Solutions containing hydrofluoric acid (HF), chloric acid (HClO3), and hydrochloric acid (HCl) are investigated as novel acidic, nitrogen oxide (NOx)-free mixtures for wet-chemical etching of silicon wafer surfaces. HF-HClO3-H2O solutions exhibit etching rates of only up to 0.12 µm min‑1 at room temperature, as the oxidizing agent chlorate (ClO3-) is not very reactive. In contrast, aqueous HF-HClO3-HCl mixtures show etching rates of up to 10.78 µm min‑1 at room temperature, as chlorine (Cl2) and chlorine dioxide (ClO2) are formed, which also serve as oxidizing agents. Depending on the HCl content isotropic or anisotropic etching behavior occurs, resulting in polished or textured surfaces with upright, inverted, and rounded pyramids. The solutions and gas phases were analyzed using Raman spectroscopy. In addition, the resulting silicon surfaces were analyzed using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM).

The review highlights the advances of coordination chemistry in the domain of homo and heteronuclear metal-organic architectures derived from compartmental ligands (CLs). It summarizes key developments reported up to 2024, focusing on the synthetic strategies and the structural characteristics of coordination complexes and frameworks derived from Schiff base CLs. Particular attention is given to how factors such as compartment size, flexible arms, skeletal length, and auxiliary ligands influence the assembly of molecular structures. The review also briefly discusses the suitability of CL-derived multinuclear homo- and heteronuclear complexes for various applications, highlighting their relevance to areas such as single-molecule magnets, catalysis, and materials. Overall, this report offers valuable insights into the design of new ligating frameworks aimed at exploiting the synergistic behaviour of multiple metal centers confined within well-defined compartments.

A series of 1,7-disubstituted tetradecaphenylheptasilanes was synthesized to prepare model compounds for terminally functionalized perphenylpolysilanes. Starting from perphenylheptasilane Ph-(SiPh2)7-Ph, two phenyl groups were substituted with triflate. The resulting triflated heptasilane TfO-(SiPh2)7-OTf was then reacted with alkali metal halides to produce the 1,7-dihalogenides X-(SiPh2)7-X (where X = F, Cl, Br, I). Additionally, an alternative synthetic route to the chlorine derivative was developed by reacting Li-(SiPh2)5-Li with Cl2SiPh2, a method that had previously only been briefly mentioned in the literature. All products were subsequently reacted with LiAlH4, and in the case of the triflate compound with (iBu)2AlH, to obtain the 1,7-dihydrogen derivative H-(SiPh2)7-H. Nearly complete conversion to the hydride was observed, except when fluorine or chlorine substituted heptasilanes were used. The compounds were analyzed using IR-, Raman-, 29Si-, 19F-, and 1H-NMR spectroscopy, as well as melting point determination. Single crystal structure analyses of H-(SiPh2)7-H, Br-(SiPh2)7-Br, and I-(SiPh2)7-I were performed, supporting the presented results.

In this work, we present a novel approach to metal-assisted chemical etching (MACE) of silicon using copper(II) ions in mixtures of hydrofluoric acid (HF) and hydrochloric acid (HCl) without the addition of an oxidizing agent. While the standard redox potential of Cu2+ is typically considered too low for silicon oxidation in HF, we observed anisotropic etching, yielding pyramidal and inverted pyramidal surface structures, with etching rates up to 14.18 mu m h-1. The presence of HCl is crucial as it prevents the significant copper film deposition seen in HCl-free solutions. Our analysis, including cyclic voltammetry and XPS, reveals that the Cu2+ ions act as a catalyst for silicon oxidation by dissolved oxygen, O2. The HCl stabilizes the reduced species, Cu+, as chloro-complexes of copper(I), maintaining the copper in solution and enabling a divalent dissolution mechanism. This work demonstrates a unique MACE regime where the metal catalyst remains dissolved, providing new insights into the complex mechanisms of silicon dissolution.

