Halogen Bonding in the Decoration of Secondary Coordination Sphere of Zinc(II) and Cadmium(II) Complexes: Catalytic Application in Cycloaddition Reaction of CO(2) with Epoxides

[Image: see text] Three new zinc(II) complexes [Zn(H(2)L(3))(2)(H(2)O)(3)] (Zn2), [Zn(H(3)L(2a))(H(2)O)(3)](n) (Zn3) (H(3)L(2a) = 2,4-diiodo-5-(2-(2,4,6-trioxotetrahydropyrimidin-5(2H)-ylidene)hydrazineyl)isophthalate) and [Zn(HL(4))(DMF)(H(2)O)](n) (Zn4) were synthesized by the reaction of Zn(II) salts with 5-(2-(2,4-dioxopentan-3-ylidene)hydrazineyl) isophthalic acid (H(3)L(3)), 2,4,6-triiodo-5-(2-(2,4,6-trioxotetrahydropyrimidin-5(2H)-ylidene)hydrazineyl) isophthalic acid (H(5)L(2)) (in the presence of NH(2)OH·HCl) and 5-(2-(2,4-dioxopentan-3-ylidene)hydrazineyl)-2,4,6-triiodoisophthalic acid (H(3)L(4)), respectively. According to the X-ray structural analysis, the intramolecular resonance-assisted hydrogen bond ring remains intact, with N···O distances of 2.562(5) and 2.573(5) Å in Zn2, 2.603(6) Å in Zn3, and 2.563(8) Å in Zn4. In the crystal packing of Zn3, the cooperation of I···O and I···I types of halogen bonds between tectons leads to a one-dimensional supramolecular polymer, while I···O interactions aggregate 1D chains of coordination polymer Zn4. These new complexes (Zn2, Zn3, and Zn4) and known [Zn(H(3)L(1))(H(2)O)(2)](n) (Zn1) (H(3)L(1) = 5-(2-(2,4,6-trioxotetrahydropyrimidin-5(2H)-ylidene) hydrazineyl)isophthalate), {[Zn(H(3)L(1))(H(2)O)(3)]·3H(2)O}(n) (Zn5), [Cd(H(3)L(1))(H(2)O)(2)](n) (Cd1), {[Cd(HL(3))(H(2)O)(2)(DMF)]·H(2)O}(n) (Cd2), [Cd(H(3)L(3))](n) (Cd-3), {[Cd(2)(μ-H(2)O)(2)(μ-H(2)L(4))(2)(H(2)L(4))(2)]·2H(2)O}(n) (Cd4), and {[Cd(H(3)L(1))(H(2)O)(3)]·4H(2)O}(n) (Cd5) were tested as catalysts in the cycloaddition reaction of CO(2) with epoxides in the presence of tetrabutylammonium halides as the cocatalyst. The halogen-bonded catalyst Zn4 is the most efficient one in the presence of tetrabutylammonium bromide by affording a high yield (85–99%) of cyclic carbonates under solvent-free conditions after 48 h at 40 bar and 80 °C.