Rationalization of Noncovalent Interactions within Six New M(II)/8-Aminoquinoline Supramolecular Complexes (M(II) = Mn, Cu, and Cd): A Combined Experimental and Theoretical DFT Study

To examine the influence of the metal ions and their counterions on crystalline networks, we have designed and synthesized six MX2/8-aminoquinoline (8-aq) (M = MnII, CuII, CdII and X = Cl–, Br–, I–, NO3–, SCN–) complexes, having the formulas [Mn(8-aq)2 I2]·(1), [Mn(8-aq)2(H2O)2](8-aq)3·Br2 (2), [Mn(8-aq)2(SCN)2] (3), [Cu(8-aq)2Cl(H2O)]·Cl·H2O (4), [Cu(8-aq)2(NO3)(H2O)]·NO3 (5), and Cd(8-aq)2I2 (6). Single-crystal X-ray diffraction analyses showed that all of the complexes have a distorted octahedral geometry, in which each 8-aq molecule acts as a bidentate ligand and coordinates to the central metal ion with its common coordination mode, to form an N,N′ chelating motif. Remarkably, the influence of the counterion on the geometry of the complex is very significant since both I– and SCN– anions are coordinated to the metal ion in compounds 1, 3, and 6, adopting a cis configuration, while a single anion occupies an axial position in compounds 4 and 5 (Cl– and NO3–, respectively) and the other counterion is not coordinated. Finally, both Br– anions are not coordinated in the cationic complex 2 (Mn metal center). In all cases, there are extended supramolecular networks due to cooperativity hydrogen-bonding and π–π stacking interactions that play an essential role in the formation and stability of the crystalline materials. The binding energies attributed to the different interactions have been evaluated using DFT calculations.