V-shaped polyoxotungstoarsenates incorporating a prism-like hexa transition-metals center:: [M6(H2O)2(AsW9O34)2(AsW6O26)]17-(M2+ = Mn2+, Co2+, Zn2+)#

Hexa transition-metals incorporated polyoxotungstoarsenates, [M-6(H2O)(2)(AsW9O34)(2)(AsW6O26)(17-) (M2+ = Mn2+, Co2+1, Zn2+), have been prepared at pH 7-8 and characterized by elemental analysis, electrochemistry, and X-ray crystallography: Na-17[Mn-6(H2O)(2)(AsW9O34)(2)(AsW6O26)]center dot 41H(2)O (1), P2(1)/c, a = 17.73(1) angstrom, b = 22.34(1)angstrom, c = 35.41(3) angstrom, beta = 95.37(3)degrees, V = 13963(14) angstrom(3), and Z = 4; Na-17[Co-6(H2O)(2)(AsW9O34)(2)(AsW6O26)]center dot 41H(2)O (2), P2(1)/c, a = 17.65(1) angstrom, b = 22.24(1) angstrom, c = 34.78(2) angstrom, beta = 95.84(2)degrees, V = 13584(13) angstrom(3), and Z = 4; Na-17[Zn-6(H2O)(2)(AsW9O34)(2)(AsW6O26)]center dot 38H(2)O (3), P2(1)/c, a = 17.6295(6) angstrom, beta = 22.2992(7) angstrom, c = 34.927(1) angstrom, beta = 95.695(2)degrees, V = 13662.8(7) angstrom(3), and Z = 4. The anion of 1-3 consists of two B-alpha [{M(H2O)}M-2(AsW9O34)](3-) units joined by a B-type hexa-vacant [AsW6O26](11-) fragment, corresponding to a removal of the edge-sharing W3O8 moiety from B-alpha [AsW9O34](9-), to form a C-2v-symmetric V-shaped geometry. Two edge-sharing MO6-octahedral triads (with M-M distances 3.2-3.4 angstrom) are well-separated with M...M distances of 5.5-8.9 angstrom. Three successive electrochemically quasi-reversible two-electron Mn-II/Mn-III waves were observed in the cyclic voltammogram of 1. M2+ ion with larger radius causes an elongation of the As center dot center dot center dot As distances. A single Na+ cation coordinated by three oxygen atoms (two belonging to B-alpha [AsW9O34](9-) and one belonging to B-[AsW6O26](11-)) in the crevice of the anion stabilizes the V-shaped structure.