Spontaneous carbon dioxide fixation:: a μ4-carbonate bridged tetranuclear zinc(II) complex of a heptadentate Schiff base

The electrochemical reaction of zinc and 2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine (H3L1) in acetonitrile in air yields the tetranuclear zinc complex [(Zn2L)(2)(CO3)].4H(2)O, which crystallises with different solvent molecules in two different systems: [(Zn2L)(2)(CO3)].4H(2)O.2CH(3)CN 1a (monoclinic, Pn) and [(Zn2L)(2)(CO)].4HO 1b (triclinic, P (1) over bar). The electrochemical reaction under a nitrogen stream leads to the isolation of crystals of [(Zn2L)(2)(CO)].0.25H(2)O.2CH(3)CN 1c (monoclinic P2(1)/c). All structures demonstrate the striking ability of this system to spontaneously x carbon dioxide. The crystals solution reveal a mu(4)-eta(2):eta(1):eta(1) binding mode for the carbonate group in all cases, leading to a tetranuclear complex by self-assembly of dinuclear units. Chemical reaction of Zn(CH3COO)(2).2H(2)O with H3L yields [Zn2L(CH3COO)].2H(2)O. Its recrystallisation allows isolating [Zn2L(CH3COO)].2H(2)O.CH3OH 2. Reaction of [Zn2L(CH3COO)].2H(2)O with (CH3)(4)NOH.5H(2)O leads, again, to the tetranuclear carbonate compound.