Engineering Three-Dimensional Chains of Porous Nanoballs from a 1,2,4-Triazole-carboxylate Supramolecular Synthon

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Glycine ethyl ester was recruited in an amine exchange process based on a transamination to afford ethyl 4H-,2,4-triazol-4-yl-acetate (L1). The acid hydrolysis of this molecule leads to quantitative isolation of 4H-1,2,4-triazol-4-yl acetic acid (L2). This versatile synthon crystallizes in a noncentrosymmetric orthorhombic space group (Fdd2) with Z = 16. This crystal structure is the first one for a 1,2,4-triazole ligand constructed from an amino acid derivative. The strong intermolecular hydrogen bonding O-H center dot center dot center dot N (2.570(3) angstrom) connects molecules into infinite one-dimensional chains running parallel to the b axis, and the structure is further extended by numerous but moderate strength hydrogen bonds (C-H center dot center dot center dot O). Prominent features of L2 are the presence of diverse potential coordinating groups such as carboxylic acid and triazole on the same framework as well as the inherent flexibility of the ligand backbone. Reaction of L1 or L2 with aq. Cu(BF4)(2) in aq. DMF gives dark blue crystals which crystallize in a noncentrosymmetric, cubic space group (1 (4) over bar 3m) and which were formulated as [Cu-3(mu(3)-O)(L2)(3). (H2O)(3)]BF4 center dot H2O (C1). The self-assembly of C3-symmetric, mu(3)-oxo bridged triangular tricopper secondary building blocks (SBB) formed an unique architecture which encompasses voluminous nanoball voids of 1 nm. The total solvent accessible volume is 4477.5 angstrom(3) which accounts for 48% of the cell volume. The crystal network stability was studied by thermogravimetric analysis (TGA) differential thermal analysis (DTA) and scanning electron microscopy (SEM) analyses. Sorption properties and gas storage capacities were measured by BET. CI shows no preference for N-2(g), but a reversible H-2(g) uptake of 21 cm(3)/g was observed, Morphology analysis by SEM on single crystals of CI shows ultrawells of square shape irregularly located on the surface, whose origin is due to desolvation or crystal defects. Mercury porosimetry measurements reveal pore size distribution with a diameter ranging from 350 nm to 2.3 mu m.