Effects of N -oxidation on the molecular and crystal structures and properties of isocinchomeronic acid, its metal complexes and their supramolecular architectures: experimental, CSD survey, solution and theoretical approaches.

Nine coordination complexes and polymer (M/L/X) based on Co, Ni, Zn, Cu (M), pyridine- N -oxide-2,5-dicarboxylic acid (H 2 pydco) (L) and either isonicotinamide (Ina), piperazine (pipz), 2,2'-bipyridine (bipy) and 1,10-phenanthroline (phen) (X) were synthesized and characterized by elemental analyses, infrared spectroscopy and single crystal X-ray diffraction. The resulting empirical formulae of the prepared complexes are [Co(H 2 O) 6 ][Co(pydco) 2 (H 2 O) 2 ]·2H 2 O (1), [M(pydco)(H 2 O) 4 ] 2 [M = Co (2), Ni (3), Zn (4)], [Co(pydco)(bipy)(H 2 O) 2 ]·4H 2 O (5), [Co(pydco)(phen)(H 2 O) 2 ]·5.135(H 2 O)·0.18(EtOH) (6), [Cu(Hpydco)(bipy)Cl]·2H 2 O (7), [Cu(Hpydco)(bipy)Cl] 2 ·2H 2 O (8), and {[AgCu(H 2 O) 2 (phen)(pydco)]NO 3 } n (9). With the exception of 9, which forms an extended structure via multiple coordination modes, all the complexes contain (H)pydco as a bidentate ligand coordinated to the metal ion via the N -oxide and the adjacent carboxylate group oxygen atom, creating a chelate ring. The metal centers exhibit either distorted octahedral (1-6) or square pyramidal (7-9) geometry. Our results demonstrate that, when acting cooperatively, non-covalent interactions such as X-H⋯O hydrogen bonds (X = O, N, C), C-O⋯π and π⋯π stacking represent driving forces for the selection of different three-dimensional structures. Moreover, in compounds 2-4, 1D supramolecular chains are formed where O⋯π-hole interactions are established, which unexpectedly involve the non-coordinated carboxylate group. The non-covalent interaction (NCI) plot index analysis reveals the existence of the O⋯π-hole interactions that have been evaluated using DFT calculations. The Cremer and Pople ring puckering parameters are also investigated. The complexation reactions of these molecules with M were investigated by solution studies. The stoichiometry of the most abundant species in the solution was very close to the corresponding crystals. Finally, the effect of N -oxidation on the geometry of complexes has been also studied using the Cambridge Structural Database. It shows that complexes containing N -oxidized H 2 pydc are very rare.