Using hinged ligands to target structurally flexible copper(II) MOFs

Abstract

Here we report two new flexible MOFs based on a bis-pyrazolylmethane 'hinged' link design that favours the formation of two distinct structural nodes within the resulting 2-D and 3-D structures. The less sterically demanding ligand H₂bcppm affords a 2-D layered MOF, {Cu₂[Cuˡˡ(NO₃)₂(bcppm)₂](DMF)₂}•2DMF (1), constructed from copper(II) paddlewheel and mononuclear octahedral copper(II) nodes. The use of a more sterically encumbered tetramethyl analogue H₂bcpdmpm induces a dramatic twisting of the ligand backbone that yields a 3-D MOF{Cu₄[Cuˡ(bcpdmpm)₂]₂(EtOH)₂(H₂O)₂}(NO₃)₂•12DMF (2) formed from a very similar mix of nodes, specifically copper(II) paddlewheel clusters and mononuclear tetrahedrally coordinated copper(I) centres. Herein we describe the crystal structures, solid-state flexibility, and gas adsorption properties of both materials.