Skip to main content
NCBI home page
ACS AuthorChoice logoLink to ACS AuthorChoice
. 2023 Sep 29;62(41):16932–16942. doi: 10.1021/acs.inorgchem.3c02628

Metallodendrimers Unveiled: Investigating the Formation and Features of Double-Decker Silsesquioxane-Based Silylferrocene Dendrimers

Aleksandra Mrzygłód †,‡, M Pilar García Armada §, Monika Rzonsowska †,‡, Beata Dudziec †,‡,*, Marek Nowicki ‡,∥
PMCID: PMC10583206  PMID: 37774086

Abstract

graphic file with name ic3c02628_0011.jpg

Dendrimers exhibiting reversible redox properties have attracted extensive attention for their potential as electron transfer mediators, catalysts, and molecular sensors. In this study, we introduce intriguing G1 and G2 dendrimers featuring double-decker silsesquioxane cores and silylferrocene moieties. Through a carefully orchestrated sequence of condensation, reduction, and hydrosilylation reactions, these compounds were synthesized and comprehensively characterized spectroscopically and spectrometrically. Our investigation also encompassed the examination of their properties, including thermal stability, solubility in common organic solvents, and electrochemical behavior. We determined that these dendrimers possess the capability to form monolayers on platinum electrodes, which we conclusively demonstrated through the probing of cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy imaging. Notably, this study marks the first-ever example of modifying double-decker silsesquioxane cores with ferrocene groups while simultaneously representing one of the scarce instances of dendrimers exhibiting an open double-decker silsesquioxane core.

Short abstract

This research focuses on the synthesis of G1 and G2 dendrimers with double-decker silsesquioxane cores and silylferrocene moieties and the verification of their properties, including thermal stability, solubility in common organic solvents, and electrochemical behavior.

Introduction

Ferrocene, as a representative of a classic organometallic compound, of a sandwich aromatic structure with iron as the central atom, is characterized by undoubtedly impressive redox properties and chemical and thermal stability. Ferrocene-based compounds found many applications from fuel additives, pharmaceuticals, catalysts, capacitors, and porous systems for dyes/heavy ion removal to electrochemical sensors.1−7 However, ferrocene itself shows poor adhesion to surfaces. Therefore, its modification using diverse systems from oligo- and polysiloxanes and graphene oxide to dendrimers makes it possible to enhance this and other properties.2,8−11

Dendrimers are specific systems with defined, mainly spherical, three-dimensional structures. Their construction can be divided into the following fragments: a multifunctional core possessing extended arms with terminal functional groups that significantly affect the properties of dendrimers.12 The arms of the dendritic systems can be built of diverse units such as polyaminoester, carbosilanes, or polyamidoamines.13−15 They are characterized by high molecular weights that correspond with a number of electroactive ferrocene terminal groups exhibiting good solubility and adhesion to electrodes.16 There are scientific reports on the use of ferrocene dendrimers as electrode modifiers for direct quantification of DEHP [di(2-ethylhexyl)phtalate],2 for monitoring of ATP2–,17 glucose,18 boric acid,19 oxidation-triggered drug delivery,20 and anion recognition,21 or as a catalyst.3,22

Organosilicon compounds are often used in dendritic systems, e.g., silanes, cyclosiloxanes, 1,3,5-trisilacyclohexane, or more complex structures such as silsesquioxanes.7,15,23−28 They are known as polyhedral oligomeric silsesquioxanes (SQs, POSS) and represent a class of hybrid organic–inorganic compounds that have garnered significant attention in the field of materials chemistry. These unique structures consist of Si atoms at the vertices of a three-dimensional cage, with O atoms bridging the silicon units.29−31 Their molecular formula can be described as [RSiO1.5]n, where R represents the organic substituents attached to the silicon atoms. This versatile architecture allows for a wide range of structural variations and functionalizations, leading to diverse properties and applications. SQs exhibit exceptional thermal stability and tunable properties, making them attractive for use in fields such as catalysis, nanomaterials, coatings, and energy storage. Furthermore, their ability to integrate organic and inorganic components provides a platform for tailoring properties and designing advanced materials with enhanced performance and multifunctionality.29−39 There are some reports of the conjunction of silsesquioxane with ferrocene in diverse combinations, e.g., to form amphiphilic systems, grafted copolymers with magnetic properties, or porous materials for dye/heavy metal absorption features.9,10,25,26,28,40−48 Some of these systems exhibit interesting electrochemical properties, influencing their application. On the contrary, the distinct types of dendrimer cores should be also mentioned, but there are significantly lower numbers of papers concerning silsesquioxane-based dendrimers using ferrocene moieties as terminal fragments.25,26,28

Herein, we present studies on the synthesis of double-decker silsesquioxane molecules exhibiting electrochemical properties, i.e., possessing silylferrocene moieties. The synthetic protocol is based on a sequence of condensation, reduction, and hydrosilylation reactions (Scheme 1). The obtained compounds, varying in the amount of silylferrocene units attached to the inorganic Si–O–Si core, were analyzed in terms of their redox properties in solution as well as on Pt electrodes using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques.

Scheme 1. General Synthetic Route for Obtaining Ferrocene Dendrimers with Double-Decker Silsesquioxane Cores via Sequences of Reactions (condensation, reduction, and hydrosilylation).

Scheme 1

Open in a new tab

Results and Discussion

Synthesis of Silylferrocene Dendrimers Anchored on a Double-Decker Silsesquioxane Core

The synthesis of DDSQ-based silylferrocene dendrimers was envisaged to exploit the DDSQ precursors equipped with four reactive arms terminated with either four (G0-DDSQ-4OSiH)39 or eight Si–H [G1-DDSQ-4Si(H)2]32 functionalities to be reacted with vinylsilyldiferrocene (Fc2MeSiVi).49 This enabled the highly efficient and selective formation of two silsesquioxane G1 and G2 dendrimers bearing either four or eight silylferrocene units attached to an open-cage DDSQ core.

The first generation of the ferrocene dendrimer (G1-DDSQ-Fc8) was synthesized with tetrafunctional DDSQ with four reactive Si–H groups G0-DDSQ-4OSiH and Fc2MeSiVi via hydrosilylation using the following stoichiometry and reaction conditions: [G0-DDSQ-4OSiH]:[Fc2MeSiVi]:[Pt2(dvds)3] = 1:4.6:6 × 10–4, 95 °C, 24 h. Note that the reactivity of the Si–vinyl moiety was influenced by the steric hindrance and electronic effects of the ferrocene units. It was manifested by the presence of a residual resonance line at 4.85 ppm, signifying unreacted Si–H moieties. To achieve full conversion of G0-DDSQ-4OSiH, a 20% excess of Fc2MeSiVi per Si–H group and a catalyst loading of 4 × 10–3 are necessary.

