A constrained disorder refinement: Reinvestigation of 'single-crystal X-ray structure of 1,3-dimethylcyclobutadiene' by M. Shatruk and I. V. Alabugin

摘要

Shatruk and Alabugin propose an alternative structural model for the observed electron density that we have attributed to the photochemical formation of 1,3-dimethylcyclobutadiene in a protective solid crystalline matrix. The main criticism from Shatruk and Alabugin concerns the modeling of the disorder in the calixarene cavity and in particular the neglect of a residual electron density close to the O1 atom. We published (Chem. Eur. J. 2011, 17, 10021) our opinion concerning this "ignored peak" in the Supporting Information of the paper. The current response to the Correspondence demonstrates that Shatruk and Alabugin have over-modeled our data by assigning a small electron density peak, which is hardly more than the density corresponding to a hydrogen atom, to an under-occupied oxygen site, using inappropriate refinement contraints. A question of refinement: In this response to the Correspondence by Shatruk and Alabugin, in which they propose an alternative structural model for the observed electron density that was attributed by us to the photochemical formation of 1,3-dimethylcyclobutadiene in a protective solid crystalline matrix, it is demonstrated that they have over-modeled our data by assigning a small electron density peak (O1A), which is hardly more than the density corresponding to a hydrogen atom, to an under-occupied oxygen site, using inappropriate refinement constraints.