The Versatility of the Dicyanamide Anion (Dca) as a Bridging Ligand: Synthesis, Structure and Theory of a Unique Ladder Chain Consisting of 2 µ1,5-dca Bridged Dinuclear Cu2(dca)2 Units with Additional µ1,3-dca Bridges Along the Chain

The synthesis and structural details of a mixed-ligand Cu(II) coordination compound, specifically catena-poly[bis(dicyanamido)(1,10-phenanthroline-5,6-dione)copper(II)] 1, are reported. The title compound was synthesized utilizing a solvothermal method by employing dicyanamide, 1,10-phenanthroline-5,6-dione (phendione) and copper(II) sulfate pentahydrate (CuSO₄•5H₂O) as the starting materials. The title compound was characterized by standard analytical and spectroscopic methods. The 3D structure was determined by single-crystal X-ray diffraction. Examination of the supramolecular interaction patterns indicates that the stability of the ladder structure is achieved by the bridging dca anions and the presence of weak hydrogen-bonding contacts, specifically C-H···O and C-H···N bonds, as well as C-O/N···π interactions. These interactions together contribute to the formation of a ladder-type infinite chain structure. The generated structure has been theoretically investigated with Hirshfeld surface analysis, QTAIM and NCI analysis to reveal the interaction energies and bonds present inside and between molecules. The non-covalent interactions present in the crystal structure were further investigated theoretically, with particular attention to the cooperative C ≡ N···π(py) and N···π(hole) interactions involving the dicyanamide ligand and nitrile moieties in the compound. The solid-state stability of compound 1 appears to be strongly influenced by the cooperative effect of H-bonding interactions as well as the C ≡ N···π(py) and N···π(hole) contacts, as confirmed by theoretical calculations.

Graphical Abstract

Synthesis, Structure and Theoretical Calculations of a Unique Ladder Chain Containing the Dicyanamido Ligand (dca), Consisting of 2 µ_1,5-dca Bridged Dinuclear Cu₂(dca)₂Units and Having µ_1,3-dca Bridges along the Chain.

One sentence essence:

catena-poly[bis(dicyanamido)(1,10-phenanthroline-5,6-dione)copper(II)] is a unique ribbon ladder, infinite chain structure with two differently bridged dicyanamide anions