During an investigation of the insufficiently known system
M1O–
M2O–
X2O
5–H
2O (
M1 = Cd
2+, Sr
2+ and Ba
2+;
M2 = Cu
2+, Ni
2+, Co
2+, Zn
2+ and Mg
2+;
X = P
5+, As
5+ and V
5+), single crystals of the novel compound dicadmium copper(II) bis[phosphate(V)], Cd
2Cu(PO
4)
2, were obtained. This compound belongs to a small group of compounds adopting a Cu
3(PO
4)
2‐type structure and having the general formula
M1
2M2(
XO
4)
2 (
M1/
M2 = Cd
2+, Cu
2+, Mg
2+ and Zn
2+;
X = As
5+, P
5+ and V
5+). The crystal structure is characterized by the interconnection of infinite [Cu(PO
4)
2]
n chains and [Cd
2O
10]
n double chains, both extending along the
a axis. Exceptional characteristics of this structure are its novel chemical composition and the occurrence of double chains of CdO
6 polyhedra that were not found in related structures. In contrast to the isomorphous compounds, where the
M1 cations are coordinated by five O atoms, the Cd atom is coordinated by six. The dissimilarity in the geometry of
M1 coordination between Cd
2Cu(PO
4)
2 and the isomorphous compounds is mostly due to the larger ionic radius of the Cd cation in comparison with the Cu, Mg and Zn cations. Sharing a common edge, two CdO
6 polyhedra form Cd
2O
10 dimers. Each such dimer is bonded to another dimer sharing common vertices, forming [Cd
2O
10]
n double chains in the [100] direction. The Cu atoms, located on an inversion centre (site symmetry ), form isolated CuO
4 squares interconnected by PO
4 tetrahedra, forming [Cu(PO
4)
2]
n chains similar to those found in related structures. Conversely, the [Cd
2O
10]
n double chains, which were not found in related structures, are an exclusive feature of this structure.
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