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  • Author: G. Bissert x
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The structure of Li2Mg2[Si4O11] was determined by single crystal X-ray diffraction. It is triclinic, space group P[unk], with a = 8.645(1) Å, b = 7.401(1) Å, c = 6.884(1) Å, α = 104.71(1)°, β = 101.08(1)°, γ = 99.41(1)°, V = 407.5(6) Å3 and Z = 2. Least -squares refinements based on 1462 observed reflections with intensities I ≥ 3σ(I) resulted in R = 0.054 and Rw = 0.036.

The main structural elements are chains of corner-linked [SiO4] tetrahedra and ribbons consisting of edge-linked [MgO6] octahedra and [LiOn] polyhedra. The [SiO4] tetrahedral chain can be described as a loop-branched dreier single chain. This structure type has not been reported for other silicates. Tetrahedral chains and octahedral ribbons are arranged in layers of tetrahedra and octahedra, respectively, which are alternately stacked parallel to (110) and are linked by shared oxygen atoms. This structural arrangement, known from the structures of pyroxenes, pyroxenoids and amphiboles, is compared in detail with that of the closely related pyroxenoid-like dreier single chain silicates. The topology of the tetrahedral-octahedral linkage which occurs at the apical oxygen atoms of the chains is similar to that in serandite, while the linkage with the basal oxygen atoms of the chains is similar to that in wollastonite. Thus, Li2Mg2[Si4O11] represents a new structural member of the family of the pyroxenoid-like single chain silicates.


High-temperature Ba2[Si4O10] is monoclinic with a = 23.202(5) Å, b = 4.661(1) Å, c = 13.613(4) Å, β = 97.54(2)°, C2/c, Z = 6. Using 635 independent intensities of h0l, h1l and h2l reflections its structure was determined and refined to a residual R of 7.3%. High-temperature Ba2[Si4O10] contains [Si4O10] Zweierschichten similar to those in sanbornite, low-temperature Ba2[Si4O10], but with different topology. The two crystallographically non-equivalent barium ions in high-temperature Ba2[Si4O10] have 8 + 2 and 9+1 near oxygen neighbours. The slightly lower degree of convolution of the [Si4O10] layers in comparison with those of sanbornite is explained by the increased ionic size of barium due to larger thermal motions.


Three salts of the common composition [EuCl2(X-tpy)2][EuCl4(X-tpy)]·nMeCN were obtained from EuCl3·6H2O and the respective organic ligands (X-tpy = 4′-phenyl-2,2′:6′,2″-terpyridine ptpy, 4′-(pyridin-4-yl)-2,2′:6′,2″-terpyridine 4-pytpy, and 4′-(pyridin-3-yl)-2,2′:6′,2″-terpyridine 3-pytpy). These ionic complexes are examples of salts, in which both cation and anion contain Eu3+ with the same organic ligands and chlorine atoms coordinated. As side reaction, acetonitrile transforms into acetamide resulting in the crystallization of the complex [EuCl3(ptpy)(acetamide)] (4). Salts [EuCl2(ptpy)2][EuCl4(ptpy)]·2.34MeCN (1), [EuCl2(4-pytpy)2][EuCl4(4-pytpy)]·0.11MeCN (2), and [EuCl2(3-pytpy)2][EuCl4(3-pytpy)]·MeCN (3) crystallize in different structures (varying in space group and crystal packing) due to variation of the rear atom of the ligand to a coordinative site. Additionally, we show and compare structural variability through the dimeric complexes [Eu2Cl6(ptpy)2(N,N′-spacer)]·N,N′-spacer (5, 6, 7) obtained from [EuCl3(ptpy)(py)] by exchanging the end-on ligand pyridine with several bipyridines (4,4′-bipyridine bipy, 1,2-bis(4-pyridyl)ethane bpa, and 1,2-bis(2-pyridyl)ethylene bpe). In addition, photophysical (photoluminescence) and thermal properties are presented.