New Helical Zinc Complexes with Schiff Base Derivatives of β‐Diketonates or β‐Keto Esters and Ethylenediamine

Abstract

The tetradentate Schiff bases H 2 L = H 2 AC [N,NЈ-ethylenebis(4-iminopentan-2-one)], H 2 MAL1 [N,NЈ-ethylene-bis-(methyl-3-iminobutanoate)], and H 2 MAL2 [N,NЈ-ethylenebis(tert-butyl-3-iminobutanoate)] were found to possess sufficient flexibility and were tailored to self assemble with zinc ions to form neutral bimetallic helicates with the overall composition Zn 2 L 2 . In solution for all ligands, an equilibrium between the tautomeric forms exists, which was confirmed by IR and NMR spectroscopy. X-ray single-crystal analysis performed for H 2 MAL1 (1) and H 2 MAL2 (2) reveals that they have similar geometrical parameters and crystallize in a trans conformation. In the crystal structures of the zinc complexes [Zn 2 (AC) 2 ]·C 6 H 6 (3), [Zn 2 (MAL1) 2 ]·0.5C 7 H 8 (4), and [Zn 2 -(MAL2) 2 ]·C 7 H 8 (5), the Schiff base ligands are helically wrapped around the two four-coordinate metal ions, which leads to an idealized D 2 symmetry. The coordination polyhedron around the Zn ions in 3-5 can be described as a tetrahedral geometry comprising two O-and two N-donor atoms of

Di‐, Tetra‐, Penta‐ and Polynuclear Zinc Complexes Supported by a Flexible Tetradentate Schiff Base Ligand

“…The Zn-O and Zn-N bond lengths in 1 compare well with [L 2 Zn 2 ] and other related species. [7,11] The C-C bond lengths within the ligand backbone [ Figure 2, b and c (as The proton NMR spectrum of 1 exhibited characteristic ligand peaks with a small amount of decomposition of free ligand. This data suggests that in deuterated benzene, a more symmetrical structure is in place, or that the tetranu- [b] 2.3399(7) [b] 2.5455 (11 clear molecule dissociates into monomeric units.…”

“…These crystals were found to be the zinc dimer [L 2 Zn 2 ]. [7] Therefore it is apparent that in solution 2 does not retain the polymeric struc- ture and at least one of the products found is [L 2 Zn 2 ]. At present, it is not known how this is product is formed, though it could arise from a redistribution reaction.…”

“…[7] The degree of association between the zinc atoms is believed to be dependent on ligand size and decreases with increasing bulk. [5] The tetradentate ligand L is able to hold the zinc atoms in closer proximity, therefore decreasing the Zn-Zn separation.…”

“…[7] To determine whether increasing the ratio of ZnEt 2 to H 2 L would lead to two zinc molecules per ligand being incorporated into the final product, thereby increasing the nuclearity of the resultant complex, the 1:2.1 reaction of Et 2 Zn with H 2 L was carried out (Scheme 1).…”

“…[6] Previous work by Kotova and co-workers found that the stoichiometric reaction of Et 2 Zn with H 2 L yielded a dinuclear helical species, [L 2 Zn 2 ]. [7] Herein we report how changing the reaction stoichiometry can increase the nuclearity of the resultant complexes to afford a tetranuclear complex, [L 4 Zn 4 ] (1), and a 1D polymer, [LZn(Et)] n (2). The reactivity of 1 and 2 with SO 2 Cl 2 , Br 2 and I 2 was investigated.…”