## 3 Results and Discussion
### Synthesis of the Metal Complexes
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline
**Complexes** & **Color** & **Yield (\%)** & **Melting Point (\({}^{\circ}\)C)** & **Solubility, \({}^{*}\) Limited** \\ \hline
**L1** & colorless & & 330 & soluble in DMSO \\ \hline
**CuL1** & yellow-green & 61 & \(>\)350 \({}^{\circ}\)C & soluble in DMSO \({}^{*}\), DMF \({}^{*}\), C\({}_{2}\)H\({}_{5}\)OH \({}^{*}\), H\({}_{2}\)O \({}^{*}\) and insoluble in THF, EtOAc, and C\({}_{6}\)H\({}_{2}\). \\ \hline
**PdL1** & brown & 72 & \(>\)350 \({}^{\circ}\)C & soluble in DMSO \({}^{*}\), DMF \({}^{*}\) and insoluble in H\({}_{2}\)O, THF, C\({}_{2}\)H\({}_{5}\)OH, EtOAc, and C\({}_{6}\)H\({}_{2}\). \\ \hline
**L2** & colorless & & 218–220 & soluble in DMSO \\ \hline
**CuL2** & yellow-green & 43 & 260–263 \({}^{\circ}\)C & soluble in DMSO \({}^{*}\) and insoluble in H\({}_{2}\)O, THF, C\({}_{2}\)H\({}_{5}\)OH, EtOAc, and C\({}_{6}\)H\({}_{2}\). \\ \hline
**PdL2** & brown & 70 & 255–257 \({}^{\circ}\)C & Soluble in DMSO \({}^{*}\), DMF \({}^{*}\) and insoluble in H\({}_{2}\)O, THF, C\({}_{2}\)H\({}_{5}\)OH, EtOAc, and C\({}_{6}\)H\({}_{2}\). \\ \hline \end{tabular}
\end{table} 
Table 2: Analytical and physical characteristics of metal complexes with 6-methyl-2-thiouracil. of PdL1 complex, the band at 3400 cm\({}^{-1}\) may refer to the stretching vibrations of molecular H\({}_{2}\)O. This band was missing in the spectrum of the CuL1 complex. In the IR spectrum of the free ligand L2, the bands at 3112 cm\({}^{-1}\) and 3093 cm\({}^{-1}\) were observed, which may refer to the stretching vibrations of N-H groups. In the spectrum of the copper complex, the same bands were observed at the same frequencies. In the IR spectrum of the PdL2 complex, these bands were shifted; the first with +5 cm\({}^{-1}\) and the second with \(-\)13 cm\({}^{-1}\) compared to those in the free ligand spectrum. This shows that the two N-H groups of the ligand participate in the coordination of PdL2. In the IR spectrum of L2, the bands at 1656 and 1243 cm\({}^{-1}\) can be attributed to the stretching vibrations of C\({}^{4}\)=O and C\({}^{2}\)=S groups, respectively. The band for the C\({}^{2}\)=S group was shifted to the lower frequencies compared to the free ligand spectrum with 11 cm\({}^{-1}\) and to the higher frequencies with 18 cm\({}^{-1}\) for the CuL2 and PdL2 complexes, respectively. The band at 3451 and 3437 cm\({}^{-1}\) in the IR spectrum of the two complexes may refer to the stretching vibrations of OH\({}^{-}\) (CuL2) and molecular H\({}_{2}\)O (PdL2), shown in Table 4. The solid-state ATR spectra confirm these findings. The stretching vibrations of C\({}^{4}\)=O and C\({}^{2}\)=S appear at 1635 and 1245 cm\({}^{-1}\) in the Raman spectrum of 6-methyl-2-thiouracil and 1661 and 1243 cm\({}^{-1}\) in that of 6-propyl-2-thiouracil, respectively. In the Raman spectrum of the CuL2, the band for the C=S group was shifted by 13 cm\({}^{-1}\) to the lower frequency. The \({}^{1}\)H NMR spectrum of 6-methyl-2-thiouracil (L1) showed four signals: a singlet at 12.29 ppm for H-1 and H-3 (overlap resonances) and the olefin proton at 5.68 ppm (H-5) and 2.06 ppm for H-1\({}^{\prime}\). These assignments were confirmed by \({}^{1}\)H-\({}^{1}\)H COSY, \({}^{1}\)H-broadband decoupled \({}^{13}\)C-NMR, DEPT-135, and HMBC spectra and are shown in Table 5. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Assignment** & **L2** & **CuL2** & **PdL2** \\ \hline v(OH) & - & 3451 & 3437 \\ \hline v(NH) & 3112 & - & 3117 \\ \hline v(NH) & 3093 & 3093 & 3080 \\ \hline v(=CH) & 3042 & 3042 & \\ \hline v(C=O) & 1656 & 1651 & 1657 \\ \hline  & 1557 & 1553 & 1545 \\ \hline v(C=S) & 1243 & 1232 & 1261 \\ \hline  & 1165 & 1166 & 1175 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Selected experimental IR data (in KBr, wavenumber in cm\({}^{-1}\)) for 6-propyl-2-thiouracil and its complexes.