Ferromagnetic Exchange Interactions for Cu612+and Mn612+Hexagons Sandwiched by Two B-α-[XW9O33]9-(X = AsIIIand SbIII) Ligands inD3d-Symmetric Polyoxotungstates
- 23 August 2006
- journal article
- research article
- Published by American Chemical Society (ACS) in Inorganic Chemistry
- Vol. 45 (19), 7698-7704
- https://doi.org/10.1021/ic060666f
Abstract
Two novel Cu6 and Mn6 hexagon sandwiched polyoxometalates, [(CuCl)6(AsW9O33)2]12- (1a) and [(MnCl)6(SbW9O33)2]12- (2a), have been synthesized and characterized by X-ray single-crystal analysis and magnetic measurements. These complexes are D3d symmetric and were isolated as [n-BuNH3]+ salts from aqueous solutions: (n-BuNH3)12[(CuCl)6(AsW9O33)2]·6H2O (1), rhombohedral, R3̄, a = 20.33(1) Å, c = 26.35(2) Å, Z = 3 and (n-BuNH3)12[(MnCl)6(SbW9O33)2]·6H2O (2). Six Cu (or Mn) atoms, each of which shows 5-fold coordination, make an approximately equatorial hexagon with a first-neighboring Cu···Cu (Mn···Mn) distance of 2.913(2) Å (3.248(1) Å) and a Cu−O−Cu (Mn−O−Mn) bond angle of 94.5(2)° (100.4(2)°). The magnetic behavior investigated by magnetic susceptibility measurements shows the ferromagnetic exchange interactions with J/k = +12.7 K (J/hc = +8.82 cm-1) and a S = 3 ground state for 1 and J/k = +0.20 K (J/hc = +0.14 cm-1) and a S = 15 ground state for 2, when only J refers to the isotropic magnetic-exchange interactions for first-neighbor atoms of the approximately equilateral Cu612+ and Mn612+ hexagons. The single-crystal ESR spectroscopy of 1 under the orientation of the magnetic field along a Cu6 hexagon's nearly 6-fold axis equal to the c axis on the variation of temperature supports the S = 3 ground state and allows an estimate of the zero-field (fine-structure) energy separation between Sz = 0 and Sz = ±1 of D = −0.182 K to be obtained.Keywords
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