Influence of Solvent in Solvothermal Syntheses: Change of Nuclearity in Mixed Valence Co^II/III Complexes of a O‑Donor-rich Schiff Base Ligand

Abstract

We have found that a change of solvent in a solvothermal synthetic method may be a useful tool to generate complexes of various nuclearities keeping the reactants, synthetic conditions, and stoichiometry the same. Although the process involves serendipity, the potential of producing change in nuclearity of discrete molecular complexes by mere change of solvent ratios provides an additional scope to tune nuclearity using the same precursors. The above methodology led us to generate three complexes of different nuclearity bearing the formula [Co^IICo^III­(H₂L)₂(OAc)]­·2CH₃OH­·H₂O (<b>1</b>), [Co^II₃ Co^III₃­(HL)₂(H₂L)₂­(OAc)₂ ]­·9CH₃OH·H₂O (<b>3</b>), [Co^II₅Co^III₄­(HL)₄(H₂L)₄(Cl)₂]­·4H₂O (<b>4</b>) [where, H₄L = 2-(3,5-di-<i>ter</i>t-butyl-2-hydroxybenzylideneamino)-2-(hydroxymethyl)­propane-1,3-diol]. Using the same reactants, stoichiometry, and solvent used to generate <b>3</b> (in solvothermal method) if we reflux on the benchtop we get the dinuclear complex <b>1</b>, but on addition of 3,5-dimethylpyrazole a tetranuclear Co^II/III complex [Co^II₂Co^III₂­(HL)₂(OAc)₂­(CH₃OH)₂(DMP)₂]­·CH₃COOH·H₂O (<b>2</b>) is obtained. All the complexes were characterized by various spectroscopic and analytical methods including single crystal X-ray crystallography. The temperature dependence of magnetic susceptibility of <b>3</b> and <b>4</b> show that the Co^II centers are weakly coupled within a single molecule and exhibit both ferro- and antiferromagnetic interactions. <b>3</b> was found to be active in conversion of 3,5-di-<i>tert</i>-butylcatechol to 3,5-di-<i>tert</i>-butylbenzoquinone and produces hydrogen peroxide