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The Binary Silicides Eu 5 Si 3 and Yb 3 Si 5 – Synthesis, Crystal Structure, and Chemical Bonding
Author(s) -
Pöttgen Rainer,
Hoffmann RolfDieter,
Kußmann Dirk
Publication year - 1998
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/(sici)1521-3749(199806)624:6<945::aid-zaac945>3.0.co;2-d
Subject(s) - silicide , crystallography , zintl phase , silicon , antibonding molecular orbital , crystal structure , chemical bond , materials science , germanide , magnetic moment , magnetic susceptibility , condensed matter physics , chemistry , germanium , metallurgy , physics , atomic orbital , electron , organic chemistry , quantum mechanics
The binary silicides Eu 5 Si 3 and Yb 3 Si 5 were prepared from the elements in sealed tantalum tubes and their crystal structures were determined from single crystal X‐ray data: I4/mcm, a = 791.88(7) pm, c = 1532.2(2) pm, Z = 4, w R2 = 0.0545, 600 F 2 values, 16 variables for Eu 5 Si 3 (Cr 5 B 3 ‐type) and P62m, a = 650.8(2) pm, c = 409.2(1) pm, Z = 1, w R2 = 0.0427, 375 F 2 values, 12 variables for Yb 3 Si 5 (Th 3 Pd 5 type). The new silicide Eu 5 Si 3 contains isolated silicon atoms and silicon pairs with a Si–Si distance of 242.4 pm. This silicide may be described as a Zintl phase with the formula [5 Eu 2+ ] 10+ [Si] 4– [Si 2 ] 6– . The silicon atoms in Yb 3 Si 5 form a two‐dimensional planar network with two‐connected and three‐connected silicon atoms. According to the Zintl‐Klemm concept the formula of homogeneous mixed‐valent Yb 3 Si 5 may to a first approximation be written as [3 Yb] 8+ [2 Si – ] 2– [3 Si 2– ] 6– . Magnetic susceptibility investigations of Eu 5 Si 3 show Curie‐Weiss behaviour above 100 K with a magnetic moment of 7.85(5) μ B which is close to the free ion value of 7.94 μ B for Eu 2+ . Chemical bonding in Eu 5 Si 3 and Yb 3 Si 5 was investigated by semi‐empirical band structure calculations using an extended Hückel hamiltonian. The strongest bonding interactions are found for the Si–Si contacts followed by Eu–Si and Yb–Si, respectively. The main bonding characteristics in Eu 5 Si 3 are antibonding Si1 2 ‐π* and bonding Eu–Si1 states at the Fermi level. The same holds true for the silicon polyanion in Yb 3 Si 5 .