Solid State Structural Variations in Copper(II) Complexes of Open-Chain and Macrocyclic Malonamide-Derived Ligands

An analysis of the molecular structure of the copper­(II) complexes with open-chain and macrocyclic malonamide-derived tetradentate ligands based on single crystal X-ray diffraction study of four copper­(II) complexes [CuL¹(H₂O)]·4H₂O, [CuL²(H₂O)], [CuL³(H₂O)], and [CuL⁴(H₂O)] (H₂L¹<b> = </b>1,4,8,11-tetraazaundecane-5,7-dione, H₂L² = 13-methyl-13-nitro-1,4,8,11-tetraazacyclotetradecane-5,7-dione, H₂L³ = 1,4,8,11-tetraazacyclotetradecane-5,7-dione, and H₂L⁴ = 1,4,8,11-tetraazacyclotridecane-5,7-dione) as well as on published data regarding related compounds revealed that the violations of planarity of the metal-amide fragments are due almost exclusively to the deviation of the copper­(II) ion from the amide plane. Both the deviation of the copper­(II) ion from the amide plane and the angle between amide planes in the 6-membered malonamide ring are strongly affected by substituents with minimal values observed in the complexes of unsubstituted ligands. The deviation of the copper­(II) ion from the basal plane of donor atoms was shown to relate to the sum of bite angles around the copper­(II) ion and roughly correlates to Cu–L_ax distances when apical ligands are present. The crystals of the macrocyclic complexes CuL² to CuL⁴ are built up from similar corrugated layers in which metal complex molecules are linked in a “head-to-tail” manner <i>via</i> NH···OC hydrogen bonds. In contrast, [CuL¹(H₂O)]·4H₂O has a lamellar crystal structure in which the layers built up of [CuL¹(H₂O)] units alternate with sheets formed by water molecules