Based on a Q-group free two-component sol-gel formulation, which was very successfully used to prepare different xerogel materials - especially coatings - for various applications, we set out to increase the mechanical flexibility and durability via the introduction of D-groups, i.e. -Si(CH3)2O- units. The tailor-made sol-gel-precursor 1,3,3,5-tetramethyl-1,1,5,5-tetraethoxytrisiloxane (TMTETS) was prepared from dimethylsilanediol (CH3)2Si(OH)2 and chlorodiethoxymethylsilane (CH3)ClSi(OC2H5)2 and then converted into sols and gels. For comparison with these TMTETS-derived systems, we prepared D-group modified sols and gels via standard alkoxysilane hydrolysis-condensation synthesis that involved methyltriethoxysilane (MTES) and dimethyldiethoxysilane (DMDES) as precursors in 2 : 1 molar ratio. The obtained xerogels were structurally analysed by solid-state NMR investigations. The mechanical properties were studied after deposition of xerogel films with thicknesses of about 5 to 10 micrometers and compared with corresponding D-unit free coatings. Leaching studies of the TMTETS- and MTES+DMDES-derived xerogels by ethanol, investigated by 29Si NMR spectroscopy and GC-MS, revealed that while both gels leached octamethylcyclotetrasiloxane (D4) in trace amounts, the release from the MTES+DMDES-derived gel was higher, and the overall distribution patterns of other D-monomers differed. In the course of this study, an efficient synthesis route for dimethylsilanediol by CO2-catalyzed hydrolysis of DMDES was established, and for a better understanding of the incorporation of D-units, the condensation behaviour of dimethylsilanediol was investigated in different solvents.

Aqueous solutions of hydrofluoric acid (HF) and perbromic acid (HBrO4) are investigated as nitrogen oxide (NOx)-free mixtures for wet-chemical etching of (100) silicon wafer surfaces. For the high amount of HBrO4 needed in this work, an improved synthesis for HBrO4 with less consumption of fluorine (F2) is reported. We investigated etching mixtures containing HF in the range of 14-22 mol L-1 and HBrO4 in the range of 0.25-0.5 mol L-1. These mixtures are polishing silicon surfaces with high etch rates of up to 2 & micro;m min-1 at room temperature. Increasing the temperature leads to higher etch rates up to 7.8 & micro;m min-1. Resulting morphologies on treated silicon surfaces are investigated by scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results indicate a reaction pathway with silicon surfaces oxidized by inserting oxygen into Si-Si-bonds by HBrO4. The reduction of HBrO4 leads to multiple Br-species in equilibria, thus altering the etching behavior and leading to different surface morphologies.

Alkaline, wet-chemical silicon etching is an essential part in the manufacturing of silicon solar cells, because the anisotropy of the etching process enables texturization of the wafer surface. Anisotropic etching in alkaline systems is traditionally attributed to the nucleophilic attack of OH- on Si-H, forming a pentacoordinated Si-atom as a transition state. This leads to (111) crystal planes being etched much slower, thus generating pyramidal structures on (100) wafer surfaces. In aqueous HF solutions with halogens as oxidants, similar surface structures are observed, even though the reactants are completely different from the alkaline solutions. The data show that in HF-HCl-Cl2 solutions, the presence of Cl3 - plays a decisive role. Trihalide ions and hydroxide ions are very similar: both are negatively charged, nucleophilic and relatively small. This suggests a similar reaction behavior. In this article, it is shown that trihalides in acidic wet-chemical silicon etching systems represent a functional analogy to hydroxide ions in alkaline systems and are responsible for anisotropic etching. The findings are supported by spectroscopic and surface analytical data.

Wet chemical etching processes are an essential part of silicon treatment in the photovoltaic and semiconductor industry. A commonly used system is HF-HNO3. In order to avoid NO x -formation, silicon can also be etched with HF-(HCl)-Cl2-mixtures. Thorough investigations into perchloric acid indicate that even Si-H terminated surfaces are inert against this very strong oxidizing agent.

