ABSTRACT
The ternary Laves phase Cd(4)Cu(7)As is the first intermetallic compound in the system Cu-Cd-As and a representative of a new substitution variant for Laves phases. It crystallizes orthorhombically in the space group Pnnm (No. 58) with lattice parameters a = 9.8833(7) Å; b = 7.1251(3) Å; c = 5.0895(4) Å. All sites are fully occupied within the standard deviations. The structure can be described as typical Laves phase, where Cu and As are forming vertex-linked tetrahedra and Cd adopts the structure motive of a distorted diamond network. Cd(4)Cu(7)As was prepared from stoichiometric mixtures of the elements in a solid state reaction at 1000 °C. Magnetic measurements are showing a Pauli paramagnetic behavior. During our systematical investigations within the ternary phase triangle Cd-Cu-As the cubic C15-type Laves phase Cd(4)Cu(6.9(1))As(1.1(1)) was structurally characterized. It crystallizes cubic in the space group Fd3m with lattice parameter a = 7.0779(8) Å. Typically for quasi-binary Laves phases Cu and As are both occupying the 16c site. Chemical bonding, charge transfer and atomic properties of Cd(4)Cu(7)As were analyzed by band structure, ELF, and AIM calculations. On the basis of the general formula for Laves phases AB(2), Cd is slightly positively charged forming the A substructure, whereas Cu and As represent the negatively charged B substructure in both cases. The crystal structure distortion is thus related to local effects caused by Arsenic that exhibits a larger atomic volume (18 Å(3) compared to 13 Å(3) for Cu) and higher ionicity in bonding.
ABSTRACT
The silver zinc hexa-deca-phosphide Ag3.73(4)Zn2.27(4)P16 is the first polyphosphide in the ternary system Ag/Zn/P. It was synthesized from stoichiometric mixtures of Ag, Zn and P in the molar ratio 4:2:16, using AgI as a mineralizing agent in a gas-phase-assisted reaction. Ag3.73(4)Zn2.27(4)P16 crystallizes in the Cu5InP16 structure type. The asymmetric unit contains two Ag/Zn sites with mixed occupancies and four P sites. One of the Ag/Zn sites is located on a twofold rotation axis. The polyanionic [P16]-substructure consists of corrugated six-membered rings that are connected into a layer via the 1-, 2-, 4- and 5-positions of the rings by a bridging P atom in each case. The layers extend parallel to the bc plane and are stacked along the a axis. Both Ag/Zn sites are tetra-hedrally coordinated by P atoms.
ABSTRACT
The first polyarsenic compound in the Cu-Cd-As system was obtained by solid-state reaction of the elements and has a refined composition of Cu(4.35â (2))Cd(1.65â (2))As(16) (tetra-copper dicadmium hexa-deca-arsenide). It adopts the Cu(5)InP(16) structure type. The asymmetric unit consists of one Cu site, a split Cu/Cd site and four As sites. The polyanionic structure can be described as being composed of As(6) rings in chair conformations which are connected in the 1-, 2-, 4- and 5-positions. The resulting layers evolve along the c axis perpendicular to the ab plane. One Cu atom exhibits site symmetry 2 and is tetra-hedrally coordinated by four As atoms. The other Cu atom, representing the split site, and the corresponding Cd atom have different coordination spheres. While the Cu atom is tetra-hedrally coordinated by four As atoms, the Cd atom has a [3 + 1] coordination with a considerably longer Cd-As distance.
