Structural insights into the usage of carboxylate ions as molecular pins

Abstract

Two series of new isostructural coordination compounds containing cobalt, nickel, copper butyrates (butyr) or isobutyrates (ibutyr) and 1,10-phenanthroline (phen), of general formulas [M(phen)3]2+·2(butyr−)·11H2O and [M(phen)3]2+·2(ibutyr−)·14H2O, were synthesized in water solutions and characterized by X-ray crystallography, IR, UV–Vis and fluorescence spectroscopy, elemental and thermal analysis. The carboxylate anions are located in an outer coordination sphere, which is a unique phenomenon in case of ibutyr coordination compounds. The studied compounds exhibit layered packing in crystal net. The “aqueous layers” consist of water molecules and carboxylate groups of carboxylate anions, assembled via hydrogen bonds to the two dimensional supramolecular networks containing multiple different cyclic motifs. Coordination units together with aliphatic ends of carboxylate anions form the “coordination moieties layers”, which are internally connected via π⋯π and C–H⋯π intermolecular interactions. The carboxylate anions function as supramolecular linkers between these layers and allow pinning them together. The spectroscopic and thermal properties have been discussed and correlated with molecular structures of the studied compounds. Due to placement of carboxylate anions out of coordination moieties, the presented compounds can be ideal standards in spectroscopic determinations of coordination type of butyr and ibutyr ions in coordination compounds. The thermal analyses of the studied compounds revealed the possibility of formation of dihydrate forms, and such dihydrated compounds cannot be produced in direct synthesis performed in aqueous media. In properly set environment the studied compounds can be thermally converted to micro- and nanoparticles of respective metal oxides.