Urotropine as a ligand for the efficient synthesis of metal-organic frameworks

Abstract

Urotropine is a cheap and promising ligand for the synthesis of metal-organic frameworks containing uncoordinated nitrogen atoms. The reactions between urotropine, dicarboxylic acids, and zinc(II) or cobalt(II) salts were studied. The optimization of the reaction conditions allows the synthesis of three urotropine-containing metal-organic frameworks, [Zn(ur)(abdc)]• •DMF•H2O (1, ur is urotropine, abdc2− is 4,4´-diazobiphenyldicarboxylate, DMF is N,N-dimethylformamide), (CH3ur)[NaCo(dmf)2(bptc)] (2, CH3ur+ is N-methylhexa methyl enetetrammonium, bptc4− is 2,2´,4,4´-biphenyltetracarboxylate), and [Co4(dmf)(ur)2(ndc)4]•5DMF (3, ndc2− is 2,6-naphthalenedicarboxylate). These compounds were structurally characterized and their thermal and adsorption properties were studied. In the three compounds, urotropine performs diff erent functions, acting as a monodentate ligand (compound 1), a bidentate ligand (compound 3), or a methylammonium counterion (compound 2).