The crystal structures of four 2-pyridineformamide thiosemicarbazone derivatives viz, (Z,Z’)-4-methyl-N'-(morpholine-4-carbonothioyl)picolinohydrazonamide (1), (Z,Z’)-4-methyl-N'-(thiomorpholine-4-carbonothioyl) picolinohydrazonamide (2) and (Z,Z’)-6-methyl-N'-(thiomorpholine-4-carbonothioyl)picolinohydrazonamide (3) and (Z,Z’)-N'-(azepane-1-carbonothioyl)-4-methylpicolinohydrazonamide (4) has been determined by single crystal X-ray diffraction analysis. Combined quantum mechanical methods (ORCA) and computation of non-spherical scattering form factors (NoSpherA2) were used for the refinement with anisotropic hydrogen atoms. The results of using independent atom model (IAM) and Hirshfield atom refinement (HAR) method based R2SCAN/ def2-TZVP functional were compared. All compounds show an improvement in the model after HAR refinement compared to independent atom model (IAM). There is a significant decrease in the residual factors with the use of anisotropic hydrogen refinement. HAR refinement provides a clearer understanding of electron delocalization, lone pairs, and the accumulation and depletion of electron density. The information obtained came from standard resolution single crystal X-ray diffraction data, indicating that high-quality structural analysis can now be performed without the need for neutron or synchrotron facilities.
One sentence essence:
Hirshfield atom refinement provides a clearer understanding of electron delocalization, lone pairs, and the accumulation and depletion of electron density.