1,2,4-Triazolyl-4-acetate: a ditopic ligand combining soft and hard donor sites in homometallic (AgI) and heterometallic (AgI/UVI) coordination polymers

1,2,4-Triazol-4-yl-acetic acid (trGly-H) has been used as a heterobifunctional ligand for preparing homometallic (Ag-I) and heterometallic (Ag-I/U-VI) coordination polymers under hydrothermal conditions. Four coordination compounds, [Ag-4(trGly)(4)]center dot 2H(2)O (1), [Ag-4(trGly)(2)(trGly-H)(2)](NO3)(2)center dot 2H(2)O (2), [(UO2){Ag-4(trGly)(4)(NO3)(2)(H2O)}]center dot 4H(2)O (3) and [(UO2)(2){Ag-6(trGly)(10)}]center dot 7H(2)O (4), have been synthesized and structurally characterized. Compounds 1 and 2 are similar and consist of tetranuclear [Ag-4(tr)(4)(COO)(2)] secondary building units (SBUs) supported by four [-N-N-] triazole bridges in the {Ag-4}-cluster plane and two carboxylate functions in the axial positions, which link the rhomboid units together into a thick layer. Addition of uranyl ions in the reaction system leads to compounds 3 and 4, where tr- and -COO--functional groups are differentiated by their coordination role: tr binds Ag+ ions, while -COO- interacts with UO22+. The crystal structure of 3 includes tetranuclear [Ag-4(tr)(4)(NO3)(2)] units linked by four [-N-N-] triazoles and two nitrate anions above and below the cluster core. In 3, uranium in a pentagonal bipyramidal {UO7} arrangement forms "cation-cation" interactions with Ag-I centers (the Ag center dot center dot center dot O=U=O distance is short, 2.600 angstrom). The 3D framework of compound 4 is constructed from hexanuclear [Ag-6(tr)(10)] SBUs in a form of hexagonal twisted prisms that are further stacked into a column motif through argentophilic (Ag center dot center dot center dot Ag) interactions of 3.06 angstrom. To explore the AgNO3/trGly-H/UO2(NO3)(2)center dot 6H(2)O system, the composition space diagram approach was employed. The defined crystallization fields of the compounds show that complex 3 is the dominant product, while 4 appears only in a high ligand concentration range. The thermal behavior and solid-state photoluminescence properties of the compounds have been investigated.