Growth of Crystalline Bimetallic Metal-Organic Framework Films via Transmetalation.

Crystalline films of the Cu(BTC) (BTC = 1,3,5-benzenetricarboxylate) metal-organic framework (MOF) have been grown by dip-coating an alumina/Si(111) substrate in solutions of Cu(II) acetate and the organic linker HBTC. Atomic force microscopy (AFM) experiments demonstrate that the substrate is completely covered by the MOF film, while grazing incidence wide-angle X-ray scattering (GIWAXS) establishes the crystallinity of the films. Forty cycles of dip-coating results in a film that is ∼70 nm thick with a root mean squared roughness of 25 nm and crystallites ranging from 50-160 nm in height. Co ions were exchanged into the MOF framework by immersing the Cu(BTC) films in solutions of CoCl. By varying the temperature and exchange times, different concentrations of Co were incorporated into the films, as determined by X-ray photoelectron spectroscopy experiments. AFM studies showed that morphologies of the bimetallic films were largely unchanged after transmetalation, and GIWAXS indicated that the bimetallic films retained their crystallinity.