Reinhard Nesper

A covalent view of chemical bonding in Laves phases CaLixAl2 − x

The series of compounds CaLixAl2 − x was synthesized and structurally characterized in order to probe the effect of valence electron concentration on both global and local structural features in main group intermetallics. CaLixAl2 − x compounds adopt Laves phase structures and show the following trend: (i) x = 0, MgCu2 type; (ii) 0.25 < x < 0.75, MgNi2 type; (iii) 0.80 < x < 1.0, MgZn2 type; (iv) 1.0 < x < 2.0, two-phase region; (v) x = 2, MgZn2 type. Extended Huckel calculations are used to examine local chemical bonding effects and to rationalize the observed bond distance trends and arrangement of atomic constituents in this system.

Ba4Si3Br2: a double salt of barium bromide and barium silicide containing a novel cyclotrisilicide unit.

A new compound of the composition Ba4Si3Br2 was obtained by reacting BaSi with a melt of BaBr2. Ba4Si3Br2 may be described as a double salt between a Zintl phase and a halide. The structure was determined by single-crystal X-ray diffraction (P21c, a= 1504.1(2), b = 884.5(1), c = 880.2(1) pm, beta = 101.93(2) degrees, R = 0.041 Rw = 0.079). The crystal structure contains isolated barium cations and bromide anions as well as novel singly bonded cyclotrisilicid units. The electronic structure has been studied by linear Muffin tin orbital (LMTO) band structure calculations, which reveal semiconducting behavior with a band gap of about 0.1 eV, and by an analysis of the electron localization function.

Sr12Mg17.8Li2.2Si20, die erste Zintl-Phase mit einer Si3-Kette

Summary. The investigation of the quarternary systems EA/Mg/Li/Si (EA=Ca, Sr, Ba) led to a new Zintl compound Sr12Mg17.8Li2.2Si20 with an interesting allylic Si3 unit. The electronic configuration was analyzed with the help of quantum chemical calculations.

Sr 12 Mg 17.8 Li 2.2 Si 20 , die erste Zintl -Phase mit einer Si 3 -Kette

Summary. The investigation of the quarternary systems EA/Mg/Li/Si (EA=Ca, Sr, Ba) led to a new Zintl compound Sr12Mg17.8Li2.2Si20 with an interesting allylic Si3 unit. The electronic configuration was analyzed with the help of quantum chemical calculations.