The compound of [Sm(NMP)_4 (H_2O)_4] [HSiMo_(12)O_(40)]·2NMP·H_2O (NMP = N-methyl-2-pyrrolidone) has been synthesized by reaction of H_4SiMo_(12)O_(40), SmCl_3 and NMP, and characterized by elemental analysis and X-ray crystal structure determination for the first time. It belongs to monoclinic space group P2_1/c, with unit cell dimensions α = 1.7501(4) nm, b = 1.8269(4) nm, c = 2.3264(5) nm, β = 106.67(3)° , V = 7.126(2) nm~3, D_c = 2.457 g/cm~3, Z = 4, R = 0.0671, wR = 0.1635. The crystal structure indicates there are four NMP and four H_2O molecules coordinated to the Sm~(3+) in the hybrid compound. Four NMP, four H_2O and one Sm~(3+) constitute a distorted dodecahedral cation which combines to the [SiMo_(12)O_(40)]~(4-) anion by static electric force. The H~+ of the molecule is between two free NMP molecules. The complex is strongly sensitive to sunlight, which results in charge- transfer by oxidation of the N-methyl-2-pyrrolidone and reduction of the polyoxometalate. The low temperature ESR spectra indicate thermal electron delocalization occurs among the Mo atoms in the title compound.

Key words: HETEROPOLYACID, CRYSTAL STRUCTURE, PYRROLIDONE P, SAMARIUM COMPLEX, THERMAL STABILITY, ESR