New Magnetically Coupled Bimetallic Complexes as Potential Building Blocks for Magnetic Materials

✍ Scribed by Scott W. Gordon-Wylie; Brian L. Claus; Colin P. Horwitz; Yan Leychkis; José M. Workman; Alexander J. Marzec; George R. Clark; Clifford E. F. Rickard; Brenda J. Conklin; Scott Sellers; Gordon T. Yee; Terrence J. Collins

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 240 KB
• Volume: 4
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/(sici)1521-3765(19981102)4:11<2173::aid-chem2173>3.0.co;2-q

✦ Synopsis

The preparation and characterization of the new binucleating ligand, 1,2,4,5-tetrakis(2-hydroxy-2-methylpropanamido)benzene, H 8 [3], and its Co III and V [5], are described. Both complexes have been characterized by X-ray crystallography, 1 H NMR, IR, and UV/Vis spectroscopy, and by electrochemical and microanalytical analyses. The electrochemical properties of [4] 2À and [5] 2À are remarkably similar, each exhibiting two one-electron oxidation processes of similar E8'; since the V V (O) sites in [5] 2À are d 0 , ligand-localized oxidation is implicated for both compounds. A deep blue vanadium species obtained upon oneelectron oxidation of [5] 2À , [5 I ] À , has a total spin, S T , of 1/2, and its EPR spectrum exhibits a single g 2 signal at 4 K. These results are consistent with the oxidized vanadium complex, [5 I ] À , as containing the ligand cation radical 3 I , that is [5

Isolation and characterization of the dark purple cobalt species, obtained upon one-electron oxidation of [4] 2À , [4 I ] À , also revealed the presence of the organic radical 3 I .

Magnetic susceptibility data for [4] 2À

revealed that exchange coupling (the Hamiltonian convention J S i ´Sj is used throughout) between the two axial S 1 Co III centers was very weak (that is J Co III ÀCo III % 0 cm À1 ). In contrast, for [4 I ] À , the ground spin state of S T 3/2 and the observed EPR spectrum and magnetic susceptibility data can be rationalized by the relatively strong antiferromagnetic coupling between each rhombic S 1 Co III ion and an S 1/2 ligand cation radical (J Co III ±3

I % 75 cm À1 ). Such a ferrimagnetic system serves to align the Co III spin centers in a common direction, an important step towards building ferromagnetic or ferrimagnetic network solids.