硼烷分子中化学键性质的研究 Ⅳ.B_4H_8X及B_4H_8的结构与成键特征

Studies on the Nature of Chemical Bonding in Boranes IV. The Structure and Bonding Characteristics of B_4H_8X and B_4H_8

用ab initio MP2/3 21G~*方法,对四角锥型硼化物B_4H_8X(X=Li^-,Be,B^+,C^(2+),B,C,N^+,BeH,BH和CH^+)及其碎片B_4H_8的结构进行了研究.结果表明,在B_4H_8X结构中,端氢(H_t)的位置受顶点帽基X的支配.帽基原子的电负性较小和配位原子轨道的弥散程度较大时,H_t处在B_n环平面下方,与帽基反向.反之,H_t与帽基同向.桥氢(H_b)的位置总是在B_n环平面之下,与X反向.进一步研究了B_4H_8X的离解能,并进行了电子相关能校正.发现结构1和2稳定性较差,结构3～10较稳定.分子碎片B_4H_8的最稳定构型为2112结构.

Using the ab initio MP2/3 - 21G* method, the structure of B4H8X(X= Li ,Be,B+ , C2+ ,B- ,C,N+ ,BeH- ,BH and CH+ )and their fragments of B4Hg have been studied. The results show that terminal hydrogen positions are controlled by the acme cap(X) in B4H8X molecules. When the cap atoms have smaller electronegntivity and the ligand orbitals have more diffusion, terminal hydrogen atoms can be obsevered below the Bn plane (against the cap). In contrast, when terminal hydrogen atoms towards the cap(X) ,the bridging hydrogen atoms are away from it. Further investigation on dissociation energies and correlation energies of B4H8X was carried out. We have observed that the structure of 1 and 2 we are unstalbe while the structure of 3~10 were reletively stable. In all fragments of B4H8, the structure with 2112 configuration is most stable.