Exceptional Crystallization Diversity and Solid-State Conversions of CdII Coordination Frameworks with 5-Bromonicotinate Directed by Solvent Media

A series of nine coordination polymers {[Cd(L)2(solvent)x](solvent)y}n have been prepared from Cd(NO3)2 and 5-bromonicotinic acid (HL) in different solvents through a layered diffusion method. By using CH3OH/H2O at different volume ratios of 1:1 and 1:3, a one-dimensional (1D) coordination species (1?a) and a three-dimensional (3D) (3,6)-connected framework (2?a center dot g1) can be obtained. A similar self-assembly process in C2H5OH/H2O or H2O/1,4-dioxane gives 2?a center dot g2 or 2?a center dot g3, which are isomorphic to 2?a center dot g1 but with different lattice solvents. Replacement of the mixed solvents with DMF/H2O (v/v 1:1 or 1:3) also gives a 1D chain complex (1?b) or a 3D microporous framework (2?b center dot g1). Similarly, MOF 2?b center dot g2 can be assembled from CH3CN/H2O as an isomorphic solvate of 2?b center dot g1. Significantly, the 3D MOF families of 2?a center dot gn and 2?b center dot gn are supramolecular isomers even though they are topologically equivalent. Also, if a mixture of CH3OH/CH2Cl2 (v/v 1:1 or 3:1) is used, a pair of distinct MOFs (3?a center dot g) and (3?b) are generated as pseudo-polymorphs that show a two-dimensional (2D) sheet and a 3D coordination framework, respectively. Furthermore, mutual solvent-induced conversions were realized between 1?a and 1?b and between 2?a center dot g1, 2?a center dot g2, and 2?a center dot g3 following the size-dependent rule of the solvent. These results are of great significance in recognizing the solvent effect upon coordination assemblies and their crystal transformations.