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

Triggered by the resounding success of cisplatin, the past decades have seen tremendous efforts to produce clinically beneficial analogues. The recent achievement of oxaliplatin for the treatment of colon cancer should, however, not belie the imbalance between a plethora of investigated complexes and a very small number of clinically approved platinum drugs. Strategies opening up new avenues are increasingly being sought using complexes of metals other than platinum such as ruthenium or gallium. Based on the chemical differences between these metals, the spectrum of molecular mechanisms of action and potential indications can be broadened substantially. Other approaches focus on complexes with tumour-targeting properties, thereby maximizing the impact on cancer cells and minimizing the problem of adverse side effects, and complexes with biologically active ligands.

Antitumour metal compounds: more than theme and variations

This Review gives a comprehensive overview of the most topical weakly coordinating anions (WCAs) and contains information on WCA design, stability, and applications. As an update to the 2004 review, developments in common classes of WCA are included. Methods for the incorporation of WCAs into a given system are discussed and advice given on how to best choose a method for the introduction of a particular WCA. A series of starting materials for a large number of WCA precursors and references are tabulated as a useful resource when looking for procedures to prepare WCAs. Furthermore, a collection of scales that allow the performance of a WCA, or its underlying Lewis acid, to be judged is collated with some advice on how to use them. The examples chosen to illustrate WCA developments are taken from a broad selection of topics where WCAs play a role. In addition a section focusing on transition metal and catalysis applications as well as supporting electrolytes is also included.

Taming the Cationic Beast: Novel Developments in the Synthesis and Application of Weakly Coordinating Anions

The chemistry of the p-block elements is a huge playground for fundamental and applied work. With their bonding from electron deficient to hypercoordinate and formally hypervalent, the p-block elements represent an area to find terra incognita. Often, the formation of cations that contain p-block elements as central ingredient is desired, for example to make a compound more Lewis acidic for an application or simply to prove an idea. This review has collected the reactive p-block cations (rPBC) with a comprehensive focus on those that have been published since the year 2000, but including the milestones and key citations of earlier work. We include an overview on the weakly coordinating anions (WCAs) used to stabilize the rPBC and give an overview to WCA selection, ionization strategies for rPBC-formation and finally list the rPBC ordered in their respective group from 13 to 18. However, typical, often more organic ion classes that constitute for example ionic liquids (imidazolium, ammonium, etc.) were omitted, as were those that do not fulfill the – naturally subjective – “reactive”-criterion of the rPBC. As a rule, we only included rPBC with crystal structure and only rarely refer to important cations published without crystal structure. This collection is intended for those who are simply interested what has been done or what is possible, as well as those who seek advice on preparative issues, up to people having a certain application in mind, where the knowledge on the existence of a rPBC that might play a role as an intermediate or active center may be useful.

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Reactive p-block cations stabilized by weakly coordinating anions

In the first part of this review, the characteristics of Au–H bonds in gold hydrides are reviewed including the data of recently prepared stable organometallic complexes with gold(I) and gold(III) centers. In the second part, the reports are summarized where authors have tried to provide evidence for hydrogen bonds to gold of the type Au⋯H–X. Such interactions have been proposed for gold atoms in the Au(−I), Au(0), Au(I), and Au(III) oxidation states as hydrogen bonding acceptors and H–X units with X = O, N, C as donors, based on both experimental and quantum chemistry studies. To complement these findings, the literature was screened for examples with similar molecular geometries, for which such bonding has not yet been considered. In the discussion of the results, the recently issued IUPAC definitions of hydrogen bonding and the currently accepted description of agostic interactions have been used as guidelines to rank the Au⋯H–X interactions in this broad range of weak chemical bonding. From the available data it appears that all the intra- and intermolecular Au⋯H–X contacts are associated with very low binding energies and non-specific directionality. To date, the energetics have not been estimated, because there are no thermochemical and very limited IR/Raman and temperature-dependent NMR data that can be used as reliable references. Where conspicuous structural or spectroscopic effects have been observed, explanations other than hydrogen bonding Au⋯H–X can also be advanced in most cases. Although numerous examples of short Au⋯H–X contacts exist in the literature, it seems, at this stage, that these probably make only very minor contributions to the energy of a given system and have only a marginal influence on molecular conformations which so far have most often attracted researchers to this topic. Further, more dedicated investigations will be necessary before well founded conclusions can be drawn.

The gold–hydrogen bond, Au–H, and the hydrogen bond to gold, Au⋯H–X

Gold(I) and silver(I) complexes of 1-methyl-5-thio-tetrazole (1) have been prepared and the coordination chemistry of this ligand toward metal-phosphine frameworks has been explored. As indicated by IR and Raman data, ligand 1 is deprotonated and the resulted anion acts as a bidentate (S,N)-tetrazole-5-thiolato unit in the new gold(I) complexes, [Au(SCN4Me)(PPh3)] (2), [{Au(SCN4Me)}2(μ-dppm)] (3), and [{Au(SCN4Me)}2(μ-dppe)] (4), while it is coordinated only through the sulfur atom as its neutral tetrazole-5-thione form in the silver(I) derivative, [Ag(HSCN4Me)(PPh3)]2(OTf)2 (5). Further characterization of the new compounds was performed using multinuclear (1H, 13C, 31P, 19F) NMR spectroscopy, mass spectrometry, and DSC measurements. Single-crystal X-ray diffraction studies revealed basically linear P-M-S arrangements in complexes 3−5. The bidentate (S,N) coordination pattern results in a T-shaped (S,N)PAu core in 3 and 4, whereas, in 5, a similar coordination geometry is achieved in the dimer associatio...

