## 3 Results
### Characterization of PMMA + Complex Composites
The morphology of composite samples enriched with complexes **(4)** and **(5)** resembles that of the composites containing complexes **(1)** and **(2)**. These composites are formed by dispersed grains with diameters of 40-200 nm, which, depending on concentration, may form larger micrometric aggregates (Figure S2). Additionally, SEM-EDX analysis confirms the presence of complexes **(2)**-**(5)** in the composite samples (Figures S3 and S4, Table S1), while the presence of complex **(1)** grains in the PMMA composites was verified in a previous SEM-EDX study [32]. A crucial aspect of our study was confirming that the investigated complexes retained their structure after being incorporated into the polymer matrix. To this end, we recorded Raman spectra of pure PMMA, complexes **(2)**-**(5)**, and PMMA + (**(2)**-**(5))** composites. Analysis of the spectra confirmed that the introduction of the studied complexes into the PMMA matrix did not significantly alter their structure (Figure 3). Key to this identification were the bands observed around 1600 cm\({}^{-1}\) (\(\upnu_{\text{as}}\)(COO)), which confirm the coordination of the carboxylate group within the \(\upalpha\)-hydroxycarboxylate ligand. Additionally, the detection of \(\upnu\)(O-CR) bands between 1200 and 1000 cm\({}^{-1}\) indicates the presence of coordinated alkoxide groups characteristic of the TOCs' structure. Weak bands appearing below 900 cm\({}^{-1}\) further suggest the presence of titanium-oxo bridges. The structural stability of complex **(1)** in the PMMA + **(1)** composite had been previously confirmed [37]. In the Raman spectra of composites containing ruthenium(III) complexes, bands around 1600 cm\({}^{-1}\) were observed, confirming the coordination of ligands. Moreover, bands in the range of 1320-650 cm  
Figure 3: Raman spectra of powders **(2)** **(a)**, **(3)** **(b)**, **(4)** **(c)**, and **(5)** **(d)**, their composites containing 20 wt.% of the complex, and pure PMMA. were attributed to (CN) group vibrations, while the band near 260 cm\({}^{-1}\) corresponds to v(Ru-O) vibrations. X-ray Absorption Near-Edge Structure (XANES) spectroscopy, utilizing synchrotron radiation, was employed to confirm the structure of complexes **(1)**-**(3)** in the composite samples. This technique involves photon absorption, where core-level electrons are excited to unoccupied states when the photon energy meets or exceeds the binding energy. The absorption edge, corresponding to the core-level energy specific to each element, makes XANES an element-selective method. Titanium L-edges are rarely studied in complex titanium clusters. The discussion of electronic structures is difficult because the observed pattern depends on crystal field splitting, spin-orbit coupling, and charge transfer effects. Also, in a theoretical approach, multiplet interactions affect the Ti L-edge spectrum [60]. However, it is known that peak numbers and their positions and profiles depend strongly on the local environment. [PERSON] et al. discussed in detail XAS spectra of several Ti(IV) complexes, among them [Ti\({}_{2}\)O\({}_{2}\)(acac)\({}_{4}\)] with bridging oxo ligands. They showed that it significantly differs from tetrahedral mononuclear complexes, and four main features are observed. Nevertheless, the described complexes did not exceed the dimer. We decided to apply the XANES method for Ti L-edges for the complicated cores observed in our structures. The energy range for titanium was carefully selected to avoid the edge regions of other elements, which is crucial for proper spectra normalization. Two detection modes were also used, differing in penetration depth; the TEY detector reaches tens of nanometers, whereas the fluorescence yield (FY) detector can go up to several hundred nanometers [61]. Signals of a powder from TEY and FY detectors are comparable, and only TEY results will be presented. For composites, the TEY detector cannot provide any signal, and so results from the FY detector will be given.