Solutions containing hydrofluoric acid (HF) and bromic acid (HBrO 3 ) are investigated as nitrogen oxide (NO x )‐free mixtures for wet‐chemical etching of (100) silicon wafer surfaces. Isotropic etching behavior with high dissolution rates of up to 10 µm min −1 is observed at room temperature, leading to polished surfaces. Anisotropic etching is observed when bromine (Br 2 ) is added to HF‐HBrO 3 solutions. Therefore, monocrystalline (100) silicon wafer surfaces are covered with random upright pyramids with edge lengths of about 5 µm. The etch rate is strongly dependent on the concentration of HBrO 3 . Silicon surfaces are analyzed by scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The gas phase is analyzed using Raman and infra red (IR) spectroscopy. The oxidation of the silicon surface by bromic acid likely takes place via oxygen insertion into the rearward silicon bonds. During etching, multiple active Br‐species are formed which alter the etching behavior.

Reactions of a series of trichlorosilanes RSiCl3 (R = Me, tBu, Bn, Ph, Vi, Cl) and the tris(trimethylsilyl) derivative of nitrilotris(methylenephenylphosphinic) acid (NTPA(SiMe3)3) proceeded with transsilylation (release of Me3SiCl) and afforded the respective silatrane-like cage compounds of the type N(CH2P(=O)(Ph)O)3SiR (NTPA (SiR), R = Me, tBu, Bn, Ph, Vi, Cl). According to single-crystal X-ray diffraction analyses (for R = Me, tBu, Bn, Ph, Vi) and DFT analyses (R = Me, Cl), these compounds accommodate [4+1]-coordinate Si atoms in a capped tetrahedral coordination sphere. The environment of the N atom is trigonal pyramidal, with the lone pair pointing toward the Si atom with N center dot center dot center dot Si distances in the range of 2.7451(12) & Aring; (R = Bn) to 2.827(5) & Aring; (R = tBu). For R = Cl, N center dot center dot center dot Si distances were calculated at the PBE0 level to be 2.748 & Aring; in the isolated molecule, 2.620 & Aring; in a chloroform solvate of the type NTPA(SiCl)(HCCl3)3. Analyses of the Intrinsic Bond Orbitals (IBOs) and Natural Localized Molecular Orbitals (NLMOs) revealed polarization of the N-located lone pair toward Si, with only marginal orbital contribution of the Si atom in the resultant NLMO (ca. 1.4% for R = hydrocarbyl, 2.2% for R = Cl, 3.3% for R = Cl(HCCl3)3).

Thorough investigations into perchloric acid indicate that even Si–H terminated surfaces are inert against this very strong oxidizing agent.

A new, less hazardous synthetic pathway to chloropentaphenyldisilane, ClSi2Ph5, has been developed. Starting from this compound and lithium diorganophosphides, the two previously unknown diorganophosphanyldisilanes (diphenylphosphanyl)pentaphenyldisilane, Ph2PSi2Ph5, and (di-iso-propylphosphanyl)pentaphenyldisilane, (i-Pr)2PSi2Ph5, were prepared. To compare these compounds with the corresponding monosilanes, the known (diphenylphosphanyl)triphenylsilane, Ph2PSiPh3, and the unknown (di-iso-propylphosphanyl)triphenylsilane, (i-Pr)2PSiPh3, were prepared, too. The former was prepared via new synthetic routes. The compounds were characterized with IR-, Raman-, 31P-, 29Si-, and 1H-NMR spectroscopy and melting point determination. Single crystal structure analyses of ClSi2Ph5 and (i-Pr)2PSiPh3 were carried out and confirm the results presented.

Solutions containing hydrofluoric acid (HF) and bromic acid (HBrO3) are investigated as nitrogen oxide (NOx)-free mixtures for wet-chemical etching of (100) silicon wafer surfaces. Isotropic etching behavior with high dissolution rates of up to 10 mu m min-1 is observed at room temperature, leading to polished surfaces. Anisotropic etching is observed when bromine (Br2) is added to HF-HBrO3 solutions. Therefore, monocrystalline (100) silicon wafer surfaces are covered with random upright pyramids with edge lengths of about 5 mu m. The etch rate is strongly dependent on the concentration of HBrO3. Silicon surfaces are analyzed by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The gas phase is analyzed using Raman and infra red (IR) spectroscopy. The oxidation of the silicon surface by bromic acid likely takes place via oxygen insertion into the rearward silicon bonds. During etching, multiple active Br-species are formed which alter the etching behavior.

