Preparation, Characterization and Voltammetric Aspects of a Silsesquioxane Organofunctionalized With Imidazole Groups and Subsequent Reaction With Silver and Potassium Hexacyanoferrate (III)

This paper describes the interaction of a octa (3-chloropropyl)octasilsesquioxane (SS) functionalized with imidazole (SSI) groups, and its subsequent reaction with silver (AgSSI) and hexacyanoferrate (III) (AgHSSI). The materials SS, SSI were characterized by infrared (FTIR); solid state C and Si nuclear magnetic resonance (NMR). The AgSSI and AgHSSI were characterized by electronic (Uv-Vis) and infrared spectroscopy (FTIR). The AgHSSI was incorporated into a graphite paste electrode and the electrochemical studies were conducted with cyclic voltammetry. The AgSSI system was studied first, followed by the AgHSSI. The spectroscopic studies reveals that preparation was conducted with success. The cyclic voltammogram of AgSSI obtained from a graphite paste electrode modified (50% m/m) exhibited a redox couple with average potential (E) of 0.01 V (vs Ag/AgCl(s), KNO3, 1.0 mol L; v = 20 mV s), attributed to the Ag/Ag redox process. The cyclic voltammogram of AgHSSI with AgHSSI (50% m/m) exhibited a single redox couple, much wider with E= 0.14 V, (vs Ag/AgCl(s), KNO3, 1.0 mol L, v = 20 mV s) attributed to the Fe(CN)6/ Fe(CN)6 process.


Introduction
Polyhedral oligosilsesquioxanes (POSS) refer to all structures that have the empirical formula (RSiO 1,5 ) n , where R can be a hydrogen or any organic group such as alkyl, methyl, aryl, vinyl, phenyl, arylene, or any organofunctional derivative thereof, n can vary between 4 and 30, but it is usually 6, 8, 10 and 12 (Cordes, Lickiss, & Rataboul, 2010;Lickiss & Rataboul, 2008;Voronkov & Lavrent'yev, 1982).Silsesquioxanes (POSS) are a class of nanomaterials with great potential in the field of nanoscience and nanotechnology.The interest in the properties of silsesquioxanes has been the subject of research in various companies and universities in the development of new materials, what can be observed with the substantial increase in the number of patents and publications related to these materials (Phillips, Haddad, & Tomczak, 2004).
The electrochemical field has few studies on modified silsesquioxanes as substrates, acting as electron mediators or electrochemical sensors.It is known that after specific chemical modification the large-surface area nanostructured materials contain metal centers, hence powerful catalysts and electrocatalysts.Imidazole, due to the presence of nitrogen donor atoms, can coordinate with a variety of transition metal ions (Joseph, Ramamurthy, & Subramanian, 2011;Yin, Xu, Qu, Zhao, & Sun, 2010).It is has long been known that imidazole has a particular affinity for electrophilic silanes (Bassindale, Codina-Barrios, Frascione, & Taylor, 2008).Thus, materials prepared using silica-based substrates functionalized with imidazole are suitable for the sorption of toxic heavy metals, such as mercury and copper.Therefore silsesquioxanes are potential candidates for organofunctionalization with imidazole groups.When compared with silica gel, the advantage of using silsesquioxanes modified by covalent attachment of organofunctional groups regards their easy preparation, high sorption capacity and fast adsorption kinetics, in addition to their good chemical stability (Rajec & Hanzel, 2003;Silveira, 2012).Within this context, particularly our interest in the silsesquioxane chemistry is to prepare multifunctional nanostructured materials that can be used as electrochemical sensors.A preliminary characterization the SSI was publish recently (Silveira, Silvestrini, Bicalho, & Do Carmo, 2013).Based on our interest above mentioned, in this paper we present the preparation, and a complementary characterization and voltammetric study of interaction of a octa-(3-chloropropyl)octasilsesquioxane (SS) functionalised with imidazol (SSI) groups, and its subsequent reaction with silver (AgSSI) and hexacyanoferrate (III) (AgHSSI).The electrochemical behavior of AgHSSI provide additional information about different species formed during their preparation.

Reagents and Solutions
Unless specially state all reagents solutions and supporting electrolytes were prepared using Milli-Q water and the reagents and solvents were of analytical grade (Merck or Aldrich) and were used as purchased.

Diffuse Reflectance
The diffuse reflectance spectra of the bulk solid binuclear complex were recorded between 350 and 1000 nm on a Guided Wave model 260 spectrophotometer, using a tungsten-halogen lamp as the radiation source, and detectors of Si and Ge.

Fourier Transform Infrared Spectra
The FTIR spectra were recorded on a Nicolet 5DXB FTIR spectrometer.About 150 mg of KBr were ground in a mortar and a sufficient quantity of the solid sample was ground with KBr to produce a 1 wt.% mixture resulting in pellets.The data collection a minimum of 64 scans was collected for each sample at a resolution of ± 4 cm -1 in the range 4000 to 400 cm -1 .

NMR Solid State Analyses
All 29 Si NMR (59.5 MHz) and 13 C NMR (75.4 MHz) solid state analyses were recorded on a Varian INOVA 300 spectrometer.The samples were packed in zirconia rotors and spun at the magic angle at 4500 Hz, after relaxation delay of 10.0 s and 6.0 s for 29 Si and 13 C respectively.All chemical shifts are reported in units (ppm) using tetramethylsilane (TMS) as external reference.

Electrochemical Measurements
Cyclic voltammograms were performed using the Microquimica (MQP1-PGST) potentiostat.The three electrode systems used in these studies consisted of a modified working electrode (graphite paste electrode) an Ag/AgCl(s) reference electrode, and a platinum wire as the auxiliary electrode.The measurements were carried out at 25C.

Synthesis of Octa-(3-chloropropyl)octasilsesquioxane (SS)
For the synthesis of octa-(3-chloropropyl)silsesquioxane (SS) a procedure following as described in the literature (Chojnowski et al., 2006;Silveira, Silvestrini, Bicalho, & Do Carmo, 2013) after minor modifications.800 ml of methanol, 27ml of hydrochloric acid(HCl) and 43 mL of 3-chloropropyliltriethoxysilane were added into a round bottom flask of 1000 mL.The system was kept under constant stirring at room temperature for 6 weeks.The solid phase was separated by filtration in a sintered plate funnel, yielding a white solid, octa-(3-chloropropyl)octasilsesquioxane (SS), which was then oven dried at 120 ºC for 4 hours.Figure 1(A) illustrates a representative scheme of this synthesis.tion of silver n as then filtered oven dried at 7 1.0×10

Figure
Figure 4. S