Decamethylsilicocene: Synthesis, Structure, Bonding and Chemistry

Bigger is better: Sterically hindered dialkyl ureas undergo nucleophilic substitution at dramatically faster rates than their less hindered counterparts (see scheme). Steric decompression upon the formation of an intermediate isocyanate can explain this counterintuitive behavior. These hindered ureas can be considered as masked reagents that liberate reactive isocyanates in situ. Detailed facts of importance to specialist readers are published as "Supporting Information". Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Review: 50 refs.

Hexagonal bronze oxides are represented by the chemical formula AxMO3, where A is an electropositive element such as alkali metal or alkaline earth metal and M is a transition metal such as Mo, W, or Re. We report the first synthesis of a tellurium-containing rhenium bronze oxide, Te0.30ReO3. The compound has an orthorhombic crystal structure, with tellurium located within the ab plane along with rhenium and oxygen, and planarly coordinated to three oxygen atoms. Electron localization function (ELF) analysis revealed that tellurium has two ELF attractors above and below the TeO3 plane and that the ELF structure around tellurium is similar to that of ClF3. Based on valence shell electron pair repulsion theory, two equatorial positions in the coordination structure of the trigonal bipyramid are occupied by lone pairs and the remaining three positions are occupied by oxygen. Electron density calculations demonstrated that the unique coordination structure of the tellurium arises from the hybridization of the 5s and 5p orbitals of tellurium with the 2p orbitals of oxygen.

1. The lone pairs on the amino nitrogen atoms in N-nitro compounds with different configurations for the N atom and various substituents have been characterized in terms of localized MO's. 2. The variation of the energy of the localized lone pair on the N atom as a function of the position of the unoccupied frontier orbital of the substituent in various conformers has been analyzed.

The isolation and characterization of thermally stable diaminocarbenes and diaminosilylenes has reawakened interest in the low-coordinated compounds of group-14 elements. The existence of these species is presumably due to interactions between the free electron pairs on the nitrogen atoms and the carbene carbon atom or the silicon atom. The present review is mainly concerned with the heavier analogues R2Ge:, R2Sn:, and R2Pb:, systems without intramolecular donor stabilization that owe their existence principally to steric shielding by the voluminous alkyl or aryl groups R. Dimerizations of these electron-sextet molecules give rise to the double-bond systems of the digermenes, distannenes, and diplumbenes; the latter species have for a long time been considered as being incapable of existence. The properties of these molecules are compared with the results of quantum chemical calculations. A separate section is devoted to the isomers of Si4R6, which include novel tetrasilacyclobutenes and the diene analogues, the tetrasilabuta-1,3-dienes.

Quantum-chemical calculations of the geometries and electronic structures of a series of dicoordinated silicon compounds SiL(2), in which L is a five-membered cyclic species suggest that the molecules are divalent silicon(0) compounds that possess two L-->Si donor-acceptor bonds and two lone-pair MOs with pi and sigma symmetry at silicon. The classification as a dicoordinate silicon compound with L-->Si<--L donor-acceptor bonds applies not only to molecules in which L is an N-heterocyclic carbene but also when L is a cyclic silylene. The recently synthesized "trisilaallene" (S. Ishida, T. Iwamoto, C. Kabuto, M. Kira, Nature 2003, 421, 725), which has a bending angle of 136.5(o) for the central moiety, and which was written as Si=Si=Si, is probably better considered as a divalent silicon(0) compound. We suggest the name silylones for the latter species in analogy to silylenes which identify divalent Si(II) compounds. This bonding interpretation explains the theoretically predicted large values for the first and second proton affinities and for the large bond dissociation energies for one and two BH(3) ligands. The calculations predict that the first protonation of the divalent silicon(0) compounds takes place at the pi lone-pair orbital, which yields protonated silylones that have a pyramidal arrangement of the ligands at the central tricoordinate silicon atom. Silylones SiL(2) could be interesting ligands for transition-metal compounds. The calculated structures and bonding situation of the analogous carbon compounds are also reported.

