BaAuP and BaAuAs, Synthesis via Disproportionation of Gold
and (2) conventional oxidation states are given with the Table 1. Interatomic distances /pm for BaAuX, X ϭ P, As (stan-
dard deviations).
signs indicating the correct polarisation: gold has a positive
charge (Auϩδ) in BaAuX and a negative one (AuϪδ) in
Atomic contact
BaAuP
BaAuAs
multiplicity
BaAu2.
Au
Ba
X
ϪX
ϪBa
ϪX
ϪAu
ϪAu
ϪBa
254.42(3)
339.61(4)
339.61(4)
339.61(4)
254.42(3)
339.61(4)
261.84(3)
345.68(3)
345.68(3)
345.68(3)
261.84(3)
345.68(3)
3
6
6
6
3
6
products have been characterised by powder diffraction,
single crystal diffraction and resistivity measurements. It
has been demonstrated that elemental gold disproportion-
ates in the presence of pnictides Ba3X2, whereby the pnic-
tides are acting as bases.
Experimental Section
Synthesis
The BaAuX (X ϭ P, As) compounds were prepared by the reaction
of Ba3X2 and Au (1:4), with BaAu2 as a by-product in stoichio-
metric amounts. An optimised synthesis, realised by the reaction of
BaX with elemental gold, leads to pure samples of BaAuP and
BaAuAs. The barium pnictides were prepared from the elements in
corundum crucibles. The crucibles were sealed in quartz ampoules,
and heated at 1020 K for 48 h.
Figure 2. Electric resistivity vs. temperature for BaAuP and
BaAuAs.
Both, BaAuP and BaAuAs, crystallise in the space group
P63/mmc (no. 194, Pearson code hP6), as previously found
by determination of the lattice constants from powder dif-
fraction data [10]. The structure represents an ordered vari-
ant of the AlB2 type of structure, similar to ZrBeSi. Com-
plex anions 2ϱ[AuX]2Ϫ are forming sheets corresponding to
hexagonal boron nitride, with the barium cations in-
between (Figure 3), resulting in a 6ϩ6 coordination for
barium, and a mutual trigonal planar coordination for the
pnictides and gold atoms (Table 1).
Stoichiometric amounts of BaX and gold powder (fine gold pow-
ders can be obtained as described previously [11]) were mixed in a
dry-box (MBraun, Garching, Germany) in an argon atmosphere
(< 0.1 ppm O2, H2O) and sealed in tantalum ampoules. The
reaction was carried out with the following temperature profile:
298
Ǟ , subsequent annealing for 48 h);
1220 K (50 K·hϪ1
1220 Ǟ 298 K (50 K·hϪ1).
The solidified black reguli are sensitive to humid air and must be
handled in an inert atmosphere.
X-ray Analysis
All samples were examined by X-ray powder diffraction. Powder
patterns were collected with a linear position-sensitive detector
with a STADI P diffractometer in DebyeϪScherrer geometry,
˚
with Ge-monochromated Cu-Kα1 radiation, λ ϭ 1.540598 A,
5 < 2θ < 100° (Stoe & Cie GmbH, Darmstadt, Germany). Samples
were sealed in glass capillaries of 0.3 mm diameter.
For single-crystal X-ray diffraction experiments, black single crys-
tals were selected in a dry-box and mounted in sealed glass capillar-
ies. Data collection, at 296(2) K, was carried out with a STADI4
four circle diffractometer (Stoe & Cie GmbH, Darmstadt, Ger-
many) and a Smart 1000 K three circle diffractometer (Bruker
AXS, Karlsruhe, Germany), respectively. The structures were
solved by direct methods and refined by full-matrix least-squares
using the SHELXTL program package [12]. Experimental details
are given in Table 2, atomic coordinates and anisotropic displace-
ment parameters are given in Table 3 and Table 4.
Figure 3. Perspective representation of the crystal structure of
BaAuP, with the margins of the unit cell (grey).
Conclusions
Electrical Resistivity
BaAuP and BaAuAs have been synthesised by solid state
Temperature dependent resistivity has been obtained for pressed
reactions from Ba3X2 (BaX) and gold. The reaction pellets using van der Pauw method [16]. The ground powders were
Z. Anorg. Allg. Chem. 2009, 1514Ϫ1516
2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Nuss, Juergen
