Stannasiloxanes: from rings to polymers

Immobilization of isolated dimethyltin species on crystalline silicates through surface modification of layered octosilicate

Single metal atoms supported on silica are attractive catalysts, and precise control of the local environment around the metal species is essential. Crystalline silica is useful as an efficient support for the incorporation of well-defined metal sites. Dimethyltin species were regularly grafted onto the layer surfaces of layered octosilicate, a type of two-dimensional (2D) crystalline silica. Dimethyltin dichlorides react with the surface silanol (SiOH) groups of the silicate layers. The formation of Si-O-Sn bonds was confirmed by 29Si magic-angle spinning (MAS) NMR. X-ray absorption fine structure (XAFS) analysis showed the four-coordinated Sn species. These results suggested the presence of well-defined dipodal dimethyltin species on the layer surfaces. The degree of modification of the silanol groups with the dimethyltin groups increased with increasing amounts of dimethyltin dichloride; however, the maximum degree of modification was approximately 50%. This value was interpreted as an alternate modification of the octosilicate reaction sites with dimethyltin groups. These results demonstrate the potential for developing highly active single metal catalysts with a high density of regularly arranged active sites on high surface area supports.

Offsets between hyperconjugations, p→d donations and Pauli repulsions impact the bonding of E-O-E systems. Case study on elements of Group 14

The nature of the E-O chemical bond (E = C, Si, Ge, Sn) is investigated in a wide range of model derivatives, such as oxonium cations, hydrogenated/methylated/fluorinated/chlorinated ethers and acyclic oligomers incorporating the E-O-E moiety. By means of density functional theory (DFT) calculations and natural bond orbital (NBO) techniques, we propose a bonding mechanism that explains the structural contrast between the organic and the inorganic counterparts of all these derivatives: the interplay between stabilizing interactions like LP(O)→σ*(E-X) hyperconjugations and LP(O)→d(E) donations with LP(O)⋯σ(E-X) vicinal Pauli repulsions (X = H, C, O, F, Cl) dictates the equilibrium structures in terms of E-O-E angles and E-O bond lengths. In addition, the present work represents the first study of oxonium ions that describes the structural discrepancies among organic derivatives and their heavier analogues. Another novel outcome for ethers and oligomers is that the two non-equivalent lone pair electrons (LPs) at the oxygen atoms impact in different manners the geometries of such derivatives, i.e. the s/p LP is correlated with the bending behaviour of the E-O-E units, while the pure p LP mainly dictates the short E-O bond distances of inorganic derivatives. Lastly, we evaluate the impact of the number of electronegative substituents, e.g. F, Cl or OEH₃ groups, on the bond patterns developed for hydrogenated or methylated ethers.

Cooperative assembly of redistributed arylgermanium-bearing alkoxysilanes in a mesostructured siloxane network

Three redistributed arylgermanium-bearing mono-, bis- and tris-triethoxysilyl arms were designed, cocondensed with TEOS to access SBA-15-type materials and embedded in chitosan to prepare functional bioplastics.

LiEC(SiMe3)3 (E = Se, Te) as a new donor of chalcogen atoms for the generation of binary [(RxGey)Ez] cage compounds with unique structural features

The reaction of GeCl2·dioxane with LiEC(SiMe3)3 (E = Se, Te) shows unexpected products different from those of the previously presented reaction system GeCl2·dioxane/LiSC(SiMe3)3. Here, LiEC(SiMe3)3 (E = Se, Te) acts as a chalcogen atom donor and simultaneously as a substituent to give cage compounds of the composition [(RxGey)Ez] with unique structural features of the Ge/E cores. The molecular structures are presented together with a possible formation mechanism of the selenium/germanium cage compound [{((SiMe3)3CGe)2GeSe4}2(μ2-Se)2] supported by quantum chemical calculations.

Assembly of discrete and oligomeric structures of organotin double-decker silsesquioxanes: inherent stability studies

Discrete and oligomeric organotin DDSQs have been synthesized and characterized, both experimentally and through computational study. The stability of these compounds remains intrigued with the organization of their structure in the crystal lattice.

New sterically hindered tin(iv) siloxane precursors to tinsilicate materials: synthesis, spectral, structural and photocatalytic studies

A series of sterically hindered tin(iv) siloxanes (1–8) were synthesized and characterized. The single-source precursors1and3were well suited for producing tinsilicate materials and it act as a photocatalyst for degradation of methylene blue.

