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We report the synthesis and single-crystal X-ray diffraction, magnetic, and luminescence measurements of a novel family of luminescent cage-like tetranuclear silsesquioxanes (PhSiO1.5)8(LnO1.5)4(O)(C5H8O2)6(EtOH)2(CH3CN)2â 2CH3CN (where Ln = Tb, 1; Tb/Eu, 2; and Gd, 3), featuring seven-coordinated lanthanide ions arranged in a one-capped trigonal prism geometry. Compounds 1 and 2 exhibit characteristic Tb3+ and Tb3+/Eu3+-related emissions, respectively, sensitized by the chelating antenna acetylacetonate (acac) ligands upon excitation in the UV and visible spectral regions. Compound 3 is used to assess the energies of the triplet states of the acac ligand. For compound 1, theoretical calculations on the intramolecular energy transfer and multiphonon rates indicate a thermal balance between the 5D4 Stark components, while the mixed Tb3+/Eu3+ analog 2, with a Tb:Eu ratio of 3:1, showcases intra-cluster Tb3+-to-Eu3+ energy transfer, calculated theoretically as a function of temperature. By utilizing the intensity ratio between the 5D4â7F5 (Tb3+) and 5D0â7F2 (Eu3+) transitions in the range 11-373 K, we demonstrate the realization of a ratiometric luminescent thermometer with compound 2, operating in the range 11-373 K with a maximum relative sensitivity of 2.0% K-1 at 373 K. These findings highlight the potential of cage-like silsesquioxanes as versatile materials for optical sensing-enabled applications.
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New luminescent cage-like tetranuclear silsesquioxanes [NEt4][(Ph4Si4O8)2(Tb3Eu)(NO3)4(OH)(EtOH)3(H2O)]·4(EtOH) (1) and [NEt4]2[(Ph4Si4O8)2(Tb2Eu2)(NO3)6(EtOH)2(MeCN)2]·4(MeCN) (2) present a tunable thermosensitive Tb3+-to-Eu3+ energy transfer driven by Tb3+ and Eu3+ emission and may be used as temperature sensors operating in the range 41-100 °C with excellent linearity (R 2 = 0.9990) and repeatability (>95%). The thermometer performance was evidenced by the maximum relative sensitivity of 0.63% °C-1 achieved at 68 °C.
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Invited for the cover of this issue are Alexeyâ N. Bilyachenko, Joulia Larionova and co-workers at the Russian Academy of Sciences, the Peoples' Friendship University of Russia, and University of Montpellier. The image depicts lanthanide-based cage-like silsesquioxanes exhibiting magnetic and luminescence properties that could constitute a particularly interesting new family related to multifunctional nanomaterials. Read the full text of the article at 10.1002/chem.202003351.
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The synthesis, structure, magnetic, and luminescence properties investigations of four new cage-like lanthanide-based silsesquioxanes (Cat)2 [(PhSiO1.5 )8 (LnO1.5 )4 (O)(NO2.5 )6 (EtOH)2 (MeCN)2 ] (where Cat+ =Et4 N+ , PPh4 P+ and Ln3+ =Eu3+ , Tb3+ and (Ph4 P)4 [(PhSiO1.5 )8 (TbO1.5 )4 (O)2 (NO2.5 )8 ]â 10MeCN are reported. They present an unusual prism-like topology of cage architectures and lanthanide-characteristic emission, which makes them the first luminescent cage-like lanthanide silsesquioxanes. One of the Tb3+ -based cages presents a magnetic spin-flip transition.
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A new "bicycle helmet"-like copper(ii),sodiumphenylsilsesquioxane Ph12Si12O12(OH)(O-)11Cu5Na(bipy)3(H2O) exhibited high catalytic efficiency in two homogeneous reactions: (i) functionalization of C-H compounds; (ii) formation of benzamides from alcohols.
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The first Ni(ii)-based metallagermaniumsesquioxane cage compound [(PhGeO1.5)10(NiO)4(NaO0.5)2] presents a sandwich-like structure where two germsesquioxane cages are linked through an {NiO}4 core and exhibits slow dynamics of the magnetization.
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A new representative of an unusual family of metallagermaniumsesquioxanes, namely the heterometallic cagelike phenylgermsesquioxane (PhGeO2)12Cu2Fe5(O)OH(PhGe)2O5(bipy)2 (2), was synthesized and structurally characterized. Fe(III) ions of the complex are coordinated by oxa ligands: (i) cyclic (PhGeO2)12 and acyclic (Ph2Ge2O5) germoxanolates and (ii) O2- and (iii) HO- moieties. In turn, Cu(II) ions are coordinated by both oxa (germoxanolates) and aza ligands (2,2'-bipyridines). This "hetero-type" of ligation gives in sum an attractive pagoda-like molecular architecture of the complex 2. Product 2 showed a high catalytic activity in the oxidation of alkanes to the corresponding alkyl hydroperoxides (in yields up to 30%) and alcohols (in yields up to 100%) and in the oxidative formation of benzamides from alcohols (catalyst loading down to 0.4 mol % in Cu/Fe).
