STA-27, a porous Lewis acidic scandium MOF with an unexpected topology type prepared with 2,3,5,6-tetrakis(4-carboxyphenyl)pyrazine

A porous scandium MOF denoted STA-27 (St Andrews Porous Material-27) has been synthesised solvothermally using the 2,3,5,6-tetrakis(4-carboxyphenyl)pyrazine anion (TCPP^4-) as the tetratopic carboxylate linker. STA-27 possesses a unique scandium-based 1D rod secondary building unit (SBU) comprising corner-sharing scandium Sc₂O₁₁ dimers connected via carboxylate groups from the linker. After activation under mild conditions STA-27 is an active Lewis acidic catalyst, while heating at elevated temperatures results in rupturing of the Sc-O-Sc linkages and a phase transition to a different topological type. Under similar synthesis conditions the smaller Al³⁺ and Ga³⁺ cations give isostructural MOFs with a different, previously reported, topology type based on chains of corner-sharing MO₄(OH)₂ octahedra: the Al-form possesses attractive properties for CO₂ adsorption.