Synthesis, characterization and XRPD studies of metal-organic frameworks containing 1,4 bis(4-pyrazolyl) and 1,4 bis(5-tetrazolyl)benzene ligands

In the last decade we have been deeply exploring the coordination chemistry of polydentate ligands possessing multiple donor sites. Nowadays we decided to increased the complexity of the polytopic N-ligands aiming at the formation of oligomeric and polymeric species with different functional properties. Inspires to the 1,4-benzene-dicarboxylate (BDC) the ligand of the highly porous and capable of H2 sorption MOF-5 proposed by Yaghi et al., and planning to employ polytopic longer spacers possessing nitrogen coordination sites (with the possibility of an exobidentate coordination), we turned our attention to the 1,4-bis(5-tetrazolyl)benzene species (C8H6N8, H2btb). After having tailored high-yield, cheap and atoxic syntheses for H2btb [1], we started coupling this ligand with a transition metal ions aiming at the formation of microcrystalline materials of well defined stoichiometry, structure and functional properties: nanoporosity, cooperative magnetism and catalytic activity. The isolated materials shows a variety of stoichiometries, each one with its own peculiar structure: homoleptic species [Ag2(btb), Cu(btb) and Co(btb)], hydrated (or solvated) compounds [Co(btb)\u20222H2O and Zn(btb)\u2022nDMF], and even hydroxo complexes [Cu2(\u3bc3-OH)2(btb)]. These compounds are either dense or moderately porous and, therefore, they are not prone to gas sorption or storage, as originally targeted [2]. In this context, we decided to develop a new strategy to synthesized the analogous 1,4-bis(4-pyrazolyl)benzene (C12H10N4, H2bpb) [1] with the hope to obtain microporous and non-dense species with the coordination of the metal transition elements. Specifically, in our research, we have coupled these ligands with Ni, Cu, Zn, Hg to afford the species Ni(bpb), Zn(bpb), Cu2(bpb) and Hg(bpb). These species are isolated by solvothermal reaction and fully characterized by elemental and thermogravimetric analysis, IR spectroscopy and we attained their full structural characterization resorting to state-of-the-art powder diffraction methods, occasionally coupled to thermodiffractometry analysis. Adsorption capacities are also studied with preliminary gas sorption analysis, towards N2, and showing attractive adsorption capacities of the compound Ni(bpb) and Zn(bpb) in agreement with their structural characterization that shows a very low density and regulars networks. [1] A. Maspero, S. Galli, N. Masciocchi, G. Palmisano, Chem. Lett., 2008, in press. [2] A.Maspero, S. Galli, V.Colombo, G.Peli, N.Masciocchi, S.Stagni, E.Barea, J.A.R. Navarro, Inorg. Chim. ACTA, 2008, in press