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The synthesis, composition, and catalytic properties of a new family of hexanuclear Cu(II)-based phenylsilsesquioxanes are described here. Structural studies of 17 synthesized compounds revealed the general principle underlying their molecular topology: viz., a central metal oxide layer consisting of two Cu3 trimers is coordinated by two cyclic [PhSiO1.5]5 siloxanolate ligands to form a skewed sandwich architecture with the composition [(PhSiO1.5)10(CuO)6]2+. In addition to this O ligation by the siloxanolate rings, two opposite copper ions are additionally coordinated by the nitrogen atoms of corresponding N ligand(s), such as 2,2'-bipyridine (compounds 1-9), 1,10-phenanthroline (compounds 10-13), mixed 1,10-phenanthroline/2,2'-bipyridine (compound 14), or bathophenanthroline (compounds 15-17). Finally, the charge balance is maintained by two HO- (compounds 1-7, 10-13, and 15-17), two H3CO- (compound 8), or two CH3COO- (compounds 9 and 14) anions. Complexes 1 and 10 exhibited a high activity in the oxidative amidation oxidation of alcohols. Compounds 1, 10, and 15 are very efficient homogeneous catalysts in the oxidation of alkanes and alcohols with peroxides.
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Herein, the effect of replacement of the surrounding solvent and/or the partial substitution of sodium ions in the cage-like copper, sodium phenylsilsesquioxane [(PhSiO1.5)12(CuO)4(NaO0.5)4(n-BuOH)6] 1 with a globular structure was investigated; the synthesis of ten new derivatives of complex 1 was performed, and their crystal structures were determined. Solvate replacement of n-butanol in 1 with dimethyl sulfoxide, acetonitrile, 1,4-dioxane/EtOH, and 1,4-dioxane/PhCN afforded the complexes [(PhSiO1.5)12(CuO)4(NaO0.5)4(DMSO)8] (2), [(PhSiO1.5)12(CuO)4(NaO0.5)4(MeCN)6(H2O)2]·2MeCN (3), [(PhSiO1.5)12(CuO)4(NaO0.5)4(C4H8O2)(EtOH)4]·0.5EtOH (4), and [(PhSiO1.5)12(CuO)4(NaO0.5)4(C4H8O2)4(H2O)3]·2PhCN·2C4H8O2·H2O (5). In an aqueous solution of EtOH, a rearrangement reaction occurred instead of substitution, which resulted in a new complex, [(PhSiO1.5)10(CuO)2(NaO0.5)2(H2O)6] (6), with a cooling tower molecular structure. Transmetalation reactions of 1 with KCl or CsF resulted in the formation of the trimetallic complexes [(PhSiO1.5)12(CuO)4(NaO0.5)2(KO0.5)2(DMF)6] (7), [(PhSiO1.5)12(CuO)4(NaO0.5)(CsO0.5)3(DMF)4(DMSO)(H2O)]·1.5DMF (8), [(PhSiO1.5)12(CuO)4(NaO0.5)2(CsO0.5)2(DMF)8]·0.5H2O (9), and [(PhSiO1.5)12(CuO)4(NaO0.5)3(CsO0.5)(DMF)4] (10). The replacement of sodium ions of 1 by the bulky non-metallic cation PhMe3N+ upon the interaction of 1 with PhMe3NCl in a MeCN medium afforded the complex (PhNMe3)2[(PhSiO1.5)12(CuO)4(NaO0.5)2(O)(MeCN)4]·4MeCN (11). X-ray analysis confirmed the successful replacement of terminal butanol molecules in all complexes and the stability of the globular cage of the parent complex under the reaction conditions, with the exceptions of complexes 6 and 9 that underwent an unprecedented reorganization of cage metallasilsesquioxane (CLMS) units into the cooling tower and sandwich-like cages, respectively. The stability of the cage during substitution reactions provides the first experimental evidence that polynuclear cage metallasilsesquioxanes can act as building blocks for the construction of coordination polymers, opening new ways for the synthesis of hybrid CLMS-based frameworks. In particular, the compounds 4, 6, 7, 9, and 10 are one-dimensional coordination polymers, and 5 and 8 are two-dimensional coordination polymers with a square lattice topology. A magnetism study of the coordination polymer compounds 5, 6, 8, and 9 showed antiferromagnetic behavior between copper centers.
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Three types of unusual cagelike copper(II) methylsilsesquioxanes, namely, nona- [(MeSiO1.5)18(CuO)9] 1, hexa- [(MeSiO1.5)10(HO0.5)2(CuO)6(C12H8N2)2(MeSiO1.5)10(HO0.5)1.33(CH3COO0.5)0.67(CuO)6(C12H8N2)2] 2, [(MeSiO1.5)10(CuO)6(MeO0.5)2(C10H8N2)2] 3, and trinuclear [(MeSiO1.5)8(CuO)3(C10H8N2)2] 4, were obtained in 44%, 27%, 20%, and 16% yields, respectively. Nuclearity and structural fashion of products was controlled by the choice of solvent system and ligand, specifically assisting the assembling of cage. Structures of 1-4 were determined by single-crystal X-ray diffraction analysis. Compounds 1 and 4 are the first cage metallasilsesquioxanes, containing nine and three Cu ions, respectively. Product 1 is the first observation of nonanuclear metallasilsesquioxane ever. Unique architecture of 4 represents early unknown type of molecular geometry, based on two condensed pentamembered siloxane cycles. Topological analysis of metal clusters in products 1-4 is provided. Complex 1 efficiently catalyzes oxidation of alcohols with tert-butylhydroperoxide TBHP to ketones or alkanes with H2O2 to alkyl hydroperoxides in acetonitrile.