A thorium(Ⅳ) nitrate complex with phosphinoxide[-CH ₂P(O)Ph₂]-substituted calixarene [L·Th(OH₂)(NO₃) 2][Th(NO₃) 6]·CH 3CN has been prepared and characterized by elemental analysis and IR spectroscopy.Its crystal structure was determined by X-ray diffraction method.It belongs to triclinic crystal system, space group P1, with a=1.990(7) nm, b=2.217(8) nm, c=2.890(10) nm; α=104.92(12)°, β=100.76(14)°, γ=93.13(10)°, Z=4, V=12.033(7) nm³, R₁=0.0901, wR₂=0.1907.The complex consists of a coordination cation and a coordination anion.In the cation the thorium(Ⅳ) is coordinated to the four phosphinoxide oxygen atoms of the calixarene, four oxygen atoms from two bidentate nitrate anions and one oxygen from a water molecule forming a nine-coordinate monocapped square antiprism.In the coordination anion, the thorium(Ⅳ) is coordinated to six bidentate nitrate.In addition, an acetonitrile molecule was encapsulated in the cavity of calixarene.

Key words: thorium(Ⅳ)nitrate complex, phosphinoxide[—CH₂P(O)Ph₂]-substituted calix[4]arene, crystal structure