Design and Study of Structural Linear and Nonlinear Optical Properties of Chiral [Fe(phen)] Complexes.

The dependence of nonlinear optical properties upon the spin state in molecular switches is still an unexplored area. Chiral [Fe( phen)] complexes are excellent candidates for those studies because they are expected to show nonlinear optical properties of interest and at the same time show photoconversion to a short-lived metastable high-Spin state by ultrafast optical pumping. Herein, we present the synthesis, crystallographic, and spectroscopic comparison of chiral [Fe( phen)] complexes obtained with chiral anions, a new lipophilic derivative of the D-symmetric (As(tartrate)), and D-symmetric tris(catechol)phosphate(V) (TRISCAT), tris(catechol)arsenate(V) (TRISCAS), and 3,4,5,6-tetrachlorocatechol phosphate(V) (TRISPHAT).

HUG and SQUEEZE: using CRYSTALS to incorporate resonant scattering in the SQUEEZE structure-factor contributions to determine absolute structure.

The resonant-scattering contributions to single-crystal X-ray diffraction data enable the absolute structure of crystalline materials to be determined. Crystal structures can be determined even if they contain considerably disordered regions because a correction is available via a discrete Fourier transform of the residual electron density to approximate the X-ray scattering from the disordered region. However, the corrected model cannot normally account for resonant scattering from atoms in the disordered region.

Absolute structure determination using CRYSTALS.

A study of post-refinement absolute structure determination using previously published data was carried out using the CRYSTALS software package. We show that absolute structure determination may be carried out optimally using the analyses available in CRYSTALS, and that it is not necessary to have the separate procedures absolute structure determination and no interest in absolute structure as proposed by Flack [Chimia (2014), 68, 26-30].

Methods of space-group determination - a supplement dealing with twinned crystals and metric specialization.

Tables for the determination of space group for single crystals, twinned crystals and crystals with a specialized metric are presented in the form of a spreadsheet for use on a computer. There are 14 tables, one for each of the Bravais-lattice types. The content of the tables is arranged so that at the intersection of rows, displaying the conditions for reflection, and of columns, displaying the Laue and crystal classes, one finds those space groups compatible with the observed Bravais-lattice type, the conditions for reflection and the Laue and crystal classes.

Absolute-structure determination: past, present and future.

Single-crystal X-ray crystallography is the major analytical technique in use today for absolute-configuration determination. The origins of absolute-structure determination, starting from Friedel's 1913 proof that the intensities of the opposites hkl and hkl are identical, are traced. The important structural principles derived from the study of chiral, but pseudo-mirror symmetric, methyprylon are described.

Absolute-Structure Determination: Past, Present and Future.

Single-crystal X-ray crystallography is the major analytical technique in use today for absolute-configuration determination. The origins of absolute-structure determination, starting from Friedel's 1913 proof that the intensities of the opposites hkl and hkl are identical, are traced. The important structural principles derived from the study of chiral, but pseudo-mirror symmetric, methyprylon are described.

TiGePt--a study of Friedel differences.

The X-ray single-crystal diffraction intensities of the intermetallic compound TiGePt were analysed. These showed beyond doubt that the crystal structure is non-centrosymmetric. The analysis revolves around the resonant-scattering contribution to differences in intensity between Friedel opposites hkl and \bar h\bar k\bar l.

Absolute-structure reports.

All the 139 noncentrosymmetric crystal structures published in Acta Crystallographica Section C between January 2011 and November 2012 inclusive have been used as the basis of a detailed study of the reporting of absolute structure. These structure determinations cover a wide range of space groups, chemical composition and resonant-scattering contribution. Defining A and D as the average and difference of the intensities of Friedel opposites, their level of fit has been examined using 2AD and selected-D plots.

Use of intensity quotients and differences in absolute structure refinement.

Several methods for absolute structure refinement were tested using single-crystal X-ray diffraction data collected using Cu Kα radiation for 23 crystals with no element heavier than oxygen: conventional refinement using an inversion twin model, estimation using intensity quotients in SHELXL2012, estimation using Bayesian methods in PLATON, estimation using restraints consisting of numerical intensity differences in CRYSTALS and estimation using differences and quotients in TOPAS-Academic where both quantities were coded in terms of other structural parameters and implemented as restraints. The conventional refinement approach yielded accurate values of the Flack parameter, but with standard uncertainties ranging from 0.15 to 0.

Analysing Friedel averages and differences.

Various practical applications of the average (A) and difference (D) of Friedel opposites are described. Techniques based on the resonant-scattering contribution to Friedel differences are applied to see whether a crystal is centrosymmetric or not, and to determine the point group of the crystal. For the validation of a structural study, plots of A(obs) against A(model), and D(obs) against D(model) are used extensively.

Non-racemic (scalemic) planar-chiral five-membered metallacycles: routes, means, and pitfalls in their synthesis and characterization.

This critical review provides a systematic classification of the synthetic routes to planar-chiral five-membered metallacycles into several routes, namely C-H bond activation, oxidative addition, transmetallation and optical resolution. As a characteristic of these bulk compounds is that they are synthesized as binary mixtures of enantiomers in proportions varying from the racemate to enantiopure, a review of absolute-configuration determination of the title planar-chiral scalemates is presented. This review is of interest to organic and organometallic synthetic chemists involved in asymmetric synthesis (97 references).

Selectivity enhancement in the Rh(II)-catalyzed cyclopropanation of styrene with (silanyloxyvinyl)diazoacetates.

The cyclopropanation of styrene with (silanyloxyvinyl)diazoacetates proceeds with exceptional diastereo- and enantioselectivity in the presence of chiral Rh(II) catalysts. 1,8-Naphthoyl-protected amino acids are the most effective Rh(II) ligands for these transformations. [reaction--see text]