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

**Nicoleta Craciun 1,2, Diana Chisca 1,2, Elena Melnic <sup>1</sup> and Marina S. Fonari 1,\***

<sup>1</sup> Institute of Applied Physics USM, Academiei Str. 5, MD-2028 Chisinau, Moldova

<sup>2</sup> Faculty of Biology and ChemistryIon Creangă State Pedagogical University, Ion Creangă Str. 1, MD-2069 Chisinau, Moldova

**\*** Correspondence: marina.fonari@ifa.md or fonari.xray@gmail.com

**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.

**Keywords:** transition metals; synthesis; crystal structure; non-covalent interactions; Hirshfeld surface
