Crystal structure, charge distribution and vibrational study of strontium monohydrogen (SrHAsO4)

Abstract

Crystals of a strontium monohydrogen arsenate were synthesized by hydrothermal method. The crystal structure of SrHAsO4 was re-investigated from single crystal X-ray data and by Charge-Distribution (CHARDI) investigation. The crystal is triclinic, space group P1−, a=7.361(1) Å, b=7.067(1) Å, c=7.466(1)Å; α=95.32(2)°, β=104.76(2)°, γ=88.11(3)°; Z=4 and V=373.93(2) Å3, the refinement converged to R1=0.026 and wR2=0.074 for 1315 reflections with (I)>2sigma(I). The crystal structure consists of protonated arsenate tetrahedra and SrOn polyhedra (n=7, 8). The arsenate tetrahedra are assembled in centrosymmetric tetramers via strong O(1)H(1)…O(5) (2.561 Å) and O(8)H(6)…O(8)i (2.509 Å) hydrogen bonds. Each tetramer forms a short linear chain. The disordered model hydrogen atoms are performed mainly by Charge-Distribution (CHARDI) analysis. The structural model is validated by both bond-valence-sum (BVS) and charge-distribution methods (CHARDI). Infrared and Raman spectra of the title compound have been investigated at room temperature. An assignment of bands due to internal modes is proposed. The A-B-C profile observed in the infrared spectrum confirms the presence of strong hydrogen bonds.