Uday Das

Acemetacin polymorphs: a rare case of carboxylic acid catemer and dimer synthons

Acemetacin is the first example of an API polymorph with a carboxylic acid catemer and dimer O–H⋯O synthons. The auxiliary stabilization to the catemer motif from stronger C–H⋯O and C–Cl⋯O interactions compared to those in the dimer structure is discussed for a polymorph pair. The crystal structure of the stable dimer polymorph was solved by structure determination from powder X-ray diffraction data (SDPD).

Conformational analysis of an acyclic tetrapeptide: ab‐initio structure determination from X‐ray powder diffraction, Hirshfeld surface analysis and electronic structure

A terminally protected acyclic tetrapeptide has been synthesized, and the crystal structure of its hydrated form, Boc‐Tyr‐Aib‐Tyr‐Ile‐OMe·2H2O (1), has been determined directly from powder X‐ray diffraction data. The backbone conformation of tetrapeptide (1) exhibiting two consecutive β‐turns is stabilized by two 4 → 1 intramolecular N―H · · · O hydrogen bonds. In the crystalline state, the tetrapeptide molecules are assembled through water‐mediated O―H · · · O hydrogen bonds to form two‐dimensional molecular sheets, which are further linked by intermolecular C―H · · · O hydrogen bonds into a three‐dimensional supramolecular framework. The molecular electrostatic potential (MEP) surface of (1) has been used to supplement the crystallographic observations. The nature of intermolecular interactions in (1) has been analyzed quantitatively through the Hirshfeld surface and two‐dimensional fingerprint plot. The DFT optimized molecular geometry of (1) agrees closely with that obtained from the X‐ray structure analysis. The present structure analysis of Boc‐Tyr‐Aib‐Tyr‐Ile‐OMe·2H2O (1) represents a case where ab‐initio crystal structure of an acyclic tetrapeptide with considerable molecular flexibility has been accomplished from laboratory X‐ray powder diffraction data. Copyright

Structural study of four benzyloxybenzoic acids and benzyloxyanilines using X-ray powder diffraction: interplay of strong and weak intermolecular interactions

Crystal structures of two benzyloxybenzoic acids (1 and 2) and two benzyloxyanilines (3 and 4) have been solved from laboratory X-ray powder diffraction data using the direct space methodology. The refinements of structures 1, 2, 3 and 4 have been carried out following the Rietveld method. The nature of intermolecular interactions in 1–4 has been analyzed through the Hirshfeld surfaces and 2D fingerprint plots. The COOH functional group generates a cyclic R22(8) synthon via intermolecular O–H⋯O hydrogen bonds in 1 and 2. An interplay of O–H⋯O and C–H⋯O hydrogen bonds, and C–H⋯π interactions in 1 and 2 facilitates the formation of three-dimensional supramolecular frameworks in 1 and a one-dimensional step-like architecture in 2. While the combination of N–H⋯π and C–H⋯π interactions link the molecules in 3 into parallel columns along the [100] direction, no such molecular assembly has been observed in 4. Hirshfeld surface analyses of 1–4 as well as a few related benzyloxybenzoic acid and benzyloxyaniline derivatives retrieved from the Cambridge structural database (CSD) indicate that about 90% of Hirshfeld surface areas in this class of compounds are due to H⋯H, C⋯H and O⋯H contacts.

Methyl-2-methyl-2-(4-methyl-phenyl)sulfonamido propanoate: structural study, supramolecular architecture and analysis of molecular surface electrostatic potential

Abstract An arylsulfonamide compound, methyl-2-methyl-2-(4-methylphenyl)sulfonamido propanoate, (1), has been synthesised and structurally characterised. Compound (1) has a staggered conformation relative to the S–N bond. The DFT-optimised molecular geometry of (1) agrees closely with that obtained from the crystallographic study. The crystal exhibits cooperation of N–H···O hydrogen bonds with C–H···O and C–H···π(arene) interactions, resulting in a three-dimensional framework featuring R22(8) and R22(10) synthons. The effect of substitution in different arylsulfonamides retrieved from the Cambridge Structural Database (CSD) on the formation of supramolecular synthons has been analysed in terms of graph-set notation. Hydrogen-bond based interactions in (1) have been complemented by molecular electrostatic potential (MEP) surface calculation. Hirshfeld surface analyses of (1) and a few related arylsulfonamides retrieved from the CSD indicate that about 80% of the Hirshfeld surface areas in these compounds are due to H···H and O···H contacts.

CCDC 1051124: Experimental Crystal Structure Determination

Related Article: Uday Das, Basab Chattopadhyay, Dipak K. Hazra, Vommina V. Sureshbabu, Alok K. Mukherjee|2016|J.Mol.Struct.|1122|290|doi:10.1016/j.molstruc.2016.06.013

3-Benzyloxybenzaldehyde: Ab initio powder structure determination and Hirshfeld surface analysis

Abstract The crystal structure of 3-benzyloxybenzyldehyde (2) has been determined from laboratory X-ray powder diffraction data. The DFT optimized molecular geometry in 2 agrees closely with that obtained from the X-ray study. The crystal packing in 2 has been compared with that of 2-benzyloxybenzaldehyde (1) and 4-benzyloxybenzaldehyde (3), and the role of weak intermolecular interactions in building supramolecular assembly in solid state has been analyzed. The Hirshfeld surface analysis of 1-3 and a few related benzyloxybenzyldehydes retrieved from the Cambridge Structural Database indicates that the H . . . H, C . . . H and O . . . H contacts can account for about 95% of the Hirshfeld surface area in this class of compounds.