The Fourier transform infrared (FT-IR) spectrum of the resulting mixture showed the disappearance of the Si–H bond in the area ca. υ̅ = 2100 cm–1 and υ̅ = 900 cm–1 confirming the complete conversion of G0-DDSQ-4OSiH (see Figure S1). A respective comparison of the 1H NMR spectra of G0-DDSQ-4OSiH, Fc2MeSiVi, and product G1-DDSQ-Fc8 is depicted in Figure 1. It confirms the disappearance of the resonance line from Si–H (4.85 ppm) and Si–CH=CH2 (5.84 ppm, JHH = 20.3, 3.7 Hz; 6.10 ppm, JHH = 14.6, 3.7 Hz; 6.47 ppm, JHH = 20.3, 14.6 Hz) in product G1-DDSQ-Fc8 (Figure 1c). Interestingly, changes were observed in the ferrocene fragment range (3.80–4.40 ppm) in G1-DDSQ-Fc8. Surprisingly, a low-field shift of the C–H peak in the cyclopentadienyl ring connected to the Si atom was detected when compared to that of substrate Fc2MeSiVi. It was not observed for similar ferrocene-containing systems with cubic T8-type silsesquioxane-based carbosilane dendrons.25 A possible explanation for this could be the difference in the chemical surroundings of the silicon atoms (their order) attached to the SQ core. Also, the steric hindrance of the silyl–ferrocenyl groups is decreased due to the different DDSQ core. As a result, these aspects could influence the shielding effect.

Figure 1.

Figure 1

Open in a new tab

Selected range of stacked 1H NMR spectra of (a) G0-DDSQ-4OSiH, (b) Fc2MeSiVi, and (c) G1-DDSQ-Fc8.

Second-generation ferrocene dendrimer G2-DDSQ-Fc16 was synthesized in an analogous way. Silsesquioxane G1-DDSQ-4Si(H)2 was obtained in a one-pot reaction, i.e., hydrosilylation followed by reduction (Si–Cl to Si–H) (Scheme 1).32 The G2 dendrimer was synthesized with DDSQ bearing eight Si–H reactive groups using a 1:9.6:8 × 10–3 [G1-DDSQ-4Si(H)2]:[Fc2MeSiVi]:[Pt2(dvds)3] stoichiometry that enabled complete Si–H conversion. Respective stacked FT-IR and 1H NMR spectra of reagents confirm the obtained results (Figures S2 and S3).

The most intriguing aspect of the synthesis of ferrocene dendrimers with a DDSQ core was the discovery of a suitable and efficient method for purifying the product from unreacted Fc2MeSiVi. Observable differences in solubility between product G1-DDSQ-Fc8 and substrate Fc2MeSiVi were noted in basic organic solvents. Substrate Fc2MeSiVi is soluble in common organic solvents, e.g., DCM, THF, toluene, or n-hexane. However, double-decker silsesquioxane G1-DDSQ-Fc8, characterized by an inorganic Si–O–Si core with exposed phenyl rings, does not dissolve in n-hexane, MeOH, or MeCN (Table S1). This fact enables us to elaborate an efficient isolation methodology using column chromatography. First, the reaction mixture was dissolved in a minimum volume of DCM and applied to a dry SiO2 column, and the solvent was allowed to evaporate overnight. The next day, the use of a THF/n-hexane eluent in a 1:80 ratio facilitated the efficient removal of Fc2MeSiVi, while product G1-DDSQ-Fc8 remained on the top of the chromatography column. The eluent was then changed to 3:2 DCM/n-hexane, and the product was easily eluted. Because both compounds are colorful, their separation was clearly visible, which is depicted in Figure 2. The product yields for G1-DDSQ-Fc8 and G2-DDSQ-Fc16 were quite high (74% and 60%, respectively). The structures of both products were confirmed by spectroscopic analyses as well as MALDI-TOF MS, which demonstrated the molecular ions at m/z 3062.3 and 5112.6, respectively (details in Figures S4–S11).

Figure 2.

Figure 2

Open in a new tab

Schematic representation of the DDSQ-based ferrocene dendrimer purification procedure.

Dendrimers G1-DDSQ-Fc8 and G2-DDSQ-Fc16 exhibited a high thermal stability. For G1-DDSQ-Fc8, only one degradation step was observed, starting at 326 °C, characterized by a T5%d of 431 °C and a T10%d of 455 °C. The major mass loss was detected in the 380–580 °C temperature range. However, for G2-DDSQ-Fc16, the mass loss began at 290 °C and T5%d = 421 °C and T10%d = 442 °C with the major mass loss in the range of 420–600 °C (Figure 3 and Table S2). This observation follows the literature for two analogous ferrocenyl carbosilane dendrimers but with an octasubstituted T8-type SQ core.25 It could be a higher-organic content derivative in the case of G2-DDSQ-Fc16 versus G1-DDSQ-Fc8. Moreover, at 700 °C the amount of residue was larger for G1-DDSQ-Fc8 (61%) than for G2-DDSQ-Fc16 (54%) due to the smaller amount of organic, aliphatic groups terminated with a ferrocene group. Interestingly, upon comparison of G1-Fc16,25 which possesses an octasubstituted T8-type core, and G2-DDSQ-Fc16, which features a double-decker T12-type core, both having the same number of Fc groups but different SQ cores, G2-DDSQ-Fc16 exhibited superior thermal stability. This observation might be attributed to the higher content of silicon atoms (due to the higher generation of the dendrimer) and the presence of phenyl groups at the DDSQ core, collectively contributing to the increased thermal stability of this system.25,50

Figure 3.

Figure 3

Open in a new tab

Thermogravimetric analysis of G1-DDSQ-Fc8 (blue) and G2-DDSQ-Fc16 (orange) performed in nitrogen.

Electrochemical Study in Solution

Dendrimers containing redox-active moieties have been the subject of extensive research due to their intriguing properties and various applications, such as electron transfer mediators, catalysts and biocatalysts, molecular sensors, and electronic devices.4,51 Among them, ferrocene derivatives stand out for their notable characteristics, and their special ability to prepare modified electrodes, due to the change in their solubility associated with the ferrocene oxidation.12

To study the electrochemical properties, the new dendrimers were tested by using CV in DCM solution at a low concentration of ferrocene centers (∼10–4 M). The choice of DCM as the solvent was made on the basis of our extensive experience with other ferrocenyl dendrimers.5,6,11,12,25 These systems exhibit high solubility in DCM, and the wide electroactivity range of this solvent makes it highly suitable for investigating electrochemical systems involving interacting ferrocene groups. The cyclic voltammograms of both compounds (Figure 4) showed two well-separated and reversible oxidation peaks of equal intensity at E01 = 0.42 V and E02 = 0.62 V for G1-DDSQ-Fc8 and E01 = 0.42 V and E02 = 0.55 V for G2-DDSQ-Fc16 (vs the saturated calomel electrode). Both compounds show, upon reversal of the scan after the second oxidation process, a narrow reduction wave indicating the presence of a stripping peak. As expected, the oxidized form of DDSQ ferrocene derivatives precipitates on the surface of the electrode, and during the reverse scan, the film partially redissolves as they are reduced. This observation is also in good accord with the literature. The two-wave redox response and the change in solubility that accompanied the change in oxidation state were published for similar systems, e.g., oligo- and poly(ferrocenylsilanes) or polysiloxanes, block copolymer, and carbosilane dendrimers contain diferrocenylsilane units.11,25,27,49,52,53 As a consequence of this change in solubility, during continuous scanning, the peak currents increase, especially for dendrimer G2-DDSQ-Fc16, indicating the formation of a film on the electrode (Figures S12 and S13). It is worth noting that the behavior of G1-DDSQ-Fc8 and G2-DDSQ-Fc16 is different from that of a simple carbosilane-based dendrimer or a dendrimer with an octa-T8SQ core with 8 or 16 ferrocene groups, respectively.11,25

Figure 4.

