Unprecedented Coordination Compounds with 4,4′-Diaminodiphenylethane as a Supramolecular Agent and Ditopic Ligand: Synthesis, Crystal Structures and Hirshfeld Surface Analysis

Abstract

In this pioneering research, mononuclear coordination complexes and coordination polymers were obtained using the conformationally flexible ditopic ligand 4,4′-diaminodiphenylethane and different metal salts (nitrates, sulfates, tetrafluoroborates and perchlorates). Seven new products, including the mononuclear complexes [Cd(2,2′-bpy)3](ClO4)2](dadpe)(4,4′-bpy) (1), [Ni(dadpe)2(H2O)4](SO4).H2O (2), one-dimensional coordination polymers {[Zn(NO3)(dadpe)(dmf)2](NO3)}n (3), {[Cd(2,2′-bpy)2(dadpe)](ClO4)2}n (4), and two-dimensional coordination polymers, {[Cd(4,4′-bpy)2(H2O)2](ClO4)2(dadpe)(EtOH)2}n (5), {[Co(4,4′-bpy)2(H2O)2](BF4)2(dadpe)(EtOH)2}n (6) and {[Cd(adi)(dadpe)](H2adi)}n (7), (dadpe=4,4′-diaminodiphenylethane, 2,2′-bpy=2,2′-bipyridine, 4,4′-bpy=4,4′-bipyridine, H2adi=adipic acid) were produced. The synthesized compounds were characterized by FTIR and single-crystal X-ray diffraction analyses. The dadpe was recorded as a neutral guest in the crystals of mononuclear complex 1 and in coordination polymers 5 and 6. In compound 2, two dadpe ligands coordinate in a monodentate mode and occupy two trans-positions in the [Ni(H2O)4(dadpe)2]2+ octahedral complex cation. Coordination polymers 3 and 4 represent single chains originating from dadpe as a bidentate linker in both. The H-donor’s possibilities of amino groups were utilized in the interconnection of coordination chains into H-bonded networks via NH(NH2)···O hydrogen bonds. The isostructural coordination polymers 5 and 6 comprise similar cationic square grids [M(4,4′-bpy)2(H2O)2]2+ [M=Cd (5), M=Co (6)], with sql topology balanced by the charge-compensated anions, while dadpe and EtOH as neutral guests are situated in the interlayer space. The neutral 2D coordination network in 7 with the sql topology originates from both adi and dadpe linkers as bidentate-bridging ligands, and the neutral H2adi is entrapped as a guest in crystal lattice. The impact of different types of intermolecular interactions was evaluated by Hirshfeld surface analysis.