Two pseudopolymorphic 1D coordination polymers of the formulas [Cd(3,3 '-pytz)(CH3OH)(2)(ClO4)(2)](n) (1) and [Cd(3,3 '-pytz)(CH3CN)(2)(ClO4)(2)](n) (2) have been prepared using the electron-deficient 3,6-bis(pyridin-3-yl)-1,2,4,5-tetrazine (3,3 '-pytz) ligand and cadmium perchlorate in the chloroform/methanol and chloroform/acetonitrile solvent system, respectively. It was observed that compounds 1 and 2 experienced one-step (CPreagent -> CPproduct) single-crystal-to-powder structural transformation to the pure water-coordinated compound [Cd(3,3 '-pytz)(H2O)(2)(ClO4)(2)](n) (3) by absorbing water vapor from air (solid-gas phase transformation). Interestingly, compounds 1, 2, and 3 undergo a different transformation path and show an in situ unique three-step (CPreagent -> CPproduct -> Ligand(intermediate) -> CPproduct) single-crystal-to-single-crystal (SCSC) structural transformation process through soaking in deionized water (solid-liquid phase transformation). In this fascinating transformation, we report for the first time the direct conversion of a ligand into a coordination polymer by a rare core-shell pathway in a solid-liquid phase transformation. In this process, we obtained compound {[Cd(3,3 '-pytz)(H2O)(4)](3,3 '-pytz)(2)(ClO4)(2)(H2O)(6)}(n) (4) (single-crystal = S, crystal = C, or microcrystal = P) as mixed compounds of core-shell L@4C and 4S or core-shell L@4P and 4P for compounds (1 and 2) and 3, respectively.
