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

Two Co II –Co III mixed‐valance complexes of molecular formulas [Co 2 (H 2 L) 2 (H 2 O) 2 ][Co 2 (H 2 L) 2 (H 2 O)( m ‐phth)] · 8(H 2 O) { 1 ; H 2 L 2– = 2‐[(2‐hydroxy‐3‐methoxybenzylidene)amino]‐2‐(hydroxymethyl)propane‐1,3‐diolato, m ‐phth = 1,3‐benzenedicarboxylate} and [Co 4 (H 2 L) 4 (H 2 O) 2 (ppda)] · 2(dmf) · 3.2(H 2 O) { 2 ; ppda = 1,4‐phenylenediacrylate; dmf = N , N ‐dimethylformamide} were synthesized and characterized by single‐crystal X‐ray diffraction and magnetic studies at low temperature. The structural determination reveals that 1 is composed of dinuclear ion pairs, namely, a cationic [Co 2 (H 2 L) 2 (H 2 O) 2 ] + ( 1 + ) and an anionic [Co 2 (H 2 L) 2 (H 2 O)( m ‐phth)] – ( 1 – ) unit. In each of these ions, the Co II and Co III centers present distorted octahedral geometries. Compound 2 is a centrosymmetric tetranuclear complex comprising two symmetry‐related dinuclear Co II –Co III units bridged by ppda anions. Alternating current/direct current (ac/dc) magnetic studies revealed that the individual Co II –Co III 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 ( D = –62.4, –95.8, and –101.9 cm –1 and E/D = 0.219, 0.216, and 0.234 for 1 + , 1 – , and 2 , respectively).