Ion-molecular Crystals as Inclusion Compounds: Van der Waals Contacts in Ionic Carbonates

摘要: Among Cambridge substances, which always include “organic”carbon, i.e., carbon contained in molecules or molecular ions,ion-molecular crystals (particularly, carbonates alkaline-earthand alkaline metals) are of special interest. Some such carbonatescontain pronounced Van der Waals (vdw) contacts between oxygenatoms carbonate groups. Thus, agglomerates (layers columns)formed by contacting groups arise (columns beingconnected a frame), and the cavities these agglomeratescations situated. The structure looks like an inclusion compound,the being hosts cations guests. Todiscuss this question we used refined value vdw radius oxygenwhich was obtained statistical treatment 8200 crystal structuresfrom Structural Database (CSD) is equal to 1.53 A for O⋯O contacts. Hence length normal supporting contact 3.06 ± 0.15 A. Such present MgCO3 CaCO3 (calcite) α-Na2CO3. There that even shorter (2.74–2.81 A)in (aragonite), SrCO3, BaCO3 Li2CO3.So it possible suppose existence specific (partly covalent)contacts substances. In β-Na2CO3, all forms K2CO3, Rb2CO3 Cs2CO3 CO3 absent; therefore they ionic (not inclusion) compounds.