New structural motifs and properties of squaric acid anions in the presence of the l-lysinium counterion

Synthesis and structural characteristic of pyridine carboxylic acid adducts with squaric acid

Squaric acid was used as a coformer to pyridine carboxylic acid cocrystallization. Adducts were obtained by evaporation from solution. Spectroscopic and theoretical studies were also performed. Thermal analysis reveals the high thermal stability of the obtained complexes.

H-Bonded anion–anion complex trapped in a squaramido-based receptor

We report the experimental observation (X-ray characterization) of an anion–anion complex (anion = hydrogen fumarate) stabilized by H-bonds that is trapped in a secondary squaramide receptor.

Polymorphism in secondary squaramides: on the importance of π-interactions involving the four membered ring

We report the crystal structures of four new squaric acid derivatives, i.e. three polymorphs of 3,4-bis((2-(dimethylamino)ethyl)amino)cyclobut-3-ene-1,2-dione (1a–c) and a cocrystal with resorcinol. A DFT study has been also carried out to investigate the supramolecular assemblies.

NH⋯O and OH⋯O interactions of glycine derivatives with squaric acid

Hydrogen-bonded complexes of glycine, sarcosine, dimethylgycine and betaine with squaric acid have been synthesized and characterized by X-ray diffraction, FTIR, NMR and DFT methods.

Biguanide and squaric acid as pH-dependent building blocks in crystal engineering

Biguanides and squaric acid are attractive partners for crystal engineering: they incorporate multiple sites that can donate or accept hydrogen bonds. Protonation equilibria in their solutions and the outcome of crystallization experiments are pH dependent: 10 different salts have been obtained from N,N-dimethylbiguanide, N-phenylbiguanide and N-o-tolylbiguanide.

Vibrational spectral studies and non-linear optical properties of L-leucine L-leucinium picrate: a Density Functional Theory approach

Single crystals of l-leucine l-leucinium picrate were grown by slow evaporation at room temperature and were characterized by X-ray powder diffraction study to confirm the crystalline nature of the synthesized compound. The optimized molecular structure, vibrational spectra and the optical properties were calculated by the Density Functional Theory (DFT) method using the B3LYP function with the 6-31G(d) basis set. Good consistency is found between the calculated results and the experimental structure, IR, and Raman spectra. The detailed interpretation of the vibrational modes was carried out. The natural bond orbital (NBO) analysis, confirms the occurrence of intermolecular hydrogen bonds that are responsible for the stabilization of the title compound, leading to high nonlinear optical (NLO) activity. The lowering in the HOMO and LUMO energy gap explains the eventual charge transfer interactions that take place within the molecules.