Single‐Ion Magnetic Behavior in Co^II–Co^III Mixed‐Valence Dinuclear and Pseudodinuclear Complexes

<jats:p>Two Co<jats:sup>II</jats:sup>–Co<jats:sup>III</jats:sup> mixed‐valance complexes of molecular formulas [Co<jats:sub>2</jats:sub>(H<jats:sub>2</jats:sub>L)<jats:sub>2</jats:sub>(H<jats:sub>2</jats:sub>O)<jats:sub>2</jats:sub>][Co<jats:sub>2</jats:sub>(H<jats:sub>2</jats:sub>L)<jats:sub>2</jats:sub>(H<jats:sub>2</jats:sub>O)(<jats:italic>m</jats:italic>‐phth)]<jats:bold>·</jats:bold>8(H<jats:sub>2</jats:sub>O) {<jats:bold>1</jats:bold>; H<jats:sub>2</jats:sub>L<jats:sup>2–</jats:sup> = 2‐[(2‐hydroxy‐3‐methoxybenzylidene)amino]‐2‐(hydroxymethyl)propane‐1,3‐diolato, <jats:italic>m</jats:italic>‐phth = 1,3‐benzenedicarboxylate} and [Co<jats:sub>4</jats:sub>(H<jats:sub>2</jats:sub>L)<jats:sub>4</jats:sub>(H<jats:sub>2</jats:sub>O)<jats:sub>2</jats:sub>(ppda)]<jats:bold>·</jats:bold>2(dmf)<jats:bold>·</jats:bold>3.2(H<jats:sub>2</jats:sub>O) {<jats:bold>2</jats:bold>; ppda = 1,4‐phenylenediacrylate; dmf = <jats:italic>N</jats:italic>,<jats:italic>N</jats:italic>‐dimethylformamide} were synthesized and characterized by single‐crystal X‐ray diffraction and magnetic studies at low temperature. The structural determination reveals that <jats:bold>1</jats:bold> is composed of dinuclear ion pairs, namely, a cationic [Co<jats:sub>2</jats:sub>(H<jats:sub>2</jats:sub>L)<jats:sub>2</jats:sub>(H<jats:sub>2</jats:sub>O)<jats:sub>2</jats:sub>]<jats:sup>+</jats:sup> (<jats:bold>1<jats:sup>+</jats:sup></jats:bold>) and an anionic [Co<jats:sub>2</jats:sub>(H<jats:sub>2</jats:sub>L)<jats:sub>2</jats:sub>(H<jats:sub>2</jats:sub>O)(<jats:italic>m</jats:italic>‐phth)]<jats:sup>–</jats:sup> (<jats:bold>1<jats:sup>–</jats:sup></jats:bold>) unit. In each of these ions, the Co<jats:sup>II</jats:sup> and Co<jats:sup>III</jats:sup> centers present distorted octahedral geometries. Compound <jats:bold>2</jats:bold> is a centrosymmetric tetranuclear complex comprising two symmetry‐related dinuclear Co<jats:sup>II</jats:sup>–Co<jats:sup>III</jats:sup> units bridged by ppda anions. Alternating current/direct current (ac/dc) magnetic studies revealed that the individual Co<jats:sup>II</jats:sup>–Co<jats:sup>III</jats:sup> unit exhibits field‐induced slow magnetic relaxation consistent with single‐ion magnet (SIM) behavior. Ab initio NEVPT2 calculations confirm large zero‐field splitting (zfs) from a first‐order spin–orbit coupling (SOC) in both complexes (<jats:italic>D</jats:italic> = –62.4, –95.8, and –101.9 cm<jats:sup>–1</jats:sup> and <jats:italic>E/D</jats:italic> = 0.219, 0.216, and 0.234 for <jats:bold>1<jats:sup>+</jats:sup></jats:bold>, <jats:bold>1<jats:sup>–</jats:sup></jats:bold>, and <jats:bold>2</jats:bold>, respectively).</jats:p>