Relationships between the carbon-oxygen stretching frequencies of carboxylato complexes and the type of carboxylate coordination

Our aim is to propose a theory which goes beyond the classical formulation of thermodynamics. This is achieved by enlarging the space of basic independent variables, through the introduction of non-equilibrium variables, such as the dissipative fluxes appearing in the balance equations. The next step is to find evolution equations for the dissipative fluxes. Whereas the evolution equations for the classical variables are given by the usual balance laws, no general criteria exist concerning the evolution equations of the dissipative fluxes, with the exception of the restrictions imposed on them by the second law of thermodynamics.

https://iopscience.iop.org/article/10.1088/0034-4885/51/8/002/pdf

Extended irreversible thermodynamics

Preceramic polymers were proposed over 30 years ago as precursors for the fabrication of mainly Si-based advanced ceramics, generally denoted as polymer-derived ceramics (PDCs). The polymer to ceramic transformation process enabled significant technological breakthroughs in ceramic science and technology, such as the development of ceramic fibers, coatings, or ceramics stable at ultrahigh temperatures (up to 2000°C) with respect to decomposition, crystallization, phase separation, and creep. In recent years, several important advances have been achieved such as the discovery of a variety of functional properties associated with PDCs. Moreover, novel insights into their structure at the nanoscale level have contributed to the fundamental understanding of the various useful and unique features of PDCs related to their high chemical durability or high creep resistance or semiconducting behavior. From the processing point of view, preceramic polymers have been used as reactive binders to produce technical ceramics, they have been manipulated to allow for the formation of ordered pores in the meso-range, they have been tested for joining advanced ceramic components, and have been processed into bulk or macroporous components. Consequently, possible fields of applications of PDCs have been extended significantly by the recent research and development activities. Several key engineering fields suitable for application of PDCs include high-temperature-resistant materials (energy materials, automotive, aerospace, etc.), hard materials, chemical engineering (catalyst support, food- and biotechnology, etc.), or functional materials in electrical engineering as well as in micro/nanoelectronics. The science and technological development of PDCs are highly interdisciplinary, at the forefront of micro- and nanoscience and technology, with expertise provided by chemists, physicists, mineralogists, and materials scientists, and engineers. Moreover, several specialized industries have already commercialized components based on PDCs, and the production and availability of the precursors used has dramatically increased over the past few years. In this feature article, we highlight the following scientific issues related to advanced PDCs research: (1) General synthesis procedures to produce silicon-based preceramic polymers.
(2) Special microstructural features of PDCs.
(3) Unusual materials properties of PDCs, that are related to their unique nanosized microstructure that makes preceramic polymers of great and topical interest to researchers across a wide spectrum of disciplines.
(4) Processing strategies to fabricate ceramic components from preceramic polymers.
(5) Discussion and presentation of several examples of possible real-life applications that take advantage of the special characteristics of preceramic polymers. Note: In the past, a wide range of specialized international symposia have been devoted to PDCs, in particular organized by the American Ceramic Society, the European Materials Society, and the Materials Research Society. Most of the reviews available on PDCs are either not up to date or deal with only a subset of preceramic polymers and ceramics (e.g., silazanes to produce SiCN-based ceramics). Thus, this review is focused on a large number of novel data and developments, and contains materials from the literature but also from sources that are not widely available.

Polymer-Derived Ceramics: 40 Years of Research and Innovation in Advanced Ceramics

π-Bonding and the Lone Pair Effect in Multiple Bonds between Heavier Main Group Elements

The success of homogeneous catalysis can be attributed largely to the development of a diverse range of ligand frameworks that have been used to tune the behavior of various systems. Spectacular results in this area have been achieved using cyclic diaminocarbenes (NHCs) as a result of their strong σ-donor properties. Although it is possible to cursorily tune the structure of NHCs, any diversity is still far from matching their phosphorus-based counterparts, which is one of the great strengths of the latter. A variety of stable acyclic carbenes are known, but they are either reluctant to bind metals or they give rise to fragile metal complexes. During the last five years, new types of stable cyclic carbenes, as well as related carbon-based ligands (which are not NHCs), and which feature even stronger σ-donor properties have been developed. Their synthesis and characterization as well as the stability, electronic properties, coordination behavior, and catalytic activity of the ensuing complexes are discussed, and comparisons with their NHC cousins are made.