Synthesis and structures of monomeric group 14 triols and their reactivity

The first stable stannanetriol and germanetriol bearing sterically congested aryl groups were synthesized by hydrolysis of the corresponding trichloro-stannane and -germane. The stannanetriol is monomeric in solution as well as in the crystalline state, as evidenced by X-ray diffraction analysis and CP-MAS NMR spectroscopy. The stannanetriol reacted with silicone grease to afford a cagelike compound having three Sn–O–Si–O–Sn linkages in the molecule. All the group 14 triols can be converted to the corresponding trihalo compounds in good yields.

Synthesis of heteroboroxines with MB₂O₃ core (M = Sb, Bi, Sn)--an influence of the substitution of parent boronic acids

The synthesis and structure of stiba-, stanna- and bismaheteroboroxines of a general formula L(E)M[(OBR)2O] supported by a N,C,N-chelating ligand L [where L = C6H3-2,6-(CH2NMe2)2, M, E = Sb, lone pair or Sn, Ph or Bi, lone pair] is reported. The target compounds are prepared by straightforward one-step reactions between oxides (LMO)2 (M = Sb or Bi) or organotin(iv) carbonate L(Ph)Sn(CO3) with four or two molar equivalents of corresponding organoboronic acid. All compounds were characterized with the help of elemental analysis, multinuclear NMR spectroscopy and on several occasions the molecular structure was determined using single-crystal X-ray diffraction analysis. The influence of both the substitution of the parent organoboronic acid and the central atom used on the feasibility of the condensation reaction was addressed. Furthermore, several heteroboroxines containing nitrogen donor functionality (i.e. NH2, NMe2, CN or 4-pyridyl) included in the boronic acid residue were synthesized and characterized with the aim to prepare boroxine-based covalent frameworks (through intermolecular N→B interactions) containing metal atoms in their structures. Although no such intermolecular bonding was detected in solution of these compounds, it was shown that the organotin(iv) heteroboroxine substituted by 4-pyridyl group forms an infinite polymeric chains via N→B interactions in the solid state. This polymer collapsed back to monomeric units upon dissolution.

Equilibrium Studies of Dibutyltin(IV)-Zwitterionic Buffer Complexation

Equilibrium studies in aqueous solution are reported for dibutyltin(IV) (DBT) complexes of the zwitterionic buffers “Good’s buffers” Mes and Mops. Stoichiometric and formation constants of the complexes formed were determined at different temperatures and ionic strength 0.1 mol·L⁻¹ NaNO₃. The results show that the best fit of the titration curves were obtained when the complexes ML, MLH₋₁, MLH₋₂ and MLH₋₃ were considered beside the hydrolysis product of the dibutyltin(IV) cation. The thermodynamic parameters ΔH^o, ΔS^o and ΔG^o calculated from the temperature dependence of the formation constant of the dibutyltin(IV) complexes with 2-(N-morpholino)ethanesulfonic acid (Mes) and 3-(N-mor-pholino)-propanesulfonic acid (Mops) were investigated. The effect of dioxane as a solvent on the formation constants of DBT–Mes and DBT–Mops complexes decrease linearly with the increase of dioxane proportion in the medium. The concentration distribution of the various complexes species was evaluated as a function of pH.

Synthesis, coordination and biological aspects of organotin(IV) derivatives of 4-[(2,4-dinitrophenyl)amino)]-4-oxo-2-butenoic acid and 2-{[(2,4-dinitrophenyl)amino]carbonyl}benzoic acid

New series of organotin(IV) complexes of aniline derivatives, R2SnL2 and R3SnL [where R = Me, n-Bu, Ph, n-Oct] have been synthesized by the reaction of HL1 and HL2 with respective organotin halides or oxides. Experimental details for the preparation and characterization (including elemental analysis, IR and multinuclear NMR (1H-, 13C- and 119Sn-) spectra in CDCl3 and EI mass spectra of both series are provided. The binding sites of the ligands were identified by means of FTIR spectroscopic measurements. It was found that in all cases the organotin(IV) moiety reacts with the oxygen of COO- group to form new complexes. In the diorganotin complexes, the COO- group is coordinated to the organotin(IV) centres in a bidentate manner in the solid state. The 119Sn NMR data and the nJ(13C-119/117Sn) coupling constant support the tetrahedral coordination geometry of the organotin complexes in non-coordinating solvents. Biological activities (antibacterial, antifungal, cytotoxicity, antileishmanial and insecticidal) of these compounds are also reported.