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稀土离子与冠醚反应的热函至今报道不多。仅1977年Izatt等用量热滴定对稀土氯化物在甲醇中与18-冠-6的反应热函进行过研究。他们发现轻稀土从La~(3+)至Gd~(3+)与冠醚反应是吸热反应,而重稀土从Tb~(3+)至Lu~(3+)与冠醚反应却没有热量产生或△H近于零。此外他们还得出了若干反常结果,我们认为,反应热量的大小与稀土盐和有机溶剂的含水量有密切关系,因三价稀土离子电荷高,牛径又不大,水合能力强,在不严格去水的条件下,所得的△H和稳定常数不甚可靠。为此,我们研究了无水硝酸镧与18-冠-6(18C6),2,3,11,12-二环已基-18-冠-6(DC-18C6),及2,3-苯并-11-甲基-18-冠-6(BC1-18C6)在无水乙腈中的配位反应,得出与Izatt等不同的结果。实验表明,所有冠醚与La~(3+)的反应均为放热反应,它们有较大的热函和较高的稳定性。
The enthalpies of rare earth ions and crown ether have not been reported until now. Only in 1977 Izatt and other calorimetric titration of rare earth chloride in methanol with 18-crown-6 reaction enthalpy studied. They found that the reaction of light rare earth with crown ether from La 3+ to Gd 3+ was an endothermic reaction whereas that of heavy rare earth from Tb 3+ to Lu 3+ did not react with crown ether Heat generation or △ H is near zero. In addition, they also come to a number of abnormal results, we believe that the size of the heat of reaction with the water content of rare earth salts and organic solvents are closely related to the high charges of trivalent rare earth ions, not large calf, hydration ability, not Strict under the conditions of water, the resulting △ H and the stability constant is not reliable. For this reason, we studied the effects of anhydrous lanthanum nitrate and 18-crown-6 (18C6), 2,3,11,12-dicyclohexyl-18-crown-6 And the coordination reaction of -11-methyl-18-crown-6 (BC1-18C6) in anhydrous acetonitrile gave different results than Izatt et al. Experiments show that all the crown ether and La ~ (3 +) reaction are exothermic reaction, they have a larger enthalpy and higher stability.