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

<jats:title>Abstract</jats:title> <jats:p>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 N,N-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) Å, α = 90, β = 121.76(2), γ = 90°, V = 3690(1) Å3, 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) Å, α = 90, β = 98.99(3), γ = 90°, V = 1692(1) Å3, and Z = 4. The casal2− 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) Å, α = β = γ = 90°, V = 7108(2) Å3, 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 Å. 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)Å, α = 90, β = 110.03(4), γ = 90°, V = 1661(1) Å3, 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.</jats:p>