Figure 4

Open in a new tab

Cyclic voltammograms of dendrimers G1-DDSQ-Fc8 and G2-DDSQ-Fc16 in CH2Cl2 with a 0.1 M n-Bu4NPF6 solution (scan rate of 20 mV s–1).

The plots of peak current versus the squared scan rate (ν1/2) were linear in all cases (see Figures S14 and S15), which are indicative of diffusion-controlled redox processes. The diffusion coefficients, D0, for both systems were calculated by means of the Randles–Sevick equation (eq 1)

graphic file with name ic3c02628_m001.jpg 1

were D0 = 1.44 × 10–4 cm2 s–1 and D0 = 4.41 × 10–4 cm2 s–1 for G1-DDSQ-Fc8 and G2-DDSQ-Fc16, respectively. This difference can explain the lesser growth of the G1-DDSQ-Fc8 current in successive cycles shown in Figures S12 and S13.

On the contrary, the two-wave redox response confirms the existence of interactions between two ferrocenyl centers connected by the bridging silicon atom. The first oxidation occurs in nonadjacent sites, which prevents the oxidation of the remaining ferrocene centers adjacent to the already oxidized ones. To determine the degree of interaction between the two iron sites, the redox potential difference (ΔEo2–1 = Eo2 – Eo1) was calculated and equals 200 mV for G1-DDSQ-Fc8 and 130 mV for G2-DDSQ-Fc16. Moreover, the partially oxidized silsesquioxanes can be classified as class II mixed-valence species according to the Robin–Day classification, and comproportionation constant Kc equals 2405 mV for G1-DDSQ-Fc8 and 158 mV for G2-DDSQ-Fc16, corresponding to the equilibrium54−56

graphic file with name ic3c02628_m002.jpg

Electrochemical Studies of Modified Electrodes

As cited above, an interesting aspect of dendrimers functionalized with ferrocene is the possibility of depositing them on several electrode surfaces to obtain electroactive films. Because both dendrimers have the same core-type structure and their electroactivity is solely attributed to the presence of ferrocene groups, it is anticipated that any variations in the electrochemical properties of both modified electrodes will depend primarily on the ferrocene:dendrimer ratio (active centers per film volume) and the characteristics of the films formed. These factors may collectively influence the electron transfer through the film, that is, potentially leading to differences in the electrochemical kinetics of the modified electrodes. The amount of electrodeposited material depends on the amount of electricity consumed in the electrolytic deposition (Faraday’s law), and this in turn can be controlled by the applied potential, the application time, and the concentration of the electroactive substance in the bulk solution. On the contrary, the structure of the obtained film can be different depending on the mode of application of the potential. When the diffusion of the dendrimer is fast enough, the potentiodynamic method (potential sweeps) allows more permeable films to be obtained, because it facilitates the formation of the polymer at nucleation sites in an orderly manner. This procedure allows precise control of the film thickness based on the number of scans. However, if the diffusion coefficient is too slow and/or the proportion of ferrocene groups is low in relation to the size of the molecule, it can be necessary to use a potentiostatic (constant potential) method with a sufficient overpotential to counteract a low level of diffusion. In this case, the films obtained are usually more compact, and the control of their thickness, based on the time, should be more difficult. For this reason, we tried to prepare electrodes by both procedures. Initially, to modify the first electrode with G1-DDSQ-Fc8, the potentiodynamic method was employed. However, the film thickness obtained was too small (Γ = 1.98 × 10–12 mol of Fc/cm2). Consequently, controlled-potential electrolysis was investigated, and an applied potential of 1.0 V for 5 min was chosen as the most appropriate condition. In the case of G2-DDSQ-Fc16, both methods can be used, through repeat cycling (20 cycles between 0.0 and 1.0 V), and controlled-potential electrolysis at 1.0 V for 5 min was the best condition. Figure 5 shows the cyclic voltammograms of the electrodes modified with both dendrimers by the described procedures.

Figure 5.

Figure 5

Open in a new tab

Steady-state voltammetric response of electrodes modified with both dendrimers (A) in CH2Cl2 with a 0.1 M n-Bu4NPF6 solution and (B) in phosphate buffer (pH 7.0) and a 0.1 M NaClO4 solution (scan rate of 20 mV s–1).

As one can see, in a non-aqueous solution, the cyclic voltammograms of all of the obtained modified electrodes also presented the two successive well-defined reversible oxidation–reduction systems, which confirm the existence of interactions between the two iron centers. In addition, one can see that the sharp peak, indicating partial redissolution due to the reduction of ferrocenium, no longer appears. This reveals the electrochemical stability of the films. Effectively, as has already been observed with other ferrocenyl dendrimers sharing similar structures and/or compositions,5,6,11,12,25 the films of these systems remain stable even in DCM. They attain their steady-state cyclic voltammograms from the first cycle, and this stability is maintained in successive cycles without any mass loss. The formal potential values, E01 and E02, calculated as the average of anodic and cathodic peak potentials, for all modified electrodes at a slow scan rate (10 mV s–1), are listed in Table 1. Note that the G2-DDSQ-Fc16 films show more defined ferrocenyl peaks due to the higher proportion of ferrocene groups in the molecule.

Table 1. Electrochemical Data of Modified Electrodes.

  G1-DDSQ-Fc8
 G2-DDSQ-Fc16
potentiostatic
 potentiodynamic
 potentiostatic
aqueous non-aqueous aqueous non-aqueous aqueous non-aqueous
Epa1 (V) 0.48 0.36 0.45 0.35 0.51 0.36
Epc1 (V) 0.42 0.33 0.37 0.34 0.39 0.34
ΔEp1 (mV) 65 30 80 10 120 20
E01 (V) 0.45 0.34 0.41 0.35 0.45 0.35
Epa2 (V) – 0.51 – 0.49 – 0.49
Epc2 (V) – 0.50 – 0.48 – 0.47
ΔEp2 (mV) – 10 – 10 – 20
E02 (V) – 0.50 – 0.49 – 0.48
α 0.47 0.51 0.51 0.52 0.54 0.51
n 0.98 1.06 0.93 1.10 1.07 1.23
ks (s–1) 1.02 – 2.03 – 0.09 –
Open in a new tab

In aqueous solution, the obtained voltammograms with the same modified electrodes showed only one reversible system, which demonstrates the overlapping interaction between the ferrocenyl units (Figure 5B). The presence of polar solvent molecules, which can be situated between the ferrocene groups, counteracts the electrochemical interactions, inhibiting the connection of two redox couples. Consequently, only one system appears. A similar observation was reported for poly(dialkylsilylenefferocenylene), siloxane homopolymers, block copolymer films, or other ferrocene dendrimers.5,6,11,25,52,53 The obtained formal potentials are also listed in Table 1.

As the electrodes used in panels A and B of Figure 5 are the same, it is clear that the electroactivity of the films improves remarkably in aqueous media. For this reason, the cyclic voltammograms in an aqueous medium will be used to calculate the coatings of the films. The film thicknesses obtained were around 3 × 10–10 mol of Fc/cm2 for dendrimer G1-DDSQ-Fc8 (potentiostatic method) and 8 × 10–10 and 7 × 10–9 mol of Fc/cm2 for dendrimer G2-DDSQ-Fc16 (potentiodynamic and potentiostatic methods, respectively).