Phenytoin from antiepileptic to covid-19: Synthesis, crystal structure, DFT, HSA, MEP and green biological study of phenytoin derivative as potential covid-19 drug candidates

Iminosulfane(phosphane)carbon(0) derivatives (iSPCs; Ar3 P→C←SPh2 (NMe); Ar=Ph (1), 4-MeOC6 H4 (2), 4-(Me2 N)C6 H4 (3)) have been successfully synthesized and the molecular structure of 3 characterized. Carbone 3 is the first thermally and hydrolytically stable carbone stabilized by phosphorus and sulfur ligands. DFT calculations reveal the electronic structures of 1-3, which have two lone pairs of electrons at the carbon center. First and second proton affinity values are theoretically calculated to be in the range of 286.8-301.1 and 189.6-208.3 kcal mol(-1) , respectively. Cyclic voltammetry measurements reveal that the HOMO energy levels follow the order of 3>2>1 and the HOMO of 3 is at a higher energy than those of bis(chalcogenane)carbon(0) (BChCs). The reactivities of these lone pairs of electrons are demonstrated by the C-diaurated and C-proton-aurated complexes. These results are the first experimental evidence of phosphorus- and sulfur-stabilized carbones behaving as four-electron donors. In addition, the reaction of hydrochloric salts of the carbones with Ag2 O gives the corresponding Ag(I) complexes. The resulting silver(I) carbone complexes can be used as carbone transfer agents. This synthetic protocol can also be used for moisture-sensitive carbone species.

NMR, FT-IR, FT-Raman, UV spectroscopic, HOMO–LUMO and NBO analysis of cumene by quantum computational methods

The analysis of time-resolved S1–Sn absorption spectra in the 0–500 ps range, together with quantum-chemical calculations, uncovered a photorecoordination reaction for the following complexes of CD6 (a bis(aza-18-crown-6)-containing dienone (ketocyanine dye) with a central cyclohexanone fragment): CD6·(Mn+)2 (M = Ba2+, Sr2+, Ca2+, K+). This process takes place over hundreds of fs and involves an “axial-to-equatorial” conformational change, with the solvation shell undergoing rearrangement as well. The characteristic photorecoordination times were found to correlate with the stability constants of the complexes. The lifetimes for the fluorescent states of CD6 and its complexes, namely CD6·(Mn+)2 (M = Ba2+, Sr2+, Ca2+, K+), are different; ergo, there is no photoejection of crowned cations into the solution. The calculated conformational profiles in the ground and excited states indicate the presence of an energy barrier in this process. A general photorelaxation pathway is suggested for CD6·(Mn+)2 metal complexes (M = Ba2+, Sr2+, Ca2+, K+). The coordination of cations via the carbonyl moiety in the dye molecule promotes photorecoordination of metal cations in the cavities of the azacrown ether fragment. Photorecoordination times were found to correlate with the degree of conjugation between the lone pairs in the N atoms of the aza-18-crown-6 ether and the π subsystem in the dye molecules (established for the CD4–CD6 metal–dye complex series, where CD4 and CD5 are related dyes with central cyclobutanone and cyclopentanone fragments, respectively).

Water scarcity emerges as a critical global challenge, with the purity of aquatic ecosystems intimately linked to ammonium concentrations. The removal of ammonium ions (NH4+) is vital for mitigating ammonium contamination and promoting the sustainability of nitrogenous resources. Capacitive deionization (CDI) utilizing organic electrodes offers a promising electrochemical solution through a unique “ion coordination” mechanism; however, its efficacy is hindered by the presence of electrochemically inert units within the molecular framework for ion capture. Here, we introduce a rod-shaped DHPZ organic compound designed as a CDI electrode, distinguished by four imine rings and lone pair electrons in sp2 orbitals. This configuration establishes a hybridized sp2-N framework that exhibits significant electron delocalization and an exceptionally low HOMO–LUMO gap of 1.18 eV, enhancing its affinity for fast, stable, and efficient NH4+ capture. The DHPZ-based CDI device achieves an impressive NH4+ removal capacity of 136.6 mg g−1 at 1.2 V, a swift removal rate of 4.55 mg g−1 min−1, and outstanding regeneration (95.76% retention after 200 cycles), positioning it among the leading technologies in current CDI devices for NH4+ adsorption. Furthermore, we have developed interconnected CDI devices for targeting NH4+ removal from real wastewater, highlighting a sustainable and innovative approach to water remediation.

