Mixed precious-group metal–organic frameworks: a case study of the HKUST-1 analogue [RuxRh3−x(BTC)2]

Abstract

This work presents the first full series of mixed precious-group metal–organic frameworks (MPG-MOFs) using ruthenium and rhodium. The obtained crystalline, highly porous and thermally robust materials were characterized by means of powder X-ray diffraction, N₂/CO₂ sorption isotherms, thermogravimetry, spectroscopy methods (IR, Raman, UV/VIS-, NMR and XPS) and as well by high resolution transmission electron microscopy (HR-TEM) with elemental mapping (HAADF-EDS). Additionally, the assignment of spectroscopic data is supported by computational (time dependent)-density functional theory methods. The materials turned out to consist of homogeneously dispersed Ru₂ and Rh₂ paddlewheel units being linked by benzenetricarboxylate (BTC) to yield a framework that is isoreticular to [Cu₃(BTC)₂] (HKUST-1, Hong Kong University of Science and Technology). However, acetate (OAc) is incorporated as an intrinsic component which compensates for missing BTC-linker defects and some Cl is coordinated to the Ru centre at an apical position. The exact empirical formula of the MPG-MOFs is derived as [Ru_xRh_3−x(BTC)_2−a(OAc)_b(Cl)_c].