM assembled.     

Organic electroluminescence using polymer networks from smectic liquid crystals

We report the synthesis of a red light-emitting and photopolymerizable smectic liquid crystal (reactive mesogen). We investigate the suitability of polymer networks formed from smectic reactive mesogens for use in organic light-emitting diodes (OLEDs). The use of mixtures of smectic reactive mesogens is shown to lower the processing temperature for the fabrication of OLEDs to room temperature. We also report efficient energy transfer from a nematic polymer network host to a smectic light-emitting dopant and polarized emission from a polymer network formed from an aligned smectic reactive mesogen.     

ThePoranthera corymbosa alkaloids. III. Molecular structure and absolute configuration of poranthericine hydrobromide

Crystals of the hydrobromide of poranthericine, C₁₅H₂₇NO, an alkaloid isolated from the plantPoranthera corymbosa Brogn. (family Euphorbiaceae) were found to belong to the orthorhombic space groupP2₁2₁2₁, with unit cell dimensionsa = 12·761,b = 15·144 andc = 8·030 Å, andZ = 4. The structure was solved by the heavy-atom method and refined with 1276 reflections to a residual of 0·091 The molecule was found to consist of three saturated six-membered rings fused on to a common central nitrogen atom, with methyl, ethyl and hydroxyl groups attached to the periphery. All rings had thechair conformation and were fusedtrans to one another. The absolute configuration was determined using the anomalous scattering power of the bromine atom.     

ThePoranthera corymbosa alkaloids,I. Crystal and absolute molecular structure of porantherine hydrobromide

The alkaloid porantherine, C₁₅H₂₃N, has been isolated fromPoranthera corymbosa Brogn. (family Euphorbiaceae). It forms a stable hydrobromide which crystallizes in the orthorhombic space groupP2₁2₁2₁, with cell dimensionsa=11·689,b = 15·190 andc = 7·721 Å. Its structure has been solved by the heavy-atom method and refined to anR of 0·063. The molecular skeleton has the form of a tertiary amine, with three fused six-membered rings centred on the nitrogen atom and a two-carbon atom bridge which holds the whole molecule rigid. The absolute configuration has been determined from the differences between Bijvoet pairs of reflexions.