This
article presents an analysis of structural transformations
that occur during the crystallization of Na-1,2-bis(tetrazol-5-yl)ethane
(H2
bte) 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.