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

Abstract

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) Å 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_{TEMPO1–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.