Synthesis, crystal structure, infrared and Raman spectra of Sr 4Cu 3(AsO 4) 2(AsO 3OH) 4·3H 2O and Ba 2Cu 4(AsO 4) 2(AsO 3OH) 3

Abstract

The two new compounds, Sr 4Cu 3(AsO 4) 2(AsO 3OH) 4·3H 2O (1) and Ba 2Cu 4(AsO 4) 2(AsO 3OH) 3 (2), were synthesized under hydrothermal conditions. They represent previously unknown structure types and are the first compounds synthesized in the systems SrO/BaO–CuO–As 2O 5–H 2O. Their crystal structures were determined by single-crystal X-ray diffraction [space group C2/ c, a=18.536(4) Å, b=5.179(1) Å, c=24.898(5) Å, β=93.67(3)°, V=2344.0(8) Å 3, Z=4 for 1; space group P4 2 /n, a=7.775(1) Å, c=13.698(3) Å, V=828.1(2) Å 3, Z=2 for 2]. The crystal structure of 1 is related to a group of compounds formed by Cu 2+–( X O 4) 3− layers ( X=P 5+, As 5+) linked by M cations ( M=alkali, alkaline earth, Pb 2+, or Ag +) and partly by hydrogen bonds. In 1, worth mentioning is the very short hydrogen bond length, D···A=2.477(3) Å. It is one of the examples of extremely short hydrogen bonds, where the donor and acceptor are crystallographically different. Compound 2 represents a layered structure consisting of Cu 2O 8 centrosymmetric dimers crosslinked by As1 φ 4 tetrahedra, where φ is O or OH, which are interconnected by Ba, As2 and hydrogen bonds to form a three-dimensional network. The layers are formed by Cu 2O 8 centrosymmetric dimers of CuO 5 edge-sharing polyhedra, crosslinked by As1O 4 tetrahedra. Vibrational spectra (FTIR and Raman) of both compounds are described. The spectroscopic manifestation of the very short hydrogen bond in 1, and ABC-like spectra in 2 were discussed.