Copper(II) compounds extended by 5-carboxysalicylaldehyde and its Schiff bases: Interplay of two metal-binding sites and intermolecular stacking contributing to their network and bulk structures

Article abstract of DOI:10.1246/bcsj.71.2365

5-Carboxysalicylaldehyde (H₂casal) formed two mixed-ligand complexes, [Cu(Hcasal)(bpy)]ClO₄ (1) and [Cu(casal)-(bpy)]·2H₂O (2) (bpy=2,2′-bipyridine) and the Schiff bases H₂L¹ and H₂L² derived by condensing H₂casal with N₂N-dimethylethylenediamine and bis(3-aminopropyl)amine, respectively, formed [Cu(L¹)]·0.25H₂O (3) and [Cu(L²)]·H₂O (4), respectively. X-Ray crystallographic studies were done for 1, [Cu(casal)(bpy)(MeOH)] (2′), [Cu(L¹)]·4H₂O (3′) and 4. 1: Monoclinic, space group C2/c, a = 18.457(5), b = 19.215(5), c = 12.237(3) A, α = 90, β = 121.76(2), γ = 90°, V = 3690(1) A³, and Z = 8. It has a dimeric structure with a perchlorato bridge between two [Cu(Hcasal)(bpy)]⁺ moieties. In the bulk the dimeric units are assembled by interligand noncovalent interactions providing a pseudo 2-D sheet. 2′: Monoclinic, space group P2₁/m, a = 9.791(4), b = 6.850(4), c = 25.56(1) A, α = 90, β = 98.99(3), γ = 90°,V = 1692(1) A³, and Z = 4. The casal^2- combines one copper at the mixed-ligand site and the carboxylato group unidentately coordinates to the adjacent molecule, providing a 1-D zipper-like chain. The 1-D chains are further assembled through the interchain bpy/bpy stacking to form a pseudo 2-D network extended on the bc plane. 3′: Tetragonal, space group I4₁/a, a = b = 16.006(3), c = 27.745(7) A, α = β= γ = 90°, V = 7108(2) A³, and Z = 16. It has a 1-D helical structure extended by Cu-NNO(spacer)OO-Cu linkages along c axis (Fig. 6): The nearest Cu-Cu separation in the chain is 9.60 A. The four water molecules exist in the helical column but are readily removed in the air. 4: Monoclinic, space group P2₁/c, a = 9.149(6),b= 17.566(6), c= 11.004(6) A, α = 90, β = 110.03(4), γ = 90°, V = 1661(1) A°³, and Z = 4. It has a 1-D zigzag chain structure extended by Cu-NNNO(spacer)O-Cu linkages. Further, the 1-D chains align through noncovalent interchain interaction to provide a pseudo 2-D sheet. The interplay of the two dissimilar metal-binding sites of H₂casal and its Schiff bases and the intermolecular noncovalent interaction contributing to the network and bulk structures of the complexes are discussed.