On the contrary, it is also possible to observe in Figure 5B the difference between the films of G2-DDSQ-Fc16 obtained by the different procedures. This observation suggests that the thicker film obtained by the potentiostatic method facilitates counterion movement and electron transfer without a concomitant resistance increment. That is, we can predict that the transfer of electrons is very fast, despite the thickness of the film. Finally, we confirm the difficulty of deposition of dendrimer G1-DDSQ-Fc8, due to the lower Fc:molecule ratio, despite using a potentiostatic method.

To study the kinetics of electron transfer through the films and characterize the redox systems in both media and in relation with preparation methods, the number of electrons exchanged and the electronic transfer coefficients, α, indicative of symmetry of the electrochemical systems, were estimated from the peak width at midheight, W1/2. At very low scan rates (10 mV s–1), the cathodic and anodic peaks should approach the reversible peaks, symmetrical with respect to the potential axis. The midheight, denoted as W1/2, becomes independent of α and approaches 90.6/n mV. At high scan rates (500 mV s–1), the cathodic peak midheight must be equal to 62.5/nα, whereas the anodic peak midheight must be equal to 62.5/n(1 – α).57 All systems show the exchange of one electron, corresponding to the ferrocene/ferrocenium redox system, and α coefficients close to 0.5, corresponding to symmetric and reversible systems. The average obtained values are listed in Table 1.

Usually, the kinetics of modified electrodes with mono- or multilayers strongly adsorbed on an electrode surface can be studied by means of the model developed by Laviron.57,58 The model is based on the variation of the cyclic voltammograms with the scan rate (v), and let us estimate if the electroactive groups are surface confined. If this occurs, the peak currents must show a linear relationship with v in some scan rate intervals.59 In addition, the linearity at high rates proves the exhaustive oxidation–reduction through the film.60 On the contrary, the study of the variation of the peak potentials with v provides significant information about the kinetics of the modified electrodes. The variation (or not) of the peak potentials versus v allows us to evaluate the existence of kinetic limitations and, where appropriate, to estimate homogeneous standard rate constant ks for the electron transfer redox system.

Figure 6 shows the cyclic voltammograms obtained in aqueous and non-aqueous media with all of the modified electrodes. The figures show very different behaviors in each medium. As one can see, all electrodes in a non-aqueous solution (Figure 6A–C) show cathodic and anodic peak separations (ΔEp) that are practically constant as the scan rate increases, and the ΔEp values are only marginally greater than zero (Table 1). This fact indicates the absence of kinetic limitations.61,62 In addition, a linear relationship between the peak currents and the scan rate was observed (insets in the graphs of Figure 6), indicating the surface-confined nature of the ferrocenyl groups and the nonexistence of charge percolation. In other words, the films show behavior like that of a monolayer film.28

Figure 6.

Figure 6

Open in a new tab

Dependence of the peak current on the scan rate of (A) G1-DDSQ-Fc8 potentiostatic, (B) G2-DDSQ-Fc16 potentiodynamic, and (C) G2-DDSQ-Fc16 potentiostatic, modified Pt electrodes in CH2Cl2 with 0.1 M n-Bu4NPF6. Insets show the linear dependence of the peak currents on the scan rate. (D) G1-DDSQ-Fc8 potentiostatic, (E) G2-DDSQ-Fc16 potentiodynamic, and (F) G2-DDSQ-Fc16 potentiostatic, modified Pt electrodes in phosphate buffer (pH 7.0) and 0.1 M NaClO4. Insets show the linear dependence of the peak current on vx. Scan rates of 10, 20, 50, 100, 200, 300, 500, and 1000 mV s–1.

In aqueous media (Figure 6D–F), the peak potentials shift with an increase in scan rate. The study of this variation allows us to estimate ks. For this study, Laviron distinguishes two cases as a function of the magnitude of ΔEp.57 For the systems, and v values, for which ΔEp > 200/n mV, ks is calculated by eq 2:

graphic file with name ic3c02628_m003.jpg 2

where R is the gas constant, F is the Faraday constant, and T is the absolute temperature. For systems, and v values, for which ΔEp < 200/n mV, Laviron provides a table with values of ΔEp as a function of parameter m–1, where m is equal to RTks/Fnv. The polynomial fit (R2 = 0.9992) of these data is calculated from eq 3:

graphic file with name ic3c02628_m004.jpg 3

In our case, the G1-DDSQ-Fc8 potentiostatic and the G2-DDSQ-Fc16 potentiodynamic films show ΔEp values of <200 mV in the 10–300 mV s–1 interval, while the G2-DDSQ-Fc16 potentiostatic film ΔEp was >200 for scan rates of >50 mV s–1. The obtained homogeneous rate constants are listed in Table 1. From these results, we can deduce that, in aqueous media, the G2-DDSQ-Fc16-modified electrode created by potentiodynamic method showed the best behavior.

With regard to the dependence of the peak current on the scan rate, Laviron demonstrated that, with multilayer films, the anodic and cathodic peak currents show a linear tendency for only large or small v. However, there is a middle range where ip becomes proportional to vx, taking x values between 0.6, a value predicted by Laviron for multilayer films with fast electron transfer, and the unit (nonexistence of charge percolation in monolayer, or assimilated, films). As shown in the insets of Figure 6D–F, the studied systems present a good linear relation between the anodic or cathodic peak (not shown) currents on v0.6 over the whole sweep rate interval for the G2-DDSQ-Fc16 electrodes prepared by both methods, and on v0.8 for the G1-DDSQ-Fc8-modified electrodes. Consequently, in agreement with Laviron’s model, we can assert that the modified electrodes have a multilayer structure with fast electron transfer.

Electrochemical Impedance Spectroscopy (EIS)

Another useful electrochemical method for measuring the interfacial properties present on the electrode surface is electrochemical impedance spectroscopy (EIS). This technique allows us to model the electrode–electrolyte interface using an equivalent circuit composed of the charge transfer resistance, which controls the electron transfer kinetics, RCT, the Warburg impedance, which represents the diffusion of ions from the bulk electrolyte to the electrode interface, W, the interfacial capacitance of the double layer, Cdl, and the electrolyte resistance, Rs.63

The Nyquist plots show the imaginary versus the real part of the impedance, which is used widely to estimate RCT and Cdl. The plot consists of a semicircular part, whose diameter represents RCT, and a linear part at low frequencies, characteristic of diffusion-controlled systems. Nonetheless, for rough surfaces, Cdl cannot describe the electronic properties of the interface correctly, because the system deviates from the ideal capacitive behavior. In these cases, one must introduce a constant phase element, CPE, that reflects the nonhomogeneity of the layer and is defined as CPE = A–1(jw)–n, where n is the interface deviation from the Randles model, taking values between 0.5 and 1, and A is a coefficient that becomes equal to Cdl when n = 1.

