Two tetranuclear hydroxide-bridged mixed-valence cobalt complexes, one having 4-nitrophenolate anions and other having 4-nitrophenol as guest, namely [(μ2-dea)2(phen)2Co2(μ3-OH)2Co2(phen)2](np)4\textbullet H2O (1), [(μ2-dea)2(phen)2Co2(μ3-OH)2 Co2(phen)2]Cl4\textbullet 2Hnp\textbullet 9H2O (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 Co4O4(OH)2 units where two cobalt ions are in Co2+ and other two are in Co3+ 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.