Attilio Immirzi

Interconnected water channels and isolated hydrophobic cavities in a calixarene-based, nanoporous supramolecular architecture

An interesting interplay of H-bond and van der Waals-like interactions in a proximal calix[4]arene dihydroquinone derivative gives rise to a nanoporous supramolecular architecture with the simultaneous existence of water channels and very large hydrophobic cavities.

Crystal structure of a mesogenic copper(II) square-planar complex bis[N-p-(n-Hexyloxy)phenyl, p-(n-heptyloxy)salicylaldiminato] copper(II)

Abstract The crystal structure of this compound, a substance which exhibits smectic meso-morphism, is triclinic, P 1 space group, with lattice constants a = 11.280(5) A, b = 13.598(1) A, c = 25.650(2) A, α = 97.85(1) A, β = 96.76(3)° and γ = 100.37(3)°. Molecules with two different conformations are present in the unit cell, and the heptyl and hexyl side-chains are extended nearly parallel to each other. The molecules are packed together in layers with their major axes inclined at 60° to the layer plane. The observed structure explains why the liquid crystal mesophases of this and related compounds are not discotic.

Single insertion of propene into a cationic zirconium(IV) complex: Isolation and X-ray crystal structure of [(C5Me5)Zr(CH2CHMeCH 2Ph)(CH2Ph)]-[B(CH2Ph)(C6F5)3]

Abstract The reaction of propene with the half-sandwich salt complex [Cp′Zr(CH 2 Ph) 2 ][B(CH 2 Ph)(C 6 F 5 ) 3 ] ( 1 ) (Cp′ = C 5 Me 5 ) affords cleanly the single-insertion adduct [Cp′Zr(CH 2 CHMeCH 2 Ph)(CH 2 Ph)][B(CH 2 Ph)(C 6 F 5 ) 3 ] ( 2 ). The crystal structure of 2 reveals an unusual ‘back-biting’ η 6 -arene coordination to the d 0 metal, accounting for the unexpected stability of this compound either towards further propene insertion or towards β-hydrogen elimination.

The crystal and molecular structure of the tetraethylammonium salt of tetrahydridopentadecacarbonyltetrarhenate(2−) in two crystallographic forms

Abstract The structure of the title compound, (NEt 4 ) 2 [H 4 Re 4 (CO) 15 ], is reported in two crystallographic modifications, I and II. Both forms axe monoclinic and the cell constants are as follows: I, a 11.355(2), b 21.204(4), c 17.416(3) A, β 94.15(2)°, space group P 2 1 / c ; II, a 21.831(4), b 17.584(3), c 11.446(2) A, β 96.02(2)°, space group P 2 1 ,/ n . Two sets of 3042 (I) and 2870 (II) independent diffraction intensities, collected by counter methods, were used for the solution and refinement of the two structures. The final conventional R factors have values 5.5% (I) and 6.3% (II), respectively. The crystal packings are compared, showing different conformations of the (NEt 4 ) + cations. The anions contain a tetrametal cluster formed by an isosceles triangle plus an apically bound metal atom; the carbonyl groups are all terminally bonded to the rhenium atoms. Some differences, present both in the metal atom clusters and in the carbonyl dispositions, are discussed and compared with a third, previously reported, crystallographic modification of the same compound.

Crystal structures of rhodacyclopentane derivatives

Abstract Two complexes containing a rhodacyclopentane ring, viz. (acac)Rh(C 6 H 8 )(py) 2 and (acac) 2 Rh 2 (C 6 H 8 )(PPh 3 ) have been studied by X-ray diffraction. The ring forms through oxidative coupling of two allene molecules giving the structure A with trivalent, octahedrally-coordinated rhodium. In the second complex the unsaturated hydrocarbon part is also π-bonded to another Rh atom, and one acac group acts as a five-electron donor.

New solutions to the problems of chain orientation and chain continuity in structure analysis of fibrous polymers. A reconsideration of the structure of polyisobutene

Two points of general interest in structural refinement of polymers based on internal coordinates are discussed: the chain orientation and the chain continuity. Using a proprietary computer program, based on revised approaches to these questions, the structure of polyisobutene has been reconsidered, using new X-ray diffraction measurements (Fuji image plate) and performing a structure refinement based on internal coordinates. Three refinement schemes, with a decreasing number of degrees of freedom, have been considered, with the conclusion that the distortion from the 83 regular helix, claimed by Tadokoro [(1979). Structure of Crystalline Polymers, p. 136. New York: Wiley-Interscience], is confirmed, though lower than supposed. The new procedures implemented for chain orientation and chain continuity work excellently.

TRY, a new computer program for crystal structure analysis from diffraction data based on internal coordinates and on a molecular modelling procedure free of redundant coordinates

A procedure is described which allows structure modelling using a number of internal coordinates that does not exceed the number of degrees of freedom of the problem. The modelling then becomes a strictly analytical procedure and structural refinement from diffraction data can be carried out avoiding the use of singular matrices. A practical ‘symbolic language’ with a simple syntax allows easy molecular building even in intricate cases. Based on this procedure, a new computer program for the study of crystal structures (TRY), particularly suited for fibrous polymers, has been created. The program is available at http:// www.theochem.unisa.it/try.html.

X-ray Diffraction Study of Mesomeric Plastic Phase of Sulfolane Whose Stability Domain Ranges Within 15.45 and 28.45 C

Abstract The presence of rotational disorder in the plastic phase of sulfolane, stable within 15.45 and 28.45 C, has been demonstrated by X-ray diffraction techniques. Sulfolane forms. hexagonal crystals with unit-cell parameters a = b = 6.05(1), c = 9.75(1) A and two molecules per unit cell. The molecules are randomly oriented about the positions (⅓ ⅔ ¼) and (⅔ ⅓ ¾) giving rise to a hexagonal close-packed structure. By using a relatively coarse molecular model the experimental diffraction amplitudes are accounted for within an error of 16% by the assumption of a wholly random orientation. Data strongly substantiate the conclusions arising from previous thermodynamic studies.

Finding crystal structures from few diffraction data by a combination of a random search with genetic algorithms.

A new procedure for performing structural analysis of crystalline materials from diffraction data by random search and genetic algorithms is described.

Constraints and restraints in crystal structure analysis

The restraint-based procedure in least-squares refinement is critiqued and the advantages of using internal coordinates are discussed.