Insights into the absorption of carbon dioxide by zinc substrates:: isolation and reactivity of di- and tetranuclear zinc complexes

The heptadentate Schiff base H3L can react with zinc acetate to form the discrete dinuclear complex Zn2L(OAc)(H2O), 1.H2O. The reaction of 1.H2O with NMe4OH.5H(2)O both in air and under an argon stream has been investigated. On one hand, this reaction in air yields the tetranuclear complex (Zn2L)(2)(CO3)(H2O)(6), 2.5H(2)O, by spontaneous absorption of adventitious carbon dioxide. This process can be reverted in an acetic acid medium, whereas the treatment of 2.5H(2)O with methanoic acid yields crystals of [Zn2L(HCOO)].0.5MeCN.1.25MeOH.2H(2)O, 3.0.5MeCN.1.25MeOH.2H(2)O. On the other hand, the interaction under an argon atmosphere of 1.H2O with NMe4OH.5H(2)O in methanol allows the isolation of the dinuclear complex Zn2L(OMe)(H2O)(4), 4.4H(2)O. Recrystallisations of 1.H2O, 2.5H(2)O and 4.4H(2)O, in different solvents, yielded single crystals of 1.MeCN.2.5H(2)O, 2.4MeOH and 4.3MeOH.H2O, respectively. The crystal structure of 2.4MeOH can be understood as resulting from an unusual asymmetric tetranuclear self-assembly from two dinuclear units, and shows three different geometries around the four zinc atoms.