From the Nyquist plots, we confirm the previous conclusions about the modified electrodes with both dendrimers by both procedures. The best film, in relation to electron transfer kinetics, was the potentiodynamic G2-DDSQ-Fc16-modified electrode, with a smaller RCT, while the same material prepared by the potentiostatic method showed the highest value (Figure 7). Table 2 collects all of the EIS results for the three types of electrodes, in comparison with those corresponding to a Pt bare electrode.7 The equivalent circuits for each electrode are shown in Figure S16.

Figure 7.

Figure 7

Open in a new tab

Nyquist plot of modified electrodes in 0.1 M KCl with a 10 mM K3[Fe(CN)6]/K4[Fe(CN)6] solution. Lines are the fits and simulations to obtain the Randles-type equivalent circuits. The inset shows a model of an equivalent circuit obtained from fit and simulation of the EIS data.

Table 2. EIS Results for the Three Types of Modified Electrodes.

electrode Rct (Ω) CPE (μF) n i0 (μA) k0 (cm s–1) χ2
bare Pt7 32 4.29 0.829 791 1.17 × 10–2 –
potentiostatic G1-DDSQ-Fc8 214 11.00 0.834 132 2.34 × 10–6 0.0095
potentiodynamic G2-DDSQ-Fc16 194 9.48 0.843 144 2.53 × 10–6 0.0025
potentiostatic G2-DDSQ-Fc16 643 5.40 0.862 42.4 7.29 × 10–7 0.0056
Open in a new tab

From the EIS data, we can calculate other important parameters such as the exchange currents (i0) and electron transfer heterogeneous constants (k0). The first parameter is calculated from eq 4:

graphic file with name ic3c02628_m005.jpg 4

where R is the gas constant, T is the absolute temperature, F is Faraday’s constant, and k0 is then obtained from eq 5:

graphic file with name ic3c02628_m006.jpg 5

where C stands for the concentration of the electroactive species in moles per cubic centimeter and A the electrode area in square centimeters.64

The obtained values (Table 2) again demonstrate that the best conductive and kinetic properties are obtained with the G2-DDSQ-Fc16 dendrimer electrodeposited by the potentiodynamic method.

Scanning Electron Microscopy (SEM) Analysis

The morphology of Pt electrodes modified with G1-DDSQ-Fc8 and G2-DDSQ-Fc16 was studied using scanning electron microscopy (SEM) (Figure 8 and Figure S15). The electrodes were prepared by controlled-potential electrolysis (E = 1.0 V for 5 min) and repeat cycling (20 potential cycles between 0.0 and 1.0 V). Both methods, cyclic voltammetry and electrochemical impedance spectroscopy, demonstrated the formation of multilayer films on the electrodes. The SEM images show how the films completely cover the surface of the platinum with an appreciable thickness compatible with a multilayer coating. Figure 8 and Figure S17a,b display the part of the Pt wire of which the right side was unimmersed in the ferrocene dendrimer solution and the left side of which the film was formed.

Figure 8.

Figure 8

Open in a new tab

Scanning electron microscopy images of Pt wires modified by G1-DDSQ-Fc8 using a controlled potential method at an E of 1.0 V for 5 min: (a and c) BSE (back-scattered electrons) images and (b and d) SE (secondary electron) detector.

The brightness of the pixels in a BSE image is closely related to the atomic mass of the nuclei of which the area is composed. This makes it possible to clearly distinguish between areas of pure platinum (bright) and areas of platinum covered by an organic layer. The layer covering the electrode is not smooth and uniform and shows an irregular granular surface with pores with cross-sectional sizes ranging from a few micrometers to 20 μm (Figure 9).

Figure 9.

Figure 9

Open in a new tab

Magnification of scanning electron microscopy BSE detection images of a Pt wire modified by G1-DDSQ-Fc8.

Conclusions

In conclusion, this study successfully demonstrated the synthesis of novel metallodendrimers with double-decker silsesquioxane cores. The G1 and G2 silylferrocene derivatives were synthesized through a series of condensation, reduction, and hydrosilylation reactions. Spectroscopic (1H, 13C, and 29Si NMR and FT-IR) and spectrometric (MALDI-TOF MS) techniques confirmed the structures of the synthesized compounds, while their thermal stability and solubility in common organic solvents were also verified. Electrochemical characterization using cyclic voltammetry revealed two distinct, well-separated reversible redox processes in the non-aqueous solution, indicating the electrochemical activity of the metal sites within the dendrimers (G1-DDSQ-Fc8 and G2-DDSQ-Fc16).

Moreover, the modification of platinum electrodes was successfully achieved by employing either controlled-potential electrolysis or repeated cycling within a specific potential range. CV, EIS, and SEM imaging confirmed the formation of electroactive films of the utilized dendrimers on the platinum electrodes. It is worth noting that this study represents the first report on modifying a double-decker silsesquioxane with ferrocene groups and a dendrimer having such core and terminal groups.

In summary, this research significantly contributes to the understanding of the synthesis, characterization, and electrochemical properties of dendrimers with double-decker silsesquioxane cores, opening up avenues for their potential applications in various fields.

Acknowledgments

The work was supported by National Science Centre (Poland) Project OPUS21 UMO-2021/41/B/ST5/02028 (B.D.) and Research University - Excellence Initiatives 048/13/UAM/0017 (A.M.) and 093/06/POB3/0008 (A.M.). The authors are grateful to Mr. Jan Jarożek for the graphical abstract.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.inorgchem.3c02628.

  • Materials, measurements, synthetic procedure, characterization data of the obtained products (Figures S4–S11), additional information about solubility (Table S1), thermogravimetric analysis (Table S2), cyclic voltammetry (Figures S12–S15), comproportionation constant (Kc) calculations (eqs S1–S8), equivalent circuits (Figure S16), and SEM images (Figure S17) (PDF)

Author Contributions

A.M.: conceptualization, methodology, investigation, data curation, and writing of the original draft. M.P.G.A.: methodology, investigation, and writing of the original draft. M.R.: investigation. M.N.: SEM analysis. B.D.: conceptualization, supervision, and review and editing. All authors read and agreed to the published version of the manuscript.

Caution! Extreme care should be taken in both the handling of the cryogen liquid nitrogen and its use in the Schlenk line trap to avoid the condensation of oxygen from air. Caution!tert-Butyllithium is extremely pyrophoric. Chlorodimethylsilane is extremely flammable as a liquid and vapor. In contact with water, they release flammable gases. These compounds must be handled using proper needle and syringe techniques with a vacuum Schlenk line. Contact with skin and the respiratory system should be strictly avoided. All manipulations with these compounds were performed following the reported safety procedures.65

The authors declare no competing financial interest.

