Bidentate ligand HL was prepared by two steps from the cheap commercial available 8-hydroxyquinoline and characterized by ESI-MS,NMR and elemental analysis methods.Mononuclear complex 1 was readily obtained in good yields by heating Co(NO3)2 and HL in solution.It belongs to monoclinic system with space group P2/c,a=10.967(7) ?,b= 8.639(5) ?,c=18.087(11) ?;V=1 656.0(17) ? 3,Z=4,Dc=1.541 mg/m3,R1=0.032 0,wR2=0.078 4.The cobalt atom found in the mononuclear unit is pentacoordinate,and adopts a distorted trigonal-bipyramidal geometry,and coordinates to four atoms N2O2 of two ligands and one pyridine N atom.The PXRD experiment showed that the crystal structure of complex 1 was truly representative of their bulk materials.From TGA results,the mononuclear complex was found to have a thermal stability.