Carboxylate-Decorated Aggregation of Octanuclear Co₄Ln₄ (Ln = Dy, Ho, Yb) Complexes from Ligand-Controlled Hydrolysis: Synthesis, Structures, and Magnetic Properties

Abstract

One-pot reactions of an asymmetric carboxy-etherp h e n o l b a s e d S c h i ff b a s e H 2 L ( 2 -( ( 2 -h y d r o x y -3methoxybenzylidene)amino)benzoic acid) with selected Ln-(NO 3 ) 3 •nH 2 O and [Co 2 (μ-OH 2 )(O 2 CCMe 3 ) 4 (HO 2 CCMe 3 ) 4 ] (Co 2 -Piv) in basic MeOH medium resulted in a family of three octanuclear complexes, [Co II 4 Ln III 4The coordination aggregates thus obtained were nicely sustained by four ligand anions and eight externally added carboxylate anions showing three different modes of intermetallic connectivity. The options for incorporating different 4f ions in an investigative synthesis, without altering the resulting intermetallic core structure, were successful for the three representative examples. Single-crystal X-ray diffraction studies revealed that the compounds are isostructural and built from two initially formed partial dicubane-type Co 2 Ln 2 L 2 units. In each of the tetranuclear parts, the metal ion centers are held together by two L 2− , two μ 3 -HO − , three Piv − bridges, one terminal Piv − , and one terminal MeOH. Four carboxylate ends of four L 2− units are responsible for connecting two Co 2 Ln 2 units into octanuclear structures. The unique distortion around the Co II centers is achieved from the facile coordination of bigger 4f ions to the adjacent hard OO sites. The distortion is further maintained by the presence of terminal COO − groups from L 2− . The dc magnetic susceptibility data revealed ferromagnetic coupling between the Co II and Ln III centers within the series, whereas the ac magnetic susceptibility measurements identified only 1, having a highly anisotropic Dy III ion, as a single-molecule magnet in the absence of any external magnetic field, with an energy barrier U eff of 12.5 K.

Modulating the structural topologies from star-shape to cross-shape for Co–Dy heterometallic complexes with slow magnetic relaxation behavior

“…Notably, the Dy–O bond lengths in 1 are dependent on the nature of the atoms, namely, the bonds formed by the alkoxido-type O atoms of L 3− (Dy1–O9 = 2.287(4) Å and Dy2–O10 = 2.247(4) Å) and the bonds formed by NO 3 − (Dy1–O11 = 2.454(5) Å and Dy2–O14 = 2.537(5) Å) represent the shortest and the longest Dy–O bonds, respectively. The coordination geometries of Dy1 and Dy2 in 1 were determined by SHAPE software, 49 indicating that Dy1 and Dy2 are the triangular dodecahedron 8,15,19,20,29,40 (TDD-8, D 2d ) and the muffin (MFF-9, C s ), 12,29 respectively, as the minimum values for the continuous shape measure (CShM) parameters of Dy1 and Dy2 are 3.061 and 1.971, respectively (Fig. 1b and c and Tables S6 and S7†).…”

“…However, the (py represent the shortest and the longest Dy-O bonds, respectively. The coordination geometries of Dy1 and Dy2 in 1 were determined by SHAPE software, 49 indicating that Dy1 and Dy2 are the triangular dodecahedron 8,15,19,20,29,40 (TDD-8, D 2d ) and the muffin (MFF-9, C s ), 12,29 respectively, as the minimum values for the continuous shape measure (CShM) parameters of Dy1 and Dy2 are 3.061 and 1.971, respectively (Fig. 1b and c and Tables S6 and S7 †).…”

“…The main reason for studying Co II –Dy or Co II/III –Dy SMMs is to improve the magnetic anisotropy of the complexes by comprehensively utilizing high anisotropy Co II and Dy III . So far, about twenty Co II – or Co II/III –Dy SMMs with different topologies like binuclear Co II Dy, 14 trinuclear Co II 2 Dy, 15,16 linear or butterfly Co II 2 Dy 2 , 17,18 Co II 4 Dy 4 , 19 and some Co II/III –Dy (ref. 20) have been reported.…”

Three angular Zn2Dy complexes showing the effect of remote coordination at Zn and counter ions on slow magnetic relaxation at Dy centres

“…These observations suggest that complex 1 might display characteristics of slow magnetic relaxation and consequently SMM behaviour. 51 From the frequency dependent ac data at temperatures from 1.9 to 10.0 K, semi-circular Cole–Cole plots were constructed and fitted using the generalized Debye model (Fig. 7).…”

Influence of bridging and chelating co-ligands on the distinct single-molecule magnetic behaviours in ZnDy complexes

“…13 The initial aim of introducing 3d–4f magnetic coupling was to enhance the performance of SMMs involving paramagnetic Ni–Ln, Cu–Ln and Co–Ln complexes. 14 Among these heteronuclear 3d–4f SMMs, however, diamagnetic 3d elements containing species like Zn–Ln complexes exhibited pronounced SMM performance than the most paramagnetic 3d–4f analogues and the homodinuclear Dy-based SMMs. 10,11 We are now working with Schiff base ligands derived from a methyl derivative of o -vanillin at the para position with respect to the phenolic-OH group to explore coordination chemistry, and the resulting Dy or Zn–Dy complexes displayed slow relaxation of magnetisation.…”