Alkali-Metal-Mediated Frameworks based on Di-(2,6-Pyridinedicarboxyate) Cobalt(II) Species

Metal-organic frameworks (MOFs) with compositional multiplicity show unique topologies as well as enhanced chemical and physical properties. The construction of mixed-metal frameworks using more than one type of metal element can provide further structural versatility and diversity. The combination of transition- and alkali-metal elements in a framework can result in interesting materials with substantial advantages. Herein, we report a synthetic strategy for the mixed transition- and alkali-metal frameworks, [Na₂Co(PDA)₂] (1) and [K₂Co(PDA)₂] (2). The solid-state structures of these frameworks show that two 2,6-pyridinedicarboxylate (PDA) ligands chelate a cobalt ion to form a Co(PDA)₂²¯ species, which in turn undergoes further assembly mediated by alkali-metal cations (Na+ or K+) to give mixed-metal framework structures. The [{KCo(PDA)₂}ˉ ·{NH₂(CH₃)₂}+], framework 3 is also prepared by a change in stoichiometry. The multiple coordination of alkali-metals to the carboxylate oxygen atoms of the PDA ligands of the Co(PDA)₂²¯ species generates unique three-dimensional architectures. As 2 and 3 react with NaOH, the coordinated K+ easily exchange with Na+ in aqueous solution, and finally crystallizes to form 1. The strong ionic character and small size of the Na+ accounts for the facile transformations of 2 and 3. Temperature-dependent magnetization studies reveal that 1 exhibits distinct magnetic susceptibility compared to 2 and 3.

from #ENT-AlexandrosSfakianakis via ola Kala on Inoreader http://ift.tt/2tTxp6d