/pdf/stable-cyclic-carbenes-and-related-species-beyond-1d50zjyjzd.pdf

Stable Cyclic Carbenes and Related Species beyond Diaminocarbenes

Das aus Lithium-dihydrogenphosphid. DME(1) und Ethylformiat im Molverhaltnis 2 : 1 mit 87 proz. Ausbeute isolierte, flussige Lithium-formylphosphid. DME liegt als Lithoxy-methylidenphosphan. DME (1) mit einem an den Sauerstoff der Carbonylgruppe gebundenen, DME-komplexierten Lithium vor. Nach Rontgenstrukturanalysen an kristallinen Derivaten [5, 6] dimerisieren Verbindungen dieses Typs unter Ausbildung eines viergliedrigen LiOLiO-Ringes; die Auswertung der NMR-Spektren ergibt fur die an der PC-Gruppe E- und Z-konfigurierten Isomeren (δ1H P: 3,87 u. 4,49; 1JHP: 150,8 u. 136,5; δ1H C: 11,4 u. 10,05; 2JHP: 6,1 u. 81,2; 3JHH: 6,6 u. 13,9; δ31P: 38,6 u. 8,8; δ13C = P: 225,0 u. 215,4 ppm; 1JCP: 41,2 u. 65,0 Hz) des in 1,2-Dimethoxyethan gelosten Acylphosphids 1 ein Molverhaltnis von 1,86 : 1.



Lithium-bis(trimethylsilyl)phosphid. 1,6 THF(1) setzt sich in 1,2-Dimethoxyethan mit Dimethylcarbonat im Uberschus nach einem bisher nicht vollig geklarten Mechanismus zu Lithoxy-methylidinphosphan. 2DME (2) um. Die auch aus Lithium-dihydrogenphosphid. DME zugangliche Verbindung 2 kristallisiert monoklin in der Raumgruppe P21/n {a = 880,6(2); b = 1296,6(2); c = 1267,4(2)pm; β = 96,07(2)° bei - 100 ± 3°C; Z = 4}. Nach der Rontgenstrukturanalyse (Rw = 0,052) weist der zu 155,5 pm bestimmte PC-Abstand einen fur die Dreifachbindung typischen Wert auf, wahrend der CO-Abstand mit 119,8 pm gegenuber dem fur eine Einfachbindung gultigen Standard von 139 pm stark verkurzt ist. Mit Winkeln von 178,5° und 170,7° am Kohlenstoff-und Sauerstoffatom ist das P COLi-Fragment erwartungsgemas linear. Charakteristische NMR-Daten sind: δ31P −384,2; δ13C 166,6 ppm; 1JCP 41,5 Hz.



Acyl- and Alkylidenephosphines. XXXIII Lithoxy-methylidenephosphine · DME and -methylidynephosphine · 2DME — Syntheses and Structures



Lithium dihydrogenphosphide · DME(1) and ethyl formate in a molar ratio of 2 : 1 react in 1,2-dimethoxyethane to give liquid lithium formylphosphide · DME in 87% yield. Since lithium complexed by the chelate ligand DME is bound to the oxygen atom of the carbonyl group, the compound has to be considered as lithoxy-methylidenephosphine · DME (1). According to x-ray structure analyses of crystalline derivatives [5, 6], molecules of this type dimerize forming a four membered LiOLiO ring. Characteristic nmr-data show the presence of an E- and Z-isomer (δ1HP: 3.87 and 4.49; 1JHP: 150.8 and 136.5; δ1HC: 11.4 and 10.05; 2JHP: 6.1 and 81.2; 3JHH: 6.6 and 13.9; δ31P: 38.6 and 8.8; δ13CP: 225.0 and 215.4 ppm; 1JCP: 41.2 and 65.0 cps); in 1,2-dimethoxyethane an E : Z ratio of 1.86 : 1 is found.



In a similar reaction of lithium bis (trimethylsilyl)phosphide · 1.6 THF(1) with excess dimethyl carbonate lithoxy-methylidynephosphine · 2DME (2) is formed via an up to now poorly understood mechanism. The compound can also be prepared from lithium dihydrogenphosphide · DME; it crystallizes in the monoclinic space group P21/n {a = 880.6(2); b = 1296.6(2); c = 1267.4(2) pm; β = 96.07(2)° at −100 ± 3°C; Z = 4}. An x-ray structure analysis (Rw = 0.052) gives a PC distance of 155.5 pm which is typical for a triple bond. The CO bond length of 119.8 pm, however, is extremely short compared to the standard value of a single bond (139 pm). Angles of 178.5° and 170.7° at the carbon and oxygen correspond with the expected linear configuration of the PCOLi backbone of the molecule, Characteristic nmr-data are as follow: δ31P-384.2; δ13C 166.6ppm; 1Jcp 41.5 cps.

