TY - JOUR

T1 - The structure of the NiO2N2 coordination center in the [Ni(Salen)] complex and its polymer: a comparative study by X-ray absorption spectroscopy and quantum-chemical calculations

AU - Korusenko, Petr M.

AU - Petrova, Olga V.

AU - Vereshchagin, Anatoliy A.

AU - Levin, Oleg V.

AU - Khramov, Evgeny V.

AU - Chumakov, Ratibor G.

AU - Soldatov, Mikhail A.

AU - Katin, Konstantin P.

AU - Konev, Alexander S.

AU - Vinogradov, Alexander S.

PY - 2025/6/24

Y1 - 2025/6/24

N2 - The atomic-electronic structure of the [NiO 2 N 2 ] coordination center in the [Ni(Salen)] complex and its polymer was studied using X-ray absorption spectroscopy (EXAFS and NEXAFS) techniques, supplemented by quantum chemical calculations.... The atomic-electronic structure of the [NiO 2 N 2 ] coordination center in the [Ni(Salen)] complex and its polymer was studied using X-ray absorption spectroscopy (EXAFS and NEXAFS) techniques, supplemented by quantum chemical calculations. Density functional theory (DFT) calculations were performed to construct initial models of the [Ni(Salen)] complex and identify structural fragments of the poly-[Ni(Salen)] polymer that determine its properties in both the reduced (Red) and oxidized (Ox) states. Based on the analysis of the Ni1 s EXAFS spectra, a d-d dimer model was found to best describe the structure and properties of the complex in the condensed state and can also be used as a simplified model for the polymer. It has been established that when moving from the complex to the poly-[Ni(Salen)]-Red, the square-planar structure of the [NiO 2 N 2 ] coordination center remains practically unchanged. However, during the oxidation of the monomers, the coordination center becomes distorted, which is most likely caused by the phenolate-quinone transformation of the ligand. The absorption bands in the Ni1 s NEXAFS spectra of the complex and its polymer are attributed to Ni1 s electron transitions to vacant molecular orbitals (MOs) of the NiO 2 N 2 quasi-molecule. In order to determine the final structural fragments responsible for the properties of the complex and polymer in both charge states, we compared the experimental Ni1 s spectra with the model spectra calculated using the self-consistent Green's function method. It was found that the d-d stacked dimer is the basic structural unit that best describes the complex in its condensed state. In the case of the polymers, these structures are tetramers formed by the cross-linking of d-d dimers with a total charge of 0 (Red) and +3 (with the BF 4 - counterion, Ox). A joint analysis of the Ni1 s and 2 p 3/2 NEXAFS spectra revealed that the local electronic structure of the [NiO 2 N 2 ] in the complex and poly-[Ni(Salen)]-Red is characterized by a similar vacant antibonding MOs. In contrast, in poly-[Ni(Salen)]-Ox, a new low-energy band appears in the Ni2 p 3/2 spectrum. This is due to Ni2 p 3/2 electron transitions to σ b 1 g MOs localized on Ni atoms with a reduced effective charge due to interactions with BF 4 - counterions.

AB - The atomic-electronic structure of the [NiO 2 N 2 ] coordination center in the [Ni(Salen)] complex and its polymer was studied using X-ray absorption spectroscopy (EXAFS and NEXAFS) techniques, supplemented by quantum chemical calculations.... The atomic-electronic structure of the [NiO 2 N 2 ] coordination center in the [Ni(Salen)] complex and its polymer was studied using X-ray absorption spectroscopy (EXAFS and NEXAFS) techniques, supplemented by quantum chemical calculations. Density functional theory (DFT) calculations were performed to construct initial models of the [Ni(Salen)] complex and identify structural fragments of the poly-[Ni(Salen)] polymer that determine its properties in both the reduced (Red) and oxidized (Ox) states. Based on the analysis of the Ni1 s EXAFS spectra, a d-d dimer model was found to best describe the structure and properties of the complex in the condensed state and can also be used as a simplified model for the polymer. It has been established that when moving from the complex to the poly-[Ni(Salen)]-Red, the square-planar structure of the [NiO 2 N 2 ] coordination center remains practically unchanged. However, during the oxidation of the monomers, the coordination center becomes distorted, which is most likely caused by the phenolate-quinone transformation of the ligand. The absorption bands in the Ni1 s NEXAFS spectra of the complex and its polymer are attributed to Ni1 s electron transitions to vacant molecular orbitals (MOs) of the NiO 2 N 2 quasi-molecule. In order to determine the final structural fragments responsible for the properties of the complex and polymer in both charge states, we compared the experimental Ni1 s spectra with the model spectra calculated using the self-consistent Green's function method. It was found that the d-d stacked dimer is the basic structural unit that best describes the complex in its condensed state. In the case of the polymers, these structures are tetramers formed by the cross-linking of d-d dimers with a total charge of 0 (Red) and +3 (with the BF 4 - counterion, Ox). A joint analysis of the Ni1 s and 2 p 3/2 NEXAFS spectra revealed that the local electronic structure of the [NiO 2 N 2 ] in the complex and poly-[Ni(Salen)]-Red is characterized by a similar vacant antibonding MOs. In contrast, in poly-[Ni(Salen)]-Ox, a new low-energy band appears in the Ni2 p 3/2 spectrum. This is due to Ni2 p 3/2 electron transitions to σ b 1 g MOs localized on Ni atoms with a reduced effective charge due to interactions with BF 4 - counterions.

UR - https://www.mendeley.com/catalogue/284be629-9722-3425-9b64-76e9060d2911/

U2 - 10.1039/d5cp01410g

DO - 10.1039/d5cp01410g

M3 - Article

JO - Physical Chemistry Chemical Physics

JF - Physical Chemistry Chemical Physics

SN - 1463-9076

ER -