Thiocyameluric acid C 6 N 7 S 3 H 3 was reacted with various aqueous solutions of metal hydroxides and other metal salts, as well as ammonia. Crystalline products were obtained from reaction mixtures containing main group metal hydroxides. Only in the case of strontium hydroxide single crystals of Sr[HC 6 N 7 S 3 ]·6H 2 O suitable for an X-ray structure analysis were formed. Similar to other cyamelurates containing anions like [C 6 N 7 O 3 ] 3– , [HC 6 N 7 O 3 ] 2– or [H 2 C 6 N 7 O 3 ] – , or analogous melonates [C 6 N 7 (NCN) 3 ] 3– , the anion [HC 6 N 7 S 3 ] 2– in the title salt is completely planar. The hydrogen atom is located at a terminal N atom, which indicates that mono- and di-hydrogen thiocyamelurates and thiocyameluric acid preferably occur as thioketone tautomeric isomers, and are not encountered in the thiol form, at least in the solid state. Since all water molecules coordinate the strontium atoms and the anions do not act as ligands the salt may be described as [Sr(H 2 O) 6 ][HC 6 N 7 S 3 ].

The liquid flame retardant tris(2-chloro-isopropyl) phosphate (TCPP) is widely used in polyurethane and polyisocyanurate rigid foams. However, TCPP is currently under assessment by the European Chemicals Agency ECHA and National Toxicology Program NTP, USA. For this reason, there is a high demand for new flame retardants with similarly good processing and application properties. This paper examines the influence of low-molecular liquid s-triazine phosphonates on the foaming behaviour and flame retardancy of polyurethane and polyisocyanurate rigid foams for building applications. The flame retardant investigations consisted of thermogravimetric analysis of the components and flame retardancy tests performed on the foams: limiting oxygen index, EN 13501 class E, and cone calorimetry. The newly developed class of s-triazine phosphonates are promising flame-retardant candidates with good processing and application properties.

Solutions containing hydrofluoric acid (HF), hydrobromic acid (HBr) and bromine (Br2) were investigated as novel acidic, NOx-free mixtures for wet-chemical etching of silicon wafers. HF–Br2-mixtures exhibit isotropic etching behaviour towards silicon, etch rates up to 4.0 ​μm ​min−1 were observed at room temperature, which are higher than the etch rates of commercially used alkaline solutions. HF–HBr–Br2-mixtures show anisotropic etching behaviour, texturing the surface of monocrystalline silicon wafers with random upright or random inverted pyramidal structures. Etch rates up to 2.4 ​μm ​min−1 were observed, the etch rate increases linearly with the concentration of Br2 in the etching solution. Silicon surfaces were investigated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The light trapping efficiency of wafers etched by HF–HBr–Br2 solutions was compared to commercially available textured wafers by UV/Vis-reflectivity measurements indicating lower reflectivities for the HF–HBr–Br2-treated samples. A reaction scheme for the anisotropic dissolution of silicon in bromine-containing aqueous HF-solutions is proposed, which involves bromine as oxidizing agent.

Urea derivatives of the general motifs R1(N(SiMe3)C(O)NR2R3)2 and [R1(NC(O)NR2R3)2SiMe2]n (R1 = difunctional organic linker, i.e., core of diisocyanate used; R2,R3= H,nPr; H,Ph; Et,Et) were synthesized by insertion of four different diisocyanates (1,6-HMDI, 2,4-TDI, 1,3-TMXDI and 4,4'-MDI) into aminotrimethylsilanes Me3SiNR2R3 and diaminodimethylsilanes Me2Si(NR2R3)2. The products obtained were analyzed by NMR and IR spectroscopy. Insertion into aliphatic aminosilanes was found to be favored for primary over secondary amino groups. For insertion into 4,4'-methylenebis(phenylisocyanate) (4,4'-MDI), good results were obtained for silanes derived from secondary amines as well. Insertion into aminosilanes with aromatic N-bound substituents turned out to be kinetically inhibited. Elucidation of molecular structures of the products by crystallography and NMR spectroscopy revealed interesting differences in N-Si connectivity, caused by steric and electronic effects of the reactants and migration of -SiMe3 and -Si(Me2)- moieties.