### Atomic and Electronic Structure of [M(Salen)] Complexes and Their Polymers  
#### 3.2.1 Xps  
Research in recent years has been characterized by individual attempts to use the XPS method to obtain information on the chemical state of functional atoms in monomers and their poly-[M(Salen)] polymers, as well as on the atomic structure of these polyatomic systems [26; 39; 43; 44; 45; 46; 48; 49; 50; 51; 52; 114]. It should be noted that all the cited measurements of XPS spectra are mainly of a test nature, and most of them were performed on laboratory installations using X-ray tubes as radiation sources with low energy resolution and insufficiently good statistics. For monomers, there are only a few works [39; 44; 45; 46; 50; 51; 52] in which the positions of binding energies of the 1s electrons of the ligand atoms (N, C, O) as well as 2\(p\), 3\(d\), or 4\(f\) electrons of the corresponding metal atoms were measured for the complexes [M(Salen)] (M = Cu, Ni, Co, Pd, Pt) using the XPS method (Table 2). From the data in Table 2, the trends in the shifts of the O 1\(s\) lines (to lower binding energies) and N 1s lines (to higher binding energies) in going from a molecule (salen without a metal) to complexes are clearly visible, which indicates a redistribution of the valence electron density between the metal and ligand atoms. However, all these measurements, with the exception of those in works [45; 46], were carried out mainly on powdered samples that can be charged as a result of X-ray irradiation, thereby distorting the real binding energies of core electrons. To eliminate charging, the H\({}_{2}\)(Salen) and [Ni(Salen)] samples for XPS measurements were prepared _in situ_ in the form of thin (about 10-50 nm thick) layers using thermal evaporation of dehydrated powders of the corresponding substances from a quartz crucible and subsequent deposition onto clean polycrystalline platinum plates under ultrahigh vacuum conditions (about 10\({}^{-9}\) mbar). Herewith, Ni 2\(p\), O 1\(s\), N 1\(s\), C 1\(s\) photoelectron spectra for the systems under study were measured using monochromatic Al K\(\alpha\) radiation (\(h\
u\) = 1486.6 eV) with an analyzer pass energy of 10 eV and good statistics (more than 10\({}^{3}\) counts at each point). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Compound**} & \multicolumn{4}{c}{**\(E_{\text{{}_{\text{{}_{\text{{}_{\text{{}_{\text{{}_{\text{\text{}_{\text{ \text{\text{\text{\text{\text{\text{\text{\text{\texttext{ }}}}}}  
The important results obtained in these works include that the carbon atoms in the complex form two groups of atoms, C\(\alpha\) (C1, C4) and C\(\beta\) (C2, C3, C5), with similar chemical (charge) states, which are associated with carbon atoms in phenyl rings or with nitrogen and oxygen atoms in phenolic and ethylenediamine fragments, respectively (see Figure 1). It was found that the observed shifts of C 1\(s\) (+1.0 eV), N 1\(s\) (+1.9 eV), and O 1\(s\) (-0.4 eV) photoelectron lines in going from H\({}_{2}\)(Salen) to [Ni(Salen)] are caused by the chemical bonding of the Ni 3\(d\) atom with salen ligand atoms and, as a result, a redistribution of valence electron density between the metal and ligand atoms (see Figure 14). It is also noted that the different signs of the chemical shifts indicate that the transfer of electron density to the O atoms in [Ni(Salen)] occurs not only from the Ni atom but also from the N and C atoms. In the case of polymers, the most interesting of the studies mentioned above are the works [26; 39], in which the XPS method, along with testing the purity and stoichiometry of polymers, was first used to study the distribution of the valence electron density and changes in the binding energies of inner-shell electrons in a large number of electro- and photoactive polymers poly-[M(Salen)] with M = Cu(II), Ni(II), Pd(II), Pt(II).