Coordination networks from zero-dimensional metallomacrocycle, one-dimensional chain to two-dimensional sheet based on a ditopic diiminopyridine ligand and group 12 metals

The reaction of a ditopic diiminopyridine ligand 2,6-bis(1-(2,6- diisopropyl-4-(pyridin-3-yl)phenylimino)ethyl)pyridine (L) with group 12 metal salts in various solvent systems afforded 12 metal-organic coordination complexes, including zero-dimensional (0D) metallomacrocycle, one-dimensional (1D) chain, and two-dimensional (2D) network structures: [Zn₄Cl ₈L₂]•2C₇H₈•2CH ₃COCH₃•3H₂O (1a), {[Zn₂Cl ₄L]•2CH₃OH•2CHCl₃•2H ₂O}_n (1b), {[ZnCl₂L]•0.5CH ₂Cl₂•0.5H₂O}_n (1c), {[ZnBr ₂L]•CH₂Cl₂}_n (2), [ZnI ₂L]_n (3), {[Zn(NO₃)₂L ₂•2C₇H₈]}_n (4), {[CdCl ₂L₂]•2CH₂Cl₂}_n (5), {[Cd(NO₃)₂L₂]•CH₂Cl ₂}_n (6), {[Cd(ClO₄)₂L ₂]•CH₂Cl₂}_n (7), {[Hg ₄(μ₂-L₂)(μ₂-Cl ₂)(μ-HgCl₂)Cl₆]•2H₂O} _n (8), {[HgBr₂L]•CH₃CN•0.5CH ₂Cl₂}_n (9), and {[HgI₂L]•0. 5CH₂Cl₂}_n (10). In these complexes, the semirigid ligand L exhibits four kinds of coordination modes [(syn, syn, syn), (syn, syn, anti), (anti, anti, syn), (anti, anti, anti)], leading to the formation of various supramolecular structures. Complex 1a is a tetranuclear metallomacrocycle. 1b contains 1D zigzag chains propagating along two different directions, which further pack into a noninterpenetrated three-dimensional (3D) framework by hydrogen-bonding interactions. Complexes 1c, 2, 3, 9, and 10 exhibit a 1D helical chain structure, while 4, 5, 6, and 7 are 1D looped-chain coordination polymers. Complex 8 displays an unprecedented pentanuclear Hg(II)-based 2D network with both HgCl₂ and Hg₂Cl ₂ bridges. It is noteworthy that 1a and 1b are supramolecular isomers formed in different solvent systems. The effects of the solvent, metal center, and anion on the different conformations adopted by the ligand and the structure of the products have been discussed. Additionally, the luminescent properties of the complexes have been investigated in the solid state, which display increased ligand-based fluorescence emission at room temperature.