https://pubs.rsc.org/en/content/articlepdf/2019/NP/C8NP00092A

Marine natural products.

Relaxor ferroelectrics were discovered almost 50 years ago among the complex oxides with perovskite structure. In recent years this field of research has experienced a revival of interest. In this paper we review the progress achieved. We consider the crystal structure including quenched compositional disorder and polar nanoregions (PNR), the phase transitions including compositional order-disorder transition, transition to nonergodic (probably spherical cluster glass) state and to ferroelectric phase. We discuss the lattice dynamics and the peculiar (especially dielectric) relaxation in relaxors. Modern theoretical models for the mechanisms of PNR formation and freezing into nonergodic glassy state are also presented.

Recent progress in relaxor ferroelectrics with perovskite structure

Gold salts and complexes have emerged in the past few years as the most powerful catalysts for electrophilic activation of alkynes toward a variety of nucleophiles under homogeneous conditions. In a simplified form, nucleophilic attack on the [AuL]-activated alkyne proceeds via π complexes 1 to give trans-alkenyl gold complexes of type 2 as intermediates (Scheme 1). This type of coordination is also a common theme in gold-catalyzed cycloisomerizations of enynes, in which the alkene function acts as the nucleophile. In the reaction of enynes with complexes of other transition metals, an Alder-ene cycloisomerization can take place by simultaneous coordination of the alkyne and the alkene to the metal followed by an oxidative cyclometalation. In contrast, this process does not occur for gold(I) since oxidative addition processes are not facile for this metal. 6 In addition, the [AuL] fragment, which is isolobal to H and HgL, adopts a linear coordination and binds to either the alkene or the alkyne. Thus, cycloisomerizations of enynes catalyzed by gold proceed by an initial coordination of the metal to the alkyne, and as illustrated in Scheme 2, the resulting complex 3 reacts with the alkene by either the 5-exo-dig or 6-endo-dig pathway to form the exoor endocyclopropyl gold carbene 4 or 5, respectively, as has been established with other electrophilic transition-metal complexes or halides MXn as catalysts. The proposed involvement of cyclopropyl metal carbenes of type 4 in the electrophilic activation of enynes by transition metals was first substantiated in reactions catalyzed by Pd(II), in which the initially formed cyclopropyl palladium carbenes undergo [4 + 2] cycloaddition with the double bond of the conjugate enyne. Strong evidence for the existence of cyclopropyl metal carbenes as intermediates was also obtained in the reaction of enynes bearing additional double bonds at the alkenyl chain with Ru(II) and Pt(II) catalysts. In these reactions, the cyclopropyl metal carbenes are trapped intramolecularly by the terminal alkene to give tetracycles containing two cyclopropanes. Gold(I) complexes usually surpass the reactivity shown by Pt(II) and other electrophilic metal salts and complexes for the activation of enynes. They are highly reactive yet uniquely selective Lewis acids that have a high affinity for π bonds. This high π-acidity is linked to relativistic effects, which reach a maximum in the periodic table with gold. However, on occasion, the stronger Lewis acidity of gold complexes can be detrimental in terms of selectivity and because of their low tolerance to certain functional groups. In these instances, the less-strongly Lewis acidic Pt(II) complexes could be the catalysts of choice. * To whom correspondence should be addressed. E-mail: aechavarren@ iciq.es. † Additional affiliation: Departamento de Quı́mica Orgánica, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain. Scheme 1 Chem. Rev. 2008, 108, 3326–3350 3326

Gold-catalyzed cycloisomerizations of enynes: a mechanistic perspective.

N-heterocyclic carbene analogues with low-valent group 13 and group 14 elements: syntheses, structures, and reactivities of a new generation of multitalented ligands.

Recently accumulated experimental evidence for aurophilic interactions in and between molecular gold(I) compounds and the results of pertinent theoretical calculations are reviewed for the period from 2007 to mid-2011. The influence of the intra- and intermolecular bonding contacts between the closed-shell metal centres, Au–Au, on the molecular and crystal structures, and the consequences of these effects for the chemical and physical properties of gold compounds are summarized for the various classes of mono- and polynuclear systems. The literature survey builds on the contents of previous reviews and relates new experimental and theoretical findings to earlier observations (353 references).

Aurophilic interactions as a subject of current research: an up-date

Tris(triphenylphosphinegold)oxonium salts

Nonlinear optical crystals of L-histidine salts

On the basis of high-resolution X-ray diffraction studies as well as quantum-chemical calculations of five carborane derivatives the peculiarities of electron density distribution functions have been analyzed. The data obtained permitted a deeper insight into the nature of unusual properties of the C-C bond in o-carborane and investigating intermolecular H ... H interactions in crystal. It was shown that such an approach allows estimating the values of lattice energy for the crystals of carboranes.

Carboranes: chemical concepts derived from the AIM study of the experimental and theoretical electron density distribution functions

Vinylidene complexes of transition metals : III. Derivatives of cyclopentadienyltricarbonyl rhenium with phenylvinylidene ligands. Crystal and molecular structure of Cp(CO)2Re[CC(Ph)C(Ph)CH2]Re(CO)2Cp

The structure of electric-field-induced ferroelectric phase of NaNbO3 has been studied by means of X-ray diffraction method. Crystal cell is orthorhombic (P21 ma) with parameters: a = 5.569. b = 7.790, c = 5.518 A, V = 239.38 A3, Z = 4. Field-induced phase transition mainly results in reversal of atomic shift directions relative to the cubic perovskite atomic positions in one half of initial orthorhombic cell. Increasing of NbO6 octahedra tilts and additional displacements of some oxygen atoms are accounted for electric field effect.

M. Yu. Antipin

Papers

Tris(triphenylphosphinegold)oxonium salts

Nonlinear optical crystals of L-histidine salts

Carboranes: chemical concepts derived from the AIM study of the experimental and theoretical electron density distribution functions

Vinylidene complexes of transition metals : III. Derivatives of cyclopentadienyltricarbonyl rhenium with phenylvinylidene ligands. Crystal and molecular structure of Cp(CO)2Re[CC(Ph)C(Ph)CH2]Re(CO)2Cp

Crystal structure of the electric-fieldinduced ferroelectric phase of NaNbO3