Synthesis, X-ray crystal structure, and EPR study of [Na(H2O)2]2[VO(H2O)5][SiW12O40]·4H2O

Abstract

Abstract The vanadyl salt [Na(H2O)2]2[VO(H2O)5][SiW12O40]·4H2O has been synthesized in mild conditions by cationic exchanges from dodecasilicotungstic acid. Structural determination and EPR study have been achieved on single crystals. They are tetragonal, space group P4/n with a=14.7759(1), c=10.4709(2) A, V=2286(1) A3 and Z=2. A three-dimensional framework built from Keggin anions [SiW12O40]4– linked by sodium cations in (110) and ( 1 1 0 ) planes generates channels along the c axis in which are localized aquo vanadyl complexes [VO(H2O)5]2+ and water molecules. Single crystal EPR spectra show eight hyperfine lines of the vanadium atom (I=7/2) which are split into 1:2:1 pattern when the magnetic field is parallel to the c axis. The triplet pattern may be attributed to weak dipolar interactions between the nearest-neighbor vanadium atoms which are 10.47 A apart in the infinite chain. A ring model was used to simulate the spectrum, and a very small antiferromagnetic exchange interaction was determined accurately. The EPR parameters determined are gx=gy=1.980, gz=1.9336, Ax=Ay=0.0072 cm–1, and Az=0.01805 cm–1, J=–0.00025 cm–1.