Synthesis, Crystal Structure And Properties Of The Bichromium(â…¢)(1,2)-substituted Tungstosilicate

A new bi-chromium(III)-substituted Keggin-type compound[N(CH3)4]4[A-β(1,2)-SiW10Cr2O36(HO)2(H2O)2]·5H2O (1), was synthesized with theconventional method from A-β-SiW9. And the transformation of β-SiW9into β-SiW10inreaction process is very scare, what’s more, the β-type is restained in the reaction process. Thestructure does not have both positional and inversion center disorder which is a rare exampleof a substituted Keggin poly. Before many research groups obtain the β-SiW10fromisomerization of γ-SiW10O368–, therefore we find a new method to combine the compounds ofβ-SiW10. A single-crystal X-ray analysis reveals the compound1crystallizes in orthorhombicsystem, space group P2(1)2(1)2(1) with a=12.495(5), b=13.068(5), c=34.428(5), V=5621.563, Z=4.In1, CrO4(OH)(H2O) and CrO3(HO)2(H2O) octahedra are corner-linked and filled (1,2)two vacancies of the A-β-SiW9O3410–. The other vacancy is occupied by a WO6octahedron,leading to a β-pseudo Keggin anion,[A-β(1,2)-SiW10Cr2O36(HO)2(H2O)2]4–. In the anionbridge oxygen atoms (O33,O21) of Cr1-O33-Cr2and Cr2-O21-W8, the terminal oxygenatoms(O16,O27) of Cr1and Cr2are protonated according to Bond Valence Sum calculation.Cyclic Voltammetry of1indicates that CrIIIhas not occured redox processes of CrIII/CrIIand1have less negative potentials than β-SiW12, due to the replace of CrIII. Photoluminescentemission peaks of CrIIIare observed at410-500nm which is attributed to the4A2gâ†'4T1gtransition confirming by theoretical calculation. In solid diffuse reflexion spectrum of1,4A2gâ†'4T2gtransition of CrIIIion occurs at λmax=634nm. And the Band gap of1is2.35ev,so1is semiconductor. The measurement of variable temperature magnetic susceptibilityindicates that in1there exists antiferromagnetic interaction between Cr3+atoms. Theconclution is consistent with other bi-nuleus metal replaced Keggin-type Polyoxometalates.