Exceptional crystallization diversity and solid-state conversions of Cd(II) coordination frameworks with 5-bromonicotinate directed by solvent media.

ABSTRACT

A series of nine coordination polymers {[Cd(L)(2)(solvent)(x)](solvent)(y)}(n) have been prepared from Cd(NO(3))(2) and 5-bromonicotinic acid (HL) in different solvents through a layered diffusion method. By using CH(3)OH/H(2)O at different volume ratios of 11 and 13, a one-dimensional (1D) coordination species (1a) and a three-dimensional (3D) (3,6)-connected framework (2a·g(1)) can be obtained. A similar self-assembly process in C(2)H(5)OH/H(2)O or H(2)O/1,4-dioxane gives 2a·g(2) or 2a·g(3), which are isomorphic to 2a·g(1) but with different lattice solvents. Replacement of the mixed solvents with DMF/H(2)O (v/v 11 or 13) also gives a 1D chain complex (1b) or a 3D microporous framework (2b·g(1)). Similarly, MOF 2b·g(2) can be assembled from CH(3)CN/H(2)O as an isomorphic solvate of 2b·g(1). Significantly, the 3D MOF families of 2a·g(n) and 2b·g(n) are supramolecular isomers even though they are topologically equivalent. Also, if a mixture of CH(3)OH/CH(2)Cl(2) (v/v 11 or 31) is used, a pair of distinct MOFs (3a·g) and (3b) 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 1a and 1b and between 2a·g(1), 2a·g(2), and 2a·g(3) 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.