In Situ Conversion of Ligand to a Coordination Polymer via a Core@Shell Crystal: A Multi-Step Phase-Dependent Structural Transformation

Abstract

Two pseudopolymorphic 1D coordination polymers of the formulas [Cd(3,3′-pytz)(CH 3 OH) 2 (ClO 4 ) 2 ] n (1) and [Cd(3,3′-pytz)(CH 3 CN) 2 (ClO 4 ) 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 (CP reagent → CP product ) single-crystal-to-powder structural transformation to the pure water-coordinated compound [Cd(3,3′-pytz)(H 2 O) 2 (ClO 4 ) 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 (CP reagent → CP product → Ligand intermediate → CP product ) 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)(H 2 O) 4 ](3,3′-pytz) 2 (ClO 4 ) 2 (H 2 O) 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.