Long wave infrared (LWIR) birefringent crystals are essential for infrared optical applications but such materials are rarely reported due to the requirements of large birefringence and wide infrared transmission range. This study proposes a facile route to create new LWIR birefringent crystal by oxygenation strategy in halides with cations containing lone pair electrons. Given the tendency of such cations to form holodirected geometry, a divalent oxygen was introduced to substitute the monovalent halogen to decrease the coordination number and activate the lone pair electrons. Our efforts in Rb+‐Sb3+‐Cl− system result three new structures, namely, Rb13Sb8Cl37, Rb3Sb2OCl7 and Rb2Sb2OCl6. The holodirected SbCl6 in Rb13Sb8Cl37 has been successfully translated to hemidirected SbOCl4 in Rb3Sb2OCl7 and Rb2Sb2OCl6, which are the first examples in alkali metal antimony(III) oxyhalides. The birefringence of Rb2Sb2OCl6 reached to 0.191@550 nm, which is 11.2 times that of Rb13Sb8Cl37 (0.017@550 nm). Large‐sized crystal of Rb2Sb2OCl6 have been successfully grown (6×6×2 mm3). It can exhibit good transmission performance in the range of 0.4–13.5 μm, indicating its potential as a promising LWIR birefringent crystal. Our research not only opens up a new material system – alkali metal antimony(III) oxyhalides, but also provides a new strategy to create LWIR birefringent crystals.

Studies of a wide range of intramolecularly five-co-ordinated silicon compounds with chelating nitrogen donors have been made, with a view to obtaining further information on the details of nucleophilic substitution reactions at silicon. The crystal structure of 2-(dimethylaminomethyl)-phenyl-1 -naphthylsilane has been determined by single-crystal X-ray diffraction (R= 0.074 for 564 observed reflections). Crystals are tetragonal, space group I, with Z= 8 in a unit cell of dimensions a= 21.845(5) and c= 7.119(2)Å. The central silicon atom shows essentially trigonal-bipyramidal co-ordination, with the axial positions occupied by the naphthyl group and the donor nitrogen atom, and the two hydrogen atoms occupying equatorial positions. Comparison with other structures reported in the literature shows that this geometry, always with axial disposition of the donor atom, is generally adopted by molecules of this type. Silicon-29, 19F, and 1H n.m.r. spectroscopic data for similar compounds with varying substituents on the silicon atom show that the same geometry is adopted by these intramolecularly co-ordinated species in solution.

Some new pentacoordinated anionic spirobicyclic silicon(IV) compounds containing the isothiocyanato group, [(C6H4O2)2SiNCS]− M+; [M=K(1), Na(2), K(18-crown-6)(3), NH4(4)], have been prepared by the activation of the silicon centre of tetracoordinated silances by NCS− ion. These compounds have been characterised by elemental analyses, IR, multinuclei (1H,13C and29Si) NMR and FAB mass spectroscopy. Synthesis of stable spirobicyclic hexacoordinated dianionic siliconates with six-and seven-membered oxygen-containing rings around silicon atoms, [(C7H4O3)2 Si(NCS)2]2−2B+; (B=PyH(5), 3-mepyH(6)4-mePyH(7)] and [(C8H4O4)2Si(NCS)2]2−2[3-mepyH]+(8), are also described. The complexes5–8 have been achieved from the reactions of appropriate cationic five-coordinate silicon (IV) intermediate with salicylic acid (5–7) or phthalic acid (8). The resulting compounds have been characterised by elemental analyses. IR multinuclei (1H,13C,29Si) NMR spectral data.

Thermolysis of bis(pentacoordinate) silicon compound bearing two 1-fluorodisilanyl units at 4- and 8-positions on 1,5-bis(dimethylamino)naphthalene ring: construction of disilapyrene skeleton and cyclophane-shaped siloxane dimer