Unusually Distorted Pseudo-Octahedral Coordination Environment Around Co^II from Thioether Schiff Base Ligands in Dinuclear [CoLn] (Ln = La, Gd, Tb, Dy, Ho) Complexes: Synthesis, Structure, and Understanding of Magnetic Behavior

Abstract

The synthesis, structural characterization, and magnetic behavior of a new family of binuclear CoII–LnIII complexes of formula [LnIIICoIIL2(NO3)3]·H2O (Ln = La, 1; Gd, 2; Tb, 3; Dy, 4; Ho, 5; HL = 3-methoxy-N-(2-(methylsulfanyl)­phenyl)­salicylaldimine) have been reported. The chosen ligand system HL has adjacent soft ONS and hard OO binding pockets ideal for selective coordination of CoII and 4f metal ions. All the complexes 1–5 exhibit a CoII center in a highly distorted octahedral geometry with the LnIII centers in bicapped square-antiprism geometry. The unique distortion about the CoII center is introduced by the coordination of 4f metal ions in the hard OO coordination site. The distortion is further supported by the presence of −SMe groups giving an S donor atom which owing to its larger size can support large bond distances and angles. The geometry around the CoII centers is intermediate between meridional and facial geometric isomers. The magnetic properties of these complexes have been investigated by a “full model” approach using CONDON with the experimental magnetochemical analysis revealing ferromagnetic Co–Ln coupling in compounds 2–5. Ab initio calculations on the X-ray crystal structures of 1–5 paint a semiquatitative picture about the contribution of the individual anisotropic centers toward the overall magnetic properties of the compounds. Theoretical analysis predicts 1 and 2 as weak single-ion magnet (SIM) and single-molecule magnet (SMM) respectively with CoII being solely responsible for the complex anisotropy. In 2, J CoGd plays a crucial role in preserving the anisotropy contribution of Co by channelizing relaxation via a higher excited exchange doublet. Because of the inefficiency of J CoTb, J CoDy, and J CoHo in quenching single-ion Ln fragment transverse anisotropy and preserving CoII high axial anisotropy (favoring rhombicity), 3–5 lack SMM behavior.

Synthesis, Structural Features and Physical Properties of a Family of Triply Bridged Dinuclear 3d-4f Complexes

“…The fit of the experimental susceptibility data using the above equation led to the following parameters: λ = −111.2 cm −1 , α = 0.88, J = +0.26 cm −1 and g = 2.06 (considered to be the same for both ions) with R = 2.52 × 10 −5 . The observed coupling constant is lower than that found for the similar di-µ-phenoxo/syn-syn acetate triply bridged compound [Co(µ-L 1 )(µ-OAc)Gd(NO 3 ) 2 ] (J = +0.7 cm −1 ) [28,29], and to those found for planar di-µ-phenoxo-bridged Co II Gd III complexes containing a compartmental ligand (J~1 cm −1 ) [30,31]. Following the considerations made for Cu II Gd III and Ni II Gd III complexes, the observed low value of J is not unexpected if we take into account that 11 has the highest hinge angle.…”

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

“…For the Dy III ion in 2, it exhibits an eight-coordinated DyO 8 environment, in which eight O atoms originated from four L 3− ligands with Dy-O bond lengths in the range of 2.239(4)-2.530(5) Å. The coordination geometry of Dy III was also determined by SHAPE software, 49 indicating that the coordination geometry of Dy1 is a square antiprism (SAP-8, D 4d ), 14,15,20,[24][25][26][27][28]31,32 as the minimum value of the CShM parameter is 1.405 (Fig. 2b and Table S8 †).…”

“…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.…”

Cation-/Ligand-Induced Solvent-Assisted Transformations of Zn(II) and Cu(II) Complexes Featuring Single-Pocket Multidentate Chelating Members

“…The cation exchange proceeds via a recurrent dissolving-exchange-crystallization phenomenon of the solvent-controlled mechanism accompanied by bond breaking and new bond formation. 65 Another recent example of inorganic systems that undergoes structural transformations for which the initial and final crystalline phases have been elucidated by single-crystal X-ray diffraction (SCXRD) includes a one-dimensional (1D) zigzag chain of Zn II -salicylaldiminato which was investigated via metal ion exchange, and this led to the formation of a new structure in conjunction with change in the coordination environment of the Zn II center. 66,67 In few ligand substitution transformations, 68−71 a C 3symmetry semi-rigid N,N′,N″-tris (3-pyridinyl)phosphoric triamide (tppa) ligand was employed to construct a discrete octahedral nanocage [Cu 6 (tppa) 8 (H 2 O) 6 ](ClO 4 ) 12 (H 2 O) 24 .…”