Supplementary Material

ic3c02628_si_001.pdf (1MB, pdf)

References

  1. van Staveren D. R.; Metzler-Nolte N. Bioorganometallic Chemistry of Ferrocene. Chem. Rev. 2004, 104 (12), 5931–5985. 10.1021/cr0101510. [DOI] [PubMed] [Google Scholar]
  2. Xiao F.; Guo M.; Wang J.; Yan X.; Li H.; Qian C.; Yu Y.; Dai D. Ferrocene-Terminated Dendrimer Functionalized Graphene Oxide Layered Sensor toward Highly Sensitive Evaluation of Di(2-Ethylhexyl) Phthalate in Liquor Samples. Anal. Chim. Acta 2018, 1043, 35–44. 10.1016/j.aca.2018.08.046. [DOI] [PubMed] [Google Scholar]
  3. Astruc D. From Sandwich Complexes to Dendrimers: Journey toward Applications to Sensing, Molecular Electronics, Materials Science, and Biomedicine. Chem. Commun. 2023, 59, 7321–7345. 10.1039/D3CC01175E. [DOI] [PubMed] [Google Scholar]
  4. García Martínez M.; Alonso B.; Casado C. M.; Losada J.; García Armada M. P. Multioperational Oxidase Biosensors Based on Carbosilane Dendrimers with Interacting Ferrocenes. Electroanalysis 2011, 23 (12), 2888–2897. 10.1002/elan.201100404. [DOI] [Google Scholar]
  5. García Armada M. P.; Losada J.; Cuadrado I.; Alonso B.; González B.; Casado C. M. A Siloxane Homopolymer with Interacting Ferrocenes as a New Material for the Preparation of Sensors Based on the Detection of Hydrogen Peroxide. Electroanalysis 2003, 15 (13), 1109–1114. 10.1002/elan.200390134. [DOI] [Google Scholar]
  6. García Armada M. P.; Losada J.; Cuadrado I.; Alonso B.; González B.; Ramírez-Oliva E.; Casado C. M. Electrodes Modified with a Siloxane Copolymer Containing Interacting Ferrocenes for Determination of Hydrogen Peroxide and Glucose. Sens. Actuators, B: Chem. 2003, 88 (2), 190–197. 10.1016/S0925-4005(02)00326-X. [DOI] [Google Scholar]
  7. Boluda A.; Casado C. M.; Alonso B.; García Armada M. P. Efficient Oxidase Biosensors Based on Bioelectrocatalytic Surfaces of Electrodeposited Ferrocenyl Polyclosiloxanes—Pt Nanoparticles. Chemosensors 2021, 9 (4), 81–100. 10.3390/chemosensors9040081. [DOI] [Google Scholar]
  8. Deriabin K. V.; Islamova R. M. Ferrocenyl-Containing Oligosiloxanes and Polysiloxanes: Synthesis, Properties, and Application. Polym. Sci. Ser. C 2022, 64 (2), 95–109. 10.1134/S1811238222700096. [DOI] [Google Scholar]
  9. Yu G.; Suzaki Y.; Abe T.; Osakada K. Introduction of Ferrocene-Containing [2]Rotaxanes onto Siloxane, Silsesquioxane and Polysiloxanes via Click Chemistry. J. Chem. Soc., Dalton Trans. 2013, 42 (2), 1476–1482. 10.1039/C2DT31406A. [DOI] [PubMed] [Google Scholar]
  10. Aliakbari R.; Kowsari E.; Naderi H. R.; Tafreshi S. S.; Ramakrishna S.; Chinnappan A.; de Leeuw N. H. Si-Containing 3D Cage-Functionalized Graphene Oxide Grafted with Ferrocene for High-Performance Supercapacitor Application: An Experimental and Theoretical Study. J. Energy Storage 2022, 50, 104635 10.1016/j.est.2022.104635. [DOI] [Google Scholar]
  11. Losada J.; García-Armada P.; Robles V.; Martínez Á. M.; Casado C. M.; Alonso B. Carbosilane Based Dendritic Cores Functionalized with Interacting Ferrocenyl Units: Synthesis and Electrocatalytical Properties. New J. Chem. 2011, 35 (10), 2187–2195. 10.1039/c1nj20190e. [DOI] [Google Scholar]
  12. Casado C. M.; Alonso B.; Losada J.; García-Armada M. P.; Campagna S.; Ceroni P.; Puntoriero F.. Wiley Book on Designing Dendrimers; Wiley-VCH: Weinheim, Germany, 2012. [Google Scholar]
  13. Mintzer M. A.; Grinstaff M. W. Biomedical Applications of Dendrimers: A Tutorial. Chem. Soc. Rev. 2011, 40 (1), 173–190. 10.1039/B901839P. [DOI] [PubMed] [Google Scholar]
  14. Abbasi E.; Aval S. F.; Akbarzadeh A.; Milani M.; Nasrabadi H. T.; Joo S. W.; Hanifehpour Y.; Nejati-Koshki K.; Pashaei-Asl R. Dendrimers : Synthesis, Applications, and Properties. Nanoscale Res. Lett. 2014, 9 (1), 247–257. 10.1186/1556-276X-9-247. [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. Kim C.; Hong J. H. Carbosilane and Carbosiloxane Dendrimers. Molecules 2009, 14 (9), 3719–3730. 10.3390/molecules14093719. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Stone D. L.; Smith D. K.; McGrail P. T. Ferrocene Encapsulated within Symmetric Dendrimers: A Deeper Understanding of Dendritic Effects on Redox Potential. J. Am. Chem. Soc. 2002, 124 (5), 856–864. 10.1021/ja0117478. [DOI] [PubMed] [Google Scholar]
  17. Xiao F.; Liang Y.; Li S.; Gu M.; Yue L. Electrochemical Behavior of Ferrocene-Terminated Hyperbranched Polyurethane and Its Directly Electrochemical Sensing to Glucose and ATP2. J. Electroanal. Chem. 2014, 733, 77–84. 10.1016/j.jelechem.2014.09.008. [DOI] [Google Scholar]
  18. Şenel M.; Nergiz C.; Çevik E. Novel Reagentless Glucose Biosensor Based on Ferrocene Cored Asymmetric PAMAM Dendrimers. Sens. Actuators, B: Chem. 2013, 176, 299–306. 10.1016/j.snb.2012.10.072. [DOI] [Google Scholar]
  19. Dervisevic M.; Şenel M.; Sagir T.; Isik S. Boronic Acid vs. Folic Acid: A Comparison of the Bio-Recognition Performances by Impedimetric Cytosensors Based on Ferrocene Cored Dendrimer. Biosens. Bioelectron. 2017, 91, 680–686. 10.1016/j.bios.2017.01.030. [DOI] [PubMed] [Google Scholar]
  20. Mu S.; Liu W.; Ling Q.; Liu X.; Gu H. Ferrocenyl Amphiphilic Janus Dendrimers as Redox-Responsive Micellar Carriers. Appl. Organomet. Chem. 2019, 33 (6), e4908. 10.1002/aoc.4908. [DOI] [Google Scholar]
  21. Deng L.; Wang L.; Yu H.; Dong X.; Huo J. Recent Progress in Synthesis of Ferrocenyl Dendrimers and Their Application in Anion Recognition. Des. Monomers Polym. 2007, 10 (2), 131–143. 10.1163/156855507780378258. [DOI] [Google Scholar]