Metallophilic bonding and agostic interactions in gold(I) and silver(I) complexes bearing a thiotetrazole unit.

The homogeneous mixture of anhydrous hydrogen fluoride aHF and antimony pentafluoride AsF5 is known as a superacidic system. The high acidity is derived from the formation of [H2F](+) [AsF6](-). No experimental evidence exists for the existence of the free acid molecule HAsF6. The reaction of trimethylsilyl N,N-dimethylcarbamate in the binary system aHF/AsF5 led to decomposition of trimethylsilyl N,N-dimethylcarbamate at -50 °C to dimethylammonium hexafluoridoarsenate and cocrystallization of HAsF6. The single-crystal X-ray structure displays an HAsF6 molecule involved in an asymmetric hydrogen bridge to the hexafluoridoarsenate anion. As a result of the incalculable situation in the crystal lattice, the molecular structure of HAsF6 is calculated by quantum chemical structure optimization of the extreme cases of [FHF-AsF5](-) (strong hydrogen bond) and HAsF6 (no hydrogen bond) at the PBE1PBE/6-311G(3df,3pd) level of theory.

The existence of hexafluoroarsenic(V) acid.

Acetamide and thioacetamide react with the superacid solutions HF/MF5 (M = As, Sb) under formation of the corresponding salts [H3CC(OH)NH2]+MF6– and [H3CC(SH)NH2]+MF6– (M = As, Sb), respectively. The reaction of DF/AsF5 with acetamide and thioacetamide lead to the corresponding deuterated salts [H3CC(OD)ND2]+AsF6– and [H3CC(SD)ND2]+AsF6–, respectively. The salts are characterized by vibrational and NMR spectroscopy, and in the case of [H3CC(OH)NH2]+AsF6– and [H3CC(SH)NH2]+AsF6– also by single-crystal X-ray analyses. The [H3CC(OH)NH2]+AsF6– (1) salt crystallizes in the triclinic space group P with two formula units per unit cell, and the [H3CC(SH)NH2]+AsF6– (2) salt crystallizes in the monoclinic space group P21/c with four formula units per unit cell. In both crystal structures three-dimensional networks are observed which are formed by intra- and intermolecular N–H···F and O–H···F or S–H···F hydrogen bonds, respectively. For the vibrational analyses, quantum chemically calculated spectra of the cations [H3CC(OH)NH2·3HF]+ and [H3CC(SH)NH2·2HF]+ are considered.

The Protonation of Acetamide and Thioacetamide in Super­acidic Solutions: Crystal Structures of [H3CC(OH)NH2]+AsF6– and [H3CC(SH)NH2]+AsF6–

Novel bright-blue luminescent complex of Zn(II) with 7-amino-methylchromen-4-one: Synthesis, photophysical properties and DFT calculations

The novel refrigerant 2,3,3,3-tetrafluoropropene (HFO-1234yf) is discussed as a replacement for 1,1,1,2-tetrafluoroethane (R-134a) due to its low global warming potential. Although it may therefore have great potential for use on a large scale, no structural data and only a fewvibrational data of the compound are known.We describe low-temperature X-ray structure analysis, vibrational spectra and combustion properties of 2,3,3,3-tetrafluoropropene. The experimental data are compared with the results of theoretical calculations. Furthermore the basic combustion properties have been investigated. Graphical Abstract Structure and Properties of 2,3,3,3-Tetrafluoropropene (HFO-1234yf)

https://www.degruyter.com/downloadpdf/j/znb.2014.69.issue-4/znb.2014-4017/znb.2014-4017.xml

Karin Lux

Papers

Metallophilic bonding and agostic interactions in gold(I) and silver(I) complexes bearing a thiotetrazole unit.

The existence of hexafluoroarsenic(V) acid.

The Protonation of Acetamide and Thioacetamide in Superacidic Solutions: Crystal Structures of [H3CC(OH)NH2]+AsF6– and [H3CC(SH)NH2]+AsF6–

Novel bright-blue luminescent complex of Zn(II) with 7-amino-methylchromen-4-one: Synthesis, photophysical properties and DFT calculations

Structure and Properties of 2,3,3,3-Tetrafluoropropene (HFO-1234yf)

Karin Lux

Papers

Metallophilic bonding and agostic interactions in gold(I) and silver(I) complexes bearing a thiotetrazole unit.

The existence of hexafluoroarsenic(V) acid.

The Protonation of Acetamide and Thioacetamide in Super­acidic Solutions: Crystal Structures of [H3CC(OH)NH2]+AsF6– and [H3CC(SH)NH2]+AsF6–

Novel bright-blue luminescent complex of Zn(II) with 7-amino-methylchromen-4-one: Synthesis, photophysical properties and DFT calculations

Structure and Properties of 2,3,3,3-Tetrafluoropropene (HFO-1234yf)

The Protonation of Acetamide and Thioacetamide in Superacidic Solutions: Crystal Structures of [H3CC(OH)NH2]+AsF6– and [H3CC(SH)NH2]+AsF6–