Facile fabrication in coordination networks: an in situ sequential replacement of linkers by successive SC–SC transformations via core@shell crystals

Abstract

A facile and in situ successive linker replacement through single-crystal-to-single-crystal (SC–SC) transformation process in cadmium coordination networks (CNs) based on 3,6-bis(pyridin-3-yl)-1,2,4,5-tetrazine (3,3′-pytz) and 4,4′-bipyridine (4,4′-bipy) in chloroform/methanol solution is reported. In this work, we synthesized a 2D square-grid homo-linker (4,4′-bipy) coordination network of {[Cd(4,4′-bipy)₂(ClO₄)₂](CHCl₃)₄}_n (1) after 24 h at room temperature. Compound 1 undergoes facile and in situ SC–SC transformation at room temperature to a 2D rectangular-grid mixed-linker (4,4′-bipy and 3,3′-pytz) coordination network of {[Cd(4,4′-bipy)(3,3′-pytz)(ClO₄)₂](CHCl₃)(MeOH)}_n (2) after two weeks through a core@shell crystal. Further, by keeping compound 2 in the mother liquor, the second SC–SC structural transformation to the 2D rhombic-grid homo-linker (3,3′-pytz) of {[Cd(3,3′-pytz)₂(H₂O)_1.4(MeOH)_0.6](3,3′-pytz)(MeOH)_1.4(ClO₄)₂}_n (3) occurs within two months. In these stepwise SC–SC transformations, we report for the first time the facile and in situ fabrication of 2D coordination networks by the replacement of linkers via the core–shell pathway. Unlike compound 3, which was stable in air, single crystals of 1 and 2 were unstable outside the mother solution, and due to the absorption of water from air, they were transformed into microcrystalline materials of {[Cd(4,4′-bipy)(H₂O)₂(ClO₄)₂](4,4′-bipy)}_n (1T) and {[Cd(3,3′-pytz)(H₂O)₂(ClO₄)₂](4,4′-bipy)}_{n=1 or ∞} (2T), respectively.