Mono-substituted cage-like silsesquioxanes of the T8-type can play the role of potential ligands in the coordination
chemistry. In this paper, we report on imine derivatives as ligands
for samarium, terbium, and erbium cations and discuss their efficient
synthesis, crystal structures, and magnetic and optical properties.
X-ray analysis of the lanthanide coordination entities [MCl3(POSS)3]·2THF [M = Er3+ (3), Tb3+ (4), Sm3+ (5)] showed that all three compounds crystallize in the same space
group with similar lattice parameters. All compounds contain an octahedrally
coordinated metal atom, and additionally, 3 and 5 structures are strictly isomorphous. However, surprisingly,
there are two different molecules in the crystal structure of the
terbium coordination entity 4, monomer (sof 65%) and
dimer (sof 35%), with one and two metal centers. Absorption measurements
of the investigated materials recorded at 300 K showed that regardless
of the lanthanide involved, their energy band gap equals 2.7 eV. Moreover,
the analogues containing Tb3+ and Sm3+ exhibit
luminescence typical of these rare earth ions in the visible and infrared
spectral range, while the compound with Er3+ does not generate
any emission. Direct current variable-temperature magnetic susceptibility
measurements on polycrystalline samples of 3–5 were performed between 1.8 and 300 K. The magnetic properties of 3 and 4 are dominated by the crystal field effect
on the Er3+ and Tb3+ ions, respectively, hiding
the magnetic influence between the magnetic cations of adjacent molecules.
Complex 5 exhibits a nature typical for the paramagnetism
of the samarium(III) cation.
In alkali metal and lanthanide coordination chemistry, triphenylsiloxides seem to be unduly underappreciated ligands. This is as surprising as that such substituents play a crucial role, among others, in stabilizing rare oxidation states of lanthanide ions, taking a part of intramolecular and molecular interactions stabilizing metal-oxygen cores and many others. This paper reports the synthesis and characterization of new lithium [Li4(OSiPh3)4(THF)2] (1), and sodium [Na4(OSiPh3)4] (2) species, which were later used in obtaining novel gadolinium [Gd(OSiPh3)3(THF)3]·THF (3), and erbium [Er(OSiPh3)3(THF)3]·THF (4) triphenylsiloxides. Crystal structures were determined for all 1–4 compounds, and in addition, IR, Raman, absorption spectroscopy studies were conducted for 3 and 4 lanthanide compounds. Furthermore, direct current (dc) variable-temperature magnetic susceptibility measurements on polycrystalline samples of 3 and 4 were carried out in the temperature range 1.8–300 K. The 3 shows behavior characteristics for the paramagnetism of the Gd3+ ion. In contrast, the magnetic properties of 4 are dominated by the crystal field effect on the Er3+ ion, masking the magnetic interaction between magnetic centers of neighboring molecules.
The synthesis and structural characterization of two new potassium triphenylsiloxides, namely, aqua(propan-2-ol)hexakis(triphenylsilanolato)hexapotassium toluene disolvate, [K6(C18H15OSi)6(C3H8O)(H2O)]·2C7H8, and diaquahexakis(triphenylsilanolato)hexapotassium, [K6(C18H15OSi)6(H2O)2], are reported. Both compounds crystallize in the triclinic space group P\overline{1}. The structure in each case resembles an alkali metal polyoxometalate-like structure, in which electrostatic interactions are observed in the metal–oxygen core. Furthermore, both compounds also resemble a reverse micelles-like architecture, in which the hydrophilic core is enclosed in a hydrophobic shell. The cores of the complexes are flanked by hydrophobic aromatic rings derived from Ph3SiO− anions, where intramolecular π-interactions between the aromatic rings and potassium cations stabilize the cores of the crystals. Moreover, in both structures, the presence of hydrogen bonds is observed; until now, no crystal structures have been described containing K atoms and triphenylsiloxide molecules in which the presence of hydrogen bonds was confirmed. Thus, these coordination entities could be considered as attractive reagents for further synthetic protocols towards heterometallic complexes.
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