Atomic Force Microscopy Study of the Influence of the Synthesis Conditions on the Single-Crystal Surface of Interdigitated Metal-Organic Frameworks

Abstract

Metal-organic frameworks (MOFs) containing two or more types of metal ions exhibit promising new functionalities. To precisely control the distribution of metal ions, the relationship between the crystal-growth mechanism and the metal-ion type is important. Therefore, we investigated this relationship by using atomic force microscopy (AFM), which provided significant information about crystal-growth processes. We focus on interdigitated MOFs of the type: {[M(ip)(bpy)]⋅solvent}_n (M=Zn or Cd, ip=isophthalate, bpy=4,4'-bipyridine, solvent=water or N,N-dimethylformamide). AFM images show two surface condition types that strongly depend on the solvent or synthetic conditions. We also demonstrate that the adsorption properties between different crystal surfaces are affected by the surface conditions. Finally, we synthesize solid-solution MOFs and observe their surface conditions. Such mechanistic insights will aid in the design of the adsorption properties of multi-metal MOFs.

Keywords: atomic force microscopy; bridging ligands; crystal growth; metal-organic framework.