Acyl- und Alkylidenphosphane. XXXIII. Lithoxy-methylidenphosphan · DME und -methylidinphosphan · 2 DME — Synthese und Struktur

[Ga4{C(SiMe3)3}4] with a Tetrahedral Ga4 Skeleton

Bis(hypersilyl)tin and Bis(hypersilyl)lead, Two Electron‐Rich Carbene Homologs

Die Reaktion von Yttrium(III)-chlorid mit der dreifachen molaren Menge LiE(SiMe3)2 (E = N, CH) ergibt die entsprechenden Yttrium-Derivate. Yttrium-tris[bis(trimethylsilyl)amid] kristallisiert in der Raumgruppe P31c mit a = 1 636,3(2), c = 849,3(2) pm, Z = 2. Das Yttriumatom ist trigonal pyramidal koordiniert mit YN-Bindungslangen von 222 pm. Entlang der c-Achse sind Benzolmolekule eingeschlossen. Die Verbindung mit E = CH kristallisiert als (Et2O)3LiCl-Addukt in der monoklinen Raumgruppe P21/n mit a = 1 111,8(2), b = 1 865,2(6), c = 2598,3(9) pm, β = 97,41(3)° und Z = 4. Die Umsetzung von Yttrium-tris[bis(trimethylsilyl)amid] mit Benzonitril ergibt einen Bis(benzonitril)-Komplex, der in der triklinen Raumgruppe P1 mit a = 1173,7(2), b = 1210,3(2), c = 1912,4(3) pm, α = 94,37(1), β = 103,39(1), γ = 117,24(1)° und Z = 2 kristallisiert. Die Amido-Liganden sind aquatorial, die Benzonitril-Molekule axial koordiniert.



Bis(trimethylsilyl)amides and -methanides of Yttrium — Molecular Structures of Tris(diethylether-O)lithium-(μ-chloro)-tris[bis(trimethylsilyl)methyl]yttriate, solvent-free Yttrium Tris[bis(trimethylsilyl)amide] as well as the Bis(benzonitrile) Complex



The reaction of yttrium(III) chloride with the three-fold molar amount of LiE(SiMe3)2 (E = N, CH) yields the corresponding yttrium derivatives. Yttrium tris-[bis(trimethylsilyl)amide] crystallizes in the space group P31c with a = 1 636,3(2), c = 849,3(2) pm, Z = 2. The yttrium atom is surrounded trigonal pyramidal by three nitrogen atoms with YN-bond lengths of 222 pm. Benzene molecules are incorporated parallel to the c-axes. The compound with E = CH crystallizes as a (Et2O)3LiCl-adduct in the monoclinic space group P21/n with a = 1 111,8(2), b = 1 865,2(6), c = 2 598,3(9) pm, β = 97,41(3)° and Z = 4. The reaction of yttrium tris[bis(trimethylsilyl)amide] with benzonitrile yields the bis(benzonitrile) complex, which crystallizes in the triclinic space group P1 with a = 1 173,7(2), b = 1 210,3(2), c = 1 912,4(3) pm, α = 94,37(1), β = 103,39(1), γ = 117,24(1)° and Z = 2. The amido ligands are in equatorial, the benzonitrile molecules in axial positions.

/pdf/bis-trimethylsilyl-amide-und-methanide-des-yttriums-36czouatv2.pdf

Bis(trimethylsilyl)amide und -methanide des Yttriums - Molekülstrukturen von Tris(diethylether-O)lithium-(μ-chloro)-tris[bis(trimethylsilyl)methyl]yttriat, solvensfreiem Yttrium-tris[bis(trimethylsilyl)amid] sowie dem Bis(benzonitril)-Komplex

Wolfgang Schwarz

Papers

Acyl- und Alkylidenphosphane. XXXIII. Lithoxy-methylidenphosphan · DME und -methylidinphosphan · 2 DME — Synthese und Struktur

[Ga4{C(SiMe3)3}4] with a Tetrahedral Ga4 Skeleton

Bis(hypersilyl)tin and Bis(hypersilyl)lead, Two Electron‐Rich Carbene Homologs

Bis(trimethylsilyl)amide und -methanide des Yttriums - Molekülstrukturen von Tris(diethylether-O)lithium-(μ-chloro)-tris[bis(trimethylsilyl)methyl]yttriat, solvensfreiem Yttrium-tris[bis(trimethylsilyl)amid] sowie dem Bis(benzonitril)-Komplex

[Ga4{C(SiMe3)3}4] mit tetraedrischem Ga4‐Gerüst