Bifunctional pyrazolate–carboxylate ligands for isoreticular cobalt and zinc MOF-5 analogs with magnetic analysis of the {Co4(μ4-O)} node

• Published in: CrystEngComm 2013-01, Vol.15 (45), p.9757-9768
• Main Authors: Heering, Christian, Boldog, Ishtvan, Vasylyeva, Vera, Sanchiz, Joaquín, Janiak, Christoph
• Format: Article
• Language: English
• Subjects: Apertures; Carbon capture and storage; Carbon dioxide; Cobalt; Ligands; Networks; Sorption; Zinc
• ISSN: 1466-8033; 1466-8033
• DOI: 10.1039/c3ce41426d

The ditopic ligands 3,5-dimethyl-pyrazolate-4-carboxylate, super(-)Me sub(2)pzCO sub(2) super(-), and 4-(3,5-dimethyl-1H-pyrazol-4-yl)benzoate, super(-)Me sub(2)pzC sub(6)H sub(4)CO sub(2) super(-), combine a pyrazolate and carboxylate functionality in axial orientation and lead to porous cobalt or zinc azolate-carboxylate frameworks that have the same cubic pcu-atopology and {M sub(4)( mu sub(4)-O)} nodes (M = Co, Zn) as MOF-5 and other IRMOFs. The microporous networks [M sub(4)( mu sub(4)-O)(Me sub(2)pzCO sub(2)) sub(3)] (M = Co, Zn) with the short linker exhibit a solvent-induced gate effect, evidenced by gas desorption hysteresis due to small pore apertures of 2.8 Aa diameter together with small amounts of high-boiling solvent remaining in the activated samples. For [Co sub(4)( mu sub(4)-O)(Me sub(2)pzCO sub(2)) sub(3)], the low-pressure H sub(2) storage capacity (1.7 wt%, 1 bar , 77 K) is higher than for MOF-5, and the CO sub(2) uptake of 20.8 wt% puts it among the top MOFs for low-pressure CO sub(2) sorption even though the BET surface is less than 1000 m super(2) g super(-1). The analysis of the magnetic properties of [Co sub(4)( mu sub(4)-O)(Me sub(2)pzCO sub(2)) sub(3)] takes into account the distribution of tetrahedra resulting from the disorder of the pyrazolate-carboxylate linker. An antiferromagnetic coupling observed for [Co sub(4)( mu sub(4)-O)(Me sub(2)pzCO sub(2)) sub(3)] arises from the interactions of the cobalt(ii) ions through the combined mu sub(4)-O + syn-syncarboxylate and mu sub(4)-O + pyrazolate bridges.