Hydroxide‐Bridged Mixed‐Valence Tetranuclear Cobalt 4‐Nitrophenol Inclusion Complex Showing Single Molecule Magnet Property

Two tetranuclear hydroxide‐bridged mixed‐valence cobalt complexes, one having 4‐nitrophenolate anions and other having 4‐nitrophenol as guest, namely [(μ 2 ‐dea) 2 (phen) 2 Co 2 (μ 3 ‐OH) 2 Co 2 (phen) 2 ](np) 4 •H 2 O ( 1 ), [(μ 2 ‐dea) 2 (phen) 2 Co 2 (μ 3 ‐OH) 2 Co 2 (phen) 2 ]Cl 4 •2Hnp•9H 2 O ( 2 ) (Hnp=4‐nitrophenol, phen=1,10‐phenanthroline, dea=di‐deprotonated diethanolamine) were synthesized and structurally characterized. Complex cation of these two complexes are based on Co 4 O 4 (OH) 2 units where two cobalt ions are in Co 2+ and other two are in Co 3+ oxidation states. Reaction of same set of reactants namely phen, Hnp and diethanolamine with cobalt nitrate in presence or absence of hydrochloric acid resulted complex 1 and 2 respectively. The two triply‐bridging hydroxides of complex 1 are in identical environment, but the complex 2 has two triply‐bridging hydroxides in slightly different environments having differences in Co‐O (hydroxide) bond distances around them. Complex 2 is ferromagnetic and shows field induced Single Molecule Magnets (SMM) behavior.