  22. Neumann P.; Dib H.; Sournia-Saquet A.; Grell T.; Handke M.; Caminade A. M.; Hey-Hawkins E. Ruthenium Complexes with Dendritic Ferrocenyl Phosphanes: Synthesis, Characterization, and Application in the Catalytic Redox Isomerization of Allylic Alcohols. Chem. - Eur. J. 2015, 21 (17), 6590–6604. 10.1002/chem.201406489. [DOI] [PubMed] [Google Scholar]
  23. Weisheim E.; Neumann B.; Stammler H. G.; Mitzel N. W. Dendrimers with 1, 3, 5-Trisilacyclohexane as Core Unit. J. Inorg. Gen. Chem., Z. Anorg. Allg. Chem. 2016, 642 (4), 329–334. 10.1002/zaac.201500812. [DOI] [Google Scholar]
  24. Li Z.; Hu J.; Yang L.; Zhang X.; Liu X.; Wang Z.; Li Y. Integrated POSS-Dendrimer Nanohybrid Materials: Current Status and Future Perspective. Nanoscale 2020, 12 (21), 11395–11415. 10.1039/D0NR02394A. [DOI] [PubMed] [Google Scholar]
  25. Herrero M.; Alonso B.; Losada J.; García-Armada P.; Casado C. M. Ferrocenyl Dendrimers Based on Octasilsesquioxane Cores. Organometallics 2012, 31 (17), 6344–6350. 10.1021/om300591p. [DOI] [Google Scholar]
  26. Fernández L.; Herrero M.; Alonso B.; Casado C. M.; Armada M. P. G. Three-Dimensional Electrocatalytic Surface Based on an Octasilsesquioxane Dendrimer for Sensing Applications. J. Electroanal. Chem. 2019, 839, 16–24. 10.1016/j.jelechem.2019.03.010. [DOI] [Google Scholar]
  27. Alonso B.; González B.; García B.; Ramírez-Oliva E.; Zamora M.; Casado C. M.; Cuadrado I. Functionalization via Hydrosilylation of Linear and Cyclic Siloxanes with Appendent First Generation Dendrons Containing Electronically Communicated Ferrocenyl Units. J. Organomet. Chem. 2001, 637–639, 642–652. 10.1016/S0022-328X(01)01140-8. [DOI] [Google Scholar]
  28. Morán M.; Casado C. M.; Cuadrado I.; Losada J. Ferrocenyl Substituted Octakis(Dimethylsiloxy)Octasilsesquioxanes: A New Class of Supramolecular Organometallic Compounds. Synthesis, Characterization, and Electrochemistry. Organometallics 1993, 12 (11), 4327–4333. 10.1021/om00035a018. [DOI] [Google Scholar]
  29. Cordes D. B.; Lickiss P. D.; Rataboul F. Recent Developments in the Chemistry of Cubic Polyhedral. Chem. Rev. 2010, 110, 2081–2173. 10.1021/cr900201r. [DOI] [PubMed] [Google Scholar]
  30. Croissant J. G.; Cattoën X.; Durand J. O.; Wong Chi Man M.; Khashab N. M. Organosilica Hybrid Nanomaterials with a High Organic Content: Syntheses and Applications of Silsesquioxanes. Nanoscale 2016, 8 (48), 19945–19972. 10.1039/C6NR06862F. [DOI] [PubMed] [Google Scholar]
  31. Dudziec B.; Marciniec B. Double-Decker Silsesquioxanes: Current Chemistry and Applications. Curr. Org. Chem. 2018, 21, 2794–2813. 10.2174/1385272820666151228193728. [DOI] [Google Scholar]
  32. Mrzygłód A.; Januszewski R.; Duszczak J.; Dutkiewicz M.; Kubicki M.; Dudziec B. Tricky but Repeatable Synthetic Approach to Branched, Multifunctional Silsesquioxane Dendrimer Derivatives. Inorg. Chem. Front. 2023, 10, 4587–4596. 10.1039/D3QI00500C. [DOI] [Google Scholar]
  33. Gon M.; Tanaka K.; Chujo Y. Recent Progress on Designable Hybrids with Stimuli-Responsive Optical Properties Originating from Molecular Assembly Concerning Polyhedral Oligomeric Silsesquioxane. Chem. - Asian J. 2022, 17 (10), e202200144 10.1002/asia.202200144. [DOI] [PubMed] [Google Scholar]
  34. Hou J.; Sun J.; Fang Q. Recent Advance in Low-Dielectric-Constant Organosilicon Polymers. Chin. Chem. Lett. 2023, 41, 2371–2381. 10.1002/cjoc.202300125. [DOI] [Google Scholar]
  35. John Ł.; Ejfler J. A Brief Review on Selected Applications of Hybrid Materials Based on Functionalized Cage-like Silsesquioxanes. Polymers 2023, 15 (6), 1452. 10.3390/polym15061452. [DOI] [PMC free article] [PubMed] [Google Scholar]
  36. Du Y.; Liu H. Cage-like Silsesquioxanes-Based Hybrid Materials. Dalton Trans. 2020, 49 (17), 5396–5405. 10.1039/D0DT00587H. [DOI] [PubMed] [Google Scholar]
  37. Li Z.; Li H.; Zhang J.; Liu X.; Gu Z.; Li Y. Ultrasmall Nanoparticle ROS Scavengers Based on Polyhedral Oligomeric Silsesquioxanes. Chin. J. Polym. Sci. 2020, 38 (11), 1149–1156. 10.1007/s10118-020-2486-7. [DOI] [Google Scholar]
  38. Li Z.; Li Z.; Hu J.; Feng X.; Zhang M.; Duan G.; Zhang R.; Li Y. Self-Assembly of Poly(Janus Particle)s into Unimolecular and Oligomeric Spherical Micelles. ACS Macro Lett. 2021, 10 (12), 1563–1569. 10.1021/acsmacrolett.1c00620. [DOI] [PubMed] [Google Scholar]
  39. Mituła K.; Duszczak J.; Brza̧kalski D.; Dudziec B.; Kubicki M.; Marciniec B. Tetra-Functional Double-Decker Silsesquioxanes as Anchors for Reactive Functional Groups and Potential Synthons for Hybrid Materials. Chem. Commun. 2017, 53 (75), 10370–10373. 10.1039/C7CC03958A. [DOI] [PubMed] [Google Scholar]
  40. Goseki R.; Hirai T.; Kakimoto M. A.; Hayakawa T. Iron Oxide Arrays Prepared from Ferrocene- and Silsesquioxane-Containing Block Copolymers. Int. J. Polym. Sci. 2012, 2012, 692604 10.1155/2012/692604. [DOI] [Google Scholar]
  41. Do Carmo D. R.; Paim L. L.; Stradiotto N. R. Ferrocene Adsorbed into the Porous Octakis(Hydridodimethylsiloxy) Silsesquioxane after Thermolysis in Tetrahydrofuran Media: An Applied Surface for Ascorbic Acid Determination. Mater. Res. Bull. 2012, 47 (4), 1028–1033. 10.1016/j.materresbull.2011.12.052. [DOI] [Google Scholar]
  42. Abad D. R.; Henig J.; Mayer H. A.; Reißig T.; Speiser B. Redox-Active Silica Nanoparticles. 9. 1 Synthesis, Electrochemistry, and Diffusion Properties of Caged Octakis(N-ferrocenoyl-3- Aminopropyl)Silsesquioxane. Organometallics 2014, 33, 4777–4783. 10.1021/om5000419. [DOI] [Google Scholar]
  43. Yan Song X.; Ping Geng H.; Li Q. F. The Synthesis and Characterization of Polystyrene/Magnetic Polyhedral Oligomeric Silsesquioxane (POSS) Nanocomposites. Polymer 2006, 47 (9), 3049–3056. 10.1016/j.polymer.2006.02.055. [DOI] [Google Scholar]
  44. Feng X.; Zhu S.; Yue K.; Su H.; Guo K.; Wesdemiotis C.; Zhang W.-B.; Cheng S. Z. D.; Li Y. T10 Polyhedral Oligomeric Silsesquioxane-Based Shape Amphiphiles with Diverse Head Functionalities via “Click” Chemistry. ACS Macro Lett. 2014, 3 (9), 900–905. 10.1021/mz500422g. [DOI] [PubMed] [Google Scholar]
  45. Yang X.; Liu H. Diphenylphosphine-Substituted Ferrocene/Silsesquioxane-Based Hybrid Porous Polymers as Highly Efficient Adsorbents for Water Treatment. ACS Appl. Mater. Interfaces 2019, 11 (29), 26474–26482. 10.1021/acsami.9b07874. [DOI] [PubMed] [Google Scholar]
  46. Song X.; Cheng B.; Xing J. The Thermal Properties of Polystyrene/Magnetic Polyhedral Oligomeric Silsesquioxane (POSS) Nanocomposites Prepared under Magnetic Field. Adv. Mater. Res. 2011, 335–336, 203–206. 10.4028/www.scientific.net/AMR.335-336.203. [DOI] [Google Scholar]
  47. Yang X.; Liu H. Ferrocene-Functionalized Silsesquioxane-Based Porous Polymer for Efficient Removal of Dyes and Heavy Metal Ions. Chem. - Eur. J. 2018, 24 (51), 13504–13511. 10.1002/chem.201801765. [DOI] [PubMed] [Google Scholar]
  48. Han D.; Liu Z. Q.; Zhou D. L.; Deng Y. Y.; Xiu H.; Zhang Q.; Chen F.; Fu Q. Facile Construction of Porous Magnetic Nanoparticles from Ferrocene-Functionalized Polyhedral Oligomeric Silsesquioxane-Containing Microparticles for Dye Adsorption. Ind. Eng. Chem. Res. 2020, 59 (20), 9532–9540. 10.1021/acs.iecr.0c01516. [DOI] [Google Scholar]
  49. Cuadrado I.; Casado C. M.; Alonso B.; Moran M.; Losada J.; Belsky V. Dendrimers Containing Organometallic Moieties Electronically Communicated. J. Am. Chem. Soc. 1997, 119 (32), 7613–7614. 10.1021/ja971496w. [DOI] [Google Scholar]
  50. Rzonsowska M.; Mituła K.; Duszczak J.; Kasperkowiak M.; Januszewski R.; Grześkiewicz A.; Kubicki M.; Głowacka D.; Dudziec B. Unexpected and Frustrating Transformations of Double-Decker Silsesquioxanes. Inorg. Chem. Front. 2022, 9 (2), 379–390. 10.1039/D1QI01363G. [DOI] [Google Scholar]
  51. Djoumessi Yonkeu A. L.; Ndipingwi M. M.; Ikpo C.; Nwambaekwe K.; Yussuf S.; Tesfay H.; Iwuoha E. Photoluminescence Quenching of a Novel Electroconductive Poly(Propylene Thiophenoimine)-Co-Poly(Ethylenedioxy Thiophene) Star Copolymer. Polymers 2020, 12 (12), 2894. 10.3390/polym12122894. [DOI] [PMC free article] [PubMed] [Google Scholar]
  52. Nguyen P.; Gómez-Elipe P.; Manners L. Organometallic Polymers with Transition Metals in the Main Chain. Chem. Rev. 1999, 99 (6), 1515–1548. 10.1021/cr960113u. [DOI] [PubMed] [Google Scholar]
  53. García Armada M. P.; Losada J.; López-Villanueva F. J.; Frey H.; Alonso B.; Casado C. M. Electrochemical and Bioelectrocatalytical Properties of Novel Block-Copolymers Containing Interacting Ferrocenyl Units. J. Organomet. Chem. 2008, 693 (16), 2803–2811. 10.1016/j.jorganchem.2008.05.038. [DOI] [Google Scholar]
  54. Richardson D. E.; Taube H. Determination of E2o - E1o in Multistep Charge Transfer by Stationary-Electrode Pulse and Cyclic Voltammetry: Application to Binuclear Ruthenium Ammines. Inorg. Chem. 1981, 20 (7), 1278–1285. 10.1021/ic50218a062. [DOI] [Google Scholar]
  55. Robin M. B.; Day P. Mixed Valence Chemistry-A Survey and Classification. Adv. Inorg. Chem. Radiochem. 1968, 10 (C), 247–422. 10.1016/S0065-2792(08)60179-X. [DOI] [Google Scholar]
  56. D’Alessandro D. M.; Keene F. R. A Cautionary Warning on the Use of Electrochemical Measurements to Calculate Comproportionation Constants for Mixed-Valence Compounds. Dalton Trans. 2004, (23), 3950–3954. 10.1039/b413980a. [DOI] [PubMed] [Google Scholar]
  57. Laviron E. General Expression of the Linear Potential Sweep Voltammogram in the Case of Diffusionless Electrochemical Systems. J. Electroanal. Chem. 1979, 101 (1), 19–28. 10.1016/S0022-0728(79)80075-3. [DOI] [Google Scholar]
  58. Laviron E.; Roullier L.; Degrand C. A Multilayer Model for the Study of Space Distributed Redox Modified Electrodes. Part II. Theory and Application of Linear Potential Sweep Voltammetry for a Simple Reaction. J. Electroanal. Chem. 1980, 112 (1), 11–23. 10.1016/S0022-0728(80)80003-9. [DOI] [Google Scholar]
  59. Murray R. W.Molecular Design of Electrode Surfaces; Wiley: New York, 1992. [Google Scholar]
  60. Laviron E.; Roullier L. General Expression of the Linear Potential Sweep Voltammogram for a Surface Redox Reaction with Interactions between the Adsorbed Molecules. Applications to Modified Electrodes. J. Electroanal. Chem. 1980, 115 (1), 65–74. 10.1016/S0022-0728(80)80496-7. [DOI] [Google Scholar]
  61. Armada M. P. G.; Vallejo E.; Villena C.; Losada J.; Casado C. M.; Alonso B. New Acetaminophen Amperometric Sensor Based on Ferrocenyl Dendrimers Deposited onto Pt Nanoparticles. J. Solid State Electrochem. 2016, 20 (6), 1551–1563. 10.1007/s10008-016-3160-4. [DOI] [Google Scholar]
  62. Abruña H. D.Electrochemical Interfaces: Modern Techniques for in-Situ Interface Characterization; VCH Publishers, 1991. [Google Scholar]
  63. Magar H. S.; Hassan R. Y. A.; Mulchandani A. Electrochemical Impedance Spectroscopy (Eis): Principles, Construction, and Biosensing Applications. Sensors 2021, 21 (19), 6578. 10.3390/s21196578. [DOI] [PMC free article] [PubMed] [Google Scholar]
  64. Bard A. J.; Faulkner L. R.. Electrochemical Methods. Fundamentals and Applications; 2001. [Google Scholar]
  65. Prudent practices in the laboratory: handling and management of chemical hazards; The National Academies Press: Washington, DC, 2011. [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

ic3c02628_si_001.pdf (1MB, pdf)

Articles from Inorganic Chemistry are provided here courtesy of American Chemical Society

RESOURCES