Influence of Structural Parameters on the Formation of Stable Na-bte Coordination Polymers

This article presents an analysis of structural transformations that occur during the crystallization of Na-1,2-bis(tetrazol-5-yl)ethane (H2bte) coordination polymers from solution. The crystal structures of six new Na-bte coordination polymers were elucidated, whereby [Na(Hbte)(CH3OH)2]n (1), [Na2(bte)(H2O)3]n (3), and [Na(Hbte)(H2O)]n (5) were isolated as intermediate phases during the formation of final products [Na(Hbte)(H2O)3]n (2), [Na2(bte)2(H2O)3]n·2NH4·H2O (4), and [Na2(Hbte)2(H2O)]n (6). The intermediates were isolated from the reaction mixture within 1 or 2 days, whereas the stable phases formed after 6 days. The intermediate formation of compounds 1, 3, and 5 in the reaction mixture, which further react to form the stable compounds 2, 4, and 6, reveals the formation pathway of the final products via the intermediate phases. The coordination strain imposed by the tetrazole rings of bte linkers, bulky solvent molecule MeOH in Na coordination sphere, and hydration affinity of the Na+ ion accounts for the instability of the intermediate phases. Along with the coordination flexibility provided by the aqua linkers, the stable phases acquire additional stability due to noncovalent interactions exhibited by the coordinated and lattice solvent molecules. The thermal decomposition behaviors of the stable phases are studied by thermogravimetric and calorimetric analyses.