四核苯甲酸锌配合物的合成与发光性质

Synthesis and Luminescent Property of Tetranuclear Zinc Benzoate

通过将流变相反应制得的苯甲酸锌Zn(C6H5CO2)2热解得到了具有无限延伸三维结构的超分子化合物四核苯甲酸锌Zn4O(C6H5CO2)6,并对其发光性质、发光机理及其与结构的关系进行了初步探讨。X射线单晶衍射测定结果表明该化合物属于单斜晶系,Ia 3d空间群,它具有很大的晶胞,晶胞参数为:a=41 0063(18) ,V=68953(5) 3,Z=48。该化合物在紫外或可见光的激发下(λex=330,460nm),可以发出类似于Zn4O(CH3CO2)6的较强荧光(λem=530nm),该发射带属于pπ (L,O2-)→4sσ(Zn2+)的配体 金属的电荷迁移跃迁发射(LMCT)。分子中4个Zn原子与中心O原子及配体的相互作用,尤其是Zn4O四面体、OZn4O12八面体结构的存在对该发射带的产生起了重要作用,决定了该化合物的发光性质。

Polynuclear complexes with d10 metals, which often possess unique structures and properties, have drawn a lot of attention. For the preparation of tetranuclear zinc carboxylate, four methods have been used: (a) by the reaction between zinc oxide and the carboxylic acid in the appropriate proportion; (b) by the thermal decomposition of the neutral carboxylate Zn(RCO2)2; (c) by the reaction of zinc oxide with the neutral carboxylate and (d) by the hydrolysis of the neutral zinc carboxylate. In the present work, a tetranuclear zinc benzoate Zn4O(C6H5CO2)6 was synthesized by the thermal decomposition of zinc benzoate Zn(C6H5CO2)2 in an inert atmosphere. Its electronic absorption, infrared, excitation and emission spectra were investigated. The nature of luminescence and the relationship between structure and luminescent property were discussed. Structure refinement showed that Zn4O(C6H5CO2)6 has a cubic structure, space group Ia3d, with great crystal cell: a=410063(18)?, V=68953(5)?3,Z=48. In the crystal all benzoates coordinate with zinc atoms in a bidentate bridging mode, four zinc atoms form a regular tetrahedron. Each Zn4O(C6H5CO2)6 molecule is in an octahedron geometry and every four adjacent molecules constitute a slightly distorted tetrahedron. The complex Zn4O(C6H5CO2)6 possesses an infinitely extended threedimensional supramolecular structure. It emits a green luminescence under the excitation of UV/blue light in solution or in the solid state. Its excitation and emission bands at 290～330 and 370nm are attributed to the ligandcentered transition. The excitation bands at about 460nm and the emission band at about 530nm are assigned to the LMCT (ligand to metal charge transfer) transition of pπ* (L,O2-)-4sσ(Zn2+). The luminescent property has relation with its particular structure. In the nature of its excitation and emission spectra, a leading role is played by the arrangement of Zn4O tetrahedron around the central oxygen atom because of the absence of similar bands for the simple mononuclear complex Zn(C6H5CO2)2. Furthermore, in addition to the Zn4O unit, the OZn4O12 one is needed to explain the nature of experimental bands. The green emission of complex Zn4O(C6H5CO2)6 makes it a possible candidate for luminescent material.