Doubly TEMPO-coordinated gadolinium(_(III)), lanthanum(_(III)), and yttrium(_(III)) complexes. Strong superexchange coupling across rare earth ions?

摘要

We prepared crystalline [RE~(_(III))(hfac)_3(TEMPO)_2] (RE = Gd, La, Y), where TEMPO and hfac stand for 2,2,6,6- tetramethylpiperidin-1-oxyl and 1,1,1,5,5,5-hexafluoropentane-2,4-dionate, respectively. The X-ray crystal structure of TEMPO-coordinated RE compounds was determined for the first time. The Gd and Y analogues are isomorphous, and the La derivative has a similar molecular skeleton. The Gd-O(TEMPO) bond lengths were 2.322(3) and 2.354(3) ? with the O-Gd-O angle of 140.36(11)°. The magnetic study clarified that [Gd(hfac)_3(TEMPO)_2] behaved as a ground S_(total) = 7/2 species. The La and Y analogues showed the superexchange interactions across the diamagnetic ions with 2J_(TEMPO_1-TEMPO2_)/k_B = -14.9(1) and ?49.8(2) K, respectively. Assuming the presence of a similar interaction like the Y derivative, the Gd-TEMPO exchange couplings are estimated with 2J_(Gd-TEMPO)/k_B = ?12.9(5) and +8.0(6) K.