Synthesis, X-ray crystal structure, and EPR study of [Na(H 2O) 2] 2[VO(H 2O) 5][SiW 12O 40]·4H 2O

• Published in: Solid state sciences Vol. 3; no. 3; pp. 329 - 338
• Main Authors: Tézé, André, Marchal-Roch, Catherine, So, Hyunsoo, Fournier, Michel, Hervé, Gilbert
• Format: Journal Article
• Language: English
• Published: Elsevier Masson SAS 2001
• Subjects: EPR spectroscopy; Heteropolyanion; Vanadyl salt; Heteropolyanion; Vanadyl salt; EPR spectroscopy
• ISSN: 1293-2558; 1873-3085
• DOI: 10.1016/S1293-2558(00)01136-5

The vanadyl salt [Na(H 2O) 2] 2[VO(H 2O) 5][SiW 12O 40]·4H 2O 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) Å, V=2286(1) Å 3 and Z=2. A three-dimensional framework built from Keggin anions [SiW 12O 40] 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(H 2O) 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 Å 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 g x = g y =1.980, g z =1.9336, A x = A y =0.0072 cm –1, and A z =0.01805 cm –1, J=–0.00025 cm –1.