Synthesis, structure, and magnetism of non-planar heptanuclear lanthanide(iii) complexes

Abstract

The reaction of the hydrazone, 2-methoxy-6-(pyridin-2-yl-hydrazonomethyl) phenol (LH) with lanthanide(III) nitrate salts in the presence of excess triethylamine afforded the heptanuclear Ln(III) complexes: [Gd₇(L)₆(μ₃-OH)₈(NO₃)₄(H₂O)]·(NO₃)₃·8CH₃CN·H₂O (1), [Tb₇(L)₆(μ₃-OH)₈(NO₃)₄]·(NO₃)₃·9CH₃CN·2CH₃OH·3H₂O (2), [Dy₇(L)₆(μ₃-OH)₈(NO₃)₄(H₂O)]·(NO₃)₃·7CH₃CN·3H₂O (3), [Ho₇(L)₆(μ₃-OH)₈(NO₃)₄]·(NO₃)₃·11CH₃CN·2CH₃OH·2H₂O (4) and [Er₇(L)₆(μ₃-OH)₈(NO₃)₄]·(NO₃)₃·8CH₃CN·2CH₃OH (5). Single crystal X-ray diffraction studies reveal that these complexes are tri-cationic, possessing three nitrate counter anions. The heptanuclear ensemble is non-planar and consists of six [L]⁻ and eight μ₃-OH ligands. These compounds show an interesting structural motif with two incomplete cubes fused to each other through a common Ln(III) ion. Compound 1 exhibits a magnetocaloric effect, with (−ΔS_m(T) = 27.7 J kg⁻¹ K⁻¹ at 3 K and under a field change of 0–7 T), while compound 3 shows slow magnetic relaxation at very low temperatures.