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

Inorganic Chemistry, vol. 59, pp. 2387–2405

Abstract

The synthesis, structural characterization, and magnetic behavior of a new family of binuclear Co II –Ln III complexes of formula [Ln III Co II L 2 (NO 3 ) 3 ]·H 2 O (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 Co II and 4f metal ions. All the complexes 1 – 5 exhibit a Co II center in a highly distorted octahedral geometry with the Ln III centers in bicapped square-antiprism geometry. The unique distortion about the Co II 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 Co II 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 Co II 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 Co II high axial anisotropy (favoring rhombicity), 3 – 5 lack SMM behavior.

Authors 6

1. Dipmalya Basak

   Indian Institute of Technology Kharagpur

   Affiliation as printed

   Department of Chemistry, Indian Institute of Technology, Kharagpur 721 302, India

2. Jan van Leusen Aachen Institute of Inorganic Chemistry

   RWTH Aachen University

   Affiliation as printed

   Institute of Inorganic Chemistry, RWTH Aachen University, D-52074 Aachen, Germany

3. Tulika Gupta

   Banaras Hindu University

   Affiliation as printed

   Department of Chemistry, Institute of Science, Banaras Hindu University, Varanasi 221005, India

4. Paul Kögerler Aachen Institute of Inorganic Chemistry

   RWTH Aachen University

   Affiliation as printed

   Institute of Inorganic Chemistry, RWTH Aachen University, D-52074 Aachen, Germany

5. Valerio Bertolasi

   University of Ferrara

   Affiliation as printed

   Dipartimento di ScienzeChimiche e Farmaceutiche, University of Ferrara, 44121 Ferrara, Italy

6. Debashis Ray corresponding

   Indian Institute of Technology Kharagpur

   Affiliation as printed

   Department of Chemistry, Indian Institute of Technology, Kharagpur 721 302, India