中文摘要：

本文建立了d^4,6络合分子二步自旋转换的量子理论.模拟计算得出了如下几点结论：①低对称畸变是d^4,6络合分子可以发生二步自旋转换的必要条件;② 对于具有任何一种低对称性的任何一种d^4,6络合物存在这种低对称畸变的一个临 界值,当畸变小于临界值时只可发生一步自旋转换,即HS LS自旋转换;而当畸变大 于临界值时则可以发生二步自旋转换,即HS←→MS和MS←→ LS自旋转换.二步自旋转换导 致磁矩曲线上产生两个拐点,与两个自旋转换点相对应,其间的Dq-距离ΔDq随畸 变量的增加而增加;③当畸变量等于临界值时络合分子的两个自旋转换点相重迭, 即与自旋转换有关的HS、MS、LS三个能级交于一点,这形成一个自旋三相点,它代 表一个由三种自旋相形成的临界状态.因此,自旋三相态或许是可以实现的;④低 对称畸变将使高自旋磁矩明显增大,可以高于6.10μB.这表明,通常用实验磁矩数 据来判断络合物中心为何种离子的方法是不可靠的;⑤低自旋磁矩可以小于1但显 大于0,表明在络合分子中过渡金属离子的轨道角动量未完全碎灭的情况.

英文摘要：

A quantum theory for describing two-step-spin-transitions of d^4＇6 complex molecules has been established on the basis of the unified-crystal-field-coupling （UCFC） theory. By simulating calculation we may conclude the following points： ① A low symmetry distortion is a necessary inner condition for any d^4＇6 complex to oeeur a two-step-spin-transition.② For any d^4＇6 complex having any low symmetry distortion there exists a critical value of such a low symmetry distortion： the complex having its distortion smaller than the critical value can and only can occur a one-step-spin-transition, i.e. a high-spin←→low-spin transition; The one having its distortion greater than the eritieal value can consequentially oeeur a two-step-spin-transition, i. e. a high-spin←→intermediate-spin transition together with a intermediate-spin←→low-spin transition, leading to two inflexions on the magnetic moment curve corresponding to the two transition points, between them the Dq-distanee △Dq will increase with increasing the distortion. ③ As for the complex having its distortion equal to the critical value, its two transition points will supertpose into one, i.e. the three lowest levels, a high-spin-, a intermediate-spin- and a low-spin-level, will intersect at one point. This is a spin-three-phasespoint, representing a critical state formed by three spin-phases. So it is predicted that such critical state will be realized in principle. ④ A low symmetry distortion increases markedly the magnetic moment of high-spin states. For example, the high-spin magnetic moment of regular octahedron d6 complexes is 5.64 μB, however a sufficient tetragonal or rhombic distortion can make it higher than 6.10μB. In view of the experimental magnetic moment is 5.10-5.70 μB for d6 configuration Fe^2＋ ion and 5.65-6.10μB for d5 configuration Mn^2＋ ion, this theoretical result indicates that the method for estimating what is the central ion of a complex only according to the magnetic moment experiment is inauthen