Magnetic Properties of Poly(propylene imine)–Copper Dendromesogenic Complexes: An EPR Study

Abstract

Copper(II) complexes formed by coordination of the Cu(II) ion with liquid-crystalline poly(propylene imine) dendrimer ligand (L) of the first (complex 1) and second (complex 2) generations with various Cu(II) contents (x = Cu/L) have been studied by electron paramagnetic resonance (EPR) spectroscopy. The existence of a redox-active blue complex 1 (x = 1.9) and the copper(II) nitrate electron transfer associated with the valence tautomerism are revealed for the first time in copper-based dendrimers. It has been shown that the electronic structure of the blue complex 1 (x = 1.9) is adequately described as a mixed-valence dimer containing d9- and diamagnetic d10-configurated copper ions, and an antiferromagnetically coupled NO3* radical arising on the nitrate-bridged counter ligand. The activation energy value found for the electron transfer is about 0.35 meV, which indicates a low-energy charge dynamic. The ability of the blue and green complexes 1 (x = 1.9) dissolved in isotropic solvents to orient themselves in the magnetic field was revealed by EPR spectroscopy. The degree of orientation of the molecular z axis (S(z)) of these complexes in the magnetic field differs, depending on the type of copper(II)-complexing site in the dendrimer ligand, and can reach 0.76, which is close to S(z) = 1 (completely aligned system). A combination of magnetic and orientational parameters indicates an NO4 environment of the Cu(II) ion in green complex 1 (x = 1.9), and confirms the chain structure with intermolecular Cu(II)-NO3-Cu(II) bridges between Cu(II) centres in columns.

Magnetic Resonance and Mössbauer Studies of Superparamagnetic γ‐Fe2O3 Nanoparticles Encapsulated into Liquid‐Crystalline Poly(propylene imine) Dendrimers

“…Therefore, the value of the length of the decyloxy chain segments surrounding the PPI core of 1.505 nm was obtained by subtracting the diameter of the core (1.86 nm) from the value of a h (4.87 nm). According to our results [15,27] and those published by other groups, [13,14,46] we may conclude that maghemite NPs are electrostatically coupled with reactive (amido and amino) nitrogen periphery atoms and incorporated among the branches of PPI dendrimers. It has also been shown that iron oxide NPs have a narrow size distribution (0.5 nm) [46] Iron oxide NPs are relatively well-separated inside the dendrimer and the suggested model for the location of the NPs is presented in Scheme 1.…”

“…[12,13] Dendrimers successfully stabilize nanoparticles, playing the role of nanoreactors, and the NPs can be formed inside or outside of the dendrimer network. [14,15] At present, only the fabrication of ferrimagnetic gFe 2 O 3 nanoparticles outside the dendrimer network has been studied. [16,17] Cationic superparamagnetic iron oxide NPs were formed by using anionic polyamidoamine dendrimers; however, in this case, the size of fabricated NPs was large and the diameter was in the range from 20 to 30 nm.…”

Iron‐Containing Poly(propylene imine) Dendromesogens with Photoactive Properties

“…Like with Cu II dendrimeric complexes, [30,31] we dissolved the 1L-(FeCl 3 ) 1.8 complex in a mixture of inert solvents (chloroform/toluene ¼ 1:1), which self-organize at room temperature to a columnar mesophase. Then, this sample was sharply cooled to the glassy state in the presence of a high magnetic field (B 0 ¼ 0.5 T).…”

“…Unfortunately, the ability of iron dendrimeric complexes to be oriented in a magnetic field (similar to that reported [30,31] ) was not revealed. This may be due to the fact that both signals observed are characterized by the isotropic g-factors, and therefore, the iron centers (in spite of being organized in columnar structures) do not possess enough magnetic anisotropy to be oriented in a magnetic field.…”

Metallomesogens: Retrospectives and Perspectives

“…[134]. Заслуживает внимания и развиваемое направление, связанное с синтезом и исследованием ЖК металлодендримеров [135][136][137].…”