导出铅(Ⅱ)—卤素键价参数的一条新途径

A New Approach to Bond Valence Parameters for Pb(Ⅱ)-halide Bonds

基于精确的晶体结构数据并设定B=0.037nm以拟合经验参数R0是通常采用的键价参数推导方法.与此相反,作者提出从分子气相电子衍射的键长设定经验参数R0,然后从晶体结构数据拟合经验参数B.以Pb(Ⅱ)—卤素键为例,PbX_2气相电子衍射Pb—X(X=F,Cl,Br,I)键长分别为0.2036,0.2447,0.2598和0.2804nm,经拟合到最佳B值分别为0.0382,0.040,0.040,0.0386nm,与普适参数B值0.037nm有一定的差距.所提出的键价参数不仅得到比较理想的键价值和计算结果,而且保留了键价参数R_0作为单价键长明确的物理意义.

The values of bond valence parameters Ro for the bonds of main group metal halides are usually obtained by systematic analysis of the crystal structure data by assuming B=0.037 nm. In this work, conversely, the values of B were proposed to be fitted with crystal structure data on assuming the values of Ro equal to the bond lengths of rg accurately determined by gaseous electron diffraction. As an example, the new sets of Ro/B for the Pb（II）--X （X=F, Cl, Br, I） bonds were obtained and fitted as 0.2036/0.0382, 0.2447/0.040, 0.2598/0.040, and 0.2804/0.0386, respectively. Compared with the values of R0=0.203, 0.253, 0.264, and 0.278 nm based on B=0.037nm for Pb（II）--X bonds reported in the literature, these new parameters were not only accurate and reliable for bond valence calculations, but also revealed the physical meaning inherent in every Ro as unit valence bond length.