用微量热法测定稀土含硫有机配合物的比热容

Determination of Specific Heat Capacity of Rare Earth Organo-sulfur Complexes by Microcalorimetry

推导了用改进的RD496-III型微热量计测定固态物质比热容的计算式.用Joule效应确定了仪器在298.15K时的量热常数和相对标准偏差分别为(63.901±0.030)μV?mW-1和0.08%,用Peltier效应测定总不平衡热.在该仪器上测定的两种标准物质(基准苯甲酸和α-Al2O3)比热容的计算值与文献值相差在0.4%以内.用本法测定了13种固态配合物RE(PDC)3(phen)(RE=La,Pr,Nd,Sm～Lu;PDC=C5H8NS-2)的比热容值,总偏差在1.0%,与稀土原子序数ZRE作图呈现“三分组现象”,说明配合物中RE3+与配体间的化学键有一定程度的共价性,显示了稀土离子4f电子云的扩大效应.

A calculation formula for determining the specific heat capacity of solid with an improved RD496-Ⅲ microcalorimeter was derived. The calorimetric constant and the relative standard deviation determined by use of Joule effect were （63.901±0.030） μV·mW^-1 and 0.08% at 298.15 K, respectively, and the total disequilibrium heat has been measured by Peltier effect. The specific heat capacities of two standard samples （benchmark benzene carboxylic acid and α-A1203） were obtained with this microcalorimeter, and differences between their calculated values and their literature ones were less than 0.4%. Accordingly, the specific heat capacities of thirteen solid complexes RE（PDC）3（phen） （RE=La, Pr, Nd, Sm-Lu; PDC= C5H8NS2^- ） were also gained by the same method with their total deviations within 1.0%. These values were plotted against the atomic number of rare earth, which presents tripartite effect. It suggests existence of a certain amount of covalent character in the bond of RE^3＋ and ligands, according to Nephelauxetic effect of 4f electrons of rare earth ions.