Crystal structures and spectroscopic properties of ester amide and diamide of squaric acid with prolinamide

We report the synthesis, spectroscopic and structural elucidation of two prolinamide derivatives of squaric acid, i.e. prolinamide ester amide of squaric acid ethyl ester (1) and prolinamide diamide of squaric acid dihydrate (2). Both compounds crystallize in non-centrosymmetric space groups, monoclinic P21 (1) and orthorhombic P212121 (2), respectively. For first time in the literature the crystal structure of homodiamide of amino acid amide of squaric acid is reported. The data for heterodiamides is also absent. Supramolecular zig-zag chains by hydrogen bonds of H2N–CO⋯HNH (3.020 Å) and HNH⋯OC(Sq) (2.972 Å) types with the participation of amide and squaric acid (Sq) fragments, –CO–NH2 and OC(Sq) are refined in (1). A helix supramolecular structure is formed in (2) by moderate intermolecular HNH⋯OC(NH2) hydrogen bond with length of 2.947 Å. The two crystallographical non-equivalent water molecules stabilized the helix by interactions of types HOH⋯OC(Sq) (2.917 Å), HOH⋯OC(NH2) (2.899 Å), H2O⋯NH2(CO) (2.972 Å), respectively. Optical and magnetic properties are investigated with a view to explain the correlation structure-properties of the newly synthesized molecules.