Polyhedral Oligomeric Silsesquioxane (POSS) Chemistry

中文版本 / Chinese version: POSS 八亚胺倍半硅氧烷：晶体结构与热性能 Four novel octa-imine-functionalized polyhedral oligomeric silsesquioxane (POSS) derivatives, designated POSS-6 through POSS-9 , have been reported by Mateusz Janeta and Sławomir Szafert in the Journal of Molecular Structure in 2025. These compounds were obtained by modular Schiff base condensation of octa(3-aminopropyl)silsesquioxane hydrochloride with the appropriate aromatic aldehyde in isolated yields ranging from 84 to 92 percent without chromatographic purification, and their structures were fully established by single-crystal X-ray diffraction. The identity of the peripheral substituent (hydroxyphenyl, bromophenyl, thiophene, or dibenzofuran) was found to govern both the non-covalent interaction topology in the solid state and the thermal behavior, with T 5% decomposition onset temperatures spanning from 305 to 326 °C across the four derivatives.

Bromination of the phenyl rings of octaphenyloctasilsesquioxane proceeds in the ortho position without any Lewis acid catalyst, in contradiction to the regiochemical rules that govern isolated aromatic substrates. The study titled “Why Do the [PhSiO 1.5 ] 8,10,12 Cages Self-Brominate Primarily in the Ortho Position? Modeling Reveals a Strong Cage Influence on the Mechanism” by M. Bahrami, H. Hashemi, X. Ma, J. Kieffer, and R. M. Laine, published in Physical Chemistry Chemical Physics in 2014, accounts for this outcome. The modeling places the bromine molecule 2.7 Å above a cage face, tilted by 30°, with a Br−Br separation of 2.32 Å and an induced dipole moment of 0.33 D, an arrangement that delivers Br δ+ to the ortho carbon. The premise of the present entry, namely that the Si 8 O 12 framework acts as an electron withdrawing center that stabilizes anionic guests and polarizes neutral molecules approaching its faces, is treated in full in the companion entry on the electronic p...

The publication titled “Amphiphilic Azo-Functionalized Polyhedral Oligomeric Silsesquioxane: Synthesis and Photo-Switched Efficient Phase Transfer via Host-Guest Encapsulation” by Bagher Eftekhari-Sis, Nasrin Amirpour, Ali Naderahmadian, Maryam Zirak, Mateusz Janeta and Ghodrat Mahmoudi, published in ChemPlusChem in 2024, presents azo-POSS, a light-switchable amphiphilic polyhedral oligomeric silsesquioxane designed for the selective removal of cationic dyes from water. The compound transfers dyes from the aqueous phase into dichloromethane with encapsulation efficiencies above 94% for methylene blue, 99% for crystal violet and 95% for thymol blue, while remaining essentially inactive toward anionic dyes. Irradiation at 365 nm isomerizes the azobenzene linker and suppresses uptake by as much as 60%, which places the separation process under direct optical control. Synthetic dyes released from textile, paper and plastics manufacturing constitute a significant and expanding category...

In an era where environmental monitoring and the rapid detection of industrial pollutants have become matters of pressing public concern, the development of advanced chemical sensors occupies a central position in contemporary materials science. A study published in Organometallics by Siripanich et al. (2022) reports a significant contribution to this field: a new class of dual-response fluorescent sensors constructed from pyrene-functionalized silsesquioxane (SQ) cages capable of selectively detecting both fluoride ions and polycyclic aromatic hydrocarbons (PAHs) with high analytical sensitivity and a rapid optical response, representing a notable advance in the design of multifunctional chemosensors.

Imine-POSS nanobuilding blocks for supramolecular hybrid materials, synthesized and structurally characterized by Janeta et al. at the University of Wrocław and published in Dalton Transactions in 2016, constitute the first complete series of fully octa-imino-functionalized polyhedral oligomeric silsesquioxane (POSS) compounds, with five single-crystal X-ray diffraction structures reported for the first time. The five compounds bearing phenyl, 4-bromophenyl, 4-nitrophenyl, 2-hydroxyphenyl, and 2-naphthyl groups form three-dimensional supramolecular networks governed by halogen bonds, CH⋅⋅⋅N contacts, and intramolecular hydrogen bonds. The 4-nitrophenyl derivative assembles a porous framework whose guest-accessible channels occupy approximately 20% of the unit cell volume, extending the structural diversity first established for the octa-imine POSS derivatives POSS-6 through POSS-9 .

Three studies, one published in Chemical Science in 2017 and two published in Chemistry – A European Journal and Journal of Catalysis in 2015, together define what a single reactive vertex on a silsesquioxane cage makes possible. The first two concern monofunctionalized POSS self-assembly, in which a platinum(II) terpyridine chromophore and a metal-free porphyrin, each carried by one cage, give solvent-switchable nanorings, nanoplates, vesicles and ordered sheets. The third turns the same architecture toward catalysis, where a cage-supported palladium center couples an aryl bromide with phenylboronic acid at a turnover number of 2.5 × 10 4 . Read together, the three papers show that one reactive arm is enough to program both morphology and catalytic behavior.