Two novel Cu-6 and Mn-6 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 D-3d symmetric and were isolated as [n-BuNH3](+) salts from aqueous solutions: (n-BuNH3)(12)[(CuCl)(6)-(AsW9O33)(2)]center dot 6H(2)O (1), rhombohedral, R (3) over bar, a = 20.33(1) angstrom, c = 26.35(2) angstrom, Z = 3 and (n-BuNH3)(12)[(MnCl)(6)-(SbW9O33)(2)]center dot 6H(2)O (2). Six Cu (or Mn) atoms, each of which shows 5-fold coordination, make an approximately equatorial hexagon with a first-neighboring Cu center dot center dot center dot Cu (Mn center dot center dot center dot Mn) distance of 2.913(2) angstrom (3.248(1) angstrom) and a Cu-O-Cu (Mn-O-Mn) bond angle of 94.5(2)degrees (100.4(2)degrees). 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 Cu-6(12+) and Mn-6(12+) hexagons. The single-crystal ESR spectroscopy of 1 under the orientation of the magnetic field along a Cu-6 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 S-z = 0 and S-z = +/- 1 of D = -0.182 K to be obtained.