Ab initio Hartree-Fock and DFT MO calculations have been used to study the conformations of [2.2.2]cyclophane π-prismands and the formation of π-complexes with silver ion and [2.2.2]cyclophanes. The lowest energy cyclophane conformations have been calculated up to the HF/6-31+G* level of theory. The silver π-complexes of the lowest energy conformations have been calculated with HF/3-21G* and B3LYP/3-21G* levels of theory. The nature of bonding in silver ion π-complexes has been studied with natural bond orbital analysis (NBO). Energies of the calculated cyclophanes and complexes, together with formation energies of those complexes, have also been discussed. The results obtained have been compared to X-ray crystal structures whenever such structures were available. Calculated and experimental X-ray structures agreed reasonably well given provision to the rather small 3-21G* basis set and the omission of triflate anion in the calculation model. The NBO analysis showed that when Ag + is bonded to the cyclophane cavity, the bonds are formed by σ-donation and d-π*-back-donation between the silver ion and the hydrocarbon skeleton, resulting in hexahapto (3×η 2 ) overall π-bonding. This is in agreement with the well-known "bondingback-bonding" scheme in transition metal carbonyl complexes. In this case the σ-donation from hydrocarbon to silver ion is the main contribution to the metal-cyclophane bonding. One dihapto (η 2 ) bonding to one aromatic ring in the present π-prismands relates by strength to a single strong hydrogen bond, which is up to 100 kJ/mol; thus the strength of this 3×η 2 bonding in these [2.2.2]cyclophane π-prismands can be compared to three simultaneous strong hydrogen bonds.

Treatment of 1,9-bis(lithiocyclopentadienyl)nonane (8b) with ZrCl 4 (THF) 2 , in dilute solution, gave the crystalline mononuclear ''large'' ansa-metallocene 3b (7% isolated). The X-ray crystal structure analysis of 3b revealed a metallocene conformation where the nonamethylene bridge is oriented toward the lateral sector of the bent metallocene wedge. An analogous structure of 3b is probable in solution, as shown by dynamic 1 H NMR spectroscopy. The activation barrier for the metallocene conformational equilibration process of 3b

The phase behavior of enantiomeric compounds as well as mixtures of enantiopure and racemic diastereomers of ethyl 4-fluoro-2,3-dihydroxystearates has been investigated using surface pressure-area isotherms and Brewster angle microscopy (BAM). All mixtures exhibit a small plateau region within the surface pressure-area isotherm at 20 degrees C, whereas the enantiopure compound shows an isotherm behavior similar to that of fatty acids. Corresponding to the film balance measurements, the BAM images demonstrate different shapes of the domains within the coexistence region of the liquid-condensed/liquid-expanded phase. The domain structures of the monolayers were visualized after Langmuir-Blodgett transfer on mica sheets by scanning force microscopy (SFM). From the SFM images it becomes obvious that small crystallites are formed for all investigated compounds; however, their molecular assembly is diverse for different enantiomers. Variations in the phase behavior can be correlated with interactions between the polar molecular moieties and the subphase and altered intermolecular interactions. Molecular modeling calculations were applied to elucidate the structural organization of these intermolecular interactions. Ab initio calculations of the minima conformers of (S,S,R)- and (S,S,S)-ethyl 4-fluoro-2,3-dihydroxystearates have been performed to predict with the HARDPACK program the two-dimensional lattice structure based on the P1 space group. These calculations showed that intermolecular hydrogen bridges are crucial for the interactions within and between the molecules.