Uncovering the Local Magnesium Environment in the Metal–Organic Framework Mg₂(dobpdc) Using ²⁵Mg NMR Spectroscopy

The incorporation of <i><i>N</i>,<i>N</i></i>′-dimethylethylenediamine into an expanded MOF-74 framework has yielded a material (mmen-Mg₂(dobpdc)) exhibiting “step-shaped” CO₂ adsorption isotherms. The coordination of mmen at the Mg open metal center is essential for the unique cooperative adsorption mechanism elucidated for this material. Despite its importance for carbon capture, there is as yet no experimental structure determination available for the underlying metal–organic framework Mg₂(dobpdc). Our ²⁵Mg solid-state NMR data unravel the local Mg environments in several Mg₂(dobpdc) samples, unambiguously confirming the formation of five-coordinate Mg centers in the activated material and six-coordinate Mg centers in the solvent- or diamine-loaded samples, such as mmen-Mg₂(dobpdc). A fraction of the Mg centers exhibit local disorder due to the framework deformation accompanied by the guest distributions and dynamics

Uncovering the Local Magnesium Environment in the Metal–Organic Framework Mg₂(dobpdc) Using ²⁵Mg NMR Spectroscopy

The incorporation of <i><i>N</i>,<i>N</i></i>′-dimethylethylenediamine into an expanded MOF-74 framework has yielded a material (mmen-Mg₂(dobpdc)) exhibiting “step-shaped” CO₂ adsorption isotherms. The coordination of mmen at the Mg open metal center is essential for the unique cooperative adsorption mechanism elucidated for this material. Despite its importance for carbon capture, there is as yet no experimental structure determination available for the underlying metal–organic framework Mg₂(dobpdc). Our ²⁵Mg solid-state NMR data unravel the local Mg environments in several Mg₂(dobpdc) samples, unambiguously confirming the formation of five-coordinate Mg centers in the activated material and six-coordinate Mg centers in the solvent- or diamine-loaded samples, such as mmen-Mg₂(dobpdc). A fraction of the Mg centers exhibit local disorder due to the framework deformation accompanied by the guest distributions and dynamics

The seventh blind test of crystal structure prediction: structure ranking methods

A seventh blind test of crystal structure prediction has been organized by the Cambridge Crystallographic Data Centre. The results are presented in two parts, with this second part focusing on methods for ranking crystal structures in order of stability. The exercise involved standardized sets of structures seeded from a range of structure generation methods. Participants from 22 groups applied several periodic DFT-D methods, machine learned potentials, force fields derived from empirical data or quantum chemical calculations, and various combinations of the above. In addition, one non-energy-based scoring function was used. Results showed that periodic DFT-D methods overall agreed with experimental data within expected error margins, while one machine learned model, applying system-specific AIMnet potentials, agreed with experiment in many cases demonstrating promise as an efficient alternative to DFT-based methods. For target XXXII, a consensus was reached across periodic DFT methods, with consistently high predicted energies of experimental forms relative to the global minimum (above 4 kJ mol−1 at both low and ambient temperatures) suggesting a more stable polymorph is likely not yet observed. The calculation of free energies at ambient temperatures offered improvement of predictions only in some cases (for targets XXVII and XXXI). Several avenues for future research have been suggested, highlighting the need for greater efficiency considering the vast amounts of resources utilized in many cases.</p