Crystal structure of the 2:1 inclusion compound between deoxycholic acid and quadricyclane

The 2:1 inclusion compound formed between deoxycholic acid (C₂₄H₄₀O₄,M _r=392.58) and quadricyclane (C₇H₈,M _r=92.14) crystallizes in space groupP2₁2₁2₁ witha=27.150(7),b=13.359(3),c=14.161(4) Å,Z=4. The structure was refined toR=0.08₆ andR _w=0.08₈ for 2079 observed reflections withI>2.5(I). The crystal packing is very similar to that found in the norbornadiene-deoxycholic acid inclusion compound and is characterized by an assembly of antiparallel pleated bilayers, formed by molecules of deoxycholic acid held together through hydrogen bonds. Quadricyclane occupies approximately the same position of norbornadiene and its atoms give rise to good van der Waals interactions with some methyl groups of deoxycholic acid. Supplementary Data relating to the article are deposited with the British Library as Supplementary Publication No. SUP 82006 (14) pages. To obtain copies, see page ii of this issue.     

Dynamic behaviour and X-ray analysis of chiral η-allylpalladium complexes. II

The DANTE technique and NOESY two-dimensional method have been employed to observe the isomerization of the chiral cationic complex [Pd(η³-CH₂CMeCH₂(P-P′)]⁺ (1a), where P-P′ = the chiral chelating ligand (S)(N-diphenylphosphino)(2-diphenylphosphinoxymethyl)pyrrolidine. The rate constant was found to be 0.5 s⁻¹ in CHCl₃ at 295 K and 1.50 s⁻¹ in the presence of added free ligand. In the latter case the epimerization proceeds by a π-σ-π mechanism via the intermediacy of a primary η¹-allylpalladium complex. Although the intermediate was not detected, the NMR findings reveal that it has the allylic terminus η¹-bonded to palladium. The structure of 1a in its PF₆⁻ salt has been determined. The compound crystallizes in the orthorhombic space group P2₁2₁2₁ with a 10.029(4) b 19.203(8) c 36.115(6) Å, Z = 8, R = 0.0572 and R_w = 0.0712 for 3716 observed reflections with I > 3σ(I).     

Smoothk-gonal curves with another fixed pencil

Let X be a smooth curve of genus g with two pencils, sayg _k ¹ andg _m ¹ . Here we show that, in general, dim|rg _k ¹ +ug _m ¹ | has the expected dimension and construct examples in which dim |rg _k ¹ +ug _m ¹ | has a prescribed value.     

Smoothing of rational m-ropes

In a recent paper, Gallego, González and Purnaprajna showed that rational 3-ropes can be smoothed. We generalise their proof, and obtain smoothability of rational m-ropes for m ≥ 3.     

Salvatore Pincherle

Commemorazione letta davanti alla Classe di Scienze fisiche, matematiche e naturali della Reale Accademia Nazionale dei Lincei nell'adunanza del 5 dicembre 1937-XVI.     

A Few Remarks About the Hilbert Scheme of Smooth Projective Curves

We discuss two conjectures by Francesco Severi and Joe Harris about the irreducibility and the dimension of the Hilbert scheme parameterizing smooth projective curves of given degree and genus.     

Thermodynamics of Hydrogen Adsorption on Metal‐Organic Frameworks

Interaction between adsorbed hydrogen and the coordinatively unsaturated Mg²⁺ and Co²⁺ cationic centres in Mg‐MOF‐74 and Co‐MOF‐74, respectively, was studied by means of variable‐temperature infrared (VTIR) spectroscopy. Perturbation of the H₂ molecule by the cationic adsorbing centre renders the H? H stretching mode IR‐active at 4088 and 4043 cm^?1 for Mg‐MOF‐74 and Co‐MOF‐74, respectively. Simultaneous measurement of integrated IR absorbance and hydrogen equilibrium pressure for spectra taken over the temperature range of 79–95 K allowed standard adsorption enthalpy and entropy to be determined. Mg‐MOF‐74 showed ΔH⁰=?9.4 kJ mol^?1 and ΔS⁰=?120 J mol^?1 K^?1, whereas for Co‐MOF‐74 the corresponding values of ΔH⁰=?11.2 kJ mol^?1 and ΔS⁰=?130 J mol^?1 K^?1 were obtained. The observed positive correlation between standard adsorption enthalpy and entropy is discussed in the broader context of corresponding data for hydrogen adsorption on cation‐exchanged zeolites, with a focus on the resulting implications for hydrogen storage and delivering.