### Atomic and Electronic Structure of [M(Salen)] Complexes and Their Polymers
#### 3.2.3 NEXAFS and EXAFS
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Compound** & **Atomic Pair** & **N 1 ** & **R 2 ** & **Ref.** \\ \hline \multirow{6}{*}{[Cu(Salen)]} & Cu–O2 & 1 & 1.86 \(\pm\) 0.04 & \multirow{6}{*}{[54]} \\  & Cu–O1 & 1 & 1.90 \(\pm\) 0.04 & \multirow{6}{*}{[55]} \\  & Cu–N2 & 1 & 1.95 \(\pm\) 0.002 & \\  & Cu–N1 & 1 & 1.95 \(\pm\) 0.002 & \\  & Cu–Cu & 1 & 3.22 \(\pm\) 0.03 & \\ \hline \multirow{6}{*}{[Co(Salen)]} & Co–O3  & 2.0 & 1.91 \(\pm\) 0.02 & \multirow{6}{*}{[55]} \\  & Co–O4  & 1.1 & 2.20 \(\pm\) 0.02 & \\  & Co–O4  & 1.1 & 2.20 \(\pm\) 0.02 & \\  & Co–N & 2.1 & 1.83 \(\pm\) 0.02 & \\  & Co–Co & 0.5 & 2.92 \(\pm\) 0.02 & \\  & Co–O3 & 1.8 & 1.90 \(\pm\) 0.02 & \\  [Co(Salen)] nanoparticles & Co–O4 & 1.1 & 2.20 \(\pm\) 0.02 & \\  & Co–N & 1.5 & 1.81 \(\pm\) 0.02 & \\  & Co–Co & 0.5 & 2.92 \(\pm\) 0.02 & \\ \hline \multirow{6}{*}{[Co(Salen)]} & Co–N & 2.0 & 1.90 & \multirow{6}{*}{[52]} \\  & Co–O & 2.0 & 1.86 & \\ \cline{1-1}  & Co–N & 2.0 & 1.90 & \\ \cline{1-1}  & Co–O & 2.0 & 1.86 & \\ \cline{1-1}  & Co–O & 1.6 & 1.99 & \\ \hline \multirow{6}{*}{[Ni(3-CH3 saltMe)] in powder} & Ni–N(O) & 3.5 & 1.83 \(\pm\) 0.02 & \multirow{6}{*}{[27]} \\  & Ni–C & 4.2 & 2.82 \(\pm\) 0.02 & \\ \cline{1-1}  & Ni–C & 2.2 & 3.20 \(\pm\) 0.02 & \\ \cline{1-1}  & Ni–N(O) & 3.2 & 1.83 \(\pm\) 0.02 & \\ \cline{1-1}  & Ni–C & 4.7 & 2.82 \(\pm\) 0.02 & \\ \cline{1-1}  & Ni–C & 2.2 & 3.20 \(\pm\) 0.02 & \\ \cline{1-1}  & Ni–N(O) & 3.8 & 1.84 \(\pm\) 0.02 & \\ \cline{1-1}  & Ni–C & 4.3 & 2.82 \(\pm\) 0.02 & \\ \cline{1-1}  & Ni–C & 1.5 & 3.21 \(\pm\) 0.02 & \\ \cline{1-1}  & Ni–N(O) & 3.8 & 1.84 \(\pm\) 0.02 & \\ \cline{1-1}  & poly–[Ni(3-CH3 saltMe)] red & Ni–C & 4.5 & 2.81 \(\pm\) 0.02 & \\ \cline{1-1}  & Ni–C & 2.0 & 3.19 \(\pm\) 0.02 & \\ \hline \multirow{6}{*}{[Pd(3-CH3 Salen)] powder} & Pd–O(N) & 4 & 1.97 \(\pm\) 0.002 & \multirow{6}{*}{[40]} \\  & Pd–C & 6 & 3.00 \(\pm\) 0.006 & \\ \cline{1-1}  & Pd–C & 2 & 3.24 \(\pm\) 0.004 & \\ \cline{1-1}  & Pd-O(N) & 4 & 1.98 \(\pm\) 0.002 & \\ \cline{1-1}  & Pd–C & 6 & 3.00 \(\pm\) 0.008 & \\ \cline{1-1}  & Pd–C & 2 & 3.28 \(\pm\) 0.009 & \\ \cline{1-1}  & Pd–O(N) & 4 & 1.97 \(\pm\) 0.002 & \\ \cline{1-1}  & Pd–C & 6 & 3.00 \(\pm\) 0.007 & \\ \cline{1-1}  & Pd–C & 2 & 3.24 \(\pm\) 0.005 & \\ \hline \hline \end{tabular} 1  
\end{table} 
Table 3: Structural information obtained from the analysis of M 1\(s\) EXAFS spectra for monomers and their polymers. The interesting results were also obtained for the monomeric complexes [Cu(Salen)] and [Co(Salen)] in the works [54; 55], where it was found that in powder crystals, these complexes are in the form of dimers with d-d stacking having a certain order. No less interesting results were obtained in the studies [27; 40] where EXAFS data are presented for [Pd(3-CH\({}_{3}\)Salen)], [Ni(3-CH\({}_{3}\)saltMe)] monomers, and their polymers in various charge states (reduced and completely oxidized). The authors found that the formal oxidation state of metals in the complexes is +2 and does not change during polymerization or surface immobilization. In addition, it was shown that the geometry of the coordination center remains practically unchanged as a result of polymerization and the redox cycle of the film, indicating that both processes are based on a ligand mechanism. It should be noted that the 1s NEXAFS spectra of functional atoms of nitrogen, oxygen, and carbon in monomers [M(Salen)] and their polymers are known only for the free salt ligand of the H\({}_{2}\)(Salen) molecule and the monomer [Ni(Salen)] complex [45; 46; 53]. The most valuable result obtained is the general similarity of the N 1\(s\) and C 1\(s\) NEXAFS spectra of the H\({}_{2}\)(Salen) molecule and the [Ni(Salen)] complex, with the exception of a low-intensity absorption band \(B_{1}\) (an additional vacant \(\pi^{\star}\) molecular orbital), which is observed in the N 1\(s\) spectrum of the complex 1.5 eV above the main absorption resonance \(B\) (lowest unoccupied \(\pi^{\star}\) molecular orbital) (Figure 16a).