Synthesis, crystal structure, infrared and Raman spectra of Sr4Cu3(AsO4)2(AsO3OH)4×3H2O and Ba2Cu4(AsO4)2(AsO3OH)3

The two new compounds, Sr4Cu3(AsO4)2(AsO3OH)4 _ 3H2O (1) and Ba2Cu4(AsO4)2(AsO3OH)3 (2), weresynthesized under hydrothermal conditions. They represent previously unknown structure types andare the first compounds synthesized in the systems SrO/BaO-CuO-As2O5-H2O. Their crystal structureswere determined by single-crystal X-ray diffraction [space group C2/c, a ¿ 18.536(4)A° , b ¿ 5.179(1)A° ,c ¿ 24.898(5)A° , b ¿ 93.67(3)1, V ¿ 2344.0(8)A° 3, Z ¿ 4 for 1; space group P42/n, a ¿ 7.775(1)A° ,c ¿ 13.698(3)A° , V ¿ 828.1(2)A° 3, Z ¿ 2 for 2]. The crystal structure of 1 is related to a group ofcompounds formed by Cu2+-(XO4)3_ layers (X ¿ P5+, As5+) linked by M cations (M ¿ alkali, alkalineearth, Pb2+, or Ag+) and partly by hydrogen bonds. In 1, worth mentioning is the very short hydrogenbond length, D . . A ¿ 2.477(3)A° . It is one of the examples of extremely short hydrogen bonds, wherethe donor and acceptor are crystallographically different. Compound 2 represents a layered structureconsisting of Cu2O8 centrosymmetric dimers crosslinked by As1f4 tetrahedra, where f is O or OH,which are interconnected by Ba, As2 and hydrogen bonds to form a three-dimensional network. Thelayers are formed by Cu2O8 centrosymmetric dimers of CuO5 edge-sharing polyhedra, crosslinked byAs1O4 tetrahedra. Vibrational spectra (FTIR and Raman) of both compounds are described. Thespectroscopic manifestation of the very short hydrogen bond in 1, and ABC-like